Calorie-cutting has long been the go-to for weight loss. But a new study suggests that one overlooked nutrient, cysteine, may hold a key to how the body burns fat.
In research published in Nature Metabolism, scientists from Pennington Biomedical Research Center and collaborating institutions found that reducing cysteine, a sulfur-containing amino acid, can help trigger fat-burning processes in the body. Specifically, lower cysteine levels were linked to the “browning” of fat, turning energy-storing white fat cells into heat-producing brown fat cells.
“In addition to the dramatic weight loss and increase in fat burning resulting from the removal of cysteine, the amino acid is also central to redox balance and redox pathways in biology,” said Dr. Krisztian Stadler, director of Pennington’s Oxidative Stress and Disease lab. “These results suggest future weight management strategies that might not rely exclusively on reducing caloric intake.”
The research involved both animal models and human participants. In one clinical trial, participants followed a calorie-restricted diet, about 14% fewer calories than usual, over two years. Analysis of their fat tissue showed lowered cysteine levels, alongside weight loss, reduced inflammation and improvements in muscle health.
“Reverse translation of a human caloric restriction trial identified a new player in energy metabolism,” said Dr. Eric Ravussin, who directs the Human Translational Physiology Lab at Pennington. “Systemic cysteine depletion in mice causes weight loss with increased fat utilization and browning of adipocytes.”
In animal studies, meals with less cysteine resulted in striking metabolic changes. Body temperature dropped by 40%, yet tissues remained undamaged, suggesting the body activates protective responses when cysteine levels fall.
Cysteine is a sulfur-containing amino acid found in many protein-rich foods, including poultry, eggs, dairy, legumes, whole grains and nuts.
The findings add a new layer to how we understand weight regulation.
“Dr. Ravussin, Dr. Stadler, and their colleagues have made a remarkable discovery showing that cysteine regulates the transition from white to brown fat cells, opening new therapeutic avenues for treating obesity,” said Dr. John Kirwan, executive director of Pennington Biomedical.
While the study's results are promising, researchers caution that more work is needed before making specific dietary recommendations about reducing cysteine intake. Because the nutrient also plays a role in immune support and antioxidant defenses, balance — not elimination — will likely be key.
This research was supported by multiple institutions, including Pennington Biomedical Research Center, Yale University and the University of Texas Southwestern Medical Center. It received funding from the National Institutes of Health, including the National Institute of Diabetes and Digestive and Kidney Diseases, the National Institute on Aging and the National Science Foundation. Additional support came from the Gruber Foundation, the McCluskey family and the Interstellar Initiative.