The popular Atkins diet could be putting people at increased risk of heart disease, according to a 25-year study.
Researchers from Sweden found the introduction of the low-carbohydrate regime led to a surge in saturated fat intake in 2004, with a spike in cholesterol levels three years later.
Study leader Professor Ingegerd Johansson, from the University of Umea, said: 'While low carbohydrate/high fat diets may help short-term weight loss, these results of this Swedish study demonstrate that long-term weight loss is not maintained and that this diet increases blood cholesterol, which has a major impact on risk of cardiovascular disease.'
Full English? A diet high in protein but low in carbohydrates can play havoc with cholesterol levels, say scientists
In 2004 there was an explosion in the popularity of low carbohydrate/high fat (LCHF) diets like Atkins in Sweden. The diets focus on cutting out sugar and starch while upping intake of fats, including saturated fat.
Its proponents, such as Dr Annika Dahlqvist, who is credited with starting the Swedish craze, argue that it helps maintain normal weight and blood sugar while freeing people to eat their favourite foods.
A poll last year suggested that a quarter of Swedes had at least partly adopted an LCHF diet. Around five per cent had taken it up seriously, leading the DietDoctor website to hail a "Swedish low carb revolution". There were even reports of stores running out of butter due to increasing demand.
The latest study was launched in 1986 after concerns about the high incidence of heart disease in northern Sweden.
Scientists analysed data on food and nutrient intake, body weight, height and cholesterol levels compiled from more than 140,000 measurements and questionnaires between 1986 and 2010.
The results showed an initial reduction in fat consumption and cholesterol levels throughout the 1990s. This coincided with the nationwide introduction of an education and food labelling programme aimed at improving diet and health. The Vasterbotten Intervention Programme (VIP) continues to this day.
After 2004, there was an unexpected change. Levels of total and saturated fat intake began to increase until they were higher than they were in 1986.
Blood cholesterol levels remained roughly unaltered between 2002 and 2007, but then showed a sharp rise.
In 2010 the average cholesterol level for men was around 5.5 millimoles per litre of blood, and for women slightly less. This was despite a significant increase in the number of people taking cholesterol-lowering drugs.
In earlier years, cholesterol levels had declined from a peak of more than six millimoles in 1986.
Over the whole 25-year period there was no sign that dieting of any kind helped people lose weight. Average body mass index (BMI), a measurement relating weight and height, showed a consistent rise in both men and women.
In their paper published in the Nutrition Journal, the researchers said the marked increase in cholesterol levels after 2007 was 'a deep concern'.
They added: 'After 2004 fat intake increased, especially saturated fat and butter-based spread for bread and butter for cooking.
'Supportive opinions in media for high-fat diets seem to have had an impact on consumer behaviours. Initially beneficial and thereafter deleterious changes in blood cholesterol paralleled these trends in food selection, whereas a claimed weight reduction by high-fat diets was not seen in the most recent years.
'In contrast, BMI increased continuously over the 25-year period. These changes in risk factors may have important effects on primary and secondary prevention of CVD (cardiovascular disease).'
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