How too much PROTEIN in middle age can shorten life

Thinking about going on one of the new low-carb, highprotein diets to lose weight? if you’re middle aged, you might want to think again. The latest research suggests that while eating more protein might help with weight loss in the short term, too much protein in midlife could shave years off your life.

in fact, cutting protein intake in middle age and boosting it again once you hit 65 could be the best way to ensure a healthier, longer life.

That’s because just as you don’t look the same at 50 as you did at 20, your metabolism changes with age and so should your diet.

‘There’s a lot of dogma about the perfect diet,’ says Steve Simpson, a professor of life sciences at the University of Sydney.

‘The presumption is that if you’re a fiveyear-old or a 60-year-old, a healthy diet is the same, but we don’t have the same nutritional requirements throughout life.’

The standard balanced diet promoted by the nhS points to five portions of fruit and veg a day, a substantial amount of starchy carbohydrates, such as rice, pasta, bread or potatoes, along with a few portions of protein-based foods and smaller amounts of dairy and fats.

But these recommendations don’t translate easily into precise proportions of protein, carbohydrate and fat — the so-called macronutrients that provide energy in the form of calories.

A number of studies suggest the ratio of these components is important for health, and ‘they change as we grow, as we reproduce and as we start to age’, says Professor Simpson.

Extensive research in a range of animals, from fruit flies and mice to grizzly bears and orangutans, shows that a high-protein diet throughout life leads to a shorter lifespan compared with a diet high in carbohydrates.

Large-scale human studies are still lacking, but evidence is starting to suggest that eating a diet high in protein — particularly from the age of 50 to 65 — has a negative impact on longevity.

One prime example is the longest-living people — the Okinawa islanders of Japan.

They have a high proportion of centenarians, with low rates of heart disease, cancer and other old age illnesses.

Their traditional diet — which comprises 80 per cent carbohydrates (mainly vegetables, especially sweet potato), 10 per cent protein (fish and soy) and 10 per cent fat — is thought to contribute to their longevity.

in 2014, Professor Simpson’s team published the results of a study of mice fed 25 different diets, each with varying ratios of protein, carbohydrate and fat.

They found a low-protein, highfat diet had the most damaging effects in terms of lifespan, ageing and health, while a conventional higher-carb, lower-protein diet had the opposite effect.

At the same time, a team at the University of Southern California analysed the diets of nearly 7,000 middle-aged people, discovering that eating a high-protein diet between the ages of 50 and 65 increased the chances of developing cancer, diabetes and other lifelimiting diseases.

The evidence suggests that in the early adult years, a diet comprising 20 per cent protein seems best: this translates to around 100g of protein per day for a typical adult. But according to Professor Simpson, ‘in later life, a lower proportion of protein and a higher proportion of complex carbohydrates, including grains, pulses and vegetables, promotes a longer life’.

however, many of today’s lowcarb diets recommend upwards of 30 to 40 per cent of total calories coming from protein.

Professor Simpson’s research suggests these are far from ideal for anyone in the long term, especially those in midlife.

‘if you increase the proportion of protein to carbohydrate, it drives ageing and a series of bad outcomes,’ he says.

FrOm the age of 65, dietary needs change again. An international collaboration of nutritional experts, known as the PrOT-AgE study, concluded that increasing protein in the diet from 65 helps protect against age-related musclewasting and staves off frailty.

The data also points to the benefits of spreading protein-rich foods throughout the day, which allows the body to break down and use it more efficiently than lumping it into one meal.

But matthew Piper, a research fellow at monash University, in melbourne, who is studying how protein levels in the diet affect longevity, says that more detailed work is needed before we change our diets.

‘The energy costs of growth and reproduction in early life decline with age, so we expect there should be a reduced demand for nutrients,’ he says. ‘We need careful analysis of life-long nutrient balance requirements.’