Eat, Drink, and Be Healthy

by Walter Willett

  The two trends encouraged by the standard dietary guidelines—decreasing the intake of all fats and increasing the intake of carbohydrates—have other troubling consequences beyond their harmful impact on HDL. Carbohydrates can and do increase weight every bit as effectively as fats if you consume more calories than you burn off. Equally harmful, white bread and other foods made from white flour, potatoes, pasta, and white rice cause large spikes in blood sugar (glucose) and insulin, something that doesn’t happen with fat, protein, and slowly absorbed carbohydrates like those from intact whole grains, beans, fruits, and non-starchy vegetables (see chapter six).

  Spikes in blood sugar and insulin place a constant and heavy demand on the pancreas to make more insulin. This is a key ingredient for adult-onset diabetes, now called type 2 diabetes, especially when paired with lack of exercise. Eating carbohydrates instead of unsaturated fats also tends to increase blood pressure.14 Finally, following a low-fat diet usually means forgoing foods such as nuts, avocados, salad dressings made with unsaturated oils, and other foods that contain beneficial monounsaturated and polyunsaturated fats. Less unsaturated fat also means less vitamin E and other valuable nutrients that travel along with fats.

  THE BENEFITS OF EATING UNSATURATED FATS IN PLACE OF SATURATED FATS

  Eating less saturated fat and more unsaturated fat improves cholesterol levels across the board. It also helps prevent heart disease in other ways. It is this message I hope to hammer home against the “All fat is bad” drumbeat. Since the first edition of Eat, Drink, and Be Healthy was published in 2001, the message that some fats are healthy has been slowly spreading. Many people have experienced the benefits of making this swap, and it has now finally become part of mainstream dietary advice, as seen by its inclusion in the 2015–2020 Dietary Guidelines for Americans.

  By steering clear of all fats, you eliminate a number of foods that can improve your long-term health. Don’t get me wrong: I wholeheartedly agree with pruning out saturated and trans fats from your diet. But the same doesn’t apply to unsaturated fats. Eating unsaturated fats instead of saturated fats or carbohydrates:

  Eggs

  * * *

  Once upon a time, eggs were seen as a healthy, eat anytime food, the centerpiece of solid breakfasts and the hearty garnishes atop salads and side dishes. The discovery of a link between blood cholesterol levels and risk of heart disease sullied that reputation. With more than 200 milligrams of cholesterol in each yolk, eggs were branded as unhealthy, to be eaten sparingly. Per capita egg consumption tumbled from more than four hundred per year in the late 1940s to under two hundred per year today15 and many people eat them with a side order of guilt.

  The dangers of eggs aren’t all they’re cracked up to be. Adding an extra 200 milligrams of cholesterol a day to the diet barely increases blood cholesterol levels in most people and boosts, in theory, the risk of heart disease by only a small amount. But eggs aren’t just packets of cholesterol. They are very low in saturated fat and contain many other nutrients that are good for you: protein, some polyunsaturated fats, folic acid and other B vitamins, vitamin D, lutein, and more. So the effect of eggs on heart disease risk can’t be predicted by considering only their cholesterol content.

  No research has ever shown that people who regularly eat eggs have more heart attacks than people who don’t eat eggs. In the late 1990s my colleagues and I looked at the egg-eating habits of almost 120,000 healthy men and women. Those who ate up to an egg a day were no more likely to have developed heart disease or to have had a stroke over many years of follow-up than those who ate less than one egg a week.16 (A later and larger meta-analysis showed no connection between egg consumption and heart disease or stroke.)17 Among those with diabetes, though, there did seem to be some connection between eating an egg a day and the development of heart disease.

  While these studies, and others like it, don’t give the green light for daily three-egg omelets, they should be reassuring to people who enjoy eggs. If your breakfast choices are an egg, a deep-fried doughnut, or a bagel made from refined flour, the egg is the better choice, especially if it is cooked in healthy vegetable oil. If you want to have the healthiest breakfast, though, a combination of oatmeal, nuts, and berries, perhaps with a topping of yogurt, would lower your LDL cholesterol and be better than a “neutral” egg-based breakfast. (This is just one of many examples highlighting that when trying to determine the healthfulness of any food, you always need to ask “Compared to what?”)

