September 23, 2014
The End of the Debate? Fat Chance

The End of the Debate? Fat Chance

by Berkeley Wellness  |  

Saturated Fat Is Okay After All... Butter Is Back!...Now Saturated Fat is Good for You? If you read such headlines in March about the latest study on fats and heart disease, you might have felt you were watching the movie Sleeper, in which Woody Allen wakes up after 200 years and finds that fatty foods like steak, cream pie, and fudge are actually healthful. While many media reports made it sound as if this study has exploded much of the accepted wisdom about heart-healthy eating, there really wasn’t much new in it. Still, it revived many debates about dietary fats—and undoubtedly left many people utterly confused.

A big deal—or not?

Written by a team of mostly British researchers, the new paper appeared in the Annals of Internal Medicine. It didn’t present any new research. Rather, it was a meta-analysis and systematic review that combined data from a selection of studies published during the past 60 years on the relationship between various types of fats and coronary events such as heart attacks.

The analysis included three groups of studies: 32 observational studies that used reported intakes of dietary fat; 17 observational studies that used more objective measures of fat intake such as blood levels of fatty acids; and 27 clinical trials that focused on fatty acid supplements, mostly involving omega-3 polyunsaturated fats from fish oil. It examined the coronary effects of the general categories of fat (saturated, monounsaturated, polyunsaturated, and trans fats), as well as of the specific fatty acids that comprise them.

Know Your Fats

Dietary fats vary in their proportion of saturated and unsaturated fatty acids. They also vary in the specific fatty acids they contain, which further determines their biological effects in the body.

The overarching finding was that there were no statistically significant associations between various types of fat and coronary events. The only exceptions were that omega-3 fats from eating fish (but not from plants or from supplements) were associated with slightly reduced coronary risk, and trans fats were linked to increased risk. This suggests that people who ignored the standard dietary guidelines and ate lots of saturated fats did not, on average, have elevated rates of coronary disease. And those with high intakes of most poly- or monounsaturated fats (supposedly heart-healthy) did not have less heart disease.

The cautious conclusion: “This analysis did not yield clearly supportive evidence for current cardiovascular guidelines that encourage high consumption of polyunsaturated fatty acids and low consumption of saturated fats.”

If you went only on the basis of this paper (at least as it was reported in the media), you might simply stop paying attention to the fat content of your foods, except to eat more fatty fish and avoid trans fats. You might even think it gives you carte blanche to eat as much saturated fat as you want. Is that a good idea? We don’t think so.

Battling analyses

This is hardly the first meta-analysis or review on fats and heart health. Some earlier ones have offered support for the general advice to cut down on saturated fats (and/or eat more polyunsaturated fats), but others have raised questions about it—without getting much media attention. For instance, a 2010 meta-analysis in the American Journal of Clinical Nutrition also found insufficient evidence to conclude that saturated fats increase the risk of cardiovascular disease; it was coauthored by Dr. Ronald Krauss, a member of our Editorial Board and the director of atherosclerosis research at Children’s Hospital Oakland Research Institute.

Meta-analyses often stir up debate. They are valuable tools because they pull together and analyze data from many studies so that patterns can become clearer. However, they can produce conflicting results because of differences in what questions were examined, how the studies were designed and selected, and how the data were used.

In the case of the new analysis, critics were quick to point out statistical errors and the omission of key studies. For example, the researchers misinterpreted one crucial study on omega-3 fats from seafood as showing no effect when it actually found a strong benefit. All it took was this one correction (made in the online version of the study) to change what seemed like no association between dietary omega-3s and coronary events to a protective effect.

Evolving science

There is no dispute that saturated fats, overall, raise blood levels of LDL (“bad”) cholesterol, but scientists have learned that this doesn’t inevitably lead to increased heart disease. The picture is not so simple, since saturated fats are not all the same, and they are never eaten in isolation. Fats in foods contain varying proportions of specific saturated fatty acids, which have different cardiovascular effects. The saturated fatty acids in chocolate, for instance, are different from those in beef and are more neutral in their effect on blood cholesterol. The same appears to be true of the fatty acids in milk and cheese.

Moreover, while saturated fats raise LDL, this is offset somewhat by the fact that they mostly increase levels of large, “fluffy” LDL particles, which are less clearly related to heart disease than the more densely concentrated smaller ones.

Foods vs. nutrients

While it makes sense for researchers to try to tease apart the health effects of individual nutrients, it can be misleading to base dietary advice on them in isolation. Where nutrients come from makes a big difference, which is why dietary guidelines should focus on foods and dietary patterns instead. Carbohydrates (which include starches and sugars) are in beans and apples as well as in pretzels and soda. Saturated fats are found in sausages and cheesecake, but also in coconut oil and salmon (though just 20 percent of salmon’s fat is saturated). Lump saturated fats all together regardless of their source, and it’s no wonder analyses don’t find clear, consistent health effects. Foods contain other substances besides fats that also affect coronary risk and health in general. Beef, for instance, may increase the risk because of its heme iron and carnitine, besides its saturated fats. In contrast, whole-fat dairy products may have heart-healthy effects because of the potassium, calcium, and other compounds in them (this is apparently not true of butter, however). Thus, it’s hard to generalize about various fats and other nutrients when context is so important.

What do people eat in place of saturated fats?

The new analysis did not address this key question. People who cut down on foods high in saturated fats often replace them with refined carbohydrates (as in white breads, pasta, and sugary baked goods), which may be why many studies find that reducing saturated fats is not beneficial. In fact, switching to refined carbs can lower HDL (“good”) cholesterol, elevate triglycerides, increase the more dangerous, smaller LDL particles, and contribute to insulin resistance, especially in people who are obese and sedentary. Even worse, many people traded saturated fats for trans fats, which were an unintended consequence of manufacturers’ use of partially hydrogenated vegetable oils in processed foods starting in the late 1980s, often to replace highly saturated tropical oils.

The best evidence still suggests that replacing saturated fats with polyunsaturated fats (including omega-3s) improves cholesterol levels and reduces the risk of cardiovascular disease. This was shown in a 2009 analysis in the American Journal of Clinical Nutrition, which included 11 observational studies, and a 2010 Harvard analysis of eight trials in the online journal PLOS Medicine.

But in the real world, it depends on where the polyunsaturated fats come from. Getting them from greasy fried foods or packaged cookies or chips won’t improve your coronary odds.

Fiber-rich foods (vegetables, fruits, beans, nuts, and whole grains) are also good substitutes for foods high in saturated fats, as are fatty fish.

As for omega-3 supplements, the finding that they do not reduce coronary risk was not a surprise, since it goes along with the results of more recent clinical trials.

Bottom line: We still advise limiting foods high in saturated fats, notably meats, and focusing more on foods rich in unsaturated fats, such as fish and nuts. Virtually all diets known to be heart-healthy tend to be low in saturated fat—that includes vegetarian and Mediterranean diets, along with DASH (Dietary Approaches to Stop Hypertension). Healthful diets focusing primarily on vegetables, fruits, beans, nuts, and whole grains have little room for saturated fats. But remember that, as far as weight control goes, fats are a double-edged sword— they can make foods satiating, but they’re calorie-dense. So moderation is the word.