Saturated Fat and Heart Disease

I'm on a low-carb diet. I believe in LC diets for people with diabetes.

However, I also have an open mind. It's possible that new evidence will show that LC diets, although they improve blood glucose (BG) levels in people with diabetes, also make something else worse.

Richard Bernstein, the physician and author of LC diet book The Diabetes Solution, has lived with type 1 diabetes for many decades, most of those years on a LC diet. And the fact that he is in excellent health in his 70s argues against this possibility. However, Bernstein has type 1 diabetes, and very little insulin resistance. There's some evidence that fat increases insulin resistance. Hence, for those of us for whom insulin resistance is a big problem, perhaps fat of any kind, or maybe only certain kinds of fat, is not a great idea.

So, I have an open mind. But unfortunately, many people in the LC community seem not to. Many of them don't have diabetes, and they have gotten great results losing a lot of weight with LC diets. So they think the LC diet with a lot of fat is the answer for everyone.

And unfortunately, the LC world is just as guilty of spinning the news as the popular science writers who blame red meat for all our problems when some study showed that people eating red meat, hot dogs, french fries, no vegetables, and sweet desserts don't fare so well on some health factor.

A good example is the blogosphere response to this recent study, a meta-analysis of the association between saturated fat and cardiovascular disease (CVD). A meta-analysis is a study in which researchers combine the results from a lot of studies, some of which aren't statistically significant because of their small size, so that the overall results are statistically significant because of the larger populations in the combined studies.

Meta-analyses are notoriously questionable, because the researchers have to decide which studies to include. If you did a meta-analysis of the percentage of the population that watched the Super Bowl (assuming lots of people had studied this fascinating question) but excluded everyone who shaved every morning, the results wouldn't be very accurate.

Nevertheless, sometimes meta-analyses can suggest possible conclusions that other scientists can then investigate more thoroughly.

And that is what this study, titled Meta-analysis of prospective cohort studies evaluating the association of saturated fat with cardiovascular disease, did.

The authors' conclusion was that "there is no significant evidence for concluding that dietary saturated fat is associated with an increased risk of CHD [coronary heart disease] or CVD. More data are needed to elucidate whether CVD risks are likely to be influenced by the specific nutrients used to replace saturated fat."

Two things are important here.

First, the fact that there's no significant evidence for something doesn't mean it's not true. It just means no one has proved that it's true. Several studies have concluded that there's no significant evidence that BG testing in people with type 2 diabetes results in lower A1c's, but most of us know that it does when patients are educated about how to use the results from their meters to change their diets and their exercise patterns. But no one has done the study that would show this.

And second, this study was about association, not cause. Something can be associated with something else but not be the cause of it. For example, coffee drinking is often associated with smoking, but drinking coffee doesn't make you smoke, and vice versa.

The types of studies this meta-analysis looked at were not the types of studies that can show cause.

What the authors found was that some studies showed that saturated fat consumption was associated with higher rates of CVD (heart attacks and strokes), and other studies showed that saturated fat consumption was associated with lower rates of CVD. When you combined the higher rates and the lower rates, you got rates that weren't significantly different.

However, they also noted another recent study that showed that when saturated fat was replaced by polyunsaturated fat, CVD rates went down. When saturated fat was replaced by carbohydrates (what dieticians have been recommending that we all do), CVD rates went up. They said there was some evidence that the ratio of unsaturated to saturated fats was more important than the amount of saturated fat. Hence they suggest that studies are needed that would investigate whether the other elements of the diet have more effect on CVD than the saturated fat.

The authors of Meta-analysis of prospective cohort studies evaluating the association of saturated fat with cardiovascular disease never say that saturated fat definitely doesn't cause CVD. They also say that "the available data were not adequate for determining whether there are CHD or stroke associations with saturated fat in specific age and sex subgroups." In other words, the jury is still out.

Nevertheless, the Internet is awash in blogs with titles like "Two major studies conclude that saturated fat does NOT cause heart disease" and "Saturated Fats Are Not Harmful."

The following are just my opinions, and I won't cite studies to back them up. I suspect that saturated fat is fine in moderation. If you want to put a couple of teaspoons of something on your vegetables, I suspect it doesn't matter if it's butter or olive oil. People on LC diets can probably eat more saturated fat because they're burning fats instead of carbohydrates for energy. I don't think eating a lot of polyunsaturated fats (vegetable oils), which are easily oxidized (damaged), is healthy.

But I don't think eating gargantuan amounts of fat of any kind is healthy, even on a LC diet. I once measured my triglyceride levels after eating an extremely high fat breakfast. You can see the results here. The triglyceride levels were astronomical.

People with diabetes probably have a disturbed lipid metabolism, so it's possible that nondiabetics would not have such astronomical triglyceride levels after pigging out on fats (for example, eating half a pizza). But headlines proclaiming that saturated fat isn't harmful will be interpreted by many people to mean that fat isn't harmful. They won't stop eating all those carbohydrates, the doughnuts and french fries and white bread. They'll just add more fat because they remember that they saw headlines saying fat doesn't cause heart disease.

The study showing no association between saturated fat consumption and CVD, despite its many limitations, is important. It should lead to more studies that will attempt to show causation or lack thereof.

I just hope the misinterpretations don't result in more unhealthy eating.