Low-carb diets should be discouraged, says study

Weight loss diets that switch out carbs in favour of meat or fat are associated with a higher mortality rate, according to a new study.

In contrast, lower mortality rates were recorded among consumers who opted for plant-based protein and fat from sources such as whole-grain bread, vegetables, nuts, peanut butter.

The trend for cutting back on, or cutting out, carbs has been one of the factors blamed for a decline in sales of bread in the UK.

However, there are signs that carbs have been back on the menu as Brits shift away from faddy diets, with Waitrose last year reporting that consumers are now opting for a more common-sense approach.

In the new study, published this week by Lancet Public Health, researchers said the data provided further evidence that animal-based low-carb diets – which have grown in popularity as a method of weight loss - should be discouraged.

The US study looked at the diets of around 15,000 adults aged 45 to 64 years over a 25-year period, and examined the association between individuals’ carbohydrate intake and cause of death.

Scientists found that diets with either a high (70% or more) or low (40% or less) percentage of energy from carbohydrates were associated with increased mortality. The minimal risk of death was observed in those who got between 50% and 55% of their energy from carbs.

“Low-carb diets that replace carbohydrates with protein or fat are gaining widespread popularity as a health and weight loss strategy,” said lead researcher Dr Sara Seidelmann, clinical and research fellow in cardiovascular medicine from Brigham and Women’s Hospital, Boston, US. “However, 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.”

Commenting following the publication of the study, Dr Ian Johnson, nutrition researcher at Norwich’s Quadram Institute Bioscience said the findings show there is nothing to be gained from long-term adherence to low-carbohydrate diets rich in fats and proteins from foods of animal origin. 

“However, it is not just the quantity of dietary carbohydrates that matters, but also their sources and composition,” he added. “There is good evidence from other research to show that most should come from plant foods rich in dietary fibre and intact grains, rather than from sugary beverages or manufactured foods containing high levels of added sugars.”

And NHS dietitian Catherine Collins said the variety of nutrients achieved with a plant based, carb-rich diet cannot be replicate on a restricted carb one. 

“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, too,” she added.

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