Paul Whiteley: The Gut-Brain Axis and Schizophrenia

Paul Whiteley, who blogs at Questioning Answers (mostly on autism research), posted this intriguing research summary from Progress in Neuro-Psychopharmacology and Biological Psychiatry on the relationship between the "gut-brain axis" and schizophrenia, which is not a new avenue of research, but is nonetheless still considered a fringe notion in the mainstream schizophrenia research.

It only makes sense that if we have an unhealthy microbiome (enteric nervous system), which we already know can cause depression, disease, and cognitive issues (a major symptom cluster in schizophrenia is cognitive distortion), then the entire system is at risk.


The full article is, of course, paywalled, but Whiteley offers a good, though too brief for me, summary of the study; and I have included the abstract from the original article.

The gut-brain axis and schizophrenia

Posted by Paul Whiteley
Saturday, 4 October 2014

A micropost to direct your attention to the recent paper by Katlyn Nemani and colleagues [1] titled: 'Schizophrenia and the gut-brain axis'. Mentioning words like that, I couldn't resist offering a little exposure to this review and opinion piece, drawing on what seems to be some renewed research interest in work started by pioneers such as the late Curt Dohan [2].

The usual triad of gastrointestinal (GI) variables - gut barrier, gut bacteria and gut immune function - are mentioned in the article, concluding that: "A significant subgroup of patients may benefit from the initiation of a gluten and casein-free diet" among other things. Not a million miles away from related suggestions when it comes to something like the autism spectrum disorders (ASDs) (see here) bearing in mind the concept of overlapping spectrums (see here) and the [plural] schizophrenias.

I'm also minded to hat-tip another research team including Emily Severance and colleagues who are going great guns when it comes to the whole GI-food link in cases of schizophrenia and beyond (see here for my recent discussion of some of her work). Another of her quite recent papers [3] on cerebrospinal fluid (CSF) levels of antibody response to wheat gluten and bovine milk in first-episode schizophrenia represents another master-class of research in this area. Their suggestion of potential evidence for a leaky blood-CSF barrier is something else which might stimulate further research in this area including some mention for the molecular handyperson that is melatonin among other things to "protect against blood-brain barrier and choroid plexus pathologies". Such findings might also be relevant for other CSF issues reported with schizophrenia in mind (see here).

And whilst we're talking all-things biological membrane permeability and schizophrenia, I'll also link to the paper by Julio-Pieper and colleagues [4] (open-access) reviewing some of the evidence on the 'controversial association' between intestinal barrier dysfunction and various conditions (also covering some of the literature with autism in mind too). Mainstream here we come?

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[1] Nemani K. et al. Schizophrenia and the gut-brain axis. Prog Neuropsychopharmacol Biol Psychiatry. 2014 Sep 17. pii: S0278-5846(14)00168-7
[2] Dohan FC. Cereals and schizophrenia data and hypothesis. Acta Psychiatrica Scandinavica. 1966; 42: 125–152.
[3] Severance EG. et al. IgG dynamics of dietary antigens point to cerebrospinal fluid barrier or flow dysfunction in first-episode schizophrenia. Brain Behav Immun. 2014 Sep 17. pii: S0889-1591(14)00462-0.
[4] Julio-Pieper M. et al. Review article: intestinal barrier dysfunction and central nervous system disorders - a controversial association. Aliment Pharmacol Ther. 2014 Sep 28.

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Nemani, K., Ghomi, R., McCormick, B., & Fan, X. (2014). Schizophrenia and the gut–brain axis. Progress in Neuro-Psychopharmacology and Biological Psychiatry. 56(2): 155–160. DOI: 10.1016/j.pnpbp.2014.08.018

* * * * *

Schizophrenia and the gut–brain axis

Katlyn Nemania, Reza Hosseini Ghomib, Beth McCormickc, Xiaoduo Fanc  

Highlights

• Several risk factors for the development of schizophrenia can be linked through a common pathway in the intestinal tract
• The microbiota composition may impact the gastrointestinal barrier, immune regulation, and metabolism seen in schizophrenia.
• A significant subgroup of patients may benefit from the initiation of a gluten and casein-free diet
• Antimicrobials and probiotics have therapeutic potential that will be elucidated by further research

Abstract

Several risk factors for the development of schizophrenia can be linked through a common pathway in the intestinal tract. It is now increasingly recognized that bidirectional communication exists between the brain and the gut that uses neural, hormonal, and immunological routes. An increased incidence of gastrointestinal (GI) barrier dysfunction, food antigen sensitivity, inflammation, and the metabolic syndrome is seen in schizophrenia. These findings may be influenced by the composition of the gut microbiota. A significant subgroup of patients may benefit from the initiation of a gluten and casein-free diet. Antimicrobials and probiotics have therapeutic potential for reducing the metabolic dysfunction and immune dysregulation seen in patients with schizophrenia.

This is wonderful to see, finally - even if it is less than honest about the existing evidence for lifestyle interventions to affect depression levels. Drugs for depression are not treating the depression, they are creating an effect of feeling better through making people, for lack of a better word, stoned.

I have seen, firsthand, a client start walking 3-5 days a week (exercise and nature/environment), begin practicing contemplative prayer (meditation), spend more time with her dog (animal therapy - goes on the walk, then fetch in the park), and start spending less time at home by joining church activities and spending time with her kids and granddaughter (socializing). These synergy of these simple changes have been more effective than years of medications and various attempts at therapy.

Lifestyle medicine for depression

Jerome Sarris, Adrienne O'Neil, Carolyn E Coulson, Isaac Schweitzer, and Michael Berk
Author Affiliations | For all author emails, please log on.

