Eat, Drink, and Be Healthy

by Walter Willett

  Other investigators have developed indices that include the same basic elements and have evaluated them in different populations and in relation to a variety of health outcomes. All of them predict better health. This convergence of evidence from many different sources makes me confident that what I recommend in this book will help you choose a diet that is healthy for a lifetime.

  Despite a few naysayers who contend that nutrition scientists can’t agree on anything,15 the convergence of Harvard’s Alternative Healthy Eating Index and the USDA’s Healthy Eating Index suggest that a broad consensus has developed around the basic elements of a healthy diet.

  The Healthy Eating Pyramid and Plate aren’t set in stone, and additional fine details are likely to emerge with further research. For example, new findings about the health effects of vegetables in chapter eight are likely to surprise many readers. Yet we can have a high level of confidence that today’s broad picture of a healthy diet will endure.

  BETTER GUIDELINES AND BETTER DIETS PAY OFF

  In spite of the back-and-forth of science, misleading dietary guidelines from the USDA, sensationalist reporting, and purposeful misinformation, the average American diet is getting better. Since the 1960s a doubling of polyunsaturated fat intake, a reduction in saturated fat intake, and a 40 percent decline in red meat consumption have contributed to a 60 percent reduction in deaths from heart disease and added years of life.

  Curious about other potentially healthy changes in the American diet, my colleagues and I applied the Alternative Healthy Eating Index to the eating patterns of a national survey of Americans. We saw steady improvements between 1999 and 2012. The changes with the biggest effects on health were the near elimination of artery-damaging trans fats and a 25 percent drop in drinking sugar-sweetened soda. There were also modest increases in eating fruits, vegetables, whole grains, and unsaturated fat.16 We estimated that these improvements in diet had prevented more than 1 million premature deaths and 12 percent of cases of diabetes between 1999 and 2012. Shortly after our report, the Centers for Disease Control and Prevention reported that new diagnoses of diabetes had declined for the first time, by a substantial 20 percent, consistent with reductions in trans fat and soda consumption.

  Although the trend in diet quality was in the right direction, the average score was still less than 50 on a scale of 110, indicating the potential for far greater improvements in health. In the pages that follow, I will describe how to boost your score to be at or near the top of the scale, where the payoffs can be huge.

  CHAPTER THREE

  * * *

  What Can You Believe About Diet?

  RESEARCH ABOUT DIET AND NUTRITION seems to contradict itself with aggravating regularity. You stop using butter and start spreading margarine on your toast, only to learn later that margarine can be as bad for you, and then later that butter isn’t as bad as it was once thought to be. After switching to bran muffins for breakfast because high-fiber diets supposedly prevent colon cancer, you hear about a big study showing that fiber doesn’t prevent colon cancer. In an early study, coffee drinking appeared to increase the chances of developing pancreatic cancer, while later research shows that coffee drinking is harmless and may even have some benefits. Some studies find that eating fish prevents heart attacks; others don’t. These flip-flops are so confusing and so common that a negative report on vitamin E and beta-carotene once goaded Boston Globe columnist Ellen Goodman to write, “There seems to be some sort of planned obsolescence now to medical news. Today’s cure is tomorrow’s poison pellet. Fresh research has a sell-by date that is shorter than the one on the cereal box.”1

  The sheer volume of information doesn’t help. Fifty years ago nutrition was a quiet backwater of medical research. For example, the longest study of health in the United States, the legendary and ongoing Framingham Heart Study, collected hardly any data on diet when it was started in 1949. Over the years, though, the trickle of information on diet and health has swelled into a fast-flowing torrent.

  It’s only natural that people want to know the latest (often confused with the best) results, whether they are looking for ways to fine-tune their diets or for that single magic key—the right food or vitamin or supplement—that will open the door to the longest, healthiest life possible. The media cater to this interest and serve up a steady stream of nutrition news.

  The problem is that newspapers, television, radio, blogs, websites, and apps tend to turn the baby steps of scientific research into “major advances,” “breakthroughs,” and “possible cures,” or highlight the confusing contradictions when one study contradicts an earlier one. This makes following health news seem like reading pages torn at random from a book or, worse, reading the pages with misprints.

  REPLACING EDUCATED GUESSES WITH EVIDENCE

  Another reason for the flip-flops is that early recommendations about diet were often based on thin evidence. The thinking behind these early recommendations was that, since people were going to eat no matter what, guidelines based on intelligent guesses were better than no guidelines at all. That’s actually a reasonable approach when there isn’t much evidence. Unfortunately, these recommendations never carried warning labels like “Educated Guess, Subject to Change.” Those educated guesses tend to be repeated thousands of times until they acquire the ring of truth.

  When researchers began learning of the possible dangers of saturated fat, for example, many recommended that people switch from butter, which is high in saturated fat, to low-saturated-fat margarine. This recommendation made sense, even though there were no studies showing that people who ate margarine instead of butter had fewer heart attacks. Then along came studies showing that margarine eaters fared worse in the heart-attack department than butter eaters. That finding was reinforced by short-term studies showing that trans fat, which was high in many margarines, had far worse effects on blood cholesterol than saturated fat.

