Why saturated fats are considered “bad”
Saturated fats are widely regarded as “bad” by the medical community. The reasoning goes like this. Eating foods rich in saturated fats, primarily animal products such as meat, milk, cheese, and yogurt, increases intake of cholesterol. Influential studies conducted by Ancel Keys starting in the 1960s, identified cholesterol as the main culprit behind rising rates of cardiovascular disease. Subsequent research suggested that low-density cholesterol (LDL-cholesterol) was actually the main culprit. Higher levels of LDL-cholesterol in blood serum have been linked in many studies to increased risk of cardiovascular disease. Medical advice typically encourages patients to reduce consumption of saturated fat to reduce serum LDL-cholesterol. Regardless of other nutritional benefits that animal products provide, such as high levels of protein, calcium, B-vitamins, the link between LDL-cholesterol and cardiovascular disease renders animal products undesirable.
But then ...
More recently, studies have found that higher intakes of certain animal products, especially dairy, predict lower risk of cardiovascular disease. In addition, the ratio of two other markers of cardiovascular risk (apolipoprotein B / apolipoprotein A1) appears to be a better measure of cardiovascular disease risk than LDL-cholesterol. Recent studies report that higher levels of saturated fat intake lower the apolipoprotein B / apolipoprotein A1 ratio, suggesting lower risk of cardiovascular disease. The evidence that supports greatly reducing saturated fat intake is more nuanced than many people realize. Replacing saturated fat with carbohydrate, especially refined, carbs, can create more problems than it solves. Plus, in order to improve our diet to reduce the risk of cardiovascular disease, we probably ought to focus in reducing the ratio of apolipoprotein B / apolipoprotein A1 rather than LDL-cholesterol. Saturated fats may not be the boogey man they’re generally portrayed to be.
Saturated, fat, carbohydrate and cardiovascular disease
Researchers reviewed the literature in 2010 regarding saturated fat, carbohydrate, and cardiovascular disease. Results of the Nurses’ Health Study, the largest controlled dietary study at the time, did not show a significant difference in cardiovascular disease, including stroke, between women who reduced saturated fat in their diet to an average of 9.5 percent of calories compared to women who had 12.4 percent saturated fat in their diet. Reducing saturated fat in the diet cannot happen alone, assuming that caloric intake remains constant. Some other dietary factor must increase. Replacing saturated fat with polyunsaturated fat in clinical trials has usually led to fewer cardiovascular events and lower serum LDL-cholesterol but also lower serum high-density cholesterol (HDL-cholesterol), the “good” cholesterol. Replacing saturated fat with carbohydrate, especially sugar and starch, predicts adverse effects on blood fats, which are associated with higher risk of insulin resistance and obesity. When carbohydrate increases in the diet from 25 to 54 percent of calories, the relative abundance of small, dense LDL-cholesterol particles (thought to be the most damaging to cardiovascular health) increases. US dietary guidelines recommend limiting saturated fat to no more than 10 percent of calories. Yet, if the typical person reduces saturated fat and increases sugar and starch, the cure may be worse than the illness.
A meta-analysis of 21 reports
Prospective epidemiological studies have shown positive, inverse or no associations between intake of saturated fat and incidence of cardiovascular disease. In a 2010 study, researchers searched the literature for relevant studies and found 21 reports that they pooled for a meta-analysis. Sixteen studies reported data for coronary heart disease, while eight reported data for stroke. Partial replacement of saturated fat with polyunsaturated fat appears to reduce the risk of coronary heart disease. However, higher intake of saturated fat was not significantly associated with increased risk of coronary heart disease, stroke, or cardiovascular disease.
The Prospective Urban Rural Epidemiology (PURE) study
An international team of researchers used data from the Prospective Urban Rural Epidemiology (PURE) study to assess links between dietary nutrients, blood fats, and blood pressure. The study included 125,287 participants from 18 countries in North America, South America, Europe, Africa, and Asia. Increased intake of total fats and each type of fat predicted higher levels of serum total cholesterol and LDL-cholesterol, which would seem to increase cardiovascular disease risk. But increased fat intake also predicted higher levels of serum HDL-cholesterol, apolipoprotein A1, and lower levels of triglycerides, ratio of triglycerides to HDL-cholesterol, and ratio of apolipoprotein B to apolipoprotein A1, all of which predict lower risk of cardiovascular disease. Increased intake of fats also predicted higher systolic blood pressure. Increasing fat (and saturated fat) intake, perhaps up to a point, would seem, on balance, to have mostly beneficial effects of cardiovascular disease risk.
