Nutrition advice has performed some spectacular flip-flops over the years. Eggs were banished from the breakfast table, then later welcomed back. Margarine was deemed healthier than butter—until researchers determined that the trans fats used to make the first generation of margarines were much harder on the heart than butter.
Yet one dietary guideline has stood fast for half a century: Saturated fat, found chiefly in meat and high-fat dairy products such as cheese, is bad—because it leads to clogged arteries, heart attacks and strokes. Now that certainty isn’t just wobbling; it’s toppling. According to recent research, saturated fat may not be a villain after all. In fact, some foods high in saturated fat may lower your risk of stroke and type 2 diabetes. And steering clear of foods just because they contain saturated fat, and eating other foods just because they are low in saturated fat, may be the unhealthiest choice of all.
One of the most prominent proponents of rewriting the book on saturated fat is cardiologist Dariush Mozaffarian, an associate professor of medicine at Harvard Medical School and the author of more than 100 scientific papers on nutrition and health. We asked him to explain why the conventional wisdom on saturated fat is misleading—and how eating it, in moderation, can sometimes be the healthiest move you could make.
Q: Saturated fat has been dietary public health enemy number one for decades. Why do you think telling people to avoid it is bad advice?
A: The recommendation to cut back on saturated fat was based on concerns that it raises the risk of heart disease. But we’ve learned that its effects are more complex than we first thought.
We’ve known since the 1960s that saturated fat raises LDL cholesterol, the “bad” cholesterol. But LDL is just one biomarker for risk. We now know that there are other cholesterol-containing particles, called HDL, that are related to a lower risk of heart disease. We also know that high levels of triglycerides in the blood, along with other factors, predict heart disease risk. Saturated fat does raise LDL cholesterol. But compared to carbohydrates, it also raises HDL cholesterol and lowers triglycerides. If we looked just at LDL, we would predict that saturated fat raises heart disease risk. If we looked at the effect of saturated fat on HDL and triglycerides, we would suppose that saturated fat lowers that risk. If we looked at the combination, we would predict that saturated fat is relatively neutral for heart disease risk compared to carbohydrates.
Q: So is saturated fat good or bad?
A: To answer that, we need to study how eating saturated fat relates to actual diseases, not simply to biomarkers such as blood cholesterol that only suggest the possibility of artery damage. Three groups of researchers have recently weighed data from all available large long-term studies that have tracked saturated-fat intake and heart attacks or strokes. All three found no association between saturated fat and heart attacks or strokes. People who consumed the highest levels of saturated fat had about the same rates of heart disease as people who consumed the least.
Q: Those are amazing results, given decades of advice to cut back on saturated fat. How do you explain them?
A: When you ask whether saturated fat is good or bad, the question should be, “Compared to what?” Compared to polyunsaturated fat from vegetable oils, saturated fat is clearly more harmful to the heart. But compared to trans fat, saturated fat is healthier. Compared to carbohydrates, a category that includes starches and grains as well as sugary foods, saturated fat is probably neutral. But compared to refined carbohydrates—the kind found in white breads, most breakfast cereals and snack foods and sweets, for -instance—many foods with saturated fat appear to be a better choice. They also seem less likely than refined carbohydrates to raise heart disease risk.
How does it all add up? In the context of the average American diet, which is mostly poor-quality carbohydrates such as starches and sugars, the amount of saturated fat eaten doesn’t significantly increase or decrease health risk. This is likely why it’s not related to risk of heart attacks when we look at large population studies.
Q: What has been the effect of the move to cut down on saturated fat in the United States?
A: In the last few decades, total-fat and saturated-fat consumption has gone down, but consumption of refined carbohydrates has soared. Low-fat versions of packaged foods, loaded with refined carbohydrates, sugars and salt, now flood the market. When people replace saturated fat with refined carbohydrates, they are unlikely to improve their health and may worsen it. That’s because these kinds of carbohydrates are more likely than saturated fat to raise the risk of heart disease and type 2 diabetes.
Q: So has the recommendation to reduce saturated fat done more harm than good?
A: The emphasis on saturated fat misleads people into thinking that foods low in saturated fat are healthier when they’re not. For example, low-saturated-fat processed meats are not healthy choices. And the desire to reduce saturated fat sometimes steers people away from foods that contain that fat but are actually healthy.
Q: What’s an example of a healthy food that contains saturated fat?
A: The average avocado contains about 4.5 grams of total fat, including about half a gram of saturated fat. This small amount has been enough for many people to suggest that you should avoid avocados. But this fruit also contains four grams of unsaturated fats, similar to those found in olive oil, as well as phytochemicals that are healthy.
