Low Carb Diet Is Bad For Thinking And Memory
Featured ArticleMain Category: Nutrition / Diet
Also Included In: Neurology / Neuroscience; Psychology / Psychiatry
Article Date: 11 Dec 2008 - 11:00 PDT
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A new study from scientists in the US found that when women went on low or zero-carb diets they performed worse on thinking and memory tests compared to reducing calories without reducing carbohydrates. When they put carbs back into their diet, their thinking and memory skills went back to normal.
The study was the work of researchers from the psychology department of Tufts University in Medford, Massachusetts. It is published in the February 2009 journal Appetite and is already available to view online.
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.
"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.
Taylor also explained that:
"Although this study only tracked dieting participants for three weeks, the data suggest that diets can affect more than just weight."
"The brain needs glucose for energy and diets low in carbohydrates can be detrimental to learning, memory, and thinking," she concluded.
"Low-carbohydrate weight-loss diets. Effects on cognition and mood."
Kristen E. D'Anci, Kara L. Watts, Robin B. Kanarek, Holly A. Taylor.
Appetite, Volume 52, Issue 1, February 2009, Pages 96-103
doi:10.1016/j.appet.2008.08.009
Click here for Article (DOI link).
Sources: Tufts University.
Written by: Catharine Paddock, PhD
Copyright: Medical News Today
Not to be reproduced without permission of Medical News Today
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Visitor Opinions In Chronological Order (6)
Incomplete Information
posted by J Nousak on 14 Dec 2008 at 12:01 amStudy participants include women aged 19-55 yrs. indicating that age is a variable that may be confounding in the analysis of results, especially with such a low number of subjects (N=9 and N=10 for Diet A and Diet B, respectively). We don't know whether or not there is a difference in cognitive ability between Diet A people and Diet B people before (italics) the study is implemented. And the small number of subjects does not allow for generalization to the larger group (i.e., the public); generally, an N = 30 per group (Diet A group being one) is the acceptable low end for providing statistical analysis that may be useful to the general public.
IOW, I need more information from the original article to determine the usefulness of the proposed interpretation of the study's meaning (or lack thereof).
JKN
The Study Result Is Misleading At Least.
posted by Robert Su M.D. on 16 Jan 2009 at 6:13 amI, a physician in semi retirement, have used carbohydrate-restricted diet for more than six years for reshaping my health without medications, particularly my cardiovascular system. Recently, I completed a book, Carbohydrates Can Kill It will be available soon.
This study used a small group of women for a period of three weeks to judge the impacts of low carbohydrate diet on the brain functions was very poorly designed. Its result is misleading at least. The authors of this study did not know about all the physiological and biochemical changes in our body as a result of restricting carbohydrate intake.
When switching from carbohydrate-rich-fat-restricted diet to carbohydrate-restricted-fat-rich diet, the body, including the brain, needs to learn to use beta-hydroxybutyrate (ketone) for its energy source. Because gluconeogenesis from proteins and fats will kick in to produce glucose and maintain a normal fasting blood glucose level with very little fluctuation during the 24/7 period, there should not have an incidence of hypoglycemia nor hyperglycemia.
The only benefit of doubt that I could attribute to this study result is the body of those women in the study was not given enough time to readjust the way to use different energy source. Unfortunately, the authors quickly blamed low carbohydrate diet for their premature findings.
I strongly suggest that the authors continue to study the impacts of restricting carbohydrates in diet on the brain functions with a group who have continued taking the diet.
devious comment on low carb diet
posted by Richard Feinman on 25 Jul 2010 at 5:20 amEven if the results meant anything, if they say "The brain needs glucose for energy and diets low in carbohydrates can be detrimental to learning, memory, and thinking," they are trying to manipulate the public. Your brain does not need dietary glucose. Otherwise, you would die if you went a couple of days without food. Do the authors not know this? Of course they do but normal standards do not apply if you can attack low-carb diets. Psychologists don't tend to include honesty and responsibility in cognitive function but the authors may want to look into their own diet.
True - low carb and memory
posted by Angela on 28 May 2011 at 6:26 pmAlthough this study seems short and lacking, I can prove and support that what it has come conclude is true. I have tried low carb diets for 3 years of high school. My grades plummeted immediately after i started the low carb diets even in the easiest courses because it was impossible for me to concentrate. Likewise, as soon as i quit the low carb diets, my grades, even in the AP classes, skyrocketed.
However, i agree that more research does have to done on this topic, which i look forward to hearing about.
It's all true
posted by Rhonda on 8 Nov 2011 at 9:51 amI agree that the studies should be longer. But I know for a fact this is true. I am gluten intolerant and my blood sugar fluctuates and I can get hypoglycemic at night. So I went on a meat, vege, occaisional fruit, some nuts/seeds and legumes diet. And have been failing in my work ever since. Just yesterday when trying to work after not being able to for weeks. I got up, got a slice of whole grain bread with nut butter and a couple pieces of candy and my brain was changed within minutes. After weeks of not being able to create (I'm an artist) I finally produced some beautiful work. I've been on this diet for long enough that I know for a fact it is bad. I am naturally a thin person so maybe I just don't have enough glucogen stores in my body to get me through. Maybe it's the overweight people who do better on this diet. I truly do not believe that one diet fits all since there are so many different body types. If your thin forget a low carb diet, you suffer. And I also have very weak and painful muscles. I stopped going to the gym because of the weakness and lack of motivation I was feeling on the low-ish carb diet. I'm just happy I figured this all out before losing everything. By the way I was able to function normally as a person. I had enough energy to go out once I was persuaded. It's just the brain that suffers with concentration not being at it's highest peak as well as muscle weakness. Those who do not experience this perhaps have enough glucogen stores for now. But give it time. A year from now perhaps when you run out and your mind starts going..eat some carbs.
Former low carber agrees with results
posted by Rick on 10 Dec 2011 at 10:47 amI have been low to zero carb for three years until just the last month. I began to notice I was extremely agitated and short tempered with people. I did a little web searching on this and found that serotonin (the chemical that affects mood, sleep, appetite, etc) cannot be made without glucose. For those of us who may be naturally low in serotonin or serotonin depleted, a low carb diet can really affect how we feel and think. In order for serotonin to be produced, the brain requires glucose and insulin in order for tryptophan to be allowed into the brain. Tryptophan is the precursor to serotonin. I started adding a cup of brown rice and a sweet potato to my daily diet of fish, nuts, vegetables, and seeds and my mood began improving immediately. I concentrate better and I have better memory and conversation skills with about 100 grams of complex carbs in my diet.
I think the issue is that most people eat too many carbs and "too many" is different for everyone. While it may be healthy for the body to reduce insulin, leptin, and glucose levels, the brain requires a certain level of sugar to function. Ketones don't cut it and when you're physically active like me, the liver just can't make enough glucose to create the proper brain chemistry.
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