High-quality diet may have led to bigger human brain: CSIR-CCMB-led international study reveals genetic link between diet and brain size

Our ancestors’ shift to higher-quality diets, especially with use of fire and consumption of meat and fruits, had likely triggered genetic changes and may have paved the way for the dramatic expansion of the human brain, deduce researchers at the CSIR-Centre for Cellular and Molecular Biology (CCMB) here in Hyderabad.

A ground-breaking international study published in the latest issue of Philosophical Transactions of the Royal Society B, involving scientists from the United States and China, has uncovered the genetic mechanisms linking diet quality and brain size in primates, shedding new light on how some species, especially humans, evolved to have such large and complex brains. It reveals that the quality of food primates eat influences not just their energy levels but also the way their brains evolve at the genetic level.

The research team, including CCMB’s Laboratory for Conservation of Endangered Species (LaCONES) Chief Scientist Govindhaswamy Umapathy (senior author), Vinay Teja Potharlanka (first author) and others, including Shao Y, Wu D, Banda N and DeCasien A., had analysed over 8,000 genes from 50 whole genomes across primate species to understand how brain size co-evolved with diet and to identify the specific genes that may have helped make it happen.

Energy intensive organs

Brain is one of the most energy-hungry organs in the body. In humans, the brain consumes nearly 20% of the total energy, despite accounting for just 2% of body weight. For many years, scientists have wondered how such an organ could have evolved and why some species have bigger brains than others.

A key idea is that better-quality diets those rich in fruits, seeds, and animal protein provide more energy, allowing for the development of larger brains. But until now, no one had clearly shown how this plays out at the genetic level.

Digging Into the Data

Researchers combined genetic, ecological, and anatomical data in a novel way by measuring the size of brains and bodies in different primates and used published information on diet composition to create a Diet Quality Index (DQI).

They then looked at how quickly brain-related genes evolved in each species using the ‘dN/dS’ ratio method, which tracks evolutionary changes in gene sequences. Using sophisticated statistical tools that account for evolutionary relationships between species, the team identified hundreds of genes whose evolution was closely linked to diet and brain size.

Genes That Build Brains—and Process Energy

Many genes linked to larger brains were involved in neurogenesis (brain cell development) and are also known to be involved in human brain disorders such as autism and microcephaly. However, several key genes were also involved in lipid and carbohydrate metabolism — the body’s way of processing fats and sugars. These include genes like ‘ELOVL6’, which helps process fatty acids, and ‘EEF1A2’, which is involved in brain development and linked to neurological conditions.

“This supports the idea that better diets provided the fuel for building bigger brains. Energy metabolism genes and brain development genes are working hand-in-hand. This link is deeply embedded in the genome,” said Dr. Umapathy.

Two-Way Evolution

The study’s best-fitting model showed that diet quality influences brain size in two ways — directly by providing energy and nutrients, and indirectly by affecting which genes were under evolutionary pressure. “It’s a feedback loop. Better brains help find better food, and better food helps build better brains. Evolution worked through genes to reinforce this loop,” said Vinay Teja Potharlanka.

Interestingly, some of the same genes that aided brain expansion may have also increased the risk for certain neurodevelopmental conditions, highlighting a potential evolutionary trade-off.

Implications for Human Evolution

Although the study did not include modern humans, the findings offer powerful insights into our evolutionary past. The team hopes future research will explore how other lifestyle and social factors like group size, parenting style, or movement patterns may have influenced brain evolution in primates. The full dataset and analysis code have been made publicly available, encouraging further exploration into the complex relationship between ecology, genetics, and cognition.