Clearing up the confusion over fat

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Coming up on Harvard Chan: This Week in Health…Clearing up the confusion over fat

{***Walter Willet Soundbite***}
(The basic message is pretty simple: Wherever possible, use liquid oils in your diet as the primary sources of fat. Using them in the diet will be a very important way to lower your risk of premature death.)

In this week’s episode, we’re marking Heart Month by revisiting one of our most popular episodes-an in-depth look at fat.

And yes, we’ll be asking: Is butter back?


Hello and welcome to Harvard Chan: This Week in Health…It’s Thursday, February 15, 2018. I’m Noah Leavitt.

February is Heart Month, and as we’ve discussed before, a critical part of heart health is choosing healthy fats.

So, in that spirit, we want to replay an older episode in which aimed to clear up the confusion over dietary fat.

So yes, we’ll be talking about whether butter is really back, but we’ll also be taking a look at healthy fats, the good fats, the beneficial fats and giving you some ideas for foods that can help you incorporate those into your diet.

And we’ll be talking about saturated and unsaturated fats-terms you’re probably very familiar with.

Foods high in saturated fat are things like red meat, butter, or cheese.

Unsaturated fats are broken down into two categories-monounsaturated and polyunsaturated-and are found in vegetable oils, nuts, seeds, and fish.

In the episode from 2016 we spoke with two of America’s leading nutrition experts.

First is Walter Willett, who at the time was the Chair of the Department of Nutrition at the Harvard Chan School.

He had recently authored a paper which looked at more than 126,000 people and found that those who consumed higher levels of unsaturated fats had a lower risk of dying during the study period. That study also highlighted the negative health effects of saturated fats, including trans fats.

And we’ll also talk to Dariush Mozaffarian, Dean of the Friedman School of Nutrition Science and Policy at Tufts University. Mozaffarian was senior author on a paper that found butter did not increase a person’s risk of premature death or heart disease.

Now, since we first recorded this episode, there have been more developments regarding saturated vs. unsaturated fats.

That includes an American Heart Association advisory last summer that strongly recommended replacing saturated fats with unsaturated fats.

The AHA says doing so can lower a person’s heart disease risk as much as cholesterol-lowering statin drugs.

We spoke to one of the authors of that advisory, Frank Sacks, professor of cardiovascular disease prevention here at the Harvard Chan School.

{***Frank Sacks Soundbite***}
(Well, the American Heart Association leadership, about two to three years ago, decided that a major reevaluation of the dietary fast that we eat is warranted in terms of relation to heart disease. One reason for the Heart Association’s decision on that is that, for a few years, there have been contrarian articles published either in the medical literature or by writers who have prominently trumpeted results that dietary fat and health had to be revised, that, in fact, it’s not really so pertinent to health what kind of fats or how much fats we eat. What we found is that, very, very clearly, saturated fat caused atherosclerosis, which is plaque- cholesterol-rich plaque in the arteries of the heart were leading up to the brain and also heart attacks and strokes in comparison to unsaturated fats. And among the unsaturated fats, the polyunsaturated fats were more protective than the monounsaturated fats. So our conclusion was reduce saturated fat and replace it with unsaturated fats, preferably polyunsaturated fats.)


If you want to hear more of that interview with Frank Sacks, and read the advisory from the American Heart Association, will have links to that-and other resources-on our website,

But now let’s jump into that episode from 2016.

We begin with Willett shedding some more light on the sources of dietary fat that we mentioned a little bit earlier in the podcast.

WALTER WILLETT: When we talk about total fat in a diet, that means fat from all sources. We get fat from animal sources, such as butter. In the old days, lard. We don’t consume too much of it now, but we get a lot of our fat from eating red meat. We get some animal fat from chicken and fish as well. And then another large part of our fat in the diet comes from vegetable sources. These would be plant oils that we add to food but also the fats that are naturally in plant foods, such as in seeds and nuts and avocados.

NOAH LEAVITT: And so when we’re looking at, I guess, maybe calling them the bad fats, so saturated fat, trans fat, what are the effects of those and is one clearly worse than the other for people?

WALTER WILLETT: When we’re looking at bad fats, by far the worst, from this study and from many other studies, is trans fat, when we look at one type of fat on a gram-per-gram basis compared to another type of fat. Saturated fat is also in this study and some other analyses, weakly related to higher risk of premature death if we compare it to the same number of calories from carbohydrate.

