The Truth About Saturated Fat: An Interview with Mark Pettus, MD


For years, mainstream medical organizations such as the American Heart Association have demonized saturated fat as a root cause of cardiovascular disease. And, for years, progressive docs — backed by meta-analyses and other studies — have shouted from the rooftops that it’s refined carbs and processed sugars — NOT saturated fat — that drive heart disease (and so many other chronic diseases).

Now, comes big news that the sugar industry bribed scientists in the 1960s to downplay the relationship between sugar and heart disease and point the finger at saturated fat instead.

“They were able to derail the discussion about sugar for decades,” Stanton Glantz, a professor of medicine at U.C.S.F. and an author of the JAMA Internal Medicine report, told The New York Times.

Fortunately, there have been forward-thinking doctors all along who’ve tried to clear the air about saturated fat. As luck would have it, we interviewed Mark Pettus, MD, associate dean of medical education at the University of Massachusetts Medical School and director of medical education, wellness, and population health at Berkshire Health Systems in western Massachusetts, about saturated fat before the big news broke on Monday.

In this interview, he debunks the many myths about saturated fat:

What is the difference in how many experts view fat now versus 30 years ago?

What jumps out at me most is the less restrictive stance with which [the dietary] guidelines now look at fats…and, in particular, foods like eggs that contain cholesterol. I think it’s finally widely accepted that eating cholesterol doesn’t affect your blood cholesterol, so you no longer see that in the current guidelines.

I also think the pendulum has swung significantly in recent years on the whole diet-heart hypothesis: The notion that fat is the reason…for heart disease has now been more universally questioned.

And I’d say the third thing is the idea that eating fat makes a person fat — again, there’s still a lot of people that think that, but in general I think the research is beginning to shift the way we think about what makes us fat.

Can you talk a little more about the relationship between saturated fat and cholesterol levels?

We spent most of the last generation looking at total cholesterol and LDL as if to suggest that those two values give you an accurate reflection of what we know to be a much more complex and nuanced issue with lipids. But, when you give people fat from a quality source and lower their carbohydrates, generally you see their triglycerides come down. That’s a good thing. You see their good cholesterol, the HDL, go up. That’s a really good thing.

What you see in the majority of people when you give them more saturated fat is a shift from the small dense LDL particles — these are the more risky, inflammatory, atherogenic types of LDL — to larger, more buoyant LDL particles.

Your total cholesterol may go up a little bit, your LDL may go up a little bit, and most doctors are going to think that’s pretty bad, but when you look at the types of LDL, for most you see a shift from small, dense, and inflammatory to larger, buoyant, and less inflammatory. Many physicians still aren’t aware of this.

Can you talk a little more about the health benefits of saturated fats?

In general, I think most saturated fats are probably much healthier than we thought — particularly when they are being ingested from quality sources and particularly if people aren’t eating a lot of refined, poor-quality carbs and sugar in their diet.

Fats can be problematic when they’re both of poor quality and when they are accompanied by poor-quality carbohydrates — that’s sort of the perfect storm for a pro-inflammatory state.

There are also many different types of saturated fat. Examples of good types of saturated fat include coconut oil and the saturated fats found in pasture-raised meats and dairy from pasture-raised animals. That’s different from what you will find in a cow that’s in a feedlot, getting grains — and the pesticide residues that come with the grains —  and antibiotics.

Saturated fats are more resistant to oxidation. And, it’s really the oxidation of fats that tend to make them more pro-inflammatory. Saturated fats — compared to many of the omega-6 vegetable oils, which are polyunsaturated — tend to be much more stable and resistant to oxidative stress.

Why is nutritional science often so contradictory and confusing?

So many studies look at large populations of people, relying on food diaries and journals, which are notoriously inaccurate, and then make these correlations based on health outcomes over a period of time that I think have been, at best, conflicting.

And when you look at biologic systems, particularly the fat in our bodies that forms the cell membranes of all of our cells, and the linings of our neurons, and brain, and nervous system, it’s intuitive that the more polyunsaturated those fats are, the more prone they’re going to be to oxidative stress and inflammation. So I think we need both, but I do think the message unfortunately has unfairly chastised saturated fats, and has not been able to distinguish good quality from bad quality, because everything’s just lumped together in most of this epidemiological research.

Why do a lot of organizations and experts still push a no-fat or low-fat message?

I think that is such an important question. I’ve been in practice almost 30 years, and I have had very academic roots all along. And there is this incredible delay…The structures and organizations and associations that…we look to for guidance and advice…are not nimble at all. They bring inherent bias. These are good people, but there’s an inherent bias that these structures tend to embrace. We all know that there are researchers who will lose grant support overnight if they suddenly go from a “fat is bad” to a “fat is perhaps actually good for us” mindset. They’ll struggle to maintain their academic integrity based on the culture they’re in. Try getting things into peer-reviewed articles when you start going against mainstream thinking, and you can find yourself out there.

You know, if you were admitted to a coronary care unit in the 1950s, you were put on a low-starch diet. I mean, that was what was restricted — bread and pasta. Fat was less the concern. And it was really Ancel Keys and other researchers who began to change the way we think about fat and demonize it.

Because our institutions don’t always serve us as objectively and as nimbly as we would like to think, it’s so important that people try different things in their own lives and then assess what impact these things have on them. People have to become co-investigators of their own lives and be willing to challenge conventional wisdom — particularly if they’re not in a place of good health and if following the advice of others has not led to positive outcomes.