Different fats have different health effects

If total fat in the diet is considered to be less of a concern, at least according to many nutrition scientists, does the type of fat matter? We know that trans-fats are harmful, but what are the health implications of monounsaturated fatty acids (MUFAs),
polyunsaturated fatty acids (PUFAs), and saturated fatty acids (SFAs)? Consumption of saturated fat is not needed for good health, and the preponderance of evidence indicates that high consumption of saturated fat (sometimes called a “bad” fat) increases harmful LDL-C and increases the risk of cardiovascular disease and some cancers. The 2015 DGAC recommends that less than 10% of total daily calories should come from saturated fat. The American Heart Association recommends aiming for a dietary pattern with only 5% to 6% of total calories derived from saturated fat. According to this recommendation, of a 2,500 calorie a day diet, fewer than 150 calories or 17 grams a day should be saturated fat. A McDonald’s Big Mac has 540 calories and a total of 30 grams of fat, of which 10 grams is saturated fat.

Research based on the Nurses’ Health Study cohort found that higher consumption of red meat and high-fat dairy products, together, the main sources of saturated fatty acids in the diet, was also associated with greater risk of coronary heart disease (CHD) events. In contrast to eating red meat, higher consumption of poultry and fish and low-fat dairy products were associated with a lower risk, and that a higher ratio of polyunsaturated to saturated fat was strongly associated with lower CHD risk.

A 2012 Cochrane meta-analysis, a study design generally considered to be of exceptionally high scientific validity, found that reducing saturated fatty acids by reducing or modifying dietary fat reduced the risk of cardiovascular events by 14%. Studies
among high-risk individuals have shown that greater consumption of MUFA and PUFA lowered the risk of cardiovascular disease and death, whereas saturated fat and trans-fat were associated with increased risk of cardiovascular disease. The evidence is not as clear for the replacement of SFA by monounsaturated fatty acids or replacement with carbohydrate and likely depends on the type and source.

Prospective cohort studies and randomized controlled trials have found lower rates of CVD when polyunsaturated fatty acids (PUFAs) from soybean, corn, and other vegetable oils replaced saturated fatty acids (SFAs). A 2010 meta-analysis of randomized controlled trials found that increasing PUFA consumption as a replacement for SFA reduced the occurrence of CHD events by 19%.

A 2015 Cochrane meta-analysis of 15 trials of at least 2 years duration found that replacing saturated with polyunsaturated fats led to an estimated 27% reduction in cardiovascular disease, but no benefits were seen for replacement of saturated fat with carbohydrates or proteins. A dose-response analysis showed that this protection was proportional to the reduction of total cholesterol, which in turn depended on the extent of reduction in saturated fat consumption.

A long-term study (24 to 30 years of follow-up), published in 2015, found that higher intakes of polyunsaturated fatty acids and carbohydrates from whole grains were significantly associated with a lower risk of CHD. Replacing 5% of energy intake from saturated fats with equivalent energy intake from polyunsaturated fatty acids was associated with a 25% lower risk of coronary heart disease, replacement with monounsaturated fatty acids decreased risk by 15%, and replacement with carbohydrates from whole grains a 9% lower risk of CHD.

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