Published: 10 April 2014

Abstract (provisional)

The prevalence of depression appears to have increased over the past three decades. While this may be an artefact of diagnostic practices, it is likely that there are factors about modernity that are contributing to this rise. There is now compelling evidence that a range of lifestyle factors are involved in the pathogenesis of depression. Many of these factors can potentially be modified, yet they receive little consideration in the contemporary treatment of depression, where medication and psychological intervention remain the first line treatments. "Lifestyle Medicine" provides a nexus between public health promotion and clinical treatments, involving the application of environmental, behavioural, and psychological principles to enhance physical and mental wellbeing. This may also provide opportunities for general health promotion and potential prevention of depression. In this paper we provide a narrative discussion of the major components of Lifestyle Medicine, consisting of the evidence-based adoption of physical activity or exercise, dietary modification, adequate relaxation/sleep and social interaction, use of mindfulness-based meditation techniques, and the reduction of recreational substances such as nicotine, drugs, and alcohol. We also discuss other potential lifestyle factors that have a more nascent evidence base, such as environmental issues (e.g. urbanisation, and exposure to air, water, noise, and chemical pollution), and the increasing human interface with technology. Clinical considerations are also outlined. While data supports that some of these individual elements are modifiers of overall mental health, and in many cases depression, rigorous research needs to address the long-term application of Lifestyle Medicine for depression prevention and management. Critically, studies exploring lifestyle modification involving multiple lifestyle elements are needed. While the judicious use of medication and psychological techniques are still advocated, due to the complexity of human illness/wellbeing, the emerging evidence encourages a more integrative approach for depression, and an acknowledgment that lifestyle modification should be a routine part of treatment and preventative efforts.

The complete article is available as a provisional PDF. The fully formatted PDF and HTML versions are in production.

Full Citation:
Sarris, J, O'Neil, A, Coulson, CE, Schweitzer, I, and Berk, M. (2014, Apr 10). Lifestyle medicine for depression. BMC Psychiatry, 14:107 doi:10.1186/1471-244X-14-107

Introduction

While modernity has provided multiple technological and medical advances including increased life-expectancy, it has come at a cost, in that a range of lifestyle issues are now negatively affecting our mental health [1]. As Hidaka [1] and Walsh [2] comment, in Western society people are increasingly becoming more sedentary and eating a poorer diet than previous generations. This, in combination with sleep/wake cycle pressures, substance misuse, and psychosocial factors such as more competition and time pressure, social isolation and less intimate engagement with the family unit, may exert a cost on mental health. Further, the combination of stress, fatigue, inactivity, and sleep deficiency in people who are “timepoor”, may advance obesity, and this in turn may promote a sedentary life with potential for resultant depression.

Due to the afore-mentioned challenges of modern urbanity, there is now the need to consider a “Lifestyle Medicine” approach for the potential prevention, promotion and management of depression. While medication and psychological interventions are first-line treatments for depression, Lifestyle Medicine offers a potentially safe and low-cost option for augmenting the management of the condition. While the evidence base remains patchy, many lifestyle or environmental factors are mutable and can provide the basis of practical interventions for the management of depression (summarised in Table 1). Lifestyle Medicine involves the application of environmental, behavioural, and psychological principles to enhance physical and mental wellbeing, adding a therapeutic and potentially preventative approach to illness [3]. This may involve modification of: diet; physical activity and exercise; relaxation and sleep-wake cycles; recreation and work-rest balance; and minimisation/avoidance of smoking, alcohol or illicit substances, in addition to the use of mindfulness-based meditation techniques [2]. Although the evidence base remains in its infancy, environmental issues are also considerations, such as reducing exposure to pollution (air, water, noise, and chemicals) and increasing time spent in nature, and are areas of current investigation. Activity scheduling such as encouraging engagement in meaningful activities and adequate social contact [1] is additionally of value. Further, Lifestyle Medicine may involve the application of clinical psychological techniques, insofar as motivational and behavioural factors are intrinsic to people trying to embrace lifestyle changes [3].

Table 1 Lifestyle Medicine for Depression

Lifestyle element................Evidence level....................Cost
Diet............................................CS, LO.................Moderate expense 
PA/Exercise..........................CS*, LO*, CTs ...............Inexpensive 
Recreation.................................OB, CTs..................Variable expense 
Relaxation/Meditation.................CTs..........................Inexpensive
Sleep......................................CS, LO, CTs...................No expense 
Environment..........................CS, LO, CTs...........Potentially not adjustable 
Socialization..............................CS, LO.........................No expense 
Animal/Pet therapy....................CS, CTs.....................Moderate expense 
Vices (smoking/alcohol)............CS, LO.................Potential to save money

CS = Cross-sectional, OB = Observational Study, LO = Longitudinal, CTs - Clinical Trials, NAT = Nature-Assisted Therapy, PA = Physical Activity. 
*Data assessing the relationship between exercise and depression has revealed mixed outcomes.