  • lowers the level of harmful LDL without also lowering the level of protective HDL

  • prevents an increase in triglycerides, another form of fat circulating in the bloodstream that has been linked with heart disease and that occurs with high-carbohydrate diets

  • reduces the development of erratic heartbeats, a main cause of sudden cardiac death

  • reduces the formation of potentially artery-blocking blood clots.

  Unsaturated fats are so important to good health that they support the foundation of the Healthy Eating Pyramid (see page 16) and are specifically mentioned in the Healthy Eating Plate (see page 19). Both acknowledge that fats and oils make up a substantial chunk of daily calories and can have long-term health benefits. As I describe later in this chapter, not all unsaturated fats are the same, but they share the same beneficial effects.

  TRACING THE HEALTH EFFECTS OF DIETARY FATS

  Until the middle of the last century, when infectious diseases like tuberculosis and influenza were leading causes of death, calorie-rich diets laden with fat were thought to provide some protection against disease and aid in recovery. As late as the 1950s, a healthy diet meant eggs, bacon, and butter-slathered toast for breakfast and roast beef and mashed potatoes with gravy for dinner.

  Our comfortable, almost thoughtless relationship with food was forever changed by separate threads of research that came together after World War II. Large studies in the late 1940s and early 1950s began to focus on diet as a cause of the skyrocketing rates of heart disease. In 1956, a University of Minnesota scientist named Ancel Keys began an international survey called the Seven Countries Study. It suggested a connection between saturated fat and heart disease: in general, the higher the amount of saturated fat in a country’s diet, the higher the rate of heart disease. Interestingly, Keys and his colleagues didn’t find any connection between the total amount of fat in the diet and heart disease. In fact, the area with the lowest rate of heart disease in the study, Crete, had the highest average total fat intake: about 40 percent of calories—mostly due to liberal use of olive oil. At around the same time, the Framingham Heart Study started tracking the health and habits of more than 5,000 men and women living in the town of Framingham, Massachusetts. One of its early findings was that high levels of cholesterol in the bloodstream were often an early signal of impending heart disease. These important studies and others pointed to diet as a key element in the path to heart disease.

  Without turning this into a textbook of nutritional epidemiology, I’ll briefly describe the consistent evidence from several kinds of studies showing the harmful effects of saturated and trans fats and the benefits that can come from replacing these harmful fats with unsaturated fats.

  Cross-Cultural Surveys: More Saturated Fat = More Heart Disease

  The country-by-country surveys of Ancel Keys and others showed that heart disease rates varied more than tenfold between Crete and Finland, the Seven Countries Study country with the highest rates. The more saturated fat in a country’s average diet, the higher the rates of heart disease. Although the Seven Countries and Framingham studies pointed to saturated fat as a major driver of heart disease, other factors, such as differences in cigarette smoking and amount of physical activity, could have contributed to the large difference in rates.

  Metabolic Studies: Good Fats Improve the Cholesterol Profile

  In the 1950s and 1960s, dozens of carefully controlled feeding studies among small groups of volunteers showed conclusively that eating satu
rated fats instead of carbohydrates led to a rise in total cholesterol, and eating polyunsaturated fats instead of carbohydrates led to a reduction in total cholesterol. Thus, for decades we have known that all fats shouldn’t be considered equal. Unfortunately, at that time the importance of other blood lipids—protective HDL in particular—wasn’t appreciated. So those studies gave an incomplete picture at best.

