USC: Methionine-Tuned Diet Made Mice Eat More, Lose Fat
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- USC researchers found that 20-month-old mice on a low-protein, methionine-supplemented "longevity diet" (LDMM) — plants and fish with added methionine — ate more food than any other group yet lost body fat while maintaining lean muscle mass, upending the assumption that weight loss requires calorie cuts.
- The LDMM-fed mice outperformed peers on standard, Western, and ketogenic diets on every measured metric: longer healthspan, less body fat, fewer frailty markers, and elevated GLP-1, growth hormone, and FGF21 — hormones tied to cardiometabolic health across species.
- First author Maura Fanti, a USC Leonard Davis research associate, said modulating a single amino acid (methionine) produced the dramatic metabolic changes, arguing that amino acid composition — not just total protein quantity — may be the productive target for dietary intervention.
- Senior author Valter Longo said the work challenges the "calorie reduction is necessary to lose weight" dogma and warned that too little methionine caused frailty while too much abolished the diet's benefits, framing the "sweet spot" of methionine as the active variable.
- A parallel analysis of more than 200,000 people by USC, the University of Toronto, and Harvard found that those eating the most animal protein had higher obesity rates and were twice as likely to have Type 2 diabetes compared with low or no animal-protein consumers — differences that held even when high-animal-protein eaters consumed fewer calories.
- The study, published in Cell Metabolism (DOI: 10.1016/j.cmet.2026.05.015), was supported by National Institute on Aging grant AG084485 and the USC Edna Jones Chair Fund, with the team now planning a controlled human clinical trial of the LDMM.
- Disclosed conflicts include Valter Longo's equity stake in L-Nutra, a medical-food company, and related patents he and co-authors Maura Fanti, Todd Morgan, and Sebastian Brandhorst have filed through USC, which has licensed related IP to L-Nutra.
Why it matters: If the methionine-specific signal holds in humans, the finding reframes a decades-old public-health message — that weight control is mostly about calories — and points dietary guidance at amino-acid composition instead. For Longo and L-Nutra, the result is also commercially material: it strengthens the scientific case for the company's methionine-tuned medical foods while entrenching Longo's lab as the leading group in the niche.
