The human brain consumes a lot of energy, and a new analysis suggests that part of this expenditure was made possible by foods naturally rich in sugars. Fruits, honey, and then cooked starchy foods would have progressively provided more glucose to hominins over the last four million years.
The starting point is simple: the brain mainly uses glucose as fuel. Yet its size increased significantly over the course of human evolution. The authors therefore looked for which food sources could provide this energy fairly regularly, at different periods, without assuming that a single type of food explains everything.
Their work is based on a model that reconstructs possible intakes of sugars and starch according to environments, available foods, and the technical transformations that emerged over time. Starch is a carbohydrate found notably in roots, tubers, and seeds. Once digested, it also provides glucose.
Early hominins would have especially benefited from the sugars naturally present in fruits. Honey, very concentrated in carbohydrates, would then have represented a particularly energy-rich resource when accessible.
An additional change appears with cooking. Heating starchy foods makes them easier to digest. This increases the amount of recoverable energy and reduces the effort needed to chew and then process certain plants. In this context, the mastery of fire would therefore have reinforced a trend already underway long before it.
The analysis also places meat consumption in a broader context. Animal products provide proteins and lipids, but they do not constitute a major direct source of glucose. The authors therefore estimate that carbohydrates may have played a more central energetic role than previously thought in the increase of brain size.
The study does not present modern sugar as beneficial without limit. Whole fruits, occasional honey, and starchy plants do not correspond to the large amounts of refined sugars available today.
The model remains a reconstruction of ancient diets, not a direct measurement of what each population ate. The next step is to further compare these estimates with archaeological evidence, dental wear traces, food residues, and data on the environments frequented by the different human species.