by Mark Hyman
A large randomized controlled study named PREDIMED (Prevención con Dieta Mediterránea), reported in the New England Journal of Medicine in 2013, showed that added fat actually reduced the risk of heart attacks and deaths by 30 percent.2 That’s as much as statin medication. This was one of the largest and best-performed nutritional experiments ever done. Some say that the low-fat group wasn’t low-fat enough, but the fact remains that added fat was beneficial.3 The researchers studied more than 7,000 people who were at risk for but had never had heart attacks. The control group was told to eat a reduced-fat diet. One group got an extra liter of olive oil a week, and another was told to eat a combination of walnuts, almonds, and hazelnuts (30 grams a day). They didn’t restrict calories to compensate for the extra fat. They had to stop the study after almost five years because it became clear that depriving the control group of fat was increasing their risk of heart attacks and death; the groups eating fat were protected against heart attacks.
Many other studies came before this that showed no link between fat and heart disease, including the Lyon Diet Heart Study, published in 1999.4 It showed that a higher-fat Mediterranean diet rich in omega-3 fats reduced death from both heart disease and all causes, including stroke, cancer, and so on. In this study, the group that lowered the omega-6 fats the most and increased the omega-3 fats the most did the best. In another small controlled trial performed on 264 men who had had heart attacks, the low-fat group ate a third less fat and 500 fewer calories per day and achieved a lower cholesterol and weight than the control group, and still there was no benefit in reducing repeat heart attacks or death.5
The Women’s Health Initiative was another study that showed no benefit in preventing heart disease from reducing fat in the diet. One of the largest diet studies ever conducted, it tracked 49,000 women over eight years and cost hundreds of millions of dollars. It showed no benefit in preventing heart disease from reducing fat in the diet. The study began in 1991, when everyone was still riding high on the low-fat bandwagon, and was designed to lower fat from 38 percent to 20 percent of daily calories. The women in the low-fat group reduced their fat only to 29 percent of their diet (because it is so hard for people to cut fat from their diets and still be satisfied), but still, there was no improvement in the low-fat group in rates of heart disease (despite significant reductions in LDL, or bad cholesterol),6 breast cancer,7 colon cancer,8 and obesity.9 Some say these women didn’t lower fat enough to have the desired effect, but if there was going to be an effect, this study should have shown something. It showed nothing. Zip. Nada.
This was similar to an earlier, very large study called the MRFIT (Multiple Risk Factor Intervention Trial), which was also designed to study the effects of saturated fat on heart disease. Again, there was no difference in outcomes for heart disease in the group that cut saturated fat.10
The proof that saturated fat isn’t the heart disease threat we thought it was just keeps rolling in. The famous Nurses’ Health Study also found no connection between fat and heart disease or fat and weight gain in more than 80,000 women studied over 20 years.11 There was an increased risk of heart disease with trans fats, and a decrease in risk from polyunsaturated fats, but it was unclear if it was the omega-3 or the omega-6 that was beneficial.
A group of independent scientists, the Cochrane Collaboration, reviewed the effect of dietary fat on heart disease and found no correlation.12 Another long-term large prospective study, of 43,000 men, the Physicians’ Health Study, found no link between total fat or saturated fat and heart disease.13 This study concluded that the connection between high-fat and saturated-fat diets and heart disease was not because of the fat, but because people who followed high-fat diets ate fewer vegetables, less fiber, more sugar, and more refined and processed foods. The study also found that higher amounts of omega-3 fats were associated with reduced risk of heart disease.
These large studies, done over decades and costing hundreds of millions of dollars, certainly would have found a connection between fat and heart disease if there were one. The only culprit they found was trans fats.
