Thursday, December 11, 2008

Junk Science Alert - Low Carb Diet Is Bad For Thinking And Memory

I can usually just ignore bad science, unless it's being proliferated in a field that I care about. That's exactly what happened today with a study on low-carb diets and cognitive function. I've been living a low-carb life for nearly two years now, and have done my research into its benefits and risks, so I know my stuff in this area.

Here are the results Medical News Today posted:
Dr Holly Taylor, professor of psychology at Tufts and corresponding author of the study, said the findings showed that:

"The food you eat can have an immediate impact on cognitive behavior."

"The popular low-carb, no-carb diets have the strongest potential for negative impact on thinking and cognition," she added.

Taylor's co-authors and research colleagues were Professor Robin Kanarek, former undergraduate Kara Watts and research associate Kristen D'Anci.

Our brain cells need glucose to work, but they have no way of storing it so they rely on a continuous supply via the bloodstream. The researchers had a hunch that reducing carbohydrate intake would reduce the body's ability to keep the brain supplied with glucose and therefore affect cognition, since glucose comes from breaking down carbohydrates.

For the study, Taylor and colleagues recruited 19 women aged 22 to 55 and let them each choose to go on either a low carb or low calorie diet as recommended by the American Dietetic Association. Nine of them chose the low carb diet and the other 10 chose the low calorie diet.

Altogether the participants attended five assessment sessions. Session 1 was just before they started on their chosen diet, sessions 2 and 3 were during the first week of dieting (when the low-carb dieters eliminated carbohydrates), and sessions 4 and 5 were in weeks 2 and 3, after the low-carb dieters started eating carbohydrates again.

During the assessment sessions the dieters performed a range of tests that measured attention, short and long term memory, visual attention and spatial memory. They also answered questions about how hungry they felt and their mood.

The results showed that:
  • Low carb dieters showed a gradual decrease on memory tasks compared with low-calorie dieters.

  • Reaction time for the low-carb dieters was slower, and their visual-spatial memory was not as good as that of the low-calorie dieters.

  • But low-carb dieters responded better than low-calorie dieters in the attention-vigilance tasks.

  • This last result is consistent with previous studies that found people on high protein or high fat diets showed short term improvements in attention.

  • Hunger levels did not vary between the two diet groups, and the only difference in mood was that the low-calorie dieters felt more confusion during the middle period of the study.
Taylor said:

"Although the study had a modest sample size, the results showed a clear difference in cognitive performance as a function of diet."

"The data suggest that after a week of severe carbohydrate restriction, memory performance, particularly on difficult tasks, is impaired," she added.
OK, I'll be the first to admit that during the FIRST WEEK of a low-carb diet, cognitive function IS impaired. It generally takes the body and the brain 1-4 weeks to adjust to ketones for energy rather than the glucose it gets from carbohydrate consumption.

During that adjustment period, people tend to feel physically sluggish, mentally slow, and emotionally volatile. This seems to be exactly what the study found.

But the brain is quite capable of functioning properly on ketones, which are a unique form of energy produced from the metabolism of proteins and fats. This is from the site:
It's a common misconception, even among doctors, that the brain can only use glucose for fuel. In actuality, it can burn either glucose or ketones, but under normal circumstances ketones aren't produced by the body. Most of the time, everyone in the world has their brain burning glucose. The only time the body would create and burn ketones in large quantities is when insufficient glucose is available as a fuel source. The way to make glucose (a basic sugar) unavailable, is to simply restrict carbohydrate consumption to 30g/day or less. For example, if you stop eating all carbs at, say, 6:00 PM on Sunday, and then do a heavy weightlifting workout Monday and Tuesday, this will deplete your liver and bloodstream of and glucose, and your muscles of glycogen. At that point, your liver will start producing ketones, so the brain has a fuel to work with, and if you consume no carbohydrates at all, the body will start converting protein into glucose as it will still need at least 30g glucose per day.
The following is from the Wikipedia entry on ketones:
The brain, in particular, relies heavily on ketone bodies as a substrate for lipid synthesis and for energy during times of reduced food intake. At the NIH, Dr. Richard Veech refers to ketones as "magic" in their ability to increase metabolic efficiency, while decreasing production of free radicals, the damaging byproducts of normal metabolism. His work has shown that ketone bodies may treat neurological diseases such as Alzheimer's and Parkinson's disease,[4] and the heart and brain operate 25% more efficiently using ketones as a source of energy.[5] Research has also shown ketones play a role in reducing epileptic seizures with the so-called high-fat, near-zero carbohydrate Ketogenic Diet. [1]
So, clearly, the brain can function on ketones and does not need glucose as its primary energy source.

If the study above had gone on for a month, they would likely have found this to be true. But they only kept the low-carb subejcts on the diet for a week which, especially for the first time doing low-carbs, is not enough time to adjust to ketones for energy (and it ignores the fact that most of those subjects were still using glycogen for energy over the first 3-4 days of the study - it takes that long to deplete muscle and liver glycogen stores).

All of this makes me wonder who funded the research - maybe one of those pseudo-scientific PETA organizations, but who knows. Either way, it's bad science.

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