But what’s really important is when we compare one type of fat with another because that represents the choice, the kind of choice we often make when we’re preparing dinner or eating out. And what we saw here was that replacing saturated fat with unsaturated fats, and particularly polyunsaturated fats, was related to a major reduction in the risk of premature death, and that’s, I think, something that people should know about. It can make an important difference in their chances of living a long and healthy life.

NOAH LEAVITT: And we’ll come back to that study in a minute, but now, we want to shift our focus a little bit from fat as a general term to specific foods, and we’re going to talk about butter. At the top of the show, I mentioned that a new study from Tufts University looked at links between butter and chronic disease and mortality. It was a meta-analysis that combined information from nine different studies and more than 600,000 people. I spoke over the phone with one of the authors, Dariush Mozaffarian, and he says the goal of the paper was to look at foods instead of simply looking at nutrients.

DARIUSH MOZAFFARIAN: You know, what we’ve learned over the last 20 years or so is that to study obesity, heart disease, diabetes, other chronic diseases, we need to move past just thinking about single nutrients and think about foods, you know? Foods are what we eat, and they seem to have different effects depending on the complex matrix of their ingredients, how they’re processed, how they’re consumed.

And there’s been a lot of concern about different foods in the diet and one of those has been butter, and so we wanted to see what the evidence is for potential major health effects of butter on deaths on heart disease and on diabetes. Because people like magic bullets, there’s been, again, a reductionist approach to make it all about one thing. Total fat is the cause of obesity. Saturated fat is the cause of heart disease. And I think those simplistic messages, which the public likes to think, there’s one thing I can do, doesn’t really work for nutrition. Nutrition is complicated, and it’s not that complicated, but it’s more complicated than kind of these single-nutrient approaches.

NOAH LEAVITT: And one of the main takeaways from the paper was that butter is a, quote, middle of the road food. So can you explain a little bit about what that means?

DARIUSH MOZAFFARIAN: Well, what we found is that whether looking at total death or heart disease or diabetes, we didn’t really find any strong signals for major effects of butter, either for good or for bad, and so that suggests that butter is neither a health food that we should be seeking out, nor the villain that’s the cause of major disease. And in a sense, what we found is it doesn’t really matter how much butter you eat. It matters what else you’re doing with your diet. So if he was a little or a lot, on average, your health will be similar. What’s much more important is, are you eating a lot of the good things in the food supply and are you avoiding a lot of the bad things? Butter’s kind of middle-of-the-road. There’s things that are healthier, and there’s things that are worse.

NOAH LEAVITT: And so the question that’s often asked of the media and headlines is, is butter back? So is it, and is that the right question to be asking?

DARIUSH MOZAFFARIAN: So there are certainly healthier choices than butter. It would be better to use extra virgin olive oil or canola oil or even many margarines that are full of healthy oils. Those are certainly better choices. But on the other hand, if you want to have some butter and eat less white bread or have some butter and eat less potatoes, or have some butter and don’t eat processed deli meats or bacon, or many other unhealthy foods, that’s probably a better choice. So it’s kind of a middle-of-the-road food, and I think, there are things that again, are more important to eat and things that are more important to avoid.

NOAH LEAVITT: Willett agrees that butter is not back, and he says the important question we should be asking is what happens when we replace butter with another kind of fat?

WALTER WILLETT: Because in a meta-analysis, they were not able to compare one type of fat with another because the individual studies that had been reported earlier had not made those comparisons consistently. Therefore, if you’re only looking at butter, per se, you’re, in principle, comparing it by default with all the rest of the calories in the diet. And if we look at the average American diet or European diet, the rest of the calories is mostly refined starch, sugar, and potatoes and some trans fat in there as well. And all of those things are bad, bad for our health. So if we’re finding butter is the same as those other sort of calories, it means that butter is not a great source of calories in terms of our health as well.

The authors of that meta-analysis did acknowledge in a discussion that given their findings, it would be better to replace butter with unsaturated vegetable oils, in terms of cardiovascular disease. And that should have really been the headline. That wasn’t the headline. Headlines were like, “Butter’s Back,” but the headline really should have been “Evidence Supports Replacing Butter with Unsaturated Healthy Fats.”

NOAH LEAVITT: So I think, what’s might be an important takeaway is that butter isn’t back, but that’s not necessarily advocating a low-fat diet. I mean there’s still a place for fat and healthy fat in the diet.

WALTER WILLETT: Well, absolutely there’s a place for healthy fats in the diet. In fact, in the paper that we just published, total fat, even the combination of total fats, compared to carbohydrates was related to lower risk of premature death, modestly but still very important. In other words, people on higher fat diets we’re better off on average than people on low-fat diets. But the important point here still is that the type of fat is what’s really most important.

