I’ve been living among stacks of nutrition research papers over the past six months while working on an update to The Dietitian’s Guide to Vegetarian Diets, a textbook for health professionals and dietetics students. The last edition was published in 2004 so my co-authors and I have looked at all of the studies on vegetarian and vegan diets that have been published since then, along with hundreds of other nutrition papers that are pertinent to vegetarianism.

I’ve learned a lot in the process. It’s reinforced my opinions about some aspects of nutrition and forced me to change my mind about others. I finished my last chapter, which focused on fat and carbohydrates and how they affect heart disease, diabetes, and obesity, yesterday.

Twenty years ago, when I first started working in the area of vegan nutrition I was a big proponent of very low-fat diets. At that time, when diets like the Ornish plan were especially popular, it really did look like this was the best approach for lowering cholesterol and controlling weight. Since then, our understanding about the role of fat in the 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 approach.

One thing we know (more or less for certain) is that replacing saturated fat in the diet with poly- or monounsaturated fat lowers blood cholesterol just as much as removing all fats from the diet. And there is evidence that eating more unsaturated fat is better as far as heart disease is concerned. Low fat diets 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 diets 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 are a wise choice for people at risk for heart disease.

Finally, heart disease is not all about 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 eating 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. Here is an example of a healthful vegan breakfast that includes some high fat foods and comes in well under the 30 gram limit:

1/2 cup tofu with mushroom and onions scrambled in ½ tbsp soft margarine
1 slice whole wheat toast with 1 tbsp peanut butter
Fresh fruit

Total fat: 20 grams

Or consider this lunch which doesn’t skimp on healthful fats:

1 cup black bean soup topped with ¼ cup cubed avocado
Tossed green salad sprinkled with 1 tbsp sunflower seeds and dressed with vinaigrette containing 2 tsp olive oil
6 ounces raspberry-flavored soy yogurt

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. 

(Here is some updated information about fat in heart healthy diets)