Comments on each Lifestyle Element:

Diet - Relationship found between dietary quality and depression; RCTs now required to validate
PA/Exercise - Strong evidence of efficacy for improving mood
Recreation - No studies exploring recreational activities for depression (aside from music therapy)
Relaxation & Meditation - Evidence supports relaxation techniques (especially with a mindfulness component) in improving mood
Sleep - Strong causal link between sleep amount and quality, and depression risk
Environment - Association between reduction of pollution and mood; CTs showing NAT improves mood
Socialization - Strong association between social support/networks and mental health
Animal/Pet therapy - Studies support the psychological benefits of animals and pets
Vices (smoking, alcohol) - Association between smoking and alcohol, and depressed mood

While lifestyle modification has been recognised by practitioners for centuries as a means by which to improve health outcomes, the field of “Lifestyle Medicine,” particularly in the context of mental health, is a relatively new field. While papers have discussed its broader application on health and in particular prevention of chronic disease and cardiovascular/metabolic conditions, little attention has been given to its application for mental health, and in particular depression, which is predicted to be the predominant cause of disability in the developed world [4], and is being argued as one of the prevalent noncommunicable disorders [5]. Some studies show that patients with sub-threshold depression rate lifestyle or psychosocial approaches as strategies that are most helpful in improving their mood [6], while patients with clinical depression have rated exercise as the most effective intervention [7].

There is a heuristic theoretical framework explaining why the modern lifestyle may be impacting mental health. Obesity [8], poor diet [9], poor/decreased sleep [10], exposure to chemicals and pollutants [11], and high stress levels [12], may potentially disrupt the hypothalamic pituitary adrenal axis, increase cortisol and increase low-grade systemic inflammation and oxidative stress. Both neuroendocrine disruption and inflammation have been linked to the aetiology of depression [13,14]. Specifically, increased levels of proinflammatory cytokines, interferon gamma and neopterin, reactive oxygen and nitrogen species and damage by oxidative and nitrosative stress, in combination with lowered levels of antioxidants, may potentially damage mitochondria and mitochondrial DNA; this may result in neurodegeneration and reduced neurogenesis [14].

This opinion paper aims to provide a context for Lifestyle Medicine by providing an overview of the lifestyle factors that are linked with depression risk before exploring the evidence and clinical application of modifying these elements. The paper firstly explores data for which there is sound evidentiary support (diet, physical activity and exercise, mindfulness meditation, management of recreational substance misuse, sleep, and social interaction), and then touches on lifestyle and environmental elements that have nascent data and are subject to confirmatory investigation (greenspace and pollutant exposure, hobbies and relaxation, and animal/pet therapy).

Read the whole article.

Turns Out the Best Diet Is Real Food, Because Science!

Well, imagine that, the best diet for health is one that is based on eating real food, not crap that comes in a box, a bag, or a can. From The Atlantic.

Science Compared Every Diet, and the Winner Is Real Food

Researchers asked if one diet could be crowned best in terms of health outcomes. If diet is a set of rigid principles, the answer is a decisive no. In terms of broader guidelines, it's a decisive yes.

James Hamblin | Mar 24 2014

Ornamental cabbage and kale in Langley, Washington (Dean Fosdick/AP)

Flailing in the swell of bestselling diet books, infomercials for cleanses, and secret tips in glossy magazines, is the credibility of nutrition science. Watching thoroughly-credentialed medical experts tout the addition or subtraction of one nutrient as deliverance—only to change the channel and hear someone equally-thoroughly-credentialed touting the opposite—it can be tempting to write off nutrition advice altogether. This month we hear something is good, and next we almost expect to hear it’s bad. Why not assume the latest research will all eventually be nullified, and just close our eyes and eat whatever tastes best?

That notion is at once relatable and tragic, in that diet is inextricable from the amount of healthy time we spend on Earth. Improvements in diet are clearly associated with significant lengthening of lifespan and dramatic decreases in risk of most chronic diseases. Combining disease and longevity into the concept of healthspan, the number of healthy years of life—fundamentally more important but less readily quantifiable than lifespan—the data in favor of optimizing our diets are even more compelling. No one is arguing that diet is less than extremely important to health and well-being, but seemingly everyone is arguing as to what constitutes the best diet.

The voices that carry the farthest over the sea of diet recommendations are those of iconoclasts—those who promise the most for the least, and do so with certainty. Amid the clamor, Dr. David Katz is emerging as an iconoclast on the side of reason. At least, that’s how he describes himself. From his throne at Yale University's Prevention Research Center, where he is a practicing physician and researcher, said sea of popular diet media is the institution against which he rebels. It’s not that nutrition science is corrupt, just that the empty promises of memetic, of-the-moment diet crazes are themselves junk food. To Katz they are more than annoying and confusing; they are dangerous injustice.

Scientific publisher Annual Reviews asked Katz to compare the medical evidence for and against every mainstream diet. He says they came to him because of his penchant for dispassionate appraisals. "I don't have a dog in the fight," he told me. “I don’t care which diet is best. I care about the truth."

Katz and Yale colleague Stephanie Meller published their findings in the current issue of the journal in a paper titled, "Can We Say What Diet Is Best for Health?" In it, they compare the major diets of the day: Low carb, low fat, low glycemic, Mediterranean, mixed/balanced (DASH), Paleolithic, vegan, and elements of other diets. Despite the pervasiveness of these diets in culture and media, Katz and Meller write, "There have been no rigorous, long-term studies comparing contenders for best diet laurels using methodology that precludes bias and confounding. For many reasons, such studies are unlikely." They conclude that no diet is clearly best, but there are common elements across eating patterns that are proven to be beneficial to health. "A diet of minimally processed foods close to nature, predominantly plants, is decisively associated with health promotion and disease prevention."