The current scientific consensus is that total fat in your diet does not affect your risk of heart disease or being overweight, and yet many doctors and dietitians still hold on to this outdated idea. It is still embedded in our popular culture, too, with thousands of low-fat foods still on grocery store shelves and menus. I recently had a patient who struggled with weight for 30 years. She was a low-fat fanatic. Her diet consisted of low-fat, high-sugar salad dressings, low-fat yogurt, and bread (naturally low-fat). She steamed her veggies and didn’t add olive oil, and ate lots of fruit. She avoided nuts, seeds, avocados, and all other fatty foods, all with no results. I recommended healthy fats like avocados and coconut oil, and despite her fat phobia, she followed my plan. In just four days, she lost six pounds and her energy skyrocketed, her brain fog disappeared, her joints didn’t hurt, and her postnasal drip stopped. She continued to lose weight on the program without starvation, deprivation, or fat or calorie restriction.
The American Heart Association, the American College of Cardiology, and the US Dietary Guidelines Advisory Committee have all given up on the low-fat message. The 2015 Dietary Guidelines Committee said that “reducing total fat (replacing total fat with overall carbohydrates) does not lower CVD risk.” But then things get a bit fuzzier. These organizations still cling to two big ideas about fat that aren’t supported by science: first, that saturated fat causes heart disease, and second, that polyunsaturated fats (vegetable oils) are protective and we should increase their intake.
Should we be eating animal fat, like butter, or not? For more than 60 years, saturated fat has been the bad guy because it does indeed raise your LDL and your total blood cholesterol level. The whole idea that LDL or total cholesterol led to heart disease came from a very few early, poorly done studies. But even as early as 1996, at the height of the high-carb, low-fat craze, in a 10-year study of 43,757 people, Harvard researchers found no link between diets high in saturated fat and cholesterol, if they accounted for the amount of fiber in the diet. In other words, when saturated fat was consumed with lots of fiber and low levels of sugar and refined carbs, there was no correlation with heart disease; it was only a problem when consumed with lots of sugar and carbs.
Unfortunately, we can’t rewrite history, and the poorly done studies condemning saturated fat led Americans to buy into the “butter is bad” dogma. So we switched to margarine, made from vegetable oil—until we realized that the trans fat it contains is, in fact, the only fat conclusively proven to cause heart attacks. We were also told to swap out saturated fats with polyunsaturated fats (like vegetable oils) because they lower cholesterol. But lowering cholesterol is not the most important consideration in reducing heart attack risk (more on that soon). And the research didn’t distinguish between omega-3 and omega-6 polyunsaturated fats, which have different effects on the body. New analysis proves the benefits of PUFAs come from the omega-3 fats in fish, nuts, and seeds, not refined omega-6 vegetable oils.
THE BREAKTHROUGH ON SATURATED FATS
Then came one big study that changed everything. A comprehensive review in 2014 led by Dr. Rajiv Chowdhury looked at seventy-two of the best studies on fat and heart disease (more than 600,000 people from eighteen countries) and came to the conclusion that there was no link between total fat or saturated fat and heart disease. The study also did not support the heavily promoted policy and guidelines to increase polyunsaturated fats (vegetable oils).14 It did find, however, that trans fats increased and omega-3 fats decreased heart disease.
The researchers looked at three different types of studies. They reviewed thirty-two population studies with 512,420 people for dietary habits; seventeen studies with 25,721 people that measured blood levels of different fats, a very good indicator of what people are actually eating rather than their recall of dietary intake; and twenty-seven randomized controlled trials including 105,085 people assessing dietary supplements of omega-3
fatty acids. For a geeky guy like me, finding this study was like hitting the jackpot.
Let me weed through for you what was buried in this groundbreaking study, because it tells so much about what is truly going on in the fat and heart disease story. The most beautiful part of this study was how it broke down all the different types of saturated fat and polyunsaturated fats and how they impact heart disease. This was radical. Often all saturated fats are lumped together as one big evil type of fat.
The truth is that saturated fat comes in lots of varieties, each with different effects. There are odd- and even-chain saturated fats and different types of polyunsaturated fats, not just omega-3s and omega-6s but different types of omega-6s. And the fact that these were actually measured in the blood of real people and not just based on shakier dietary recall records (do you really remember what you ate for lunch a week ago?) makes these really important to pay attention to.
