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Background

Cardiovascular diseases remain the leading cause of death worldwide, and identifying effective strategies for prevention and treatment is of major importance. Atherosclerosis is the main underlying cause of cardiovascular disease. It develops through a series of processes in the vesselwall involving the accumulation of lipids and inflammatory products. Approximately 80% of cardiovascular disease is considered preventable. The most important risk factors include overweight, hypertension, dyslipidaemia, elevated blood glucose (diabetes), and smoking. These risk factors are strongly linked to socioeconomic factors, and overweight and obesity are often the common initial pathway. A healthy diet plays a central role in influencing these risk factors. It is estimated that about one quarter of cardiovascular morbidity in the Nordic countries could be prevented through healthier dietary habits. The Low-Carbohydrate High-Fat (LCHF) is a common low-carbohydrate diet in Sweden and has been used mostly for weight loss or glucose control. The reduction in carbohydrates typically leads to increased fat intake, but it is unclear whether other dietary aspects, such as fat quality, fibre intake or choice of foods can be optimized to improve cardiovascular risk. Anecdotal reports have described individuals on LCHF diets with extreme lipid abnormalities. Although low-carbohydrate diets have been studied in several trials, few are large or long enough to draw firm conclusions about long-term effects on cardiovascular risk factors. We therefore aimed to investigate how individuals following an LCHF diet in real-life setting differ in terms of dietary intake and cardiovascular risk factors, and how variation in macronutrients and food choices influences these risk factors. We also aimed to synthesise evidence from randomized clinical trials on low-carbohydrate diets in a systematic review to better assess long-term effects.

Methods

We recruited 100 volunteers who self-reported an LCHF diet. We conducted dietary interviews and measured body weight, blood pressure, and blood lipid levels. We then analysed associations between macronutrient intake, food choices, and cardiovascular risk factors using regression analyses. For the systematic review, we searched multiple databases for randomised controlled trials comparing low-carbohydrate diets with other dietary patterns and reporting outcomes on weight, blood lipids, or blood pressure. We assessed study quality and performed meta-analyses. We also conducted meta-regression analyses to examine how variations in carbohydrate and fat intake across studies influenced effects on weight, blood pressure, and blood lipids.

Results

Intake of carbohydrates, fat and proteins, in median percentage of total energy intake (E%), was 8.6 E%, 72 E% and 16.9 E% respectively. Fat and saturated fat intake exceeded recommended levels, and fibre intake was below recommendations. The group had slightly elevated levels of total cholesterol, LDL cholesterol, and HDL cholesterol, while triglyceride levels were somewhat lower compared to the general population. Lower salt intake and higher intake of fermented dairy products were associated with better blood pressure. Lower intake of dietary cholesterol and eggs was associated with more favourable lipid profile. In the systematic review, low-carbohydrate diets were more effective at lowering weight and blood pressure compared with control diets, but the magnitude of these effects was small and likely not clinically meaningful. Effects on blood lipids varied, with increases in LDL and HDL cholesterol and decreases in triglycerides. These effects were also small and unlikely to be clinically important. Effects were more pronounced at lower carbohydrate intake and higher fat intake. The effects were smaller and more uncertain beyond 12 months.

Conclusions

The LCHF group had lower carbohydrate intake than expected, indicating that very low carbohydrate diets can be followed by motivated individuals. Lipid levels were slightly elevated but less extreme than suggested by anecdotal reports. Reduced intake of salt, dietary cholesterol, butter, and eggs, and increased intake of fermented dairy products, may have favourable effects on cardiovascular risk factors. The systematic review suggests that low-carbohydrate diets have small but likely not clinically meaningful effects on weight, blood pressure, and blood lipids. The effects were smaller and more uncertain beyond 12 months.