Moderate carbohydrate intake is best for health, new study suggests

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Eating carbohydrates in moderation seems to be optimal for health and longevity, according to a new report published in The Lancet.

The observational study of more than 15,400 people in the USA found that diets both low (lower than 40 per cent energy) and high (more than 70 per cent energy) in carbohydrates were linked with an increase in mortality, while moderate consumers of carbohydrates (between 50 and 55 per cent of energy) had the lowest risk of mortality.

The primary findings, confirmed in a meta-analysis of studies on carbohydrate intake including more than 432,000 people from over 20 countries, also suggest that not all low-carbohydrate diets appear equal – eating more animal-based proteins and fats from foods like beef, lamb, pork, chicken and cheese instead of carbohydrate was associated with a greater risk of mortality. Alternatively, eating more plant-based proteins and fats from foods such as vegetables, legumes, and nuts was linked to lower mortality.

Dr. Sara Seidelmann, who led the research, said: ‘We need to look really carefully at what are the healthy compounds in diets that provide protection. Low-carb diets that replace carbohydrates with protein or fat are gaining widespread popularity as a health and weight loss strategy. 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. Instead, if one chooses to follow a low carbohydrate diet, then exchanging carbohydrates for more plant-based fats and proteins might actually promote healthy ageing in the long term.’

Previous randomised trials have shown low carbohydrate diets are beneficial for short-term weight loss and improve cardiometabolic risk. However, the long-term impact of carbohydrate restriction on mortality is controversial with prospective research so far producing conflicting results. What’s more, earlier studies have not addressed the source or quality of proteins and fats consumed in low-carb diets.

Walter Willett, the co-author of the study, said: ‘These findings bring together several strands that have been controversial. Too much and too little carbohydrate can be harmful but what counts most is the type of fat, protein, and carbohydrate.’

The authors note some limitations including that dietary patterns were based on self-reported data, which might not accurately represent participants’ food consumption; and that their conclusions about animal-based sources of fat and protein might have less generalisability to Asian populations which tend to have diets high in carbohydrates, but often consume fish rather than meat. Finally, given the relatively small number of individuals following plant-based low-carb diets, further research is needed.

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