What story do these blood levels of fatty acids tell us? Hang in there with me; this is where all the nuggets of insight are that explain what’s really at the root of this whole cholesterol, fat, saturated fat, and polyunsaturated fat story.
First let’s look at what they found out about saturated fats. As you know by now, there are different types of saturated fats: myristic acid, pentadecanoic acid, palmitic acid, margaric acid, stearic acid, lauric acid, and so on. They are classified as odd- or even-chain. Some come from diet; some are produced mostly in the liver. Here’s where it gets interesting. The kinds of saturated fats circulating in the blood that were associated with heart disease were even-chain palmitic and stearic acid. And guess what: Most palmitic and stearic acids in the body are produced in your liver when you eat carbohydrates. They don’t come from eating fat. That’s right. Carbs and alcohol (a form of sugar), not saturated fat, trigger high blood levels of stearic and palmitic acid. This is kind of shocking news. (Just a note about alcohol: It doesn’t trigger much insulin secretion, and small amounts may be protective against heart disease.)
Another interesting finding was that the odd-chain fats, such as margaric acid, that come from dairy fat like butter actually showed a reduction in risk of heart disease. Yes, you read that right: Butter showed a reduction in heart disease risk! Grass-fed animals have more of these odd-chain protective fats.
This study also showed no benefit from the omega-6 fats in vegetable oils; in fact, it showed that these tend to cause heart disease. It also showed that omega-3 fats from fish or supplements were the most protective against heart disease.
On the other hand, the omega-6 fat called arachidonic acid was the only omega-6 found to reduce risk of heart disease. It is not in vegetable oil, but instead is made by the body and is also found in the highest amounts in poultry, eggs, and beef. One of the main authors of the study, Dariush Mozaffarian, from Tufts University, had previously published a study that recommended swapping out saturated fats for polyunsaturated vegetable oils.15 Now he moved toward this conclusion: “Current evidence does not clearly support cardiovascular guidelines that encourage high consumption of polyunsaturated fatty acids and low consumption of total saturated fats.”
This turns things upside down, doesn’t it? Let’s review.
Saturated fats (palmitic acid and stearic acid) in your blood that cause heart attacks come from eating sugar and carbs, not fat.
Saturated fats (margaric acid) that come from dairy and butter show a reduced risk of heart disease.
Omega-6 fats from vegetable oils show no benefit and may increase risk of heart attacks.
Omega-6 fats from poultry, eggs, and beef (arachidonic acid) seem to be protective.
Omega-3 fats from fish are the most protective.
The conclusion? Avoid most vegetable oils. Eat more butter, fish, chicken, eggs, and meat. And stay away from sugar and carbs. Boy, did we get this wrong!
This was far from the only study that redeemed the sullied reputation of saturated fat. There have been a slew of studies that have been mostly ignored by policy makers and medical associations. In a review of twenty-one studies done with almost 350,000 people over the span of 23 years, saturated fat was not shown to be associated with increased risk of heart attacks, stroke, or death.16 One of the lead authors of this review, Dr. Ronald Krauss, was formerly the head of the Dietary Guidelines Committee at the American Heart Association. He fought their fervent belief in the dangers of saturated fat and ultimately left the association because of this difference of opinion. Other scientists have spoken out, noting that the current recommendations do not reflect the scientific evidence. Dr. Robert Hoenselaar from the Netherlands found that the “results and conclusions about saturated fat intake in relation to cardiovascular disease, from leading advisory committees, do not reflect the available scientific literature.”17
A diverse group of scientists published a review in the journal Open Heart. They went way back and looked at all the randomized controlled trials comparing high- and low-fat diets done up to 1983—around the time the government recommended that Americans cut the fat, saturated fat, and cholesterol from their diets. None of these randomized trials showed that if you lowered total fat, saturated fat, or cholesterol, there was a reduction in heart disease. They stated that the governments of the United States and UK were guilty of telling their citizens (276 million altogether) to cut total and saturated fat in their diets without having any evidence from the gold standard of studies, randomized controlled trials.18
Our dietary recommendations are based on the idea that saturated fats in our diet cause elevated cholesterol levels. But even this is being called into question. In one review published in 2014, the authors noted that there was very little data to show that saturated fats in the diet caused elevated cholesterol.19 What they found was striking. Only in the case of omega-3 deficiency (which affects more than 90 percent of the population) do saturated fats cause a problem. To put this another way: When you have enough omega-3 fats in your diet, the effect of saturated fat on your cholesterol is either neutral or beneficial.20
This conclusion was confirmed by a dramatic study published in Lipids in 2010 that compared the effects of a very low-carb, high-fat diet with either high amounts of omega-6 or high amounts of saturated fats. The researchers examined blood levels of fats, cholesterol, and inflammation before and after different dietary changes.21 They controlled diets by providing all the food (remember, in studies where participants provide their own food, there are unknown variables). When they then measured blood levels of important markers of cardiovascular health (including blood levels of saturated fat, cholesterol, and inflammation markers), they found that more than doubling the dietary intake of saturated fat had no impact. That’s right: ingesting twice as much or more saturated fat had no impact on blood levels of saturated fat. Even more striking, the group that ate more dietary saturated fat, in the absence of sugar or refined carbs, had lower levels of inflammation across the board. Remember, this wasn’t a study of populations, but a true experiment where researchers provided all the food and measured true and immediate responses of the body to different diets, so these are highly reliable results.
SATURATED FATS AND INFLAMMATION
There is evidence that saturated fats cause inflammation in humans and animals, and that is not a good thing because inflammation is an underlying cause of heart disease, obesity, type 2 diabetes, cancer, and dementia. But there are some important caveats. It seems that saturated fats cause inflammation only in the context of two things: low levels of omega-3 fats and high levels of carbohydrates. Take out the high-carb foods and add omega-3-rich foods or supplements, and saturated fat is not a problem.
The data on omega-3 fats and how they interact with saturated fat is interesting. It is estimated that up to 90 percent of Americans have insufficient levels of omega-3 fats. I do omega-3 testing in my office and see this almost every day. When you don’t have enough omega-3 fats in your diet and you eat saturated fat, the saturated fat stimulates the production of arachidonic acid, w
hich turns into inflammatory molecules called eicosanoids. (There are both inflammatory and anti-inflammatory eicosanoids.) No omega-3s and too much saturated fat is bad news.
But add a little omega-3 into your diet and the saturated fats actually reduce inflammation by inhibiting or turning off genes that produce cytokines (inflammatory molecules), and they promote the production of anti-inflammatory eicosanoids. When consumed with a diet rich in omega-3 fats, saturated fat leads to lower triglycerides22 and an increase in HDL, or good cholesterol, and it promotes the formation of large, light, fluffy, less harmful LDL particles.23
In one study of overweight men and women, researchers found that even in the face of a high-fat diet (55 percent) and high saturated fat (25 percent of calories), there was no impact on inflammatory markers or oxidative stress, two things we know drive heart disease and aging in general.24
In other studies, saturated fat seems to promote inflammation only in the presence of too many carbs or too little fiber, or there is no connection at all.25 (The key to eating more fat, as you’ll learn in Part III, is also eating more fiber.) In one study where the same people were given either butter or soybean oil at different times, there was no increase in inflammatory markers.
Even more striking, only saturated fat was able to reverse liver damage caused by inflammation in rats when they consumed sugar in the form of alcohol.26 Polyunsaturated fat had no effect. In this study, saturated fat—mostly MCT, or medium-chain triglycerides, from coconut oil—was found to be therapeutic in reversing liver damage even in the face of continued alcohol intake. (But that doesn’t mean you can drink as much as you want—it’s still sugar!) Considering that nonalcoholic steatohepatitis (NASH—commonly known as fatty liver), caused by too much sugar and carbs, is now the most common liver disease and the leading cause of liver transplants, cutting the carbs and boosting the saturated fats may be part of the solution.