  To a scientist, this is the normal path of scientific progress—a recommendation based on a good guess is tested and toppled by one based on better science. To the rest of the world, though, it is a frustrating contradiction.

  The amount and quality of sound scientific information on diet and health have grown enormously over the past thirty years. That makes today’s evidence-based recommendations more certain and less likely to undergo radical changes than those made three decades ago. As the quest for new and better knowledge about diet and health continues, rest assured that even today’s recommendations will probably be subject to some fine-tuning, even though the big picture is unlikely to change appreciably.

  CONTRADICTIONS ARE INEVITABLE

  Nutrition research seems to generate more than its share of contradictory results. That’s partly because the media pay special attention to nutrition—because of the public’s interest—while inorganic chemistry, geology, and many other disciplines escape this daily scrutiny.

  It’s also because medical science has its own special rhythm, one that doesn’t fit with the media’s need to tell compelling but simple stories. Efforts to present “balanced” articles by quoting opposing views can sometimes confuse things even further.

  For nutrition research, the rhythm is more a cha-cha—two steps forward and one step back—than a straight-ahead march. If you look at the day-to-day results, which are reported more like sports scores than scientific research, it’s easy to wonder why researchers can’t get it right the first time.

  They can’t because these conflicts and contradictions are the way science works. It happens this way in every field, from archaeology to zoology, nuclear physics to nutrition. Men and women carry out studies and report their results. Evidence accumulates. Like dropping stones onto an old-fashioned scale, the weight of evidence gradually tips the balance in favor of one idea over another. It is only when this happens that you should make changes in your life.

  The size of the stone clearly makes a difference. As we describe on pages 30–35, most studies are like sand grains or small pe
bbles. Very few are like boulders.

  WORKING WITH REAL PEOPLE POSES SPECIAL CHALLENGES

  Nutrition scientists usually can’t exert the same kind of control over their research subjects that chemists and zoologists can. Instead they must work with unpredictable, independent, mostly uncontrollable subjects: people.

  Here are a few of the challenges that nutrition researchers face:

  • People don’t eat “human chow” meal after meal after meal. Instead, diets change from day to day, week to week, and season to season. What you usually eat now is probably a bit (or maybe a lot) different from what you used to eat two years ago or will eat two years from now. These changes are driven by personal taste, cultural changes, new developments in agriculture and technology, and changes in work and family life. Disease and aging can also change what people eat.

  • Many studies depend on people accurately reporting what they eat. That’s a challenging task: Try remembering exactly what you ate one day last week. Despite this difficulty, people are fairly accurate about reporting their longer-term eating pattern. But because they aren’t perfect, there’s almost always some imprecision when linking diet and disease.

  • The foods you eat each day contain thousands of different natural chemicals, some known and well studied, some known and unstudied, many completely unknown and currently unmeasurable. So far we’ve figured out what only a small percentage of them do in the body. And then there are the artificial compounds added as preservatives, stabilizers, flavor enhancers, and more. This makes it difficult to draw strong conclusions about a specific vitamin, mineral, or other molecule from studies of foods and diseases. Knowing exactly what is in different foods, how food compounds interact, and what they all do in the body are important jobs for the future.

  • Calculating the nutrients a person gets from the foods she or he eats—how much saturated fat, fiber, vitamin E, and so on—is tricky, since it depends on sometimes sketchy information about food composition.

  • Almost everyone eats some fat, fiber, sugar, starches, fruits, vegetables, vitamins, and so forth. That means nutrition researchers are faced with the difficult task of measuring how much of something is eaten, not just whether it is part of the diet.

  • Heart disease, cancer, diabetes, osteoporosis, cataracts, and other chronic diseases almost always develop over many years or even decades. They also have other causes beside diet, including genes, physical activity, smoking, stress, and other factors yet to be identified.

  DIFFERENT METHODS FOR DIFFERENT PROBLEMS

  To get around these problems, nutrition scientists use a variety of research methods.2

  Randomized Trials

  These are often considered the gold standard by which other studies are usually judged. In these carefully controlled studies, half of a group of volunteers is randomly assigned to the experimental diet or treatment, and the other half is assigned to a comparison diet or treatment (called the control) or possibly to no treatment at all. After a preset time, the number of people in the experimental group who have developed the predetermined “endpoint”—death, heart attack, broken hip, and so on—is compared with the number in the control group.

  For example, say you want to know if vitamin C prevents age-related memory loss. You would round up a large group of volunteers, then randomly assign some to take a daily vitamin C tablet, while the others take an identical tablet that contains an inactive ingredient that tastes like vitamin C (a placebo). After ten or twenty years you would compare the percentage of people in the vitamin C group who have experienced memory loss with the percentage in the placebo group.

  This kind of study has plenty of advantages. If it is large enough, the randomization process does a good job of making sure the people in the experimental group are very similar to those in the control group in terms of age, health, exercise, and other possibly important factors. So the only thing different between the two groups is the diet or treatment.

