Low-carb Diets May Cut Years Off Life, Study Suggests

Scientists have linked ever-fashionable low-carb diets to shorter life expectancies in a study published Thursday in the journal The Lancet Public Health.

Researchers probing the link between nutrition and mortality in 15,400 U.S. participants discovered those who lived longest tended to eat a diet consisting of 50 percent carbohydrates. The team linked high-carb and low-carb diets to a slightly higher risk of death.

The results were no surprise to some experts. "No aspect of nutrition is so hotly contended on social media than the carb versus fat debate, despite the long term evidence on health benefits firmly supporting the higher carb argument," Catherine Collins, a dietician with the U.K.'s National Health Service told Science Media Centre (SMC). "The sheer variety of nutrients achieved with a plant based, carb-rich diet cannot be replicated on a restricted carb one."

Researchers followed participants for 25 years on average and tracked factors including diet, age and mortality. Statistical analyses revealed participants who ate about half carbohydrates (50 to 55 percent) tended to outlive their high- and low-carb counterparts. The team estimated that when they hit 50 years old, these people had about 33 years ahead of them.

Those who ate high-carb diets (70 percent or more) could expect to live about a year less than the half-carbohydrate group, the BBC explained. But the results were more dramatic for people eating low and extra-low-carb diets. People who ate between 30 and 40 percent carbs could expect to live 2.3 years less than the half-carb group. Those eating just 30 percent or less carbohydrates faced a life expectancy four years lower than the half-carb group.

But if you still want to go low-carb, a plant-heavy diet might be best. Those eating a low-carb diet rich in plant-based protein and fats had a slightly lower risk of mortality.

"Our data suggests that animal-based low-carbohydrate diets, which are prevalent in North America and Europe, might be associated with shorter overall life span and should be discouraged," study author and clinical and research fellow at Brigham and Women's Hospital, in Boston, said in an emailed statement.

"Instead, if one chooses to follow a low-carbohydrate diet, then exchanging carbohydrates for more plant-based fats and proteins might actually promote healthy aging in the long term."

Potatoes are seen inside a planter on a field outside Vaudoy-en-Brie, near Paris, on April 23. Scientists have linked ever-fashionable low-carb diets to shorter life expectancies in a new study. Christian Hartmann/Reuters

Research participants reported the amount of carbs they ate themselves, which limits the study. It was also observational, so it can't determine cause and effect. But independent scientist Nita Forouhi from the University of Cambridge still praised the study's "robust" design. Forouhi told SMC: "[It unravels] a clear message: Moderate carbohydrate intake of 50 to 55 percent of total energy, and not a low-carb diet, is optimal for longevity."

It's important to remember, she said, where nutrients come from. The study shows that replacing carbs with fats derived from plants, not animals, may be beneficial. Carbs themselves should come from plants rich in fiber, rather than sugary drinks and processed foods, Ian Johnson from Quadran Institute Bioscience, told SMC.

"[The research says] extreme intakes are undesirable and that the bottom line is that a balanced diet providing about half of the food energy from carbohydrates is best for health."