New study reveals how low‑protein diets enhance exercise ability through a surprising energy trade-off
Researchers from Monash University have uncovered how long‑term dietary protein restriction can surprisingly improve weight‑bearing exercise ability - by reshaping how the body budgets energy and activating brown fat thermogenesis. The study, published in the Journal of Sport and Health Science, provides new biological insight into the longstanding mystery of diet‑induced thermogenesis.
In the study, male mice fed a chronic protein-restricted diet showed improved treadmill endurance, better movement economy and lower energy expenditure during physical activity, despite having higher resting thermogenesis. The researchers found that these effects were driven by reduced body weight and adiposity, caused by the activation of brown adipose tissue via liver‑derived fibroblast growth factor 21 (FGF21).
“Our findings show that a low‑protein diet shifts the entire energy landscape of the body,” said Associate Professor Adam Rose, a Lab Head at Monash’s Biomedicine Discovery Institute and senior author of the study.
“By activating brown fat thermogenesis through FGF21, the body burns more energy at rest. But because the mice become leaner, they actually expend less energy during movement - and that makes exercise feel easier and more effortless,” Associate Professor Rose said.
The research demonstrates that although protein‑restricted mice increased resting energy burn, this was offset by lower energy used during exercise, resulting in balanced overall daily energy expenditure.
“What’s fascinating is that the higher thermogenesis doesn’t always translate into higher total energy burn,” Dr Patrcia Rusu, lead author and research fellow within the lab of Associate Professor Rose, explained.
“Instead, the reduced body weight means the animals require less energy to move. It’s an elegant biological trade‑off - one that may help explain why diet‑induced thermogenesis exists in the first place,” Dr Rusu said.
The team also discovered that without FGF21, the benefits of protein restriction on exercise ability, movement economy and brown fat activation were completely lost.
“This work establishes FGF21 as the crucial messenger connecting diet composition, body weight, brown fat function, and exercise performance,” Associate Professor Rose said.
“It provides a compelling rationale for why mammals may have evolved this energy‑balancing mechanism in response to low‑protein environments.”
The findings offer new avenues for exploring how diet composition - beyond calories alone - shapes metabolic health, physical performance and energy balance.
Read the full paper published in The Journal of Sport and Health Science, A nutrient-hormone axis pivots an energy trade-off between resting thermogenesis and movement expenditure.
DOI: 10.1016/j.jshs.2026.101132
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About the Monash Biomedicine Discovery Institute at Monash University
Committed to making discoveries that will relieve the future burden of disease, Monash Biomedicine Discovery Institute at Monash University brings together more than 120 internationally renowned research teams. Spanning seven discovery programs across Cancer, Cardiovascular Disease, Development and Stem Cells, Infection, Immunity, Metabolism, Diabetes and Obesity, and Neuroscience, Monash BDI is one of the largest biomedical research institutes in Australia. Our researchers are supported by world-class technology and infrastructure, and partner with industry, clinicians and researchers internationally to enhance lives through discovery.