High-Protein Diets Are Nearly As Bad For You As Smoking

Salvatore Caruso, who, at 108, is the second oldest man in Italy. Like many others in the small Italian town of Molochio, with one of the highest prevalence of centenarians in the world, Salvatore maintained a low-protein, plant-based diet for the majority of his life, but switched to a higher-protein diet after moving in with his son’s family once he became frail. Photo: Thierry de Lestrade.

Controlling how much animal protein you eat and when may be key to a long and healthy life.

Two groups of researchers, one in the US and one in Australia, have released details on two studies into diets and on the effects of animal protein.

The first study suggests that eating moderate to high levels of animal protein during middle age increases the cancer risk and leads to a shorter lifespan.

However, older people, around the mid 60s onward, benefit from a higher protein intake.

The second team of researchers investigated 25 diets and found that a high-protein, low-carbohydrate diet led to a shorter lifespan in mice.

The University of Southern California’s Dr Valter Longo said:

“We studied simple organisms, mice, and humans and provide convincing evidence that a high-protein diet — particularly if the proteins are derived from animals — is nearly as bad as smoking for your health.”

The researchers, analysing on 6,831 middle-aged and older adults, found those who reported more than 20% of their calories coming from animal protein were four times more likely to die of cancer or diabetes.

A moderate-protein diet was associated with a three-fold increase in cancer deaths.

These effects were either abolished or reduced in individuals eating a plant based high-protein diet.

However, for people older than 65 years the effects on mortality were reversed.

Those who consumed high amounts of protein had a 28% reduced risk of dying from any cause and a 60% reduced risk of dying from cancer.

Similar beneficial effects were observed for the moderate-protein-intake group.

Additional experiments in mice suggested that aging reduces the body’s ability to absorb or process proteins.

In the second study, Australian scientists tested hundreds of mice on 25 different diets.

Investigators found a high-protein, low-carbohydrate diet resulted in reduced food intake and body fat, but it also led to a shorter life.

A low-protein, high-fat diet had the most detrimental effects.

A low-protein, high-carbohydrate diet was best, resulting in a longer life, despite also increasing food intake and body fat.

The researchers also found that, contrary to popular opinion, calorie restriction had no beneficial effect on lifespan.

Caloric restriction without malnutrition has been consistently shown to increase longevity in a number of animal models, including yeast, worms and mice.

Co-author Professor David Le Couteur at the University of Sydney says the advice we are always given is to eat a healthy balanced diet.

“But what does that mean?” he says.

“We have some idea, but in relation to nutritional composition we don’t know terribly well. This research represents an important step in finding out.”

The investigators predict that a diet with moderate amounts of high-quality protein that is also relatively low in fat and high in complex carbohydrates will yield the best metabolic health and the longest life.

“We have shown explicitly why it is that calories aren’t all the same — we need to look at where the calories come from and how they interact,” says senior author Professor Steve Simpson, also of the University of Sydney.

“This research has enormous implications for how much food we eat, our body fat, our heart and metabolic health and ultimately the duration of our lives.”

The studies are published in the journal Cell Metabolism.

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