Fruit, honey and other naturally sweet foods may have helped fuel the evolution of the human brain, according to new research from the 爆料王 and the University of Glasgow.听
Published in听,听the study modelled the glucose needs of humans and their ancestors from four million years ago until recently, finding natural sugars supplied large amounts of energy to support growing brains before the advent of cooking made starch-rich foods like tubers and grains easier to digest.听
鈥淩aw starch does not release glucose, meaning early humans likely relied on naturally sweet foods long before grains became a regular part of the diet,鈥 said lead author听, Professor of Human Nutrition at the 爆料王听Charles Perkins Centre听补苍诲听School of Life and Environmental Sciences.
The findings offer a different perspective on the longstanding scientific view that meat consumption was the key driver of human evolution. They may also provide insight into why we often crave sweet food.听
鈥淲hile animal foods were important, the brain鈥檚 need for glucose has received little attention from palaeoanthropologists,鈥 Professor Brand-Miller said.听
Over a period of four million years, human brain size increased from around 300 grams in early hominins to about 1500 grams in modern humans. As brains grew, so did demand for glucose, which is also required by other tissues including red blood cells, kidneys and reproductive organs.听
鈥淭he human brain is unusually large for our body size and requires substantial amounts of energy,鈥 Professor Brand-Miller said. 听
鈥淕lucose is the brain鈥檚 primary energy source, and for much of human evolution, would have come from carbohydrates found in foods such as fruit and honey.鈥
Modelling the nutritional demands of a growing brain
The researchers developed a model spanning approximately four million years of human evolution to examine whether dietary carbohydrates could meet the increasing glucose demands of a growing brain. They calculated what they describe as 鈥渙bligatory glucose demand鈥 鈥 the glucose required by the brain, red blood cells, kidneys and reproductive tissues including the fetus, placenta and mammary glands 鈥 and compared this with likely food sources available to our ancestors at different stages of evolution.听
The model included six evolutionary stages and assessed how changing proportions of animal and plant foods affected carbohydrate availability.
The researchers combined evidence from food composition, metabolism, physiology, fossil isotope studies, dental morphology, archaeology, primate diets and genetics to estimate how humans met their glucose needs as brain size increased.听
This modelling suggests earliest hominins (such as 鈥楲ucy鈥, whose brain was the same size as a chimpanzee),听Homo habilis听补苍诲听Homo erectus听were likely highly reliant on carbohydrate-rich foods, particularly fruit. Later, as the use of fire and cooking became more widespread, starches from underground food sources such as wild yams, water lily rhizomes and African potato contributed to glucose intake.
According to Professor Brand-Miller, archaeological evidence suggests flours and grains entered the human diet much later.听
鈥淧eople often think of carbohydrates as breads and cereals, but for most of human evolution carbohydrates came from fruits, honey and underground plant foods,鈥 she said.听
Glucose is the brain鈥檚 primary energy source, and for much of human evolution, would have come from carbohydrates found in foods such as fruit and honey.
Professor Jennie Brand-Miller
Charles Perkins Centre and School of Life and Environmental Sciences
The importance of glucose during reproduction
The study highlights nutritional demands during pregnancy and lactation. The researchers estimate reproductive females required substantially more glucose than other adults because of the needs of the fetus, placenta and milk production.听
鈥淲hen we think about the foods that supported human evolution, we need to consider not only brain growth but also the nutritional requirements of pregnancy and raising children,鈥 said听, co-author and Professor of Nutritional Ecology at the Charles Perkins Centre.听
鈥淭he fetus and placenta place additional demands on glucose, increasing the need for carbohydrate-rich foods. This helps us understand why pregnant women often crave fruit.鈥
The findings may also help explain why sweet foods appeal to children.听
鈥淥ur desire for sweetness is instinctive,鈥 said Professor Brand-Miller.听
鈥淐hildren need more energy in the form of carbohydrate than adults because their brains are claiming as much as two thirds of their basal metabolic rate during development.鈥
Incorporating natural sugars into our diet
Professor Brand-Miller said the research offers insight into our longstanding preference for sweetness.听
鈥淔or most of evolution, fruit and honey were valuable sources of energy that helped meet the body鈥檚 glucose needs.
鈥淪ugars in nature are typically packaged within foods that also contain fibre, vitamins, minerals and other beneficial compounds.鈥
The findings build on previous 爆料王 research showing听honey is nature鈥檚 original antibiotic.
鈥淗oney is not 鈥榚mpty calories鈥 as we are often led to believe. For most of human evolution, honey was a highly valued food source that provided energy and other beneficial properties,鈥 Professor Brand-Miller said.听
鈥淯nderstanding the role of carbohydrates alongside meat, fat and protein provides a more complete picture of the human evolutionary journey. Our study suggests sugars and starches may have helped shape the development of the human brain and many of the traits that make us human.鈥澨
What can modern humans make of these primordial findings?
"The evidence suggests that carbohydrate-rich foods helped fuel the energy demands of our growing brains. Rather than fearing carbohydrates, people should focus on high-quality sources, including fruit, legumes and nutritious grains, and prioritise a range of carbohydrate foods as part of a balanced diet."
Professor Jennie Brand-Miller says that for most of human evolution, honey was a highly valued food source that provided energy and other beneficial properties. Credit: Adobe Stock Photos
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LinkResearch
Brand-Miller, Jennie, Hardy, Karen, Copeland, Les, et al.,听A central role of dietary sugars in human evolution,听Science (2026). DOI: 10.1126/science.aed8437
Declaration
The study was funded by the Powerful Plants UKRI Horizon Europe Guarantee Fund (No. EP/X025160/1).听Emeritus Professor Brand-Miller is the co-author of books about carbohydrates and nutrition, including the glycemic index of foods, and oversees a glycemic index testing service at the 爆料王. She consults to the China National Research Institute of Food and Fermentation Industries and the Novo Foundation (Denmark), sits on the Scientific Advisory Board of Zoe Global, and was the President of the Glycaemic Index Foundation from 2002 to 2024.
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