Eat, Drink, and Be Healthy
Page 11
OMEGA-3 FATS: A SPECIAL BENEFIT
One type of polyunsaturated fat deserves extra attention, even though it makes up a small part of the fat in our diet. These are the omega-3 fatty acids (also called n-3 fats). They are essential fats, which means your body needs them for normal functions but can’t make them from scratch. There are three key types of omega-3 fats in our diet. Since their names are a mouthful, I’ll use their abbreviations: ALA (alpha-linolenic acid), EPA (eicosapentaenoic acid), and DHA (docosahexaenoic acid).
As polyunsaturated fats, they have two or more extra-strong double bonds joining neighboring carbon atoms. The first double bond is on the third carbon from the end. ALA, with eighteen carbons, is sometimes called a medium-chain omega-3 fat; EPA and DHA are sometimes called long-chain omega-3 fats because EPA contains twenty carbons and DHA contains twenty-two.
ALA is the main omega-3 fatty acid in most Western diets. It’s found in a variety of vegetable oils (especially soybean and canola oils) as well as walnuts, leafy vegetables, and some animal fat, especially from grass-fed animals (see the table on page 82). EPA and DHA come mainly from fish and so are sometimes referred to as the marine omega-3s. Your body uses ALA primarily for energy. It can also transform this polyunsaturated fat into EPA and DHA, although it can’t do the reverse.
What makes omega-3 fatty acids so special? For one thing, they are necessary to make cell membranes throughout the body. Membranes hold the contents of cells together, and determine what comes in and what goes out. DHA, for example, is the most abundant fatty acid in the human brain.2 For another, they provide the starting point from which some hormones are made. These omega-3–derived hormones perform functions such as regulating blood clotting, helping artery walls contract and relax, and turning inflammation on and off. Equally important, omega-3 fats have been shown to help prevent or treat heart disease and stroke. They may help control lupus, eczema, and rheumatoid arthritis. They may also help prevent dementia, loss of vision from macular degeneration, and other chronic conditions.
The strongest evidence for a beneficial effect of omega-3 fats is in preventing death from heart disease. These fats help the heart beat at a steady clip and keep it from lapsing into dangerous, sometimes fatal erratic rhythms. These arrhythmias, as they are called, cause many of the nearly 300,000 sudden cardiac deaths that occur each year in the United States—half of which happen to people with no history of heart disease.
Omega-6 Confusion
Several popular books are based on the idea that eating too much omega-6 fats from good sources such as corn, sunflower, and soybean oils is bad for health. Omega-6 worriers claim that higher intakes of these increase inflammation throughout the body and increase the risk of asthma, heart disease, many types of cancer, autoimmune disease, neurodegenerative diseases, and more. But this is merely a theory, which has not been borne out by the many studies that have examined it. In fact, several dozen studies have looked at the effects of omega-6 fats on inflammation. Remarkably, none show an increase and about half show a reduction in chronic inflammation, which is a good thing.
Alpha-Linolenic Acid in Various Foods
* * *
Food
Serving
Weight grams
Alpha-linolenic acid grams
Flaxseed oil
1 tbsp.
13.6
6.91
English walnuts
1 ounce
28
1.90
Canola oil
1 tbsp.
14
1.30
Soy oil
1 tbsp.
13.6
0.95
Mayonnaise
1 tbsp.
14
0.85
I Can’t Believe It’s Not Butter!
1 tbsp.
14
0.76
Generic soy margarine
1 tbsp.
14
0.49
Italian salad dressing
1 tbsp.
14
0.45
Shedd’s Spread Country Crock
1 tbsp.
14
0.44
Olivio Spread
1 tbsp.
14
0.43
Beef
6 ounces
170
0.38
Benecol Light
1 tbsp.
14
0.38
Brussels sprouts, raw
1 cup
88
0.18
Corn oil
1 tbsp.
13.6
0.14
Promise Soft Margarine
1 tbsp.
14
0.11
Almonds
1 ounce
28
0.11
Kale, raw
1 cup
67
0.09
Olive oil
1 tbsp.
13.5
0.08
Hazelnuts
1 ounce
28
0.06
Cashews
1 ounce
28
0.06
Safflower oil
1 tbsp.
13.6
0.05
Whole milk
1 cup
244
0.05
Cheddar cheese
1 ounce
28
0.05
Chocolate
1 bar
44
0.04
Spinach, raw
1 cup
30
0.04
Peanuts
1 ounce
28
trace
Source: Connor, W. “Alpha-Linolenic Acid in Health and Disease.” American Journal of Clinical Nutrition (May 1999): 827–28; and analyses performed at Harvard School of Public Health.
