Popular food group linked to doubled type 2 diabetes risk in 200,000-person study

Scientists at the University of Southern California have uncovered a surprising link between high protein intake and accelerated ageing - with new research suggesting that cutting back on one specific amino acid, rather than calories, could be the key to a longer, healthier life.

The study, published in Cell Metabolism, found that a modified Mediterranean-style diet with carefully calibrated levels of methionine - an amino acid found in eggs, meat and dairy - helped extend healthspan in mice, while separate data from over 200,000 people linked high animal protein consumption to double the risk of type 2 diabetes.

Elderly mice following this "longevity diet" demonstrated notable improvements across several health markers.

The animals experienced an extended healthspan, shed body fat, and exhibited fewer indicators of age-related frailty compared to those on alternative eating regimens.

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The dietary approach appeared to deliver sufficient but modest quantities of methionine alongside other essential amino acids, according to senior author Valter Longo.

Longo's team tested their hypothesis by feeding 20-month-old mice one of four distinct dietary regimens.

These included a standard diet, a Western-style plan rich in fats and sugars, a low-carbohydrate ketogenic approach, and the low-protein longevity diet supplemented with methionine.

The mice consuming the modified Mediterranean diet consistently outperformed all other groups.

Perhaps most remarkably, these animals actually consumed greater quantities of food than their counterparts on alternative diets.

Despite taking in equivalent calories to the other groups, they nonetheless reduced their body fat while preserving lean muscle tissue.

These metabolic advantages only materialised when methionine was maintained at levels that were low yet adequate.

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The researchers also identified elevated levels of GLP-1 and other metabolic signalling molecules in mice fed the longevity diet.

The research team bolstered their animal findings with an examination of dietary and health records from over 200,000 individuals.

This analysis, conducted jointly by investigators from USC, the University of Toronto and Harvard University, revealed striking patterns among human participants.

Those who adhered to predominantly plant-based eating habits displayed markedly lower rates of obesity.

The data proved even more compelling regarding metabolic disease.

Individuals consuming the highest quantities of animal protein faced double the risk of developing type 2 diabetes when compared with those eating minimal or no animal-derived foods.

Intriguingly, these disparities persisted despite the high animal protein group generally consuming fewer calories overall.

Those same participants also tended to follow otherwise healthier dietary patterns, yet still experienced worse metabolic outcomes.

Maura Fanti, the study's first author and a research associate at USC Leonard Davis, expressed surprise at the potency of a single amino acid adjustment.

"We expected different diets to produce different outcomes, but what really impressed us was how modulating just a single amino acid, methionine, in the longevity diet could produce such dramatic metabolic changes," she said.

"It points to the idea that amino acid composition, not just overall protein quantity, may be the target of strategic metabolic interventions."

Longo noted that the findings challenge conventional wisdom about weight management. "This challenges the dogma that calorie reduction is necessary to lose weight," he observed.

The research team intends to conduct controlled clinical trials in humans to verify whether comparable benefits emerge.

The study disclosed that Longo holds an equity interest in L-Nutra, a medical foods company.

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