Replacement of fats with carbohydrate predicted negative effects on blood fats. Replacement of saturated fats with unsaturated fats improved some cardiovascular risk markers (LDL-cholesterol, blood pressure) and worsened others (HDL-cholesterol, triglycerides). Medical authorities generally recommend reducing dietary fat. As a practical matter, that usually involves increasing carbohydrate intake. The most recent research suggests that the ratio of apolipoprotein B to apolipoprotein A1 is the best blood fat marker for cardiovascular disease risk. Thus, the singular focus on LDL-cholesterol does not adequately capture the net effects of dietary nutrients with regard to cardiovascular disease risk.
More from the PURE Study
Investigators with the PURE study also evaluated associations among fats, carbohydrates, mortality, and cardiovascular disease among 135,335 participants with an average age of 50 years in 18 countries. Their results do not support the prevailing recommendation to limit saturated fat intake to less than 10 percent of calories. In fact, their results point in the opposite direction. Compared to participants in the lowest quintile of percent of daily energy from total fat, those in the highest quintile had significant 23, 30, and 18 percent lower risks of total mortality, cardiovascular mortality, and stroke, respectively, over 7 years of follow-up. With respect to types of fat, participants in the highest quintiles of saturated, monounsaturated, and polyunsaturated fat intake had significant 14, 19, and 20 percent lower risks of total mortality, respectively, compared to those in the lowest quintiles. Interestingly, participants in the highest quintile of carbohydrate intake had significant 28 and 36 percent higher risks of total and cardiovascular disease-related mortality, respectively, compared to participants in the lowest quintile. Substituting carbohydrates, especially refined carbs, for fat might be counterproductive from a health standpoint. Carbohydrate intake was highest in regions with low- and middle-income countries. Thus, it’s possible that high carbohydrate intake is a proxy for poverty and limited access to health care, which might lead to higher mortality risk. Neither total nor saturated fat intake showed any detrimental effect on mortality.
Still more from the PURE study
Dietary guidelines recommend minimizing consumption of whole-fat dairy products, which are a source of saturated fats and presumed to increase LDL-cholesterol, thereby increasing the risk of cardiovascular disease and mortality. The PURE study recorded consumption of dairy products (milk, yoghurt, and cheese) for 136,384 individuals using country-specific validated food frequency questionnaires. If saturated fats are bad, then increased intake of dairy products ought to show increased risk of cardiovascular disease. Compared to participants with no dairy consumption, those with two or more daily servings of dairy had 17, 23, and 34 percent lower risk of all-cause mortality, cardiovascular mortality, and stroke, respectively, over 9 years of follow-up. No significant association with myocardial infarction (heart attack) appeared. Compared to participants with no milk or yogurt intake, those with at least one serving per day of either had 10 and 14 percent lower risks, respectively, of any cardiovascular event. Cheese and butter consumption were not significantly associated with the number of cardiovascular events. Dairy consumption was associated with lower (not higher) risk of mortality and major cardiovascular disease events
The EPIC-Oxford Study
A 2016 report from the EPIC-Oxford study did not show a significant link between vegetarianism and death due to stroke. A 2019 update of the EPIC-Oxford study confirmed the earlier report. The new results for 48,188 participants showed that vegetarians had a 20 percent higher risk of having a stroke compared to meat eaters over an average follow-up of 14 years. For every 100 persons over a 10-year period, the vegetarians would have three more cases of stroke than the meat eaters. Thus, the absolute difference in stroke risk for vegetarians was small relative to meat eaters. This same study found that vegetarians and fish eaters had a 13 percent lower risk of ischemic heart disease (caused by a blood clot the heart). Curiously, other research shows that hypertension accounts for the highest fraction of risk of stroke. Yet in the EPIC-Oxford study, vegetarians had twice the incidence of hypertension than meat eaters. This study illustrates the potential pitfalls of ascribing “healthy” or “unhealthy” to any particular approach to eating.
This blog post does not purport to be a thorough review of the relevant existing literature. Rather, my purpose is to alert readers to the complexities of understanding the possible benefits and harms of saturated fat. Saturated fats may not be “bad,” at least in the sense that they have few or no redeeming features. Saturated fat may be beneficial at least in some circumstances. Furthermore, replacing dietary fat with refined carbohydrates likely leads to less healthful diets. Health messages that focus on replacing refined carbs with complex carbs might reduce cardiovascular disease risk more than a focus on limiting saturated fat.