Proponents of the idea that omega-6 fats are harmful focus on the benefits of a lower ratio of omega-6 to omega-3 fats. There’s no doubt that many Americans could benefit from getting more omega-3s. But there is also strong evidence that omega-6s, which make up the majority of the polyunsaturated fats in our diet, help shape healthy cholesterol levels and reduce heart disease. In the Nurses’ Health Study, the ratio of omega-3 to omega-6 fatty acids wasn’t linked with risk of heart disease because both of these were beneficial.3 In 2016, our group examined consumption of different types of fat in relation to deaths from all causes. We found that omega-6 fatty acids were more strongly linked to lower death rates than omega-3 fats. This suggests that a higher ratio of omega-6 to omega-3 fats is desirable if this can be achieved by increasing omega-6 fats, not by decreasing omega 3 fats.4
Of course, too much of a good thing can pose problems, and we really don’t know the upper limit of healthy omega-6 or omega-3 fat intake for optimal health. We do know, though, that reducing omega-6 fatty acids from the current amounts in the average American diet is likely to wipe out many of the gains we have made in preventing deaths from heart disease over the last fifty years.
TRANS FATS—A SPECIAL CONCERN
There’s a family of fats you should definitely stay away from: the trans fats. These are mostly man-made fats that almost invisibly became a substantial part of the American diet. Thanks to long-awaited FDA rulings, that has changed in the past fifteen years.
A century ago, the average American ate a minuscule amount of trans fats, which naturally occur in meat and milk. By the early 1990s, however, trans fats contributed an average of 2 to 3 percent of total calories, with many people taking in double or triple this amount. That’s because the food industry had found hundreds of uses for partially hydrogenated oils, the main source of artificial trans fats. These included margarines, vegetable shortenings, doughnuts, commercial baked goods such as packaged pastries and cookies, powdered creamer, and the fats used for deep-frying fast food in restaurants.
How bad are trans fats
for us? Like saturated fats, trans fats raise levels of harmful LDL cholesterol. They are particularly good at boosting levels of small, dense LDL particles, the kind that are most damaging to arteries. They elevate levels of triglycerides and lipoproteins, both unhealthy trends that have been linked with heart disease. They lower the level of protective HDL cholesterol, something that saturated fats don’t do. They promote the formation of blood clots inside blood vessels, which can trigger heart attacks and strokes. They cause inflammation, an overactivity of the immune system that plays key roles in the development of heart disease, diabetes, and other leading causes of death and disability. They also increase insulin resistance, a precursor of diabetes and its complications.
The rise in the amount of trans fats made and eaten in the United States suspiciously paralleled the rise in heart disease throughout much of this century. In the Nurses’ Health Study, women who ate the most trans fats (about 7 grams of trans fats a day, or about 3 percent of daily energy) were more than 50 percent more likely to have developed heart disease over a fourteen-year period than those who ate the least (slightly over 1 percent of daily calories).5 The risk of diabetes also increased steadily with greater consumption of trans fat.6 Higher intake of trans fat has also been associated with greater risk of gallstones and dementia.
For the longest time, trans fats existed as stealth fats because food makers didn’t have to list them on food labels. The only way you could have known that trans fat was in a particular food was to scrutinize the ingredients list and recognize “partially hydrogenated vegetable oil” or “vegetable shortening,” the giveaways for trans fats. But even then you couldn’t tell how much trans fat was present.
After a long campaign led by Fred A. Kummerow, now professor emeritus of food science and human nutrition at the University of Illinois, along with the Center for Science in the Public Interest and members of our Department of Nutrition, the FDA in 2003 ruled that trans fats were even more harmful than saturated fats and had to be included on the Nutrition Facts label by 2006. This let consumers know which foods contained trans fats and also provided a strong incentive for manufacturers to remove them from their products.
The FDA took an even bigger step in 2015 when it ruled that partially hydrogenated oils, which are the main source of harmful trans fats in food, are no longer “generally recognized as safe.”7 At the time, Susan Mayne, the director of the FDA’s Center for Food Safety and Applied Nutrition, wrote in the FDA Voice blog that “it has become clear that what’s good for extending shelf-life is not equally good for extending human life.”8
By the time of the FDA’s 2015 decision, earlier educational efforts and bans on trans fats by many cities and states had already driven the vast majority of trans fats out of the U.S. food supply. (We weren’t the first, though, as Denmark and other countries had banned trans fat years earlier.)
In the 2015 ruling, food companies were given until 2018 to stop using trans-containing partially hydrogenated oils. Any companies wanting to continue to use them after 2018 must get the FDA’s special approval to do so, which is unlikely to happen.
We have estimated that eliminating trans fats from our food supply would prevent between 72,000 and 220,000 heart attacks or heart disease deaths per year.9 The Center for Science in the Public Interest projected that this would save $50 billion in medical costs a year.
SOME FATS ARE GOOD FOR YOU
There’s a good reason we haven’t seen a payoff from recommendations to reduce fat in the diet. In spite of the scorn heaped upon dietary fat and the anti-fat recommendations that once came from the country’s leading health organizations, the truth is that some fats are good for you, and it is important to include these good fats in your diet. In fact, eating more good fats—and staying away from bad ones—is high on the list of healthy nutritional strategies.
Dietary fat gets much of the blame for causing heart disease and stroke, the leading killers in the United States and around the world. In the United States alone, more than 1.5 million people have heart attacks or strokes each year, and these two conditions account for about one-third of all deaths. The cost of heart disease and stroke is close to $320 billion a year, including the costs of lost productivity.10
Dietary fats aren’t the only factors that affect the risk of heart disease. Smoking, being overweight or obese, and inactivity contribute a substantial share of deaths and disability. But managing the type of fat you eat is an important way to prevent heart disease.
