My recent post on low-fat vegan diets inspired some good and thoughtful comments, which I really appreciate. Coincidently, just a few days after I posted, an important study was published that supported some of what I was saying. There are lots of studies to support the content of that post (I don’t make this stuff up; I swear) and the idea that eating some fat is good for you is hardly a new idea. But this was a particularly interesting bit of research coming just on the heels of the discussion here.
And so I wanted to talk about that study and also respond to some of the issues that were raised by my last post. Especially in regard to one comment which pointed out that the Ornish Program isn’t going to stop working just because new research has been published.
That’s true. I’m not saying that the Ornish Program doesn’t work. I’m saying that, based on what we know about fat and heart disease, it is probably not the best approach. And more importantly, the reasons why it works most likely have nothing to do with the low-fat aspect of the diet.
In fact, the Ornish study didn’t prove anything about low-fat vegan diets at all. Aside from the fact that the diet isn’t vegan, the program is a comprehensive lifestyle makeover and it’s not possible to determine which aspects of the program were responsible for the benefits. For one thing, as soon as you add exercise into the mix, it becomes really difficult to give diet much credit—because exercise is probably far more important for reducing disease risk than any dietary change you can make.
But even assuming that the benefits are all or mostly due to the diet used in the program, it doesn’t follow that you need to reduce all fats in order to reap those benefits. That’s because the various low-fat vegan diets that have been used to reverse heart disease have two important things in common: they are low in saturated fat and they produce weight loss. Both of these factors reduce heart disease. So if people in these studies are losing weight and eating less saturated fat, there is just no way we can say that it is the low total fat content of the diet that is responsible for their improved health. And, in fact, the research really does suggest otherwise.
The new study that was published last week was a meta-analysis of randomized clinical trials (RCTs). (Not all studies carry the same weight in scientific research but RCTs are considered to be the gold standard.) The researchers, who are well-respected Harvard scientists, found that simply replacing saturated fat with polyunsaturated fat reduced coronary heart events (like heart attacks) by 19%. (And a reduction in heart attacks is a much more meaningful outcome that a reverse in atherosclerosis.) Not only that, but for every 5% increase in unsaturated fat consumed (as a replacement for saturated fat), heart disease risk went down by 10%.
It’s fair to assume that people who also adopt a vegan diet (in addition to reducing saturated fat and increasing polyunsaturated fat) might have even better outcomes. Vegan diets have the added benefits of more fiber, antioxidants and other good things in plant foods. There is every reason to believe that a vegan diet based on whole plant foods, and including some good sources of unsaturated fat, is the best heart healthy way to eat.
In a study published last year by Dr. David Jenkins, a vegan diet rich in plant protein and fats (43%!) produced a better blood cholesterol profile than a diet high in complex carbohydrates and it was just as effective for weight loss. The subjects also found it more satisfying. These are just a couple of the studies that make the case that type of fat is more important than amount of fat in the diet for heart disease prevention. (This is true only up to a point of course and I am not recommending a 43% fat diet!)
So to summarize from this post and my previous one:
- Replacing saturated fat with either carbohydrate or unsaturated fat will lower blood cholesterol. (This is not at all a controversial idea.)
- Replacing saturated fat with unsaturated fat produces a better cholesterol profile than replacing it with carbohydrate. (Again, this is well-recognized, although experts debate about how much it matters in different population groups. For women, people with diabetes, and those who are overweight and/or sedentary, it probably matters a lot.)
- Heart health benefits seen with very low-fat diets are largely attributable to weight loss and a lower saturated fat intake.
- Fat intake should probably be moderate and definitely spread out through the day to avoid single high-fat meals.
- Some high-fat foods like nuts and possibly soyfoods have specific heart-health benefits that have nothing to do with blood cholestrol levels.
The bottom line is that the current research suggests that very low-fat diets are not necessarily the best way to eat. Or at the very least, they are not the only good way to eat.