New research highlights a critical role for carbohydrates, including natural sugars and starches, in the evolution and expansion of the human brain over the past four million years. A study by researchers from the University of Sydney and the University of Glasgow, published in the journal Science, challenges the long-held belief that meat consumption was the primary driver of human brain development. Instead, the findings suggest that the brain's high demand for glucose made carbohydrates essential for our ancestors.[news-medical+6]
Brain's High Glucose Demand
The human brain is remarkably energy-hungry, even though it makes up only about two percent of an adult's body weight. It consumes roughly 20 to 25 percent of the body's resting energy.This energy demand is even higher in young children, where the developing brain can use as much as two-thirds of their basal metabolic rate.[sci+6]
Glucose is the brain's main energy source. While the body can produce some glucose from other nutrients, this process is limited and not very efficient.This means early humans needed a consistent supply of glucose from their diet to support their growing brains.[sci+3]
Researchers calculated the "obligatory glucose demand" for humans and their ancestors across different stages of evolution. They found that adult glucose needs ranged from about 150 to 250 grams daily, depending on factors like sex and reproductive status. Young children required around 125 grams of glucose each day.[sci+1]
Sweet Foods Paved the Way
The new study modeled the glucose needs of humans and their ancestors from four million years ago up to recent times. It found that natural sugars from foods like fruit and honey likely supplied the energy needed for growing brains long before cooking made starchy foods easier to digest.Early hominins, for example, may have gotten more than 65 percent of their energy from natural sugars.[news-medical+7]
Professor Jennie Brand-Miller, a human nutrition scientist at the University of Sydney and lead author of the study, explained that the human brain is unusually large and requires substantial energy. She noted that glucose is its primary fuel, and for much of human evolution, this would have come from carbohydrates found in fruits and honey.[news-medical+1]
"Our desire for sweetness is instinctive," Professor Brand-Miller told reporters.She added that children need more carbohydrate energy than adults because their brains demand a significant portion of their metabolic rate during development.Evidence of tooth decay in fossil primates and early hominids also suggests a diet rich in soft, sugary foods.[news-medical+2]
Cooking Unlocked Starches
As human evolution progressed, the mastery of fire and cooking introduced another major source of glucose: starchy foods. Cooking tubers, seeds, and grains made these carbohydrate-rich foods much easier to digest, leading to significant changes in human diets and brain development.[news-medical+9]
Professor Les Copeland from the University of Sydney, a co-author on related research, stated that cooking starchy foods was central to the dietary shift that sparked and maintained the growth of the human brain.This advancement in starch digestion provided a readily available source of glucose, allowing for the accelerated increase in brain size that occurred around 800,000 years ago.[sydney+4]
Modern humans also show genetic adaptations for digesting starches. Researchers point to evidence in salivary amylase genes, which produce enzymes that break down starch in the mouth. While other primates typically have only two copies of these genes, modern humans have an average of about six copies. This genetic difference allows for more efficient starch digestion.[sydney+2]
Rethinking Evolutionary Narratives
These findings offer a different view on the long-standing scientific idea that meat consumption was the main driver of human evolution.While animal foods provided important nutrients, the brain's specific need for glucose has often been overlooked by anthropologists.[news-medical+9]
"While animal foods were important, the brain's need for glucose has largely received little attention from anthropologists," Professor Brand-Miller said.The research suggests that dietary carbohydrates, alongside meat, were essential for the evolution of modern large-brained humans.[news-medical+4]
Karen Hardy, a researcher with the Catalan Institution for Research and Advanced Studies, also emphasized this point. "We believe that while meat was important, brain growth is less likely to have happened without the energy obtained from carbohydrates," she said.[sydney]
The studies also challenge the modern "Paleo diet" trend, which often avoids starch-rich vegetables and grains. Researchers suggest that early humans would not have evolved on a low-carbohydrate diet, as the high glucose demands of their large brains would not have been met.[sydney+4]
Lessons for Modern Diets
The evidence suggests that carbohydrate-rich foods helped meet the high energy demands of our ancestors' growing brains. Rather than fearing carbohydrates, people should focus on high-quality sources.[news-medical+3]
This includes whole fruits, legumes, and nutritious grains. Prioritizing a range of carbohydrate foods as part of a healthy diet aligns with the evolutionary journey of human nutrition.The research reinforces that a diverse diet, including both animal products and various carbohydrate sources, has been key to human development.[news-medical+3]
Ultimately, understanding the crucial role of carbohydrates alongside meat, fat, and protein gives a more complete picture of how humans evolved. Sugars and starches were not just incidental foods but fundamental to shaping the human brain and many of the traits that define us.[sci+1]
