PARIS • Middle-aged people who get roughly half their daily calories from carbohydrates live several years longer on average than those with low-carb and high-carb diets, researchers reported.
Those with high-carb diets even managed to outlive those with low-carb diets by three years, while those with moderate carbohydrate consumption outlived those with low-carb by four years.
The findings, published in The Lancet journal on Thursday, challenge a trend towards so-called Paleo diets that shun carbohydrates in favour of animal protein and fat.
Proponents of these "Stone Age" diets argue that the rapid shift 10,000 years ago to grains, dairy and legumes has not allowed the human body enough time to adapt to these high-carb foods.
For the study, under 40 per cent of energy intake from carbohydrates qualifies as a low-carb regimen, though many such diets reduce the share to 20 per cent or less.
At the other extreme is a 70 per cent or higher share of carbohydrates such as pasta, rice, cakes and sugary drinks. Such a diet can also reduce longevity, but by far less, the scientists found.
"Low-carb diets that replace carbohydrates with protein or fat are gaining widespread popularity as a health and weight-loss strategy," said lead author Sara Seidelmann, a researcher at Brigham and Women's Hospital in Boston.
"However, our data suggests that animal-based, low-carbohydrate diets might be associated with shorter overall lifespan and should be discouraged."
Replacing meat with plant-based fats, such as avocados and nuts, and proteins, such as soya products and lentils, reduces the risk of mortality, Dr Seidelmann and her team found.
The optimal balance of food groups for longevity remains hotly debated. Many studies have concluded that eating carbohydrates in moderation - 45 to 55 per cent calories - is best, but others report improved short-term, cardio-metabolic health with high-protein, high-fat diets.
Measures of metabolic health include blood pressure, good and bad cholesterol, and blood sugar levels.
The team pored over the medical histories of nearly 15,500 men and women who were aged 45-64 when they enrolled - between 1987 and 1989 - in a health survey spread across four locations in the US.
Participants filled out detailed questionnaires about their dietary habits - what foods, how much, how often and so on. Over a 25-year, follow-up period, more than 6,000 of the men and women died.
People who got 50 to 55 per cent of their calories from carbohydrates outlived those with very low-carb diets, on average, by four years, and those with high-carb diets by one year.
A review of medical records of another 432,000 people from earlier studies confirmed the results, which are also in line with World Health Organisation recommendations.
"There is nothing to be gained from long-term adherence to low-carbohydrate diets rich in fats and proteins from animal origins," said Mr Ian Johnson, a nutrition researcher at Quadram Institute Bioscience in England.
But carb quality, not just quantity, is crucial he added. "Most should come from plant foods rich in dietary fibre and intact grains, rather than from sugary beverages or manufactured foods high in added sugar."