Scientists Identify Diet That May Trigger Fat Burning Without Exercise

Researchers at the University of Southern Denmark have discovered that reducing two specific amino acids in the diet may trigger the body to burn more calories, without eating less or exercising more. Their findings, published in eLife, suggest a potential new pathway for obesity treatment.

Instead of exposing the body to cold temperatures to stimulate thermogenesis—the process of generating heat and burning calories—the scientists tested whether diet alone could activate this “internal heat engine.” They focused on lowering methionine and cysteine, amino acids found in high amounts in animal-based proteins such as meat, eggs, and dairy.

In experiments conducted over seven days, mice fed a diet low in methionine and cysteine showed a 20% increase in thermogenesis compared to mice on a standard diet. Importantly, the animals ate the same amount of food and maintained similar activity levels. Yet they lost significantly more weight. According to lead researcher Jan-Wilhelm Kornfeld, the effect was nearly as strong as keeping mice at 5°C continuously—an environment known to dramatically increase calorie burning.

The extra energy expenditure occurred in beige fat, a type of fat located under the skin in both mice and humans. Beige fat is also activated during cold exposure, suggesting it responds similarly whether stimulated by temperature or diet. Co-author Philip Ruppert noted that beige fat “doesn’t care” what triggers the burning response.

While the research was conducted only in mice, the findings raise the possibility that diets lower in animal proteins—or future functional foods—could help boost energy expenditure. Researchers are now exploring whether combining such dietary strategies with obesity medications like Wegovy may enhance weight loss outcomes in humans.

REFERENCE: Philip MM Ruppert, Aylin S Güller, Marcus Rosendal, Natasa Stanic, Jan-Wilhelm Kornfeld. Dietary sulfur amino acid restriction elicits a cold-like transcriptional response in inguinal but not epididymal white adipose tissue of male mice. eLife, 13 October 2025 DOI: 10.7554/eLife.108825.1