Dairy is another example of how a focus on saturated fat can lead people astray. We’ve tended to treat all foods that contain saturated fat the same—unprocessed red meat, processed meat, cheese, yogurt and milk. But each of those foods contains a variety of components, some good and some not so good. Given equivalent serving sizes, processed meat is associated with far higher risks of type 2 diabetes and heart disease than unprocessed meat, even though their saturated-fat content is about the same. Many low-saturated-fat processed deli meats, which are currently marketed as healthy choices, could be much worse for your health than unprocessed red meats that contain more saturated fat. Similarly, even though dairy foods are the top source of saturated fat in the U.S., people who eat the most dairy do not have a higher risk of heart attacks and actually may have a lower risk of type 2 diabetes and stroke.
Q: Do researchers know if full-fat milk is healthier than reduced fat?
A: We don’t have firm evidence. Very few long-term studies have compared the health effects of full-fat dairy versus reduced-fat dairy. Even fewer have compared the health effects of different types of dairy, such as butter, milk, cheese and yogurt. The few that have been done have shown mixed results. Some suggest that reduced-fat dairy is better for heart disease or type 2 diabetes risk. Others suggest that whether you consume full-fat or -reduced-fat dairy, the risks are the same. Still others suggest that full fat may be better, because there may be specific fatty acids in dairy fat, or compounds that go along with the fat, that protect against disease. I don’t think we have enough evidence to alter the existing dietary guidelines that recommend low-fat dairy. But we also don’t have clear evidence that low-fat dairy is a better choice than whole-fat dairy.
Q: Studies have shown that some meats increase heart disease risk. Is saturated fat the culprit?
A: Saturated fat may not be the main problem. For instance, red meat also contains other potentially harmful nutrients, such as a certain type of iron that may raise the risk of type 2 diabetes. Processed meats have sodium, which increases blood pressure and risk of stroke. Low-fat hot dogs and processed deli turkey have less saturated fat than a steak, for example, but also contain, on average, up to four times as much sodium per gram. Research from our group and others shows that processed meats, such as bacon, bologna, deli meats and sausages, pose a risk of heart disease and type 2 diabetes that’s two or three times as high as the risk posed by unprocessed meat, even when the -saturated-fat content is the same.
So saturated fat alone is not a useful metric for making a healthy choice. Consider a typical deli sandwich made with low-fat processed meat. It may contain little or no saturated fat. But processed meat is typically very high in sodium. Processed cheese is also high in salt. It’s even worse if the meat and cheese are served on refined white bread, loaded with refined carbohydrates. In terms of health risks, that sandwich is a cardiovascular bomb. You’d be better off eating a home-cooked steak. Of course, the best choices would still be conventionally healthy options such as fish, nuts, vegetables, fruits and whole grains.
Q: What about the epidemic of overweight and obesity? Are fatty foods more likely to make people fat?
A: That’s what we once thought. We also thought that high-fat diets raised the risk of heart disease. But evidence has proved that the proportion of total fat in a person’s diet has no effect on heart disease. Growing evidence indicates that this is also true for obesity. Dietary fat doesn’t make people fat. When we studied how specific foods related to weight gain over time, the main culprits were starches, such as potatoes, refined carbohydrates and sugars—in other words, poor-quality carbohydrates.
Q: Is saturated fat more dangerous for some people than others?
A: For someone who is young, lean and active and whose only risk factor is elevated LDL, reducing saturated fat might be helpful as long as it’s replaced with polyunsaturated fats, such as vegetable oils. But more and more Americans are overweight and sedentary. They typically have low HDL, insulin resistance and elevated triglycerides, a combination of risk factors called metabolic syndrome. Refined carbohydrates are a bigger risk for them than saturated fat, especially from dairy foods, which may actually improve metabolic syndrome. For people with metabolic syndrome, a focus on reducing consumption of potatoes, sugars, white bread and other refined carbs is most important, together with increasing consumption of healthy foods such as fish, fruits, vegetables, nuts, whole grains, vegetable oils and moderate amounts of dairy.
Q: If we toss out the focus on saturated fat, what should the message be?
A: I want to be clear. I’m not saying that saturated fat is good for you. I’m saying that our historical emphasis on cutting back on saturated fat has led to some bad choices. We should focus our recommendations on foods, not single nutrients like saturated fat. Last year Simon Capewell, DSc, a professor of clinical epidemiology at the University of Liverpool, and I drew up a list of dietary priorities that could reduce heart disease deaths by half in the U.S. and around the world. Limiting saturated fat doesn’t make the cut, because we don’t think that on its own it offers much benefit. We estimate that getting Americans to add two servings of nuts a week to their diets would reduce cardiovascular mortality by 11 percent. Replacing refined grains and starches with a serving of whole grains every day would decrease heart-related deaths by an additional 10 percent. Adding an extra serving of fruits and vegetables a day would reduce heart disease mortality by 15 percent more. Those simple changes would make a far bigger dent in heart disease than anything we could expect from reducing saturated fat.
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