The Link Between Diet and a Big Brain

Carbohydrates have been getting a bad reputation for too long. Weight-watchers and health enthusiasts shun carbs like the plague and countless diets harp on banishing carbohydrates altogether from our meals. But now all this is about to change. Scientists say that throughout the history of human evolution, carbohydrates have played a crucial role in making our brains bigger (read: smarter and more efficient).

These findings add to the knowledge that consumption of meat and cooked food had a hand in the development of the brain. With all these findings, think twice before you jump into a diet that asks you to do away with specific food groups.

Our brains get a kick out of sugar

The human brain has grown in size and capability over the last two million years, after man started eating meat and cooked food. Although a recently published study does not dispute these findings, it also asserts that the roles of meat and cooked food have been highlighted to the exclusion of the significance of carbs. The study, in particular, focuses on the role of plant-based starchy food.

Here’s the chain of thoughts (backed by research findings) that made scientists arrive at this conclusion.

Finding #1: The brain needs glucose to function

By volume, the human brain may occupy only a small portion in the body. But it uses 25 percent of the body’s total energy needs and 60 percent of total blood glucose requirements to function effectively. The glucose needs of the brain cannot be met on a low-carb diet. It is not likely that the human brain could have evolved without our ancestors consuming a lot of carbs.

It is possible that the scientists were influenced by the findings of an earlier study. According to this study, humans produce some lactate even at rest. During anesthesia, the proportion of lactate in the arteries increases significantly, but the brain still does not use it. The brain uses up the arterial lactate and glucose only when it is activated, like when exercising or indulging in some mental activity. During this experiment, scientists discovered that the brain used up more lactate and glucose when active and this amount was in proportion to the amount present in the arteries.

They also noted that the metabolic activity of the brain decreased (read: the brain worked less) when the amount of lactate available for uptake decreased. This finding, in particular, led researchers to deduce that the functionality of the brain is closely associated with the availability of glucose.

Finding #2: Our ancestors started to eat cooked starch just a few centuries before their brains started an accelerated phase of growth

Plant-based starch items were readily available to our ancestors millions of years ago. So it is likely that they included these in their diets; after all, they didn’t have much to choose to from.

The findings of some archaeological and genetic research studies reveal some interesting correlations. During the period of human evolution, there was a spurt in the development of the brain from around 800,000 years ago. Our ancestors started eating cooked food from just before this period. Now, cooked starch products are more easily digested than their raw forms. So it is likely that man was eating cooked starch during the centuries before his brain started to develop in rapid bursts.

Finding #3: Man is genetically programmed to optimally break down and absorb starch

The genetic and archaeological studies revealed a critical finding. Salivary amylase genes started multiplying in humans from about a million years ago. Salivary amylase is instrumental in breaking down starch rapidly and making it available to the body for absorption. It is interesting to note that man has more salivary amylase gene copies (approximately six, but the number varies across individuals) than any other primate (only two). So there is a reason why Mother Nature intended for man to be able to make optimal use of starch.

Finding #4: The action of salivary amylase on starch keeps blood glucose levels in check

Several studies have pointed out the adverse effects of low blood glucose levels on cognitive performance. According to one research paper, the performance of the subjects in an experiment on executive and non-executive functions declined considerably after a period of fasting that lowered their blood glucose levels. The tasks included memory recall, decision-making, attention, visual and auditory processing, and verbal fluency.

On the other hand, another study notes that high “normal” blood glucose levels can shrink the amount of white and grey matter in the brains of the elderly.

From these two findings, it is clear that although human brains need glucose to function, it is critical that blood glucose levels should also be regulated. Individuals with more copies of the salivary amylase gene can absorb starch more efficiently and thus are better equipped to keep their blood glucose levels under control.

The implications of the above findings

The above findings have immense implications for future dietary research studies.

Scientists are now a step closer to deciphering the right food mix that can contribute to brain health. Their studies and the resultant findings can help doctors, nutritionists, psychiatrists, and counselors create diet plans for their patients. Schools can evaluate the nutritional value of the lunches they serve and re-think the menus, if required.

Most importantly, these findings should make the common man or the woman on the street, anxious about his expanding waistline or her muffin top, think twice before embracing a carbohydrate-free diet.

Scientists should now also look into how plant-based starchy food works on the brain to improve the latter’s functionality or what components in these foods help the brain. The knowledge can help them come up with dietary alternatives or pharmacological solutions for people who may be allergic to starchy food.


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Hardy, K., Brand-Miller, J., Brown, K., Thomas, M., & Copeland, L. (2015). The Importance of Dietary Carbohydrate in Human Evolution The Quarterly Review of Biology, 90 (3), 251-268 DOI: 10.1086/682587

Mandel, A., & Breslin, P. (2012). High Endogenous Salivary Amylase Activity Is Associated with Improved Glycemic Homeostasis following Starch Ingestion in Adults Journal of Nutrition, 142 (5), 853-858 DOI: 10.3945/jn.111.156984

Mortby, M., Janke, A., Anstey, K., Sachdev, P., & Cherbuin, N. (2013). High “Normal” Blood Glucose Is Associated with Decreased Brain Volume and Cognitive Performance in the 60s: The PATH through Life Study PLoS ONE, 8 (9) DOI: 10.1371/journal.pone.0073697

Quistorff, B., Secher, N., & Van Lieshout, J. (2008). Lactate fuels the human brain during exercise The FASEB Journal, 22 (10), 3443-3449 DOI: 10.1096/fj.08-106104

Image via Syda Productions / Shutterstock.

Viatcheslav Wlassoff, PhD

Viatcheslav Wlassoff, PhD, is a scientific and medical consultant with experience in pharmaceutical and genetic research. He has an extensive publication history on various topics related to medical sciences. He worked at several leading academic institutions around the globe (Cambridge University (UK), University of New South Wales (Australia), National Institute of Genetics (Japan). Dr. Wlassoff runs consulting service specialized on preparation of scientific publications, medical and scientific writing and editing (Scientific Biomedical Consulting Services).
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