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Saturated Fat and Cardiovascular Disease Risk Factors

Synopsis

Many recent studies such as randomized clinical trials have investigated the role of saturated fat on cardiovascular disease risk factors, particularly on blood lipid markers, as well as metabolic syndrome. The new evidence suggests that saturated fat may not be detrimental to those cardiovascular risk factors.

Highlights

• The impact of saturated fat on blood lipid levels depends on the nutrient it replaces and food sources of saturated fat;
• Carbohydrate restricted diets appear to be beneficial compared to low fat diets in terms of their impact on blood lipids;
• Improved blood lipid levels were observed with the consumption of butter;
• Improvement in cardiovascular risk factors was observed with carbohydrate restricted diets.

The Evidence

A 2010 randomized crossover study investigated the postprandial lipemic response to alpha-linolenic acid-rich oil, butter, and olive oil in 29 healthy men aged 26 to 67 years.¹

• With butter, plasma triacylglycerol levels were significantly reduced by 34% compared to olive oil (p < 0.05), and nonsignificantly lower by 25% compared to linolenic acid-rich oil (p > 0.05);
• Similar to olive oil, there was a significant increase in HDL cholesterol with the butter diet between 0 hr: 1.37 (95% CI: 1.25-1.49, p < 0.05) and 7 hr: 1.42 (95% CI: 1.30-1.54, p < 0.05);

In a 2010 randomized, cross-over, controlled trial, an isocaloric carbohydrate restricted high saturated diet was compared to a carbohydrate restricted diet higher in unsaturated fat in 8 men aged 35 to 58 years.²

• Fasting plasma total cholesterol and LDL cholesterol were higher following the carbohydrate restricted high saturated diet compared to the carbohydrate restricted diet higher in unsaturated fat;
• There was no significant change in the total cholesterol/HDL cholesterol or LDL cholesterol/HDL cholesterol ratios;
• For both diets, there was a dramatic decrease in triacylglycerol and triacylglycerol/HDL cholesterol ratio;
• Blood glucose, insulin and insulin resistance were not significantly different from baseline or between diets;
• There were no significant differences in any of the serum inflammatory markers between diets.

In a 2009 randomized controlled dietary intervention trial that compared a carbohydrate restricted diet to a low fat diet over a 12-week period in 40 overweight men and women with atherogenic dyslipidemia, aged 18 to 55 years, it was found that carbohydrate restriction, rather than a low fat diet may improve features of metabolic syndrome and cardiovascular risk.³

• Compared to the low fat diet, the carbohydrate restricted diet led to a significant reduction in fasting glucose, and a more considerable decrease in fasting insulin responses and postprandial insulin responses to a meal high in fat;
• With the carbohydrate restricted diets there was a significant decrease in small LDL particles, an increase in HDL cholesterol, and a reduction in triacylglycerol levels;
• The effect of a low fat diet on HDL cholesterol was minimal;
• The total cholesterol/HDL ratio was reduced more in the carbohydrate restricted diet than in the low fat diet;
• There was a slight reduction in the ratio Apo B/Apo A-1 in the carbohydrate restricted group, but the ratio was slightly worse in the low fat diet group.

In a 2010 cross-sectional study, which included 1,004 Japanese men and women aged 40 to 59 years, the relationship between dietary polyunsaturated to saturated fatty acid ratio to cardiovascular risk factors and metabolic syndrome was examined.⁴

• After control for possible confounding variables, dietary polyunsaturated to saturated fatty acid ratio was significantly and inversely related to serum total and LDL cholesterol;
• Dietary polyunsaturated to saturated fatty acid ratio did not significantly relate to single metabolic risk factors or the prevalence of metabolic syndrome.

Another 2009 cross-sectional study, conducted among 443 Tehranian adults 18 years or older, concluded that saturated fat and cholesterol intakes had no combined effect on serum LDL cholesterol level.⁵

• After adjusting for confounding variables, such as age, sex and body mass index, no significant effect of saturated fat and cholesterol intakes on LDL and total cholesterol concentrations;
• There was no main effect of saturated fat and cholesterol intakes on triacylglycerols with and without adjustment for confounding factors.

Conclusion

The evidence appears to indicate that the source of saturated fat and the nutrient it replaces is key in determining the impact it will have on blood lipids and other cardiovascular risk factors.

Butter does not appear to have a detrimental impact and may in fact have a beneficial impact on blood lipid levels. However, more randomized controlled trials are needed to confirm these findings.

Carbohydrate-restricted diets appear to be beneficial compared to low fat diets in terms of their impact on blood lipid levels. It also appears that diets higher in polyunsaturated fats have a favourable effect on blood lipids. Furthermore, the evidence suggests that carbohydrate intake rather than the type of fat is related to metabolic syndrome.

More randomized controlled dietary intervention studies, including mechanistic studies, are needed to provide more definitive conclusions.

Moreover, more research is needed to investigate and better understand the impact regarding the food source of saturated fat on cardiovascular risk factors including emerging risk factors such as inflammation and insulin resistance.

For more information:

• Types of Saturated Fatty Acids and Cardiovascular Disease
• Summary of Data on Cardiovascular Diseases and Milk Products

Keywords: cardiovascular disease, coronary heart disease, dietary factors, saturated fat, stroke, trans fat

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