 

 

Katz, Meller/Annual Reviews

Among the salient points of proven health benefits the researchers note, nutritionally-replete plant-based diets are supported by a wide array of favorable health outcomes, including fewer cancers and less heart disease. These diets ideally included not just fruits and vegetables, but whole grains, nuts, and seeds. Katz and Meller found "no decisive evidence" that low-fat diets are better than diets high in healthful fats, like the Mediterranean. Those fats include a lower ratio of omega-6 to omega-3 fatty acids than the typical American diet.
The Mediterranean diet, which is additionally defined by high intake of fiber, moderate alcohol and meat intake, antioxidants, and polyphenols, does have favorable effects on heart disease, cancer risk, obesity, metabolic syndrome, and "is potentially associated with defense against neurodegenerative disease and preservation of cognitive function, reduced inflammation, and defense against asthma."
They also found carbohydrate-selective diets to be better than categorically low-carbohydrate diets, in that incorporating whole grains is associated with lower risks for cancers and better control of body weight. Attention to glycemic load and index is "sensible at the least." Eating foods that have high glycemic loads (which Katz says is much more relevant to health outcomes than glycemic index—in that some quality foods like carrots have very high indices, which could be misleading) is associated with greater risk of heart disease.
Finally, in a notable blow to some interpretations of the Paleo diet, Katz and Meller wrote, "if Paleolithic eating is loosely interpreted to mean a diet based mostly on meat, no meaningful interpretation of health effects is possible." They note that the composition of most meat in today's food supply is not similar to that of mammoth meat, and that most plants available during the Stone Age are today extinct. (Though it wouldn't surprise me to learn that Paleo extremists are crowd-funding a Jurassic Park style experiment to bring them back.)
Just because Katz is not one to abandon his scientific compass under duress of passion does not mean he is without passion, or unmoved by it in his own ways. The subjects of media headlines and popular diet books are dark places for Katz. "It’s not just linguistic, I really at times feel like crying, when I think about that we’re paying for ignorance with human lives," he told me. "At times, I hate the people with alphabet soup after their names who are promising the moon and the stars with certainty. I hate knowing that the next person is already rubbing his or her hands together with the next fad to make it on the bestseller list."
"The evidence that with knowledge already at our disposal, we could eliminate 80 percent of chronic disease is the basis for everything I do," Katz said. Just as he was finishing his residency in internal medicine in 1993, influential research in the Journal of the American Medical Association ("Actual Causes of Death in the United States") put diet on a short list of the lifestyle factors blamed for half of deaths in 1990. "Here we are more than 20 years later and we’ve made just about no progress."
A nod to the fact that popular media is not totally lost, Katz borrows from the writer Michael Pollan, citing a seminal 2007 New York Times Magazine article on "nutritionism" in concluding that the mantra, "Eat food, not too much, mostly plants" is sound. "That’s an excellent idea, and yet somehow it turns out to be extremely radical."
Though Katz also says it isn’t nearly enough. "That doesn't help you pick the most nutritious bread, or the best pasta sauce. A member of the foodie elite might say you shouldn't eat anything from a bag, box, bottle, jar, or can." That's admittedly impractical. "We do need to look at all the details that populate the space between where we are and where we want to be."
The current review is in pursuit of that, as is a system for determining the nutritional value of foods that Katz recently spent two years developing. It's called NuVal, and it offers consumers a single numeric value to determine foods' worth, as opposed to a complex nutritional panel. The number does things like differentiate intrinsic from added nutrients. "If you don’t do that, the best thing in the whole damn food supply is Total cereal. Total is basically a completely vapid flake delivery system for multivitamins. You could skip the cereal and take the multivitamin."
"If you eat food direct from nature," Katz added, "you don’t even need to think about this. You don't have to worry about trans fat or saturated fat or salt—most of our salt comes from processed food, not the salt shaker. If you focus on real food, nutrients tend to take care of themselves."
The ultimate point of this diet review, which is framed like a tournament, is that there is no winner. More than that, antagonistic talk in pursuit of marketing a certain diet, emphasizing mutual exclusivity—similar to arguments against bipartisan political rhetoric—is damaging to the entire system and conversation. Exaggerated emphasis on a single nutrient or food is inadvisable. The result, Katz and Meller write, is a mire of perpetual confusion and doubt. Public health could benefit on a grand scale from a unified front in health media: Endorsement of the basic theme of what we do know to be healthful eating and candid acknowledgement of the many details we do not know.
"I think Bertrand Russell nailed it," Katz told me, "when he said that the whole problem with the world is that fools and fanatics are so sure, and wise people always have doubts. Something like that."

Vegetarians Are Thinner but Less Healthy than Omnivores in New Study

For a few decades now, vegetarians have been arguing that eating meat is unhealthy and leads to diseases such as "hypertension, cholesterol problems, some chronic degenerative diseases, coronary artery disease, type II diabetes, gallstones, stroke, and certain cancers." A new study from Nathalie T. Burkert, et al (PLoS ONE, Feb 7 2014; 9(2): e88278) finds that vegetarians have a lower BMI than omnivores (on average) but that they are more likely to have allergies, mental health issues, and various forms of cancer.

However, the authors are clear in the discussion that this study has very specific limitations that prevent any broad conclusions being drawn (especially that there was no difference in smoking behavior among the four groups - it seems even vegetarians smoke in Austria).

[T]he survey was based on cross-sectional data. Therefore, no statements can be made whether the poorer health in vegetarians in our study is caused by their dietary habit or if they consume this form of diet due to their poorer health status. We cannot state whether a causal relationship exists, but describe ascertained associations. Moreover, we cannot give any information regarding the long-term consequences of consuming a special diet nor concerning mortality rates. Thus, further longitudinal studies will be required to substantiate our results.