NOAH LEAVITT: And so the recent study that Willett mentioned earlier actually look at the effects of unsaturated fats. The lead author was Dong Wang, a doctoral candidate in the Department of Nutrition and Epidemiology at the Harvard Chan School. And again, this study looked at more than 126,000 people and found that those who consumed higher levels of unsaturated fats had a lower risk of dying during the study period.

WALTER WILLETT: This study was taking a big look at the relationship between the total percentage of calories from fat in our diet in relation to total mortality and also specific types of fat in our diet in relation to total mortality and specific causes of death. So this is a very comprehensive look at the relationship between diet and health.

NOAH LEAVITT: And what were the specific types of fat that you were looking at?

WALTER WILLETT: We looked at four main categories of fat, first of all, trans fat, which is industrially-processed vegetable oil that’s been partially hydrogenated, second, saturated fat, again, mostly from butter and red meat. And then we looked at monounsaturated fats, which, to a large extent, come from some plant oils like canola oil and olive oil, but also we get some of it, some monounsaturated fats from avocados and some other seeds and nuts. Then we also looked at polyunsaturated fat in our diet, a lot of that does come from vegetable oils, particularly soybean oil, corn oil in our diet. And we looked at all those individually, all of those types of fat, in relation to total mortality and cause-specific mortality.

NOAH LEAVITT: And so I know the takeaway from the paper is that consuming higher amounts of these unsaturated fats was then associated with lower overall mortality. So can you kind of explain what that means and then maybe it break it down a little bit for us?

WALTER WILLETT: One of the critical issues when we’re looking at any major source of calories in the diet is the comparison. And in this case and in most studies where we’ve been able to do comparisons, we’ve compared each type of fat with carbohydrate and then one type of fat with another, because that represents the trade-offs that we would normally make in our decisions about ordering if we’re eating out or preparing our food at home.

In this particular study, we’re looking at relationship between total fat in our diet as a percentage of calories and then specific types of fat in the diet. And when we’re looking at total mortality, of course, we’re all going to die at some point in time. So we’re really not talking about being immortal but rather our chances of death during the next few years.

NOAH LEAVITT: And do we know why unsaturated fats are so beneficial?

WALTER WILLETT: We’ve known for perhaps 40 or 50 years that unsaturated fats, compared to saturated fats, will improve blood cholesterol fractions, they specifically will reduce LDL, the bad cholesterol in our blood, but it’s pretty clear that polyunsaturated fats do quite a bit more than just reducing the LDL, the bad cholesterol in our blood. They can be anti-inflammatory. They can help reduce the risk of thrombosis, and we’re learning more about other benefits of polyunsaturated fat in the diet.

This is dealing with many complex biological pathways. Polyunsaturated fats are a critical part of every cell in our body. They make up the large majority of our brain. They are the building block for many biologically-active compounds related to clotting or inflammation. So these are really very, very important molecules.

One question that some people have had is whether the polyunsaturated fats, specifically omega-6 polyunsaturated fats, are pro-inflammatory. There’s a myth going around that omega-6 polyunsaturated fats are toxic and pro-inflammatory and bad for us. That’s based on zero data, really. And this study showed that omega-6 polyunsaturated fats were the best of all. In fact, they were what was driving the majority of the benefit of overall polyunsaturated fat and also total fat.

NOAH LEAVITT: So when we’re looking at unsaturated fats, did the benefit kind of extend beyond heart disease?

WALTER WILLETT: We’ve known for a long time that the type of fat is important for risk of heart disease. What was, I think, very interesting in this analysis, and I should point out this was very large. It was about 125,000 people, men and women followed for up to 32 years, and during that time about 33,000 people had died. So this is not a little study. This is long-term, many repeated measurements of diet, and many, many people who died prematurely.

And again, not surprisingly, we found lower risk of cardiovascular disease, particularly lower risk of heart disease, but what was also really interesting we saw that replacing saturated fat with polyunsaturated fat was also related to lower risk of cancer and neurodegenerative disease as well. And particularly the neurodegenerative disease was very interesting, because until recently, we’ve not had much that we could offer, in terms of preventing this. That means we need to dig down more deeply, try to understand that better, but again, it looks like there’s a lot more going on than just reducing our LDL cholesterol.

NOAH LEAVITT: One of the things I wanted to touch on that you mentioned there is this idea of, the choices you’re making as you’re preparing dinner or maybe making your lunch. So how is it important to think about a study like this and results like this, kind of in terms of your total diet and all that and the choices you’re making every day?

