Twenty years ago, when I first started working in the area of vegan nutrition I was a big proponent of very low fat diets, with no saturated fat and little or no unsaturated fat.
At that time, when low fat diet plans like the Ornish diet were especially popular, it really did look like this was the best weight loss diet & diet for lowering cholesterol.
Since then, our understanding about the role of fat in our diet has changed a lot and the situation is far more complex than we originally thought. Anyone who is taking a serious and honest look at the research on diet and heart disease has to question the low fat diet plan approach.
One thing we know (more or less for certain) is that replacing saturated fats in the diet with poly- or monounsaturated fats is as good for lowering cholesterol as removing all fats from the diet.
And there is evidence that eating more unsaturated fats is better as far as heart disease is concerned.
Low fat diet plans are associated with a drop in HDL cholesterol, which is the "good" cholesterol. If HDL drops as much as LDL (the bad) cholesterol, there is actually no net gain as far as heart disease is concerned.
There are still a lot of questions about how much HDL really matters, but most research suggests that it matters a lot, especially for women.
Reducing all fats in the diet and replacing them with carbohydrates can also boost triglyceride levels. Some studies show that if most of the carbohydrate comes from whole fiber-rich plant foods (as opposed to refined carbs), this doesn't happen. Other studies show it happens no matter what kind of carbohydrates people eat.
Very low fat diet plans also produce a type of LDL-cholesterol that is very small and dense and more easily incorporated into artery-blocking plaque. Because of these effects on HDL levels, triglycerides, and LDL size, many researchers question whether very low fat diets plans are a wise choice for people at risk for heart disease.
Finally, heart disease is not all about lowering cholesterol. There are other diet factors that have nothing to do with blood cholesterol levels but affect the health of the arteries. Some high fat foods - nuts in particular, but also soyfoods - appear to have benefits for heart disease that aren't related to cholesterol levels. Unfortunately some low fat vegan diet plans severely limit these foods or even eliminate them altogether.
And while low fat diet plans have been promoted for weight loss, they tend not to be effective over the long term. Some research shows that including higher fat foods - like nuts or avocado - in meals helps to make reduced-calorie diets more satisfying and actually promotes better long-term weight control.
This isn't to suggest that vegans should have a free-for-all with fats. In fact, there is good evidence that eating large amounts of fat all at once can raise risk for heart disease. Because of that, some experts recommend consuming no more than 30 grams of fat at one sitting.
That could be a problem for the average omnivore or for those who regularly eat at places like fast food restaurants. But for a vegan who is not indulging in tons of baked goods or fatty snacks, it's not at all.
Total fat: 20 grams
Total fat: 22 grams
Some low-fat vegan diets strive for fat intakes that are as low as 10% of calories. But the World Health Organization says that no one should go below a 15% fat diet and that women of childbearing age should consume diets that are at least 20% fat. They suggest that intakes up to 30 or even 35% of calories can be healthful.
The idea that we need to avoid all dietary fats, including healthful plant ones, is outdated and perhaps even harmful. But even if eating a very low-fat diet is perfectly safe, there is no evidence that it has any advantages over a diet that includes some fat-rich plant foods.
Foods like avocado, nuts and nut butters, olives, tofu, dressings and sauces add interest and variety to vegan diets. As always with diets that take veganism a step beyond what is necessary, very low-fat diets add a layer of restriction that can make vegan diets look limiting and unappealing.
My recent post on low-fat vegan diets inspired some good and thoughtful comments, which I really appreciate. Coincidentally, 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.
I wanted to talk about that study and respond to issues that were raised by my last post. Especially in regard to one comment which pointed out that the Ornish diet isn't going to stop working just because new research has been published.
That's true. I'm not saying that the Ornish diet 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 Ornish 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 Ornish diet 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 or 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%. A reduction in heart attacks is a much more meaningful outcome than 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!)
Savvy Veg Note: It's well worth linking to the original posts to read the excellent comments, and Virginia's thoughtful, knowledgeable replies:Fat In Vegan Diets: How Low Should You Go More on Low-Fat Diets & an Update on Heart-Healthy Fats