A diet low in protein but supplemented with precise amounts of methionine—an amino acid found in eggs, meat, and dairy—significantly extended healthspan and reduced frailty and fat mass in mice, according to a study published in the journal Cell Metabolism. Researchers led by Valter Longo of the USC Leonard Davis School of Gerontology, in collaboration with teams from the University of Toronto and Harvard University, found that modulating this specific amino acid, rather than just total protein intake, may be a key factor in metabolic health and longevity.
How Amino Acid Modulation Impacts Longevity
The researchers tested four different dietary patterns on mice aged 20 months: a standard diet, a high-fat/high-sugar Western diet, a ketogenic diet, and a "longevity diet" that was low in protein but supplemented with methionine (LDMM). Mice on the LDMM diet showed lower body fat, reduced frailty, and a longer period of life spent in good health compared to the other groups.
According to Maura Fanti, a research associate at USC Leonard Davis and first author of the study, the team was surprised by how the modulation of a single amino acid could drive such drastic metabolic changes. The study suggests that the composition of amino acids is a vital target for metabolic interventions. The LDMM-fed mice also showed improved cardiometabolic biomarkers, including increased levels of signaling molecules like GLP-1, which influence metabolism and aging.
Comparing Protein Intake and Health Outcomes
The research team analyzed existing health and dietary data from more than 200,000 people to see if these findings held weight in human populations. They discovered that participants with the highest intake of animal proteins—which are typically richer in methionine and other essential amino acids—had a higher prevalence of obesity and double the risk of diabetes compared to those who consumed little to no animal protein.
This correlation persisted even when the high-animal-protein group consumed fewer calories and maintained what is generally considered a healthier nutritional profile. These findings challenge the dogma that calorie reduction is necessary for weight loss.
The Role of Methionine in the Longevity Diet
The study highlights that the source and specific amino acid profile matter significantly. Methionine is an essential amino acid. However, the study found that an insufficient intake of methionine led to frailty, while an excess of the amino acid nullified the health benefits of the diet.
The "longevity diet" modeled in the study draws inspiration from the eating patterns of long-lived populations, such as traditional Italian and Okinawan diets, which are traditionally plant-based and low in protein. By supplementing these plant-based diets with small, sufficient amounts of methionine, researchers were able to achieve weight loss without the loss of lean muscle mass.
The researchers note that while the metabolic pathways in mice and humans differ, the consistency of the findings across species is encouraging. Valter Longo and Maura Fanti have indicated that the next step for this research is a controlled clinical trial in humans to determine if the LDMM diet produces similar effects in people.
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