A surge in popularity of "low-carb" diets may have contributed to rising cholesterol levels, researchers have warned.
A team led by Professor Ingegerd Johansson of Umea University, Sweden, analysed diet and medical information on men and women followed for 25 years.
They explain that in the 1970s, men in northern Sweden had among the highest rates of heart diseases in the world.
Starting in 1985, a series of interventions were put in place at both individual and population level. This included better food labelling, healthy information, cooking demonstrations and health examinations and counselling including diet advice.
Study participants regularly reported their food intake and had their body weight, height and cholesterol measured.
Overall fat intake fell for both sexes between 1986 and 1992, then rose again after 2002 for women – and after 2004 for men.
Carbohydrate intake fell this century after rising in the last – possibly reflecting the growing idea, popularised by the Atkins Diet, that reducing carbohydrate is the most effective way to lose weight.
But at the same time, cholesterol levels fell in the period up to 2004 and then began to rise after 2007, the researchers report. And weight levels continued to increase.
Protein remained unchanged. Wine intake rose sharply for both sexes, and beer intake rose among men.
Full details appear in the journal Nutrition Journal. The authors say that the increase in cholesterol coincided with the increase in fat intake, especially saturated fat and fats for spreading.
They report that the rise in fat consumption from 2004 "coincided with introduction of a positive media support for low carbohydrate/high-fat diet".
"These changes in risk factors may have important effects on primary and secondary prevention of cardiovascular disease," they conclude.
Professor Johansson said: "The association between nutrition and health is complex. It involves specific food components, interactions among those food components, and interactions with genetic factors and individual needs."
Associations among 25-year trends in diet, cholesterol and BMI from 140,000 observations in men and women in Northern Sweden. Johansson, I. et al. Nutrition Journal (in press).
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