  One of the early and most compelling pieces of evidence to challenge the emphasis on cutting back on all fat and eating more carbohydrates came from an experiment by two Dutch scientists.18 They recruited forty-eight volunteers for an eight-week study. For the first seventeen days, all of the volunteers ate a typical Western diet with about 40 percent of calories from fat. For the next thirty-six days, half of the volunteers were assigned to a diet in which part of the saturated fat was replaced by olive oil, while the other half followed a diet in which some of the saturated fat was replaced by carbohydrates. In both groups, total cholesterol levels plummeted (see Figure 13).19 But in the high-carbohydrate group, levels of protective HDL cholesterol also fell, while triglycerides rose—both changes that increase the chances of having a heart attack or developing some other form of heart disease. In the olive oil group, a healthy trend was seen for total cholesterol without the unhealthy changes in HDL and triglycerides. The benefits of cutting back on carbohydrates and adding in more unsaturated fats seen in that study have been confirmed by many research groups.

  One of these confirmatory studies, from the University of Washington, documented that these changes weren’t fleeting.20 In this study, 444 men with high cholesterol were asked to follow one of four diets, containing either 30 percent, 28 percent, 22 percent, or 18 percent of fat. After a year, all four diets had lowered harmful LDL cholesterol. But the two lowest-fat diets also dropped the level of protective HDL cholesterol and raised the level of triglycerides.

  Figure 13. Blood Fat Responses to Olive Oil vs. Carbohydrates. A diet rich in unsaturated fat (olive oil) improved HDL cholesterol and triglyceride levels compared with a diet rich in carbohydrates.

  The more we learn about cholesterol in the bloodstream, the more we realize that even though total cholesterol is a decent red flag for heart disease risk, what’s really important are the different cholesterol subtypes. The best cholesterol profile is one with a low level of harmful LDL and a high level of protective HDL. This relationship is neatly captured as a ratio of total cholesterol to HDL. Ideally, the ratio should be less than 3.5. The Dutch study, and the many others that have repeated this test, leave no doubt that eating carbohydrates instead of saturated fats—the typical low-fat diet—has little effect on the ratio of LDL to HDL, and that eating unsaturated fats instead of saturated fats improves it.

  Cohort Studies: More Good Fats = Less Heart Disease

  The connection between dietary fat and heart disease has long been murky, stirred up by many small and short-term studies. To make sense of this important relationship, my colleagues and I completed in 2016 what was the most detailed and comprehensive analysis of dietary fat and health to date.21 We used information provided by 126,233 initially healthy women and men participating in the Nurses’ Health Study and the Health Professionals Follow-Up Study, who were followed for up to thirty-two years. Every two years from the start of the study, we asked the participants about smoking, weight, physical activity, medical diagnoses, medications, and other things that could affect their disease risk. Every four years we asked them to complete detailed questionnaires about their diets. From the diet data we were able to calculate their intakes of various types of fat by using routinely updated databases on the fat composition of thousands of foods.

  During the study period, 33,304 of the participants died. We confirmed each cause of death by examining medical records and death certificates. Somewhat to our surprise, participants with the highest intake of total fat (about 42 percent of calories) were 16 percent less likely to have died during the course of the study as those with the lowest total fat intake (25 percent of calories).

  My colleagues and I suspect that the lower risk among those with higher-fat diets was due in part to the greatly improved quality of fat in the American diet following the near elimination of partially hydrogenated oils rich in trans fats (see “Trans Fats,” page 83) and their replacement by unsaturated oils.

  Even more important than the finding for total fat were the strong relationships between specific types of fat and death. When compared to the same number of calories from carbohydrates, trans fats were most strongly associated with increased risk of dying during the study, saturated fats with a slightly higher risk, monounsaturated fats with a moderately lower risk, and polyunsaturated fats with a substantially lower risk. When we looked at types of polyunsaturated fat, omega-6s were strongly linked to a lower risk of dying during the study, while the link with omega-3s was weak.

  The findings of this study almost exactly replicate what we had reported nearly twenty years before from a study of heart disease in women.22

  What was surprising in the 2016 study was that the benefits of unsaturated fats extended to deaths from other causes as well, including cancer, respiratory disease, and neurodegenerative conditions like Alzheimer’s disease. The biological basis for some of these findings, especially neurodegenerative disease, is not well understood and is the topic of ongoing investigation.

