Humans have big brains, and those brains come with a big appetite for energy. The focus on what fueled the evolution of our massive noggins has centered on protein from meat, but a new analytical review published today in Science is reframing the story around a much sweeter center: glucose.
“While animal foods were important, the brain’s need for glucose has largely received little attention from anthropologists,” study author Jennie Brand-Miller said in a statement.
Nutritional scientists from the University of Sydney and University of Glasgow modeled dietary intake versus energy needs for varying brain and body sizes across 4 million years of hominin evolution. The models relied on data from the dietary composition of primates, fossil dental isotopes and morphology, genetics, and more. Over this 4-million-year period, brain size of hominins quintupled from 300 grams in Australopithecus afarensis to 1,500 grams in modern Homo sapiens, and metabolic needs increased accordingly.
Read more: “Why Is the Human Brain So Efficient?”
By calculating the “obligatory glucose demand” (the amount of energy required to run the brain, the body, and produce offspring) and comparing it to energy available from food sources, they determined simple carbohydrates played an outsized role in the development of outsized brains. According to the team, natural sugars from fruit, honey, and other sweet foods provided roughly 20 to 35 percent of energy intake throughout hominin evolution. After our ancestors tamed fire, they were able to unlock the complex carbohydrates in starchy foods, like tubers.
The study helps explain why we have such a sweet tooth, especially children whose brains can burn up to nearly two-thirds of the calories they consume. It also puts a new spin on the popular paleo diet. “The evidence suggests that carbohydrate-rich foods helped fuel the energy demands of our growing brains,” Brand-Miller said. “Rather than fearing carbohydrates, people should focus on high-quality sources, including whole fruits, legumes, and nutritious grains, and prioritize a range of carbohydrate foods as part of a healthy diet.”
So go ahead and drizzle some honey on that steak—your inner hominin deserves it. 
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Lead image: Yevheniia / Adobe Stock
