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Replacement of Saturated Fat with Other Nutrients

Synopsis

Current nutritional guidelines recommend decreasing saturated fat intake to improve blood lipids and reduce cardiovascular risk. However, the effect on cardiovascular health may vary depending on which nutrient replaces saturated fat in the diet, e.g., omega-3 or omega-6 polyunsaturated fats or carbohydrates.

Highlights

  • The effect of substituting saturated fat with polyunsaturated fatty acid (PUFA) is not clear and may depend on whether it is omega-3 or omega-6 PUFA;
  • Substituting saturated fat with omega-6 PUFA could increase cardiovascular mortality risk, but long-chain omega-3 fatty acids appear to be associated with a reduced risk of coronary heart disease;
  • There is insufficient evidence regarding the replacement of saturated fat by monounsaturated fatty acid (MUFA), but limited findings suggest a reduced coronary heart disease risk;
  • Substituting saturated fat with trans fat has a detrimental effect on blood lipid profile;
  • Substituting saturated fat with high glycemic index carbohydrates appears to increase cardiovascular disease risk.

The Evidence

In a 2014 meta-analysis by Chowdhury et al., the association between dietary fatty acids and coronary disease was evaluated. It was found that:1

  • Saturated fat and omega-6 PUFA were not associated with coronary risk;
  • Higher omega-3 PUFA intake, particularly long-chain omega-3 PUFA, was associated with a decreased risk of coronary disease, with a relative risk of 0.87 (95% CI: 0.78-0.97);
  • MUFA was not associated with coronary heart disease risk;
  • Higher trans fat intake was associated with an increased risk of coronary disease.

Several other studies have looked specifically at the replacement of saturated fat by other nutrients.

A meta-analysis investigated the association between dietary linoleic acid (an omega-6 fatty acid) and the risk of coronary heart disease. The authors examined 13 prospective cohort studies, for a total of 310,602 individuals.2

  • A 5% energy increment in linoleic acid to replace saturated fat was associated with a 9% lower risk of coronary heart disease events (95% CI: 0.87-0.96) and a 13% lower risk of coronary heart disease mortality (95% CI: 0.82-0.94);
  • Substituting 5% of the energy from carbohydrates by linoleic acid was associated with a 10% and 13% lower risk of coronary heart disease events and mortality, respectively.

Ramsden et al. published an updated meta-analysis in 2013 of interventions that examined the replacement of saturated fat with respect to all-cause and cardiovascular mortality.3

  • When saturated fatty acids were substituted by linoleic acid, non-significant trends were observed towards higher risk of mortality from cardiovascular disease and coronary heart disease;
  • When saturated fatty acids were replaced by both omega-3 and omega-6 PUFA, a significant decrease in cardiovascular mortality was observed.

In 2010, the Food and Agriculture Organization of the United Nations published a report of an expert consultation on fats and fatty acids. It was concluded that:4

  • There is convincing evidence that replacing saturated fat with PUFA lowers the risk of coronary heart disease;
  • There is insufficient evidence on the effect that replacing saturated fat with MUFA may have on CHD risk;
  • There is probable evidence that replacing saturated fat with refined carbohydrates has no benefit on coronary heart disease, and may even increase its risk;
  • With regards to blood lipid levels, there is convincing evidence that:Replacing saturated fat with PUFA decreases LDL cholesterol and total-to-HDL cholesterol ratio,
  • Replacing saturated fat with MUFA decreases LDL cholesterol and total-to-HDL cholesterol ratio, but to a lesser extent than replacement with PUFA,
  • Replacing saturated fat with carbohydrates decreases both LDL and HDL cholesterol, but does not change total-to-HDL cholesterol ratio,
  • Replacing saturated fat with trans fatty acids decreases HDL cholesterol and increases total-to-HDL cholesterol ratio.

A 2010 meta-analysis of randomized controlled trials had also concluded that there is strong evidence that consumption of polyunsaturated fat as a replacement for saturated fat lowers coronary heart disease risk.5

  • The pooled risk reduction for coronary heart disease events in the intervention groups compared to the controls was 19%, with a relative risk of 0.81 (95% CI: 0.70-0.95, p = 0.008);
  • For each 5% energy of increased polyunsaturated fat instead of saturated fat, there was a 10% reduction in the risk of coronary heart disease, with a relative risk of 0.90 (95% CI: 0.83-0.97).

A 2010 prospective cohort study of 53,644 Danish women and men aged 50 to 64 years suggested that replacing saturated fatty acids with low glycemic index carbohydrates is associated with a lower risk of myocardial infarction, whereas replacing saturated fatty acids with high glycemic index carbohydrates is associated with a higher risk of myocardial infarction.6

  • After adjustments for confounding variables such as body mass index, smoking status and physical activity, the hazard ratio for myocardial infarction per 5% energy intake increase from carbohydrates and a concomitant lower energy intake from saturated fatty acids was 1.04 (95% CI: 0.92-1.17);
  • There was a non-significant inverse association between substitution of low glycemic index carbohydrates for saturated fatty acids and risk of myocardial infarction, with a hazard ratio of 0.88 (95% CI: 0.72-1.07);
  • There was no association between substitution of medium glycemic index carbohydrates for saturated fatty acids and risk of myocardial infarction, with a hazard ratio of 0.98 (95% CI: 0.80-1.21);
  • There was a significant association between the substitution of high glycemic index carbohydrates for saturated fatty acids and increased risk of myocardial infarction, with a hazard ratio of 1.33 (95% CI: 1.08-1.64).

Conclusion

The effects of replacing saturated fat with PUFA are uncertain. Increasing omega-6, but not omega‑3 PUFA, may increase cardiovascular mortality risk.

Replacing saturated fat with high glycemic index carbohydrates appears to increase the risk of cardiovascular disease.

The food source of saturated fat may be an important modifier and needs to be assessed.

Additional randomized controlled trials on the replacement of saturated fat, including trials assessing the food source of saturated fat, with other types of fats or macronutrients are needed to provide more definitive answers.

Keywords: cardiovascular disease , coronary heart disease , saturated fat , stroke


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