HOW DIETARY GUIDELINES HAVE DISTORTED THE FAT FACTS
The traditional link between diet and heart disease goes like this: (1) Too much fat in the diet increases cholesterol levels in the blood. (2) Too much cholesterol in the bloodstream increases the chance of having a heart attack or stroke or developing some other form of cardiovascular disease. (3) Eating less fat should decrease rates of heart disease.
Except it doesn’t work that way.
Dietary Fat and Body Fat
* * *
You may be thinking, Hold on a second. Won’t eating more fat make me fatter, something I know is definitely bad for my health? True, but only if you add extra fat to your diet without cutting anything out of it. Remember, the goal here isn’t adding more fat to your diet. It’s cutting back on bad fats (eliminating trans fat and limiting saturated fat) while increasing good fats (monounsaturated and polyunsaturated fats) and keeping the number of daily calories constant. Do that and you won’t gain weight.
If you follow a low-fat diet and your level of protective HDL is low, your triglyceride level is high, or you are having trouble controlling your weight, think about cutting back on carbohydrates—especially highly processed ones—and adding in foods that deliver unsaturated fat.
Even though there’s a nice, intuitive feel to the notion that eating more fat makes you fatter, for most people, there’s little evidence to confirm it. For example, randomized trials comparing low-fat diets against higher-fat (low-carb) diets show that both can help people lose weight.11 On average, though, most people do better on lower carbohydrate, higher fat diets (see “A Low-Carb Diet May Help,” page 53).12
In the United States, the gradual reduction in the fat content of the average diet—from over 40 percent of calories in the 1960s to about 33 percent today—has been accompanied by a gradual increase in average weight and a dramatic increase in obesity.
In short, the amount of fat in your diet doesn’t necessarily make you fat. If you usually eat more calories than you burn, you’re going to gain weight regardless of whether your calories mostly come from fat, carbohydrates, or protein. If you keep your calories constant, though, you won’t gain weight if you cut back on saturated fat, refined carbohydrates, and sugar and eat more unsaturated fat.
The relatively simple diet-heart hypothesis leaves out a lot. An important omission is that different fats have different effects on cholesterol. What’s more, there are many ways that dietary fat can affect heart disease other than through the single channel of total cholesterol. Dietary fats influence how much harmful LDL and protective HDL are in your bloodstream, how your blood clots, how susceptible your heart is to erratic rhythms, and how the inner lining of your blood vessels responds to stress—and probably affects other pathways to heart disease we haven’t yet discovered.
Tragically, public policy based on the oversimplified diet-heart hypothesis doesn’t cover these alternate pathways. For years we have been urged to use fats and oils “sparingly” and to choose diets low in saturated fat and cholesterol. Only recently have our Dietary Guidelines for Americans provided any guidance about the proven benefits of unsaturated fats.
None of the overly simplistic advice tells you that eating unsaturated fats instead of saturated fats can improve the levels of cholesterol and other fats in your bloodstream, fortify your heart against erratic heartbeats, or help counteract a number of processes that underlie atherosclerosis, the gradual clogging and narrowing of arteries.
SIMPLER GUIDELINES AREN�
��T ALWAYS BETTER
Back in 1957, with only a limited amount of hard data at hand, the American Heart Association (AHA) set out its first dietary guidelines.13 Although the AHA hedged its bets with liberal use of the word “may,” its first guidelines were remarkably on target. They said: (1) Diet may play an important role in the development of heart disease. (2) Both the fat content and the total calories in the diet are probably important. (3) The ratio between saturated and unsaturated fats may be the basic determinant, and people should get more unsaturated fat and less saturated fat. (4) A wide variety of other factors besides fat, both dietary and nondietary, may be important.
Four years later the AHA was still suggesting that people increase their intake of unsaturated fat.
Over the years, though, as expert panels discussed and sometimes fought over the most effective public health message, the AHA, the National Cholesterol Education Program, and other influential groups decided that Americans couldn’t grasp a concept as nuanced as good fat/bad fat. Instead they settled on the simpler “Fat is bad” message.
There’s no question that the public heard and heeded this message. Today, fats and oils make up about 33 percent of the calories in the average diet, compared with 40 percent in the 1960s. If this reduction meant we were eating less potentially harmful saturated fat, that would be great news and would show up as lower rates of heart disease. But we’ve thrown out the baby with the bathwater, mainly cutting back on beneficial unsaturated fats.
REPLACING FATS WITH CARBOHYDRATES CREATES A NEW PROBLEM
Reducing the amount of fat in the diet almost always means adding something else. If you follow the standard dietary guidelines, that “something else” has traditionally been carbohydrates, usually foods rich in simple or highly processed carbohydrates, such as sugar, white bread, white rice, and potatoes. Replacing foods rich in saturated fat with those rich in refined carbohydrates lowers total cholesterol levels a bit. But it also lowers levels of protective HDL cholesterol. (Replacing saturated fat with whole grains is a much healthier option.)