Eat, Drink, and Be Healthy

by Walter Willett

  • Your microbiome. Billions of bacteria, fungi, viruses, and other microbes—collectively called your microbiome—live quietly inside your intestines. They help digest your food; protect you against microbes that can cause disease; make vitamins such as vitamin B12, thiamine, and riboflavin; and more. It’s possible but unproven that your microbiome helps regulate your weight.13 Some types of gut bacteria seem to be better at releasing calories from food or causing inflammation, either of which can lead to weight gain. But we still don’t know if the microbiome is causing weight gain or weight gain is changing the microbiome.

  In addition to all of the above, we have what I call the overproduction problem. U.S. farmers produce about 4,000 calories’ worth of food a day for every man, woman, and child in America.14 That’s nearly double what the average person needs. The almost inevitable consequence of this surfeit is a system that encourages full-tilt consumption. Producers and food manufacturers want us to eat more of their products, and they are competing with one another to exploit our weaknesses. The food industry spends billions of dollars a year learning the best ways to entice us to buy more and eat more, and then acts on that knowledge. The keen senses we have inherited for salt and sweetness that were once needed for survival (our taste for sweet things, for example, helped early humans sort through leaves to find the tender young ones with a ready supply of energy) are continually exploited. The sugar and salt content of products have been ratcheted up to increase our expectations for sweetness and saltiness and get us to eat—and buy—more.

  Adding to the problem is the fact that food is sold everywhere: gas stations sell doughnuts and sandwiches, bookstores and department stores offer coffee and sweets, and you can get full, belly-busting meals at sporting events and concerts. Restaurants contribute by ratcheting up portion sizes. Modest servings of nouvelