Forget meat: Scientists say fruit and honey helped build the human brain

A study in Science says fruit, honey and cooked starches may have fuelled human brain growth. The findings challenge meat-first theories and highlight glucose as a key evolutionary driver.

In Short

• The brain uses 20 per cent of resting energy in adults
• In young children, brain energy demand can rise to 66 per cent
• Models across six evolutionary stages tested diets against glucose needs

For decades, scientists and diet enthusiasts have credited meat as the fuel that powered the evolution of the human brain.

But a new study published in the journal Science is challenging that long-held belief, suggesting that fruit, honey, and later cooked starches may have been just as important, if not more so, in shaping modern human intelligence.

The research argues that the human brain's extraordinary growth over the past four million years was driven by a steady supply of glucose, the body's preferred fuel for brain activity.

While animal foods provided essential nutrients, researchers say carbohydrates may have played a crucial role in meeting the energy demands of an increasingly complex brain.

The study tracked the evolution of hominins from Australopithecus afarensis, which had a brain weighing about 300 grams, to modern Homo sapiens, whose brain can weigh up to 1,500 grams.

Despite accounting for only 2 per cent of an adult's body weight, the human brain consumes around 20 per cent of the body's resting energy and as much as 66 per cent in young children.

Scientists modeled dietary patterns across six stages of human evolution, examining how different combinations of plant and animal foods could satisfy the body's glucose requirements.

They found that early human ancestors were likely highly dependent on fruit and other sweet foods, obtaining more than 65 per cent of their energy from sugars.

As humans learned to control fire and cook food, starchy plants increasingly replaced fruit sugars as a reliable source of glucose. The researchers argue that this shift helped support larger brains, reproduction, and child development.

The findings also draw on evidence from fossil teeth, stable isotope studies, color vision, dental cavities, and human genetics. Together, these clues suggest that early hominins were adapted to diets rich in carbohydrates rather than exclusively meat-heavy menus.

"Our modern physiology and anatomy, including sweet taste receptors, smaller teeth, jaw, gut, and genetic variations relating to glucose metabolism, suggest genetic selection driven specifically by dietary carbohydrates," researchers noted in the paper.

The study does not dismiss the importance of animal foods.

Instead, it proposes a more balanced picture of human evolution, one in which sweet fruits, honey, and cooked starches helped provide the energy needed for the growth of the most complex organ on Earth.

In other words, humanity's biggest evolutionary leap may have owed as much to nature's sugars as to the hunt.

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