The study, published in Lancet Public Health last month, observed levels of carbohydrate intake, health and longevity in 15,000 middle-aged people over a 25-year period.
It concluded that the disease-related association between carbohydrate intake and death was “U-shaped”, with the lowest risk occurring in those whose carbohydrate intake made up 50–55% of overall energy consumption.However, when some of the carbohydrate was replaced by proteins and fat from plant sources, the risk of death was found to be lower.
While conceding that diets could change a lot over a lifetime, Dr Ian Johnson, nutrition researcher and emeritus fellow at Quadram Institute Bioscience, felt that the risk of death was “convincingly shown” to be lowest in those participants who obtained about half their calories from carbohydrates.
“The risk was highest in those who ate a low carbohydrate diet in which the calories were replaced mostly by fats and proteins from animal foods,” Johnson added.
NHS dietitian Catherine Collins said supporters of the “cult” of low-carb, high-fat eating would no doubt disagree with the research. However, she believed such diets compromised the essentials of a healthy diet.
“The sheer variety of nutrients achieved with a plant based, carb-rich diet cannot be replicated on a restricted carb one,” said Collins.
“Reducing carbs means dietary fat intake must rise – and in doing so, this increases not only the post-meal cardiac risk associated with higher circulating fat levels, but also boosts saturated fat intake as well.”
Contentious issue of low-carb diets
Professor Nita Forouhi of the University of Cambridge Epidemiology Unit said the study took the contentious issue of low-carb diets head-on, and peeled away layers of complexity with “robust methods and thorough analyses to unravel a clear message”.
“A really important message from this study is that it is not enough to focus on the nutrients, but whether they are derived from animal or plant sources,” Forouhi added.
“When carbohydrate intake is reduced in the diet, there are benefits when this is replaced with plant-origin fat and protein food sources. Many low-carb diet regimes do not make this distinction.”