In addition, the study does not break down the nutrient consumption of any of the four groups (1. vegetarian, 2. carnivorous diet rich in fruits and vegetables, 3. carnivorous diet less rich in meat, and 4. carnivorous diet rich in meat), for example, carbohydrate intake (and sources), fatty acid intake and ratios, and ratios of macronutrients in the overall diet.

One other limitation that authors emphasize is that there is no way to know (based on information gathered) if the vegetarians are consuming said diet as a result of their health issues or of their health issues are a result of their diet (much less likely, even though I believe a vegetarian diet is not generally a healthy approach to eating).

Nutrition and Health – The Association between Eating Behavior and Various Health Parameters: A Matched Sample Study

Nathalie T. Burkert, Johanna Muckenhuber, Franziska Großschädl, Éva Rásky, and Wolfgang Freidl

Abstract

Population-based studies have consistently shown that our diet has an influence on health. Therefore, the aim of our study was to analyze differences between different dietary habit groups in terms of health-related variables. The sample used for this cross-sectional study was taken from the Austrian Health Interview Survey AT-HIS 2006/07. In a first step, subjects were matched according to their age, sex, and socioeconomic status (SES). After matching, the total number of subjects included in the analysis was 1320 (N=330 for each form of diet – vegetarian, carnivorous diet rich in fruits and vegetables, carnivorous diet less rich in meat, and carnivorous diet rich in meat). Analyses of variance were conducted controlling for lifestyle factors in the following domains: health (self-assessed health, impairment, number of chronic conditions, vascular risk), health care (medical treatment, vaccinations, preventive check-ups), and quality of life. In addition, differences concerning the presence of 18 chronic conditions were analyzed by means of Chi-square tests. Overall, 76.4% of all subjects were female. 40.0% of the individuals were younger than 30 years, 35.4% between 30 and 49 years, and 24.0% older than 50 years. 30.3% of the subjects had a low SES, 48.8% a middle one, and 20.9% had a high SES. Our results revealed that a vegetarian diet is related to a lower BMI and less frequent alcohol consumption. Moreover, our results showed that a vegetarian diet is associated with poorer health (higher incidences of cancer, allergies, and mental health disorders), a higher need for health care, and poorer quality of life. Therefore, public health programs are needed in order to reduce the health risk due to nutritional factors.

Introduction

Our diet has an impact on our well-being and on our health. Studies have shown a vegetarian diet to be associated with a lower incidence of hypertension, cholesterol problems, some chronic degenerative diseases, coronary artery disease, type II diabetes, gallstones, stroke, and certain cancers [1]–[7]. A vegetarian diet is characterized by a low consumption of saturated fat and cholesterol, due to a higher intake of fruits, vegetables and whole-grain products [3], [4], [8]. Overall, vegetarians have a lower body mass index [1], [4], [5], [7], [9]–[12], a higher socioeconomic status [13], and better health behavior, i.e. they are more physically active, drink less alcohol, and smoke less [9], [13], [14]. On the other hand, the mental health effects of a vegetarian diet or a Mediterranean diet rich in fruits, vegetables, whole-grain products and fish are divergent [9], [15]. For example, Michalak et al. [16] report that a vegetarian diet is associated with an elevated prevalence of mental disorders. A poor meat intake has been shown to be associated with lower mortality rates and higher life expectancy [17], and a diet which allows small amounts of red meat, fish and dairy products seems to be associated with a reduced risk of coronary heart disease as well as type 2 diabetes [18]. Additionally, evidence concerning lower rates of cancer, colon diseases including colon cancer, abdominal complaints, and all-cause mortality is, however, inconsistent [5]–[7], [19]–[22].

Not only is the intake of certain nutrients, like red meat, associated with an increased health risk [18], [23]–[26], high-caloric intake also plays a crucial role [23], [27]. Moreover, there seems to be proof that lifestyle factors like physical activity may be more crucial in lowering disease rates than individual dietary habits [20], [28]–[29]. While, generally speaking, diets based on plants, like vegetarian diets, seem to be associated with a certain health benefit, a lower risk to contract certain chronic diseases [30], and the ability to improve health [31]–[32], restrictive and monotonous vegetarian diets include the risk of nutritional deficits [2], [18], [19], [30], [33]. Baines et al. [9] report that vegetarians take more medication than non-vegetarians.

To summarize, a number of studies have shown vegetarian diets and diets with poor meat intake to be associated with lower mortality rates for certain diseases. Research about the dietary habits in Austria is, however, rather sparse and mainly focused on genetic factors [33]–[36]. Therefore, the aim of this study was to investigate health differences between different dietary habit groups among Austrian adults.

Methods

Study Design and Study Population

The sample for this cross-sectional study was taken from the Austrian Health Interview Survey (AT-HIS) which ran from March 2006 to February 2007 [37]. The AT-HIS is a standardized survey which is conducted at regular intervals in Austria (currently every eight years). The subjects included in the survey form a representative sample of the Austrian population. They were chosen from the central population register and are distributed across the different geographic regions of Austria. The AT-HIS is part of the European Health Interview Survey (E-HIS; http://www.euhsid.org), an important high-quality survey. The interviews were conducted by free-lancers engaged by the Austrian Statistic Agency. To ensure that all interviews were conducted in the same way, interviewers had to participate in a training day where they were instructed on how to conduct the survey. Time measurement, non-response analyses, and analyses of error dialogs were performed in order to ensure consistency between interviewers. Additionally, all interviewers were supervised by field supervisors. Overall, 15474 individuals, aged 15 years and older, were questioned in computer-assisted personal interviews (CAPI; 54.7% female; response rate: 63.1%).

