Did our love for sugar make us smarter? Scientists uncover sweet secret behind bigger brains

Naturally-sweet foods helped fuel human brain evolution significantly, new research suggests. Scientists from the University of Sydney and the University of Glasgow jointly conducted this study.

Published in Science, the study modelled glucose requirements across 4 million years of evolution. Researchers found that natural sugars supplied substantial energy before cooking became widespread.

Over four million years, the human brain's size expanded from the initial 300 grams. Modern human brains now weigh around 1.5kg on average. As brains grew larger, glucose demand increased across various bodily tissues. This includes red blood cells, kidneys and reproductive organs.

According to lead author Professor Jennie Brand-Miller, raw starch doesn't release usable glucose easily. This means early humans likely depended on naturally-sweet foods. Grains became dietary staples much later, once cooking developed properly.

These findings challenge the long-held view about meat's evolutionary importance. Brand-Miller noted that the brain's glucose requirements had received relatively little scientific attention. This gap may also explain humanity's persistent craving for sweet foods.

“While animal foods were important, the brain’s need for glucose has received little attention from palaeoanthropologists,” the University of Sydney quoted Professor Brand-Miller as saying.

“The human brain is unusually large for our body size and requires substantial amounts of energy,” Professor Brand-Miller added.

Researchers developed a detailed model spanning six distinct evolutionary stages. They calculated the "obligatory glucose demand" needed by the brain and related tissues. This was then compared against likely food sources available throughout different periods.

The team combined evidence from multiple scientific disciplines. These included food composition, fossil isotopes, dental morphology and primate diets.

Early hominins likely relied heavily on fruit-based carbohydrates. Later, cooking enabled starches from tubers like wild yams to contribute meaningfully.

According to Brand-Miller, archaeological evidence places grains much later in human diets. For most of evolutionary history, carbohydrates primarily came from fruit and honey instead.

The study also examined nutritional demands during pregnancy and lactation. Reproductive females typically require substantially more glucose than other adults.

According to co-author Professor David Raubenheimer, foetal and placental development significantly increases carbohydrate needs. This helps explain why pregnant women often crave fruit.

Natural instinct for sweetness

These findings may also explain children's natural attraction toward sweet foods. Brand-Miller described humanity's preference for sweetness as “instinctive”.

“Our desire for sweetness is instinctive,” Brand-Miller said.

“Children need more energy in the form of carbohydrates than adults because their brains are claiming as much as two-thirds of their basal metabolic rate during development,” he added.

According to Brand-Miller, natural sugars typically occur alongside beneficial nutrients. This includes fibre, vitamins and minerals found within whole foods. The research builds upon earlier findings describing honey as nature's original antibiotic.

According to her, honey shouldn't be dismissed as merely empty calories. Throughout human evolution, honey has provided valuable energy and additional health benefits.

Rather than avoiding carbohydrates, researchers suggest prioritising high-quality sources instead. This includes fruit, legumes and nutritious whole grains within balanced diets.

“People often think of carbohydrates as breads and cereals, but for most of human evolution carbohydrates came from fruits, honey and underground plant foods,” she said.