WALTER WILLETT: This study, I think, does relate to the kind of choices we make every day. For example, if we’re sauteing some food or frying some food at home, the choice might be butter or margarine versus a liquid oil, like canola oil or olive oil or soybean oil. And definitely, one is going to be better off in terms of the risk of dying prematurely if we use one of those liquid vegetable oils instead of say butter or lard or hard margarines.

NOAH LEAVITT: And I wanted to talk about some of those alternative vegetable fats, like a soybean oil, because I know in the public, there’s a lot of talk about GMOs, a concern about GMOs. I mean, should that be a consideration for people, or from their perspective of their health, if it’s a GMO oil it is not going to affect their health. How do GMOs play into all of this?

WALTER WILLETT: Yeah, I don’t think GMOs really play an important picture in this relationship. The genetic alterations that have been created for producing, say, soybean oil or corn oil in this country, don’t affect the fatty acid composition. There are some bigger, broader issues about uses of GMOs in reducing genetic diversity, perhaps some implications for environmental changes, but the direct effects are really, I think, not relevant for this kind of analysis.

NOAH LEAVITT: And so I imagine that for people who are researching, this is a pretty exciting time, because it seems like there’s more data to look at than ever before. But I also imagine for people, the consumers, it maybe is a little bit more of a confusing time because there’s so much information. So as we kind of see this increased volume of data coming out, what’s the take-away for people at home as they’re looking to make healthy food choices?

WALTER WILLETT: Unfortunately, the word I’ve heard on the street is that people are confused and I think there is some good reason for that. There have been some very bad studies done not too long ago. For example, there was a very large meta-analysis that concluded that the type of fat in the diet was not important at all, seeming to reverse 40 years of research on this topic, and, of course, that made headlines. But if you looked back at that meta-analysis it was just layered with errors, but most fundamentally, they couldn’t, because it was using already published data, they couldn’t compare one type of fat with another and that’s what really is most important.

For the average person, now, who doesn’t want to dig down into the research and understand the mechanisms in all of this, all these issues that are pretty exciting for us, the basic message is pretty simple. Wherever possible, use liquid oils in your diet as the primary sources of fat. Yeah, if you want to have a little butter now and then, OK. I have it a couple times a year for dipping my lobster in, in the summertime. But on a day-to-day basis, all of the liquid vegetable oils are healthy. It’s probably good to have a mix of them, a variety of them, because they provide different types of fatty acids. But using them in the diet will be a very important way to lower your risk of premature death.

NOAH LEAVITT: And so as we wrap up this episode, it’s clear that when it comes to fat, there’s a lot we’ve learned and much we still need to learn, but there are some things the experts definitely agree on. Here is Mozaffarian again.

DARIUSH MOZAFFARIAN: So I think that there’s pretty strong consensus about the handful of foods that are really good for us and the handful of foods that are really bad for us. And the things that are really good are fruits, vegetables, nuts, whole grains, beans, fish, yogurt, clearly all very healthy. And the things that are bad are mostly processed starches and sugars, you know, loads of white bread and crackers and breakfast bars and energy bars and all the processed foods that are also often high in sodium or trans fat.

And then a lot of other foods, eggs, butter, chicken, seem to fall in the middle. And then there’s foods that we’re just starting to learn about like coffee, tea, garlic, cocoa, that we need to kind of understand their health effects more.


That was our 2016 episode on dietary fats.

Again, if you want to learn more about this topic, we’ll have some resources on our website,

And a reminder that you can always find us on SoundCloud, iTunes or Stitcher.

February 15, 2018 — February is Heart Month, so in this week’s podcast we’re revisiting one of our most popular episodes: an in-depth look at dietary fat. We’ll share tips for including more beneficial fats in your diet, plus we’ll give you the bottom line on butter and health. You’ll hear from two experts: Walter Willett, professor of epidemiology and nutrition, and Dariush Mozaffarian, dean of the Friedman School of Nutrition Science and Policy at Tufts University.

You can subscribe to this podcast by visiting iTunes, listen to it by following us on Soundcloud, and stream it on the Stitcher app or on Spotify.

Visit our archive page to download all of our past episodes.

Learn more

Listen to our podcast with Frank Sacks on the American Heart Association Advisory on saturated fats (Harvard Chan School news)

Higher consumption of unsaturated fats linked with lower mortality (Harvard Chan School news)

Little to no association between butter consumption and chronic disease or total mortality (Tufts University)

Fats and cholesterol (Nutrition Source)

Different Dietary Fat, Different Risk of Mortality (Nutrition Source)