Obesity is now one of the world’s biggest health challenges. Nearly 900 million adults worldwide are living with obesity, driving up rates of diabetes, heart disease, and certain cancers.
Traditional weight‑loss methods often don’t deliver lasting results, so researchers are searching for new answers. One promising option is GLP‑1 drugs, which help people lose weight more effectively than older treatments. But there’s a catch: these medicines also lower the body’s natural calorie burn, and scientists still don’t know what that means for long‑term health.
Researchers are searching for new ways to help the body burn more energy. A recent study from the University of Southern Denmark asked a bold question: Can diet alone switch on thermogenesis, the process by which the body burns calories by producing heat?
We already know one natural trick: cold exposure. Shivering may be uncomfortable, but it forces the body to crank up its calorie burn to stay warm. Decades of research show that both mice and humans use more energy in the cold, thanks to the activation of special heat‑producing fat cells.
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Now, researchers are exploring whether diet could mimic this effect, turning meals into a metabolic spark plug that helps fight obesity.
In this study, researchers focused on reducing the levels of two amino acids in food: methionine and cysteine. These building blocks of protein play many roles in the body, from making proteins and regulating genes to protecting DNA, balancing oxidation, and fueling energy production.
Animal‑based foods like meat, eggs, and dairy are packed with methionine and cysteine. In contrast, plant‑based foods such as vegetables, nuts, and legumes contain much lower amounts. Interestingly, plant-rich diets have long been linked to healthier aging.
That means vegetarians and vegans, by avoiding animal products, naturally eat less methionine and cysteine than people who regularly consume meat. This difference may help explain why plant‑based diets are often associated with better long‑term health outcomes.
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A team of researchers has discovered that tweaking diet can be nearly as effective as living in constant cold to burn calories. In experiments with mice, diet‑induced thermogenesis, triggered by lowering two amino acids, methionine and cysteine, produced almost the same weight loss as keeping the animals at a chilly 5 °C around the clock.
Working with colleagues Aylin Güller, Marcus Rosendahl, and Natasa Stanic, the team adjusted amino acid levels in the mice’s food over seven days. The results were striking: mice on the low‑methionine, low‑cysteine diet burned more calories than those on a standard diet.
Lead researcher Jan‑Wilhelm Kornfeld explained: “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.”
The extra calorie burn came from beige fat, a special fat under the skin that can switch into heat mode. It’s the same fat that fires up when you’re shivering in the cold, and in this study, it lit up during both diet‑induced and cold‑induced thermogenesis.
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“This tells us that beige fat doesn’t care whether the burning is triggered by cold or by diet,” says Philip Ruppert.
Ruppert, a molecular biologist with a PhD, was at SDU when the study was performed and is now at Cornell University in New York.
“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,” he says.
Researchers believe the next frontier is finding safe ways to boost the body’s calorie burn without demanding big lifestyle changes. One idea is to design functional foods naturally 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.
This discovery suggests that well-designed diets might someday match the calorie-burning effects of cold exposure. This could provide new methods to combat obesity without the discomfort of cold temperatures.
Journal Reference:
Philip MM Ruppert, Aylin S Güller, Marcus Rosendal, Natasa Stanic, and 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. DOI: 10.7554/eLife.108825.1