Women who regularly eat a low carbohydrate, high protein diet are raising their risk of developing cardiovascular disease, according to a study published online today in the BMJ.
The short-term benefits of weight loss from such diets appear to be outweighed by longer-term cardiovascular harms they may cause such as heart disease and stroke.
Low carbohydrate-high protein diets are often used for body weight control.
Although they may be nutritionally acceptable if the protein is mainly of plant origin (such as nuts) and the reduction of carbohydrates applies mainly to simple and refined ones (such as unhealthy sweeteners, drinks and snacks), the general public does not always recognise and act on this guidance.
Previous studies on the long-term consequences of these diets on cardiovascular health have come up with inconsistent results, so an international team of researchers assessed 43,396 Swedish women aged between 30 and 49 over a 15-year period.
Women completed a dietary and lifestyle questionnaire and diet was measured on the low carbohydrate-high protein (LCHP) score where a score of two would equal very high carbohydrate and low protein consumption, through to 20, which would equal very low carbohydrate and high protein consumption. Factors likely to influence the results were taken into account including smoking, alcohol use, diagnosis of hypertension, overall level of activity and saturated/unsaturated fat intake.
The researchers found that over the 15-year period, 1,270 of the women suffered a cardiovascular event – 55% ischaemic heart disease, 23% ischaemic stroke, 6% haemorrhagic stroke, 10% subarachnoid haemorrhage and 6% peripheral arterial disease.
If women decreased their carbohydrate intake by 20g a day and increased their protein intake by 5g, they had a 5% increased risk of cardiovascular disease. These amounts are relatively small – 20g of carbohydrate is the same as a small bread roll and 5g of protein is the equivalent of one boiled egg.
The incidence of cardiovascular outcomes increased with an increasing LCHP score.
The authors stressed that the actual numbers were small – an extra 4-5 cases of cardiovascular disease per 10,000 women per year – compared with those who did not regularly eat a low carbohydrate, high protein diet.
Nevertheless, they said this was a 28% increase in the number of cases and that these results were worrying in a population of young women who may be exposed to these dietary patterns and face the excess risk for many years.
The study argues that increasing level of education and physical activity reduced the risk of cardiovascular disease whilst increasing levels of smoking increased the risk.
The authors concluded: “Low-carbohydrate, high protein diets used on a regular basis and without consideration of the nature of carbohydrates or the source of proteins are associated with increased risk of cardiovascular disease.”
This study did not, however, address the questions concerning the possible benefit of short-term effects of LCHP diets that can be used to control weight or insulin resistance.
Victoria Taylor, senior dietitian at the British Heart Foundation, said: “This study highlights the need for us to achieve balance in our diets, rather than pitting nutrients against each other.
“Eating a mixture of all food groups, rather than cutting anything out completely, will help you to stay healthy inside and out.”