While 0.2% of the interviewees were pure vegetarians (57.7% female), 0.8% reported to be vegetarians consuming milk and eggs (77.3% female), and 1.2% to be vegetarians consuming fish and/or eggs and milk (76.7% female). 23.6% reported to combine a carnivorous diet with lots of fruits and vegetables (67.2% female), 48.5% to eat a carnivorous diet less rich in meat (60.8% female), and 25.7% a carnivorous diet rich in meat (30.1% female). Since the three vegetarian diet groups included a rather small number of persons (N=343), they were analyzed as one dietary habit group. Moreover, since the vegetarian group was the smallest, we decided to match each of the vegetarians (1) with an individual of each other dietary habit group (carnivorous diet rich in fruits and vegetables (2), carnivorous diet less rich in meat (3) and a carnivorous rich in meat (4)).

Matching Process

In a first step, subjects consuming a vegetarian diet were identified (N=343). All vegetarians were categorized according to their sex, age (in age-groups spanning 5 years, e.g. 20- to 24-year-olds), and socioeconomic status (SES). Each such vegetarian was then matched with one subject consuming a carnivorous diet rich in fruits and vegetables, one individual eating a carnivorous diet less rich in meat, and one subject consuming a carnivorous diet rich in meat. Only 96.2% of the vegetarians were included in the analyses, since not all of them corresponded to a subject of the same sex, age, and SES from a different dietary habit group. Therefore, the total number of analyzed subjects was 1320 (comprising 330 vegetarians, 330 subjects consuming a carnivorous diet rich in fruits and vegetables, 330 individuals eating a carnivorous diet less rich in meat, and 330 subjects consuming a carnivorous diet rich in meat). Each dietary habit group was set-up according to the demographic characteristics shown in Table 1.

Table 1
Data definition and structure for each of the four dietary habit groups.

Ethical Approval

The study was carried out in compliance with the principles laid down in the Helsinki Declaration. No minors or children were included in the study. Verbal informed consent was obtained from all subjects, witnessed, and formally recorded. The Ethics Committee of the Medical University of Graz approved the consent procedure as well as the conductance of this study (EK-number: 24–288 ex11/12).

Variables and Measurements

Face-to-face interviews were conducted by questioning the subjects about their socio-demographic characteristics, health-related behavior, diseases, medical treatments, and also psychological aspects.

The independent variable in this study was the dietary habit of individuals. Concerning eating behavior, the respondents were given a list of six different dietary habits and asked which one describes their eating behavior best (1=vegan, 2=vegetarian eating milk/eggs, 3=vegetarian eating fish and/or milk/eggs, 4=carnivorous diet rich in fruits and vegetables, 5=carnivorous diet less rich in meat, 6=carnivorous diet rich in meat). Participants described their dietary habit, without interviewers giving a clear definition of the various eating categories. Since, overall, only 2.2% of all participants consumed a vegetarian diet, these individuals were analyzed as one dietary habit group. We created a scale that would reflect the animal fat intake for each dietary habit (1=vegetarian diet, 2=carnivorous diet rich in fruits and vegetables, 3=carnivorous diet less rich in meat, 4=carnivorous diet rich in meat).

Since age, sex, and the socioeconomic background of subjects all have an influence on health [38]–[41], we matched the subjects according to these variables in order to control for their influence. The SES of the subjects (ranging between 3 and 15) was calculated using the following variables: net equivalent income, level of education, and occupation. Net equivalent income was calculated based on an equivalence scale provided by the OECD [42], and divided by quintiles. Level of education was measured by an ordinal variable, distinguishing between (1) basic education (up to 15 years of age), (2) apprenticeship/vocational school, (3) secondary education without diploma, (4) secondary education with diploma, and (5) university education. The occupation of the subjects was differentiated into the following five levels: (1) unskilled worker, (2) apprentice/skilled worker, (3) self-employed/middle job, (4) qualified job/academic, (5) executive position. To verify the combination of variables that served to calculate the SES, correlations with the different variables were calculated. They ranged between r=.70 and r=.80.

The body mass index (BMI) and lifestyle factors (physical activity, smoking, and alcohol consumption) were included as covariates in all analyses. The BMI was calculated by dividing the weight of a person in kilograms by the square of their height in meters (kg/m2) [43]. Physical exercise was measured using the short version of the International Physical Activity Questionnaire (IPAQ), a self-reported instrument, which asks for an estimate of the total weekly physical activity (walking, moderate- and vigorous-intensity activity) performed during the last week. The short version of the IPAQ does not discriminate between leisure-time and non-leisure time physical activity. The total MET score was calculated by weighting the reported minutes per week within each activity by a MET energy expenditure estimate that was assigned to each category [44]. Smoking behavior was measured as the number of cigarettes smoked per day. Alcohol consumption was surveyed as the number of days on which alcohol was consumed during the last 28 days.

The dependent variables focusing on ill-health included self-perceived health, ranging from 1 (very good) to 5 (very bad), and impairment to health, ranging from 1 (very impaired) to 3 (not impaired). We further assessed the presence of 18 specific chronic conditions (asthma, allergies, diabetes, cataract, tinnitus, hypertension, cardiac infarction, apoplectic stroke, bronchitis, arthritis, sacrospinal complaints, osteoporosis, urinary incontinence, gastric or intestinal ulcer, cancer, migraine, mental illness (anxiety disorder or depression), and any other chronic condition). Each condition was coded as present (1) or absent (0). We calculated a total frequency score by summing up the chronic conditions present (0–18, sum index). Additionally, a vascular risk score was calculated by summing up the variables “hypertension”, “enhanced blood cholesterol level”, “diabetes”, and “smoking” (0–4, sum index). Each variable was coded as present (1) or absent (0).

