Scientists Discover a Diet That Burns Fat Like Cold Exposure, Leading to Significant Weight Loss

By tweaking just two amino acids in the diet, researchers found a way to mimic the fat-burning effects of cold exposure.

Shivering in the cold is hardly enjoyable, yet for some people, it carries an appealing side effect—the body uses more energy to stay warm than it does in comfortable temperatures. Multiple studies have shown that cold exposure reliably increases energy expenditure in both humans and mice. This natural process of generating heat by burning energy is known as thermogenesis.

Scientists and pharmaceutical companies have long been searching for ways to activate this same mechanism without actually lowering body temperature, essentially “tricking” the body into feeling cold to promote fat burning.

Instead of focusing on temperature, obesity researchers Philip Ruppert and Jan-Wilhelm Kornfeld from the Department of Biochemistry and Molecular Biology (BMB) at the University of Southern Denmark explored a different approach: stimulating thermogenesis through diet.

Amino acids methionine and cysteine

Their work centered on two amino acids, methionine and cysteine.

Through a series of experiments in mice, the team discovered that changing the amount of these amino acids in the animals’ diet produced effects comparable to continuous cold exposure at five degrees Celsius. The mice on a diet low in methionine and cysteine showed nearly the same level of energy burning and weight loss as those kept in the cold.

This research, conducted with BMB colleagues Aylin Güller, Marcus Rosendahl, and Natasa Stanic, was published in the journal eLife. Over a seven-day period, the scientists modified the animals’ diets and found that those fed reduced levels of methionine and cysteine expended more energy than mice on a normal diet.

High levels of amino acids in animal proteins

“The mice that burned the most energy ate the same amount of food as the others, and they didn’t move more or less. We saw a 20% increase in their thermogenesis. They lost more weight, and it was not because they ate less or exercised more—they simply generated more heat,” explains Jan-Wilhelm Kornfeld.

He is a molecular biologist, and Danish Diabetes and Endocrine Academy (DDEA) professor the Novo Nordisk Foundation Center for Adipocyte Signaling at BMB, University of Southern Denmark.

Methionine and cysteine are amino acids that are found at high levels in animal proteins and in low levels in foods like vegetables, nuts, and legumes that promote healthy aging. Thus, vegetarians and vegans, who don’t eat meat, eggs, or dairy products, naturally consume less methionine or cysteine than meat-eaters.

Where fat was burned

“We know from other studies that vegetarians and vegans are, in several respects, healthier than meat-eaters. We haven’t tested a methionine/cysteine-restricted diet in humans, only in mice, so we can’t say for certain that the same effect would occur in people—but it’s absolutely a possibility,” says Philip Ruppert, a molecular biologist and PhD, who was at SDU, when the study was conducted, but now is at Cornell University in New York.

Because the research was performed in mice, the findings should be viewed as an early step toward understanding how diet influences thermogenesis in humans. Animal studies like this allow scientists to explore biological mechanisms that would be difficult or unethical to test directly in people.

While the results suggest that adjusting certain amino acids could potentially help the body burn more energy, further research is needed to confirm whether the same processes occur in humans and to determine how such diets might safely be applied in real-world settings.

The researchers also examined where in the body this increased energy burning took place. It occurred in the so-called beige fat depots, the type of fat stored beneath the skin in both mice and humans. Fat was burned in these depots during both cold-induced and diet-induced thermogenesis.

“This tells us that beige fat doesn’t care whether the burning is triggered by cold or by diet,” says Philip Ruppert.

Maybe basis for new obesity treatments

The research team believes the next interesting step could be to explore whether obesity treatments could be developed to boost energy expenditure without requiring any major effort from the patient.

They are also interested in developing novel functional food products that are low in methionine and cysteine.

“It would also be interesting to study whether Wegovy patients experience additional weight loss if they switch to a diet without the amino acids methionine and cysteine—in other words, a diet free of animal proteins,” says Kornfeld.

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

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