Cooked Carbohydrates May Have Boosted Human Brain Growth Over Time

Karen Hardy  ICREA, Catalan Institution for Research and Advanced Studies Departament de Prehistòria Facultat de Filosofia i Lletres Universitat Autònoma de Barcelona Barcelona, Interview with:
Dr. Karen Hardy 
ICREA, Catalan Institution for Research and Advanced Studies
Departament de Prehistòria
Facultat de Filosofia i Lletres
Universitat Autònoma de Barcelona
Barcelona, Spain


MedicalResearch: What is the background for this study? What are the main findings?

Dr. Hardy: There continues to be little clear agreement on what quantitatively constitutes a healthy diet. The global increase in the incidence of obesity and diet-related metabolic diseases have intensified interest in ancestral or “Palaeolithic” diets as it is clear that to a first order of approximation our physiology should be optimized to the diet that we have experienced during our evolutionary past. However, reconstructing ancestral diets is very challenging, and exactly what was eaten during the Palaeolithic remains largely unknown.

Until now, there has been a heavy focus on the role of animal fats and protein in the development of the human brain and there is little doubt that increases in meat consumption from around 3.4 million years ago, was a major driver. However, the role of carbohydrates, particularly in the form of starch-rich plant foods, has largely been overlooked. But the human brain today uses up to 25 % of the body’s energy budget and up to 60 % of blood glucose as a general rule, while pregnancy and lactation in particular, place additional demands on the body’s glucose budget. In this study we integrated multiple lines of evidence from human genetics, archaeology, anthropology, physiology, and nutrition, to hypothesise that cooked carbohydrates played an important part in the evolution of the body, and particularly the brain, over the last 800,000 years.

Our results suggest that while meat was important, brain growth is less likely to have happened without the energy obtained from carbohydrates. While cooking has also been proposed as contributing to early brain development, it has a particularly profound effect on the digestibility of starch. Furthermore, humans are unusual among primates in that they have many copies of the salivary amylase gene (average of around six salivary amylase genes, other primates have only two) leading to more efficient starch digestion. This suggests that cooking starch-rich plants and having more amylase coevolved. We don’t know exactly when the number of amylase gene copies multiplied, but genetic data suggest it was in the last million years; a timeframe that brackets archaeological evidence for cooking and when our brain size increase accelerated (around 800,000 years ago). Salivary amylases are largely ineffective on raw crystalline starch, but cooking substantially increases both their energy-yielding potential and glycemia.

MedicalResearch: What should clinicians and patients take away from your report?

Dr. Hardy: A reliable source of glycemic carbohydrate is necessary to support the normal functioning of our brain, kidney medulla, red blood cells, and reproductive tissues, and should not be omitted from the diet because of popular misconceptions about what constitutes a ‘Palaeolithic’ diet. However, eating too much high glycaemic starchy food can contribute to obesity and increase the risk of diet-related disease. Encourage people to focus on low-glycaemic index carbohydrate sources, such as beans, small seeds, whole grains and nuts, and avoid excess highly processed carbohydrate.

MedicalResearch: What recommendations do you have for future research as a result of this study?

Dr. Hardy: Further work is required on the amylase gene cluster as the locus remains incompletely characterized, particularly regarding when amylase gene copy number increased. Such information could come from comparison for different amylase gene copies, or from ancient DNA studies. The importance of preformed glucose is currently an active area of research and evidence for the essential nature of glucose in brain growth and function, and in fetal development, is likely to increase. More archaeological information on the widespread adoption of fire for cooking is also needed.


Hardy, K, Brand Miller, J, Brown, KJ, Thomas, MG, Copeland, L. 2015. The importance of dietary carbohydrate in human evolution. The Quarterly Review of Biology; 90(3)251-268 DOI: 10.1086/682587

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Dr. Karen Hardy (2015). Cooked Carbohydrates May Have Boosted Human Brain Growth Over Time