  Unfortunately, randomized trials are often impossible to do when it comes to nutrition. Getting people to prepare and eat special meals for a long time is difficult. So is getting people to take a vitamin pill or placebo for maybe a decade or more. Given the large number of volunteers needed, the cost of running a randomized trial can be astronomical. The Women’s Health Initiative—which tested the effect of reducing dietary fat to 20 percent of calories and increasing consumption of fruits and vegetables on the development of breast cancer, heart disease, and other chronic conditions among almost 60,000 women in the 1990s—cost more than $2 billion and didn’t yield clear answers on this important question, in part because there was actually very little difference in fat intake between women assigned to follow a low-fat diet and those following the comparison “usual diet.”

  A major limitation of randomized trials of vitamins and other nutritional supplements is that many or most of the participants may already be getting enough of the factor being studied in their normal diets. That could mean missing an important benefit in people with lower intakes. For example, randomized trials of folic acid supplementation conducted in the United States after the FDA required companies to fortify flour with this important B vitamin showed little overall effect on risk of cardiovascular disease. But a trial conducted in China, where folic acid levels were low, found an important reduction in strokes.3 This makes it likely that at least some people in the U.S. with low folic acid intake would also benefit from getting more of this vitamin.

  The ability of randomized trials to give misleading results is vividly illustrated by their failure to detect a benefit in stopping smoking, probably the single most important step a person can take to improve their health.4 This happened in a classic trial called the Multiple Risk Factor Intervention Trial. The reason it didn’t detect a benefit for quitting smoking is almost surely because many of the participants who stopped smoking took it up again, and the seven-year study wasn’t long enough to see the full benefits for those who did quit permanently.

  Cohort studies

  Another effective method involves following large groups of “free-living humans”—regular people like you—for long periods of time. These cohort studies start with a group of people who often have something in common, like an occupation or place of residence. They are asked about their diets, smoking and drinking habits, education, occupation, medical conditions, and other possibly relevant things. The group is then followed for a period of time, ideally a decade or more, either directly with occasional checkups and mailed questionnaires or indirectly by monitoring death certificates. Once the study has gone on long enough, researchers can examine the accumulated information to test a variety of hypotheses. They can, for example, determine if people in the cohort who eat the most fiber have different rates of colon cancer from those who eat the least fiber, or if those who consume the most folate, an important B vitamin, have lower rates of heart disease than those who consume the least folate. Such long-term studies have yielded some of the best insights so far into the link between diet and health.

  By gathering information at the beginning, before specific diseases have occurred, cohort studies avoid the skewed recall sometimes seen among people who develop a particular disease—and who would like to find an explanation for it. Cohort studies such as the Nurses’ Health Study, the Health Professionals Follow-Up Study, the Adventist Health Studies, and others (see “Key Cohort Studies,” page 31) use carefully tested questionnaires to determine what the participants eat. The Nurses’ Health Studies and Health Professional’s Follow-Up Study, both conducted by my research group, are unique because the participants fill out dietary questionnaires many times over the course of the study. This is important in long-term follow-up studies because diets change greatly over time due to individual preferences and changes in the food supply.

  Randomized controlled trials are sometimes held up as the “best” evidence. But cohort studies can answer questions that aren’t possible in such trials, such as long-term effects of die
t. Trials can’t evaluate the effects of diet or weight during childhood or adolescence on health during adulthood or old age. They also can’t test something potentially harmful, like trans fats: it would now be unethical to do a trial in which half of the participants were given diets containing a high level of these artery-clogging fats.

  Key Cohort Studies

  Dozens of cohort studies of diet and health are in progress. They have already provided us with important information on connections between diet and disease, and will produce a flood of data over the coming years. They include:

  • American Cancer Society. In 1992, the American Cancer Society launched the Cancer Prevention Study II–Nutrition Cohort, which has been following the health of 132,000 men and women to explore possible connections between alcohol use, exercise, diet, and other factors on the development of cancer. The Cancer Prevention Study-3, begun in 2006, adds another 300,000 participants with greater racial and ethnic diversity.

  • Adventist Health Studies. These include studies of 27,658 male and female California Seventh-day Adventists, a group chosen because many members of this religion are vegetarians. The newer Adventist Health Study-2 is following 96,000 church members from the U.S. and Canada.

  • Black Women’s Health Study. This cohort, started in 1995, is following 59,000 black women to explore why they are more likely than other women to develop high blood pressure, breast cancer earlier in life, diabetes, stroke, and lupus.

  • European Prospective Investigation into Cancer and Nutrition and Study (EPIC). This is a collaborative study started in 1993 in nine European countries. In all, 440,000 men and women have been enrolled.

  • Health Professionals Follow-Up Study. A study of 51,529 male health professionals (dentists, veterinarians, pharmacists, optometrists, osteopathic physicians, and podiatrists) who were between the ages of forty and seventy-five in 1986. Like the participants of the Nurses’ Health Study, these men have been completing health, diet, and lifestyle updates every other year.