@article {333884, title = {A central role for dietary sugars in human evolution}, journal = {Science}, volume = {393}, year = {2026}, month = {2026/08/06}, pages = {574-581}, abstract = {

INTRODUCTION

What foods enabled the evolution of the large human brain? Currently, that diet is usually framed around increasing intake of animal foods: meat, protein, fat, and omega-3 fatty acids. In evolutionary terms, we take an earlier standpoint and reframe hominin diet reconstruction around the need for glycemic carbohydrate as a source of glucose to support brain metabolism and encephalization. Hominins have existed for about 4 million years, their brain size increasing from 300 g in\ Australopithicus afarensis\ to 1500 g in\ Homo sapiens. Weighing only 2\% of adult body weight, it now represents 20\% of basal metabolic rate, 66\% in a 5-year-old. Although the driving force is unknown, we do know that this exorbitantly expensive organ is fueled primarily by glucose. Humans can synthesize glucose from precursors such as gluconeogenic amino acids, but the process is inefficient and finite.

RATIONALE

We started with metabolic and nutritional considerations, including the rate of glucose oxidation by the brain (~5 mg/min per 100 g). We calculated total obligatory glucose demand (g/day) by the brain, red cells, kidneys, and reproductive organs (fetus, placenta, and mammary glands). In six incremental steps based on the ratio of animal food to plant food, we modeled dietary intake and carbohydrate availability against obligatoryglucose demand according to brain and body size. At step 1, we used the known dietary composition of chimpanzee diets with an animal:plant energy ratio of 5:95. At step 6, we applied two ratios based on contemporary warm-climate hunter-gatherers: 35:65 and 50:50. We integrated multiple lines of evidence, including food composition, metabolism and physiology, fossil isotope ratios, dental morphology, and genetic changes, to corroborate our findings.

RESULTS

In human males, estimated total glucose demand is 150 to 200 g/day, in reproductive females 200 to 250 g/day, and in young children ~125 g/day. Carbohydrate availability in the diet ranges from 400 g/day at step 1 to 230 g/day at step 6. The earliest hominins were likely frugivorous, consuming \>65\% of energy as sugars in fruit and other sweet products. Once fire was mastered, cooked starch increasingly replaced sugars as the source of glucose. At a ratio of 35:65 animal to plant energy (E), anatomically modern humans consumed 19\%E as protein, 25\%E as sugars, and 25\%E as starch. Carbohydrate balance, the gap between dietary carbohydrate intake and glucose demand, becomes negative with higher ratios, increasing the likelihood of ketosis in reproductive females.

CONCLUSION

Rises and falls in the availability of fruit and honey with seasons, fluctuating climates, and geographic region may have driven foraging behaviors that increased brain growth and complexity, and even extinctions. Although animal foods were clearly instrumental, changes in intake of sugars and starches also shed light on human development, health, and disease. Multiple lines of evidence, including color vision, teeth morphology, dental caries, and stable isotope ratios, suggest that the diet of early hominins was high in sugars. 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.

}, isbn = {0036-80751095-9203}, doi = {http://dx.doi.org/10.1126/science.aed8437}, url = {https://www.science.org/doi/10.1126/science.aed8437}, author = {Brand-Miller, Jennie and Hardy, Karen and Raubenheimer, David and Copeland, Les} }