A dependent variable concerning health care was created as the sum index of the number of doctors consulted in the last 12 months (0–8, sum index). Each of the 8 medical treatments (general practitioner, gynecologist, urologist, dermatologist, ophthalmologist, internist, orthopedist, and ENT physician) was coded as “consulted” (1) or “not consulted” (0). The number of vaccinations was analyzed by calculating a sum index combining 8 different vaccinations (influenza, tetanus, diphtheria, polio, FSME, pneumococci, hepatitis A and B; 0–8, sum index). Each vaccination was coded as present (1) or absent (0). In addition, preventive health care was analyzed by calculating a sum index of the variables “preventive check-ups”, “mammography”, “prostate gland check-up”, and “Papanicolaou test” (0–4, sum index). Each variable was coded as present (1) or absent (0).

The dependent variable concerning quality of life was measured using the short version of the WHOQOL (WHOQOL-BREF) [45]. Four domain scores (physical health, psychological health, social relationships, and environment) were calculated. These domain scores ranged between 4 and 20.

Statistical Analysis

In a first step subjects with different dietary habits (vegetarian, carnivorous diet rich in fruits and vegetables, carnivorous diet less rich in meat, carnivorous diet rich in meat) were matched according to their sex, age, and SES. Differences in lifestyle factors (BMI, total MET score, number of cigarettes smoked per day, and alcohol consumption in the last four weeks) between the different dietary habit groups were calculated by multivariate analysis of variance.

In order to analyze the differences between the dietary habit groups, multivariate analyses of variance were calculated for the three domains: (1) health (self-reported health, impairment due to health problems, number of chronic conditions, vascular risk), (2) health care (number of visits to the doctor, number of vaccinations, number of used preventive care offers), and (3) quality of life (physical and psychological health, social relationships, and environment). To address the bias of lifestyle factors impacting health, analyses of variance were calculated, controlling for the aforementioned lifestyle variables (BMI, physical activity, smoking behavior, and alcohol consumption).

In the domain of “health”, the two variables “self-reported health” and “impairment due to health problems” were originally assessed using an ordinal scale. Therefore, we controlled the results using non-parametric tests (Kruskal Wallis Test). Since the results were the same, only results of the analyses of variance are reported.

In addition, Chi-square tests were calculated for the aforementioned 18 chronic conditions in order to establish which one occurs significantly more often, depending on the form of nutrition. p-values <.050 were considered as statistically significant. All analyses were calculated using IBM SPSS software (version 20.0) for Windows,

Results

Participant Characteristics and Lifestyle Differences between the Dietary Habit Groups

In total, we analyzed the data of 1320 individuals (330 in each dietary habit group). Each dietary habit group was set-up according to the demographic characteristics shown in Table 1. Overall, 23.6% of all subjects were male and 76.4% female. 40.0% of the individuals were younger than 30 years, 17.8% between 30 and 39 years, 17.6% between 40 and 49 years, 9.4% between 50 and 59 years, 8.4% between 60 and 69 years, 4.4% between 70 and 79 years, and 2.4% than 80 years or older. 30.3% of the subjects had a low SES (they had an SES score of ≤6), 48.8% a middle one (SES between >6 and ≤10), and 20.9% had a high SES (SES>10).

Our multivariate analysis regarding lifestyle showed a significant main effect for the dietary habit of individuals (p=.000), showing that the different dietary habit groups differ in their overall health behavior. However, results of the univariate analyses showed that the dietary habit groups only differ concerning their BMI and their alcohol consumption.

Concerning BMI: vegetarians have the lowest mean BMI (M=22.9), followed by subjects eating a carnivorous diet less rich in meat (M=23.4), rich in fruits and vegetables (M=23.5), and rich in meat (M=24.9). Heavy meat eaters differ significantly from all other groups in terms of their BMI (p=.000).

Concerning physical exercise: no significant difference was found in the total MET score between the various dietary habit groups (p=.631).

Concerning smoking behavior: the number of cigarettes smoked per day did not differ between the various dietary habit groups (p=.302).

Concerning alcohol consumption: Subjects following a vegetarian diet (M=2.6 days in the last 28 days) or a carnivorous diet rich in fruits and vegetables (M=3.0 days) consume alcohol significantly less frequently than those eating a carnivorous diet less rich in meat (M=4.4 days) or rich in meat (M=4.8 days; p=.000).

Health Differences between the Dietary Habit Groups

In the domain of health, the multivariate analysis of variance showed a significant main effect for the dietary habit of individuals (p=.000). Overall, vegetarians are in a poorer state of health compared to the other dietary habit groups. Concerning self-reported health, vegetarians differ significantly from each of the other groups, toward poorer health (p=000). Moreover, these subjects report higher levels of impairment from disorders (p=.002). Vegetarians additionally report more chronic diseases than those eating a carnivorous diet less rich in meat (p=.000; Table 2). Significantly more vegetarians suffer from allergies, cancer, and mental health ailments (anxiety, or depression) than the other dietary habit groups (Table 3). Subjects who eat a carnivorous diet rich in meat more often report urinary incontinence (p=.023). No differences between individuals consuming different forms of diet were found regarding their vascular risk (p=.150; Table 2).

Table 2
Differences in health and health care between the different dietary habit groups.

Table 3
Differences in suffering from various chronic conditions between the different dietary habit groups.

