It is well known today that carbohydrates are a rich source of energy. Several recent studies have suggested we should cut on carbs to lose weight. However, for our ancient ancestors, gathering carbohydrates for their energy could have been the trigger to the evolution of human brain.

A group of British researchers,  by looking at past work on human evolution, had the intuition that once ancient humans learned to cook, by using starchy foods like root vegetables or grasses they got access to a rich source of calorie that fueled the evolution of the human brain.

It was previously suggested that the early brain began developing and growing in volume at least 2.5 million years ago. Researchers studying Paleolithic diets believed that this process began after early humans learned to butcher and processed meat with stone tools. However, a group of British researchers came to a different conclusion. According to Mark Thomas, an evolutionary geneticist at University College London, the brain truly accelerated in increasing its size only around 800,000 years ago.

The recently discovered remains of a hunter-gatherer dating between 14,000 and 15,000 years ago show signs of oral disease and dental caries in the upper teeth. According to the paleo-anthropologist Louise Humphrey, these findings challenge the idea that the original Paleolithic diet was inherently healthy. She added that it is more likely that all depended on what wild foods were available.

In a new paper published in The Quarterly Review of Biology, Thomas and colleagues sustain their hypothesis that the brain suddenly began evolving faster because our ancient ancestors discovered a better brain food. Thomas says that at that point, human populations started to consume more carbs-rich foods and developed the use of fire. Those two improvements "were critical to the expansion of the brain."

Carbs, the starches, are an ideal brain food, according to Thomas, since our human brains have an absolute requirement for glucose. And a diet rich in carbs allows the body to not spend extra energy converting other nutrients into glucose to feed the brain.

Starch-digesting enzymes called amylases could work much more efficiently than they could on raw vegetables once humans began cooking vegetables. According to Thomas, cooked potatoes, for example, provide starches that can be digested about 20 times faster than if they would be uncooked. And, since the earliest evidence for fire comes from around the 500 to 800,000-year period, Thomas explained that the logical conclusion is that was the moment when carbs turned into a major source of energy that triggered our brain evolution.