How much of our existence do we owe to sugar?

It may be time to rethink our relationship with the sweet stuff

In 2017 researchers studying primate brains made a curious discovery: Across more than 140 species, primates that ate fruit had larger brains, on average, than their meat- or leaf-eating peers. The findings suggested that increases in brain size in primates were driven by food—or perhaps foraging—rather than complex social interactions, another leading theory.

For Jennie Brand-Miller, it was “a light bulb moment.” Fruit is full of sugar, and our brain relies on glucose, a sugar, as its primary energy source. That led Brand-Miller, an emeritus professor of human nutrition at Australia’s University of Sydney, to wonder whether sugary food might have had a hand in human evolution.

Now, in a new analysis published in Science on Thursday, Brand-Miller and her colleagues argue that sugar played a “central” part in human evolution, particularly early on. “No matter what period of human evolution, sugars were playing an important role,” she says.

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Brand-Miller and her colleagues relied on existing data about the size of various hominin species and information gleaned from the fossil record about their diets to model the breakdown of sugars, protein, fiber, starch and fat in the hominin diet over time. The analysis spans approximately four million years—starting with Australopithecus afarensis, or “ Lucy ,” one of the first hominins believed to walk on two legs, and ending with the diets of modern humans in foraging communities.

The findings suggest that early hominins may have gotten as much as 66 percent of energy from sweet food such as fruit and honey. Over the span of human evolution, hominins accumulated 20 to 25 percent of their energy from these foods, the analysis found.

The results don’t mean animal-based products such as meat or fish didn’t matter, Brand-Miller emphasizes. “We believe that this is two parallel stories, that a balanced diet means you get sufficient protein, fat and carbohydrate,” she says.