  I must offer a word of caution when interpreting these results. When I say “compared to the same number of calories from carbohydrates,” I mean the kinds of carbohydrates actually being consumed by the study participants, which included a large amount of sugar and refined starch. Total fat wouldn’t have looked as good, and saturated fat would have looked even worse, if we had compared them to the same number of calories from whole grains. I’ll explore these distinctions further in chapter six.

  This analysis provides a big picture of the relationship between the amount and type of dietary fat in our diets and health. It isn’t an isolated finding but rather stands with findings from many studies of various designs conducted by many investigators around the world. Based on the concordance of this work, I’m confident we can be guided by this overall picture of dietary fat: Choose foods rich in polyunsaturated and monounsaturated fats, like nuts, salmon, and avocado, over those rich in saturated fats, like red meat. And don’t eat those that contain artificial trans fats.

  Clinical Trials: Replacing Saturated Fats with Unsaturated Fats Saves Lives

  Clinical trials bear out the overall picture of dietary fats I have been drawing in this book: some fats are good for health and others aren’t. Early trials—most of which were done decades ago, were very small, and enrolled people who already had heart disease—showed that eating less total fat, usually by eating more carbohydrate-rich foods like white rice and potatoes, did little for the heart and blood vessels.

  In stark contrast to that work, clinical trials in which volunteers were randomly assigned to either a standard Western diet, which is relatively rich in saturated fats, or a diet in which some saturated fats were replaced with polyunsaturated fats have shown benefits such as lower levels of total cholesterol and harmful LDL cholesterol and, more important, reductions in heart disease of one-third or more. (As discussed earlier, “polyunsaturated fats” means both omega-6 and omega-3 fatty acids, which wasn’t acknowledged when these trials were conducted.)

  One of the most impressive clinical trials was the Lyon Diet Heart Study. Begun in 1988, this French trial set out to test whether a Mediterranean-type diet could prevent second heart attacks or heart-related deaths among heart attack survivors. Half of the 605 volunteers were asked to follow a low-fat diet. The other half were asked to follow a Mediterranean-type diet that included olive oil, whole-grain bread, extra root and green vegetables, fruit every day, more fish and poultry and less red meat, and a special margarine rich in omega-3 fats.

  Figure 14. Lyon Diet Heart Study. Heart attack survivors eating a Mediterranean-type diet had fewer second hear
t attacks and deaths from heart disease than those on a low-fat, high-carbohydrate diet.

  The trial, which was supposed to run for five years, was stopped after just two and a half years because the benefits of the Mediterranean-type diet were so compelling (see Figure 14): a 70 percent reduction in new heart attacks or deaths from all causes.23 When the investigators checked in on the participants a few years later, the benefits of the Mediterranean diet, including a reduced risk of cancer, were still in evidence. Interestingly, most of those who had been asked to follow the Mediterranean-type diet were still doing so several years after the trial had ended.24

  A more recent clinical trial shows that a similar type of diet can prevent first heart attacks in relatively healthy people. Researchers recruited nearly 7,500 residents of Spain to take part in the Prevención con Dieta Mediterránea (PREDIMED) trial. All of the volunteers were over age fifty-five. None had ever been diagnosed with heart disease, although all were at high risk for developing it. One-third of the participants were asked to follow a Mediterranean-style diet and were also given a liter of extra-virgin olive oil each week. Another third were asked to follow a Mediterranean-style diet but instead of olive oil were given about seven ounces a week of walnuts, hazelnuts, and almonds. The third group was asked to follow a low-fat diet.

  The trial was stopped early, after just under five years of follow-up, when it became clear that participants in the Mediterranean-diet groups were experiencing fewer cardiovascular events—heart attacks, strokes, and deaths from cardiovascular disease—than those in the low-fat diet group, just as had been seen in the Lyon Diet Heart Study. The difference was impressive: 83 cardiovascular events in the Mediterranean diet plus nuts group (8 per 1,000 participants), 96 in the Mediterranean diet plus olive oil group (8 per 1,000 participants), and 106 in the low-fat diet group (11 per 1,000 participants).25 That difference may not sound like a lot, but if it were applied to the United States, it would translate into tens of thousands fewer hospitalizations and deaths from heart disease each year if everyone shifted to this diet.