Differences in Health Care between the Dietary Habit Groups

Our multivariate analysis regarding health care has shown a significant main effect for dietary habits (p=.000) and confirmed that, overall, subjects with a lower animal fat intake demonstrate worse health care practices. Vegetarians and subjects eating a carnivorous diet rich in fruits and vegetables consult doctors more often than those eating a carnivorous diet less rich in meat (p=.003). Moreover, vegetarians are vaccinated less often than all other dietary habit groups (p=.005) and make use of preventive check-ups less frequently than subjects eating a carnivorous diet rich in fruits and vegetables (p=.033; Table 2).

Differences in Quality of Life between the Dietary Habit Groups

Regarding quality of life, the main effect of the multivariate analysis of variance showed no significant difference between the dietary habit groups (p=.291). The results obtained in the univariate analyses of variance, however, revealed that vegetarians have a lower quality of life in the domains of “physical health” (p=.026) and “environment” (p=.037) than subjects consuming a carnivorous diet less rich in meat. Moreover, vegetarians have a lower quality of life regarding “social relationships” than individuals eating a carnivorous diet rich in fruits and vegetables, or those with a carnivorous diet less rich in meat (p=.043). All results are shown in Table 4.

Table 4
Differences in quality of life between the different dietary habit groups.

Discussion

Overall, our findings reveal that vegetarians report poorer health, follow medical treatment more frequently, have worse preventive health care practices, and have a lower quality of life. Concerning the variable “eating behavior”, we tried to generate a variable that would reflect the animal fat intake (1=vegetarian, 2=carnivorous diet rich in fruits and vegetables, 3=carnivorous diet less rich in meat, 4=carnivorous diet rich in meat). The mean BMI of subjects is coupled in nearly linear progression with the amount of animal fat intake. This is in line with previous studies showing vegetarians to have a lower body mass index [1], [4], [5], [7], [9]–[12].

Our results have shown that vegetarians report chronic conditions and poorer subjective health more frequently. This might indicate that the vegetarians in our study consume this form of diet as a consequence of their disorders, since a vegetarian diet is often recommended as a method to manage weight [10] and health [46]. Unfortunately, food intake was not measured in more detail, e.g. caloric intake was not covered. Hence, further studies will be necessary to analyze health and its relationship with different forms of dietary habits in more detail.

When analyzing the frequency of chronic diseases, we found significantly higher cancer incidence rates in vegetarians than in subjects with other dietary habits. This is in line with previous findings, reporting that evidence about cancer rates, abdominal complaints, and all-cause mortality in vegetarians is rather inconsistent [5]–[7], [19]–[22]. The higher cancer incidence in vegetarians in our study might be a coincidence, and is possibly related to factors other than the general amount of animal fat intake, such as health-conscious behavior, since no differences were found regarding smoking behavior and physical activity in Austrian adults as reported in other studies for other countries [9], [13], [14]. Therefore, further studies will be required in Austria in order to analyze the incidence of different types of cancer and their association with nutritional factors in more depth.

Several studies have shown the mental health effects of a vegetarian diet to be divergent [9], [15], [16]. Vegetarians in our study suffer significantly more often from anxiety disorder and/or depression. Additionally, they have a poorer quality of life in terms of physical health, social relationships, and environmental factors.

Moreover, the use of health care differs significantly between the dietary habit groups in our study. Vegetarians need more medical treatment than subjects following another form of diet. However, this might be due to the number of chronic conditions, which is higher in subjects with a vegetarian diet.

Among the strengths of our study are: the large sample size, the matching according to age, sex, and socioeconomic background, and the standardized measurement of all variables. Other strengths of our study include considering the influence of weight and lifestyle factors on health, e.g. physical exercise and smoking behavior.

Potential limitations of our results are due to the fact that the survey was based on cross-sectional data. Therefore, no statements can be made whether the poorer health in vegetarians in our study is caused by their dietary habit or if they consume this form of diet due to their poorer health status. We cannot state whether a causal relationship exists, but describe ascertained associations. Moreover, we cannot give any information regarding the long-term consequences of consuming a special diet nor concerning mortality rates. Thus, further longitudinal studies will be required to substantiate our results. Further limitations include the measurement of dietary habits as a self-reported variable and the fact that subjects were asked how they would describe their eating behavior, without giving them a clear definition of the various dietary habit groups. However, a significant association between the dietary habit of individuals and their weight and drinking behavior is indicative for the validity of the variable. Another limitation concerns the lack of detailed information regarding nutritional components (e.g. the amount of carbohydrates, cholesterol, or fatty acids consumed). Therefore, more in-depth studies about nutritional habits and their effects on health are required among Austrian adults. Further studies should e.g. investigate the influence of the various dietary habits on the incidence of different cancer types. To our knowledge this is the first study ever in Austria to analyze differences in terms of dietary habits and their impact on health. We admit that the large number of participants made it necessary to keep the questions simple, in order to cover the large sample. Overall, we feel that our results are of specific interest and contribute to extant scientific knowledge, notwithstanding some limitations regarding causes and effects.

Conclusions

Our study has shown that Austrian adults who consume a vegetarian diet are less healthy (in terms of cancer, allergies, and mental health disorders), have a lower quality of life, and also require more medical treatment. Therefore, a continued strong public health program for Austria is required in order to reduce the health risk due to nutritional factors. Moreover, our results emphasize the necessity of further studies in Austria, for a more in-depth analysis of the health effects of different dietary habits.

Funding Statement
The authors have no support or funding to report.

References available at the PLoS ONE site.