But eliminating cysteine, which is found in high-protein foods, from human diets would be challenging

May 20, 2025 | 08:00pm

Mice lacking this amino acid lost 30% of their body weight

But eliminating cysteine, which is found in high-protein foods, from human diets would be challenging

Gene-edited mice were used to elucidate the role of cysteine in weight loss.Credit: Connect Images/Alamy

Gene edited mice that are unable to create an important amino acid lose weight extremely rapidly, a finding that could lead to the development of drugs targeting the amino acid in the future.

In a study published in Nature this week¹, US and Canadian researchers show that cysteine, an amino acid found in high-protein foods such as meat and wholegrains, plays a major part in weight loss and metabolism. Mice lacking the enzyme cystathionine γ-lyase — which breaks down other molecules into cysteine — lost 30% of their weight in one week when their diet also lacked food containing cysteine.

The benefits of diets that restrict certain amino acids — including cysteine and methionine — have been shown in animal studies, says co-author Evgeny Nudler, a biochemist at the New York University Grossman School of Medicine. But researchers were unsure as to which amino acids were most strongly implicated.

“Our findings suggest that many of these positive effects are actually driven by cysteine limitation rather than methionine,” Nudler says. This suggests that cysteine plays an important part in the benefits seen with these diets, including extended lifespan and fat loss.

Gene-edited mice

Nudler and his colleagues compared weight loss among mice with the cystathionine γ-lyase enzyme removed through gene editing against what was seen in controls that still had the enzyme. The researchers tested a control diet against ten other diets lacking either cysteine or one of the nine essential amino acids, such as phenylalanine, methionine or tryptophan.

They found that mice lacking the cystathionine γ-lyase enzyme experienced the most significant weight loss, nearly 31%, on the cysteine-free diet compared with mice on the other diets. Whereas mice that still had enzyme did not lose weight on the diet that lacked cysteine.

Mice that still had enzyme were able to lose weight, about 25%, but only when the diet lacked cysteine and methionine and calories were restricted.