Am Fam Physician. 2021;104(2):235-236
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Does reducing saturated fat intake decrease morbidity and mortality related to cardiovascular disease (CVD)?
Reducing saturated fat in the diet for at least two years decreases the risk of combined cardiovascular events (relative risk [RR] = 0.83; 95% CI, 0.70 to 0.98; number needed to treat [NNT] for primary prevention = 56). However, there is little to no effect on cardiovascular mortality, all-cause mortality, or individual cardiovascular events.1 (Strength of Recommendation: B, based on inconsistent or limited-quality patient-oriented evidence.)
CVD continues to be the leading cause of death in the United States and worldwide.2,3 Up to one-third of deaths globally are directly attributable to CVD, 85% of which are associated with heart disease and stroke. In the United States, heart disease is consistently the leading cause of death, and stroke is currently the fifth. The American Heart Association estimates that 45% of the U.S. population will have some form of CVD by 2035.4 As of 2016, more than 10.3% of primary care visits have been related to CVD, and up to 55% of visits include management of CVD risk factors (e.g., hypertension, dyslipidemia, diabetes mellitus).4 In an effort to determine the role of diet in CVD prevention, this review assessed if reducing saturated fat intake resulted in decreased cardiovascular morbidity and mortality.
This Cochrane review included 15 randomized controlled trials (RCTs) published between 1965 and 2019 that involved 56,675 adults 46 to 66 years of age.1 Participants were living in developed nations of North America, Europe, and Australia/New Zealand and had varied levels of CVD risk. They were followed for an average of 4.7 years (range = 2 to 8 years). The largest study was the 2006 Women's Health Initiative, involving 29,294 women; sensitivity analyses excluding this study did not alter the major findings of this review, as outlined below. Blinding of study participants was largely not possible given the dietary interventions and need to follow instructions. The review included studies that intentionally sought a reduction in saturated fat intake, or that produced a statistically significant (P < .05) reduction in saturated fat intake, compared with usual diet, a control diet, or a diet higher in saturated fat. Interventions included dietary advice to alter intake in 15 of 16 intervention arms (across the 15 studies), such as reducing saturated fats and/or substituting with polyunsaturated fat, monounsaturated fat, carbohydrate, or protein.
Advice was given face-to-face in 13 of 16 arms (unclear in three) to individual participants, groups of participants, or those with a combination of individual and group visits. The frequency of visits ranged from three to 18 in the first year and quarterly to annually in subsequent years. Advice was given by a dietitian (nine of 16 intervention arms), nutritionist (one arm), or trained nurse (one arm); it was unclear who gave advice in four arms. In addition to advice, three studies (four arms) also provided supplements (i.e., 85 g of soya oil per day, 0.5 L of soy bean oil per week plus sardines in cod liver oil, 80 g of corn oil per day, or 80 g of olive oil per day). In one study, patients were not given advice, but two-thirds of saturated fats were substituted with unsaturated fats in older men living in a residential facility. The primary outcomes assessed were all-cause mortality, CVD mortality (from myocardial infarction, stroke, or sudden death), and combined CVD events. Combined CVD events were defined as cardiovascular death, cardiovascular morbidity (nonfatal myocardial infarction, angina, stroke, atrial fibrillation, peripheral vascular disease, heart failure), and unplanned interventions (coronary artery bypass grafting or angioplasty).
Reducing saturated fat intake did not affect all-cause mortality (55,858 participants and 3,518 deaths; 11 RCTs) or cardiovascular mortality (53,421 participants and 1,096 deaths; 10 RCTs), even when controlling for multiple variables, based on moderate-quality evidence. It did result in a 17% reduction in combined CVD events (RR = 0.83; 95% CI, 0.70 to 0.98; 53,758 participants, 4,538 of whom had CVD events; 12 RCTs) for a minimum of two years (average = 4.7 years), based on moderate-quality evidence. This equates to an NNT of 56 in primary prevention trials. The NNT in secondary prevention trials was 53. In subgroup analysis, the greater the baseline saturated fat intake, degree of saturated fat reduction, or degree of cholesterol reduction, the greater the reduction in CVD events, although this finding was not statistically significant. Similarly, subgroup analysis of specific nutrients used to replace saturated fats (i.e., polyunsaturated fats, monounsaturated fats, carbohydrates, or protein) did not show statistically significant reductions in CVD events with any one replacement nutrient, although substitution with polyunsaturated fats and carbohydrates had a greater nonsignificant trend toward CVD event reduction.1
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