Sugar Re-enters the Human Evolution Story
A Science review models fruit sugars and later cooked starch as important brain fuel across four million years, without endorsing modern added sugar.
The 60-second version
A Science review models fruit sugars and later cooked starch as major glucose sources during human brain evolution.
Key points
- The model spans four million years and constrains diets by brain, body and reproductive glucose demand.
- Some scenarios assign more than 25% of energy to sugars, but these are estimates supported indirectly by several evidence streams.
- The argument broadens meat-centred accounts and does not endorse refined added sugar today.
Verdict. A useful, evidence-rich evolutionary model with substantial reconstruction uncertainty and no direct prescription for modern diets.
The argumentBrain evolution needed glucose as well as protein
The review reframes human diet evolution around the glucose demands of a growing brain and reproduction. Before cooked starch became easy to digest, the authors argue that fruit and honey could supply glucose; later, pounding and cooking made roots, tubers and other starches more useful.
MethodA four-million-year constraint model
The team estimated glucose demand for the brain, blood cells, kidneys and reproductive tissues as hominin bodies and brains changed. Six dietary steps ranged from a chimpanzee-like plant-heavy pattern to warm-climate hunter-gatherer plant-animal mixtures.
ResultsFrom fruit sugar to cooked starch
| Early reconstruction | A fruit-heavy diet could supply more than 65% of energy as sugars before efficient starch cooking. |
|---|---|
| Anatomically modern human scenario | At 35% animal and 65% plant energy, the model assigns 19% to protein, 25% to sugars and 25% to starch. |
| High animal-food scenarios | Available carbohydrate can fall below estimated obligatory glucose demand, especially for reproductive females. |
The authors compare the calculations with physiology, food composition, stable isotopes, teeth and caries, colour vision, archaeology and genetic changes linked to carbohydrate metabolism. These sources support plausibility but cannot reconstruct one universal ancestral menu.
The finding broadens the evolution story; it does not turn a model into an ancient food diary.
UncertaintyWhy the percentages are not measurements
- 1. Fruit and honey availability varied sharply by season, climate and geography.
- 2. Fossils and isotopes do not directly preserve grams of sugar eaten.
- 3. Modern hunter-gatherers are analogues, not unchanged replicas of extinct hominins.
- 4. Different species and technologies make a single ancestral diet unlikely.
Modern healthAncient sugar is not a soft-drink argument
Whole fruit, occasional honey and processed tubers came with fibre, scarcity, seasonality and high activity. Refined added sugar and ultra-processed foods create a different exposure. Evolutionary demand for glucose does not establish a healthy modern dose.
TakeawayUse the paper to revise the story
Human brain expansion probably relied on flexible combinations of animal foods, fruit, honey, starch, processing and cooking. For current diet choices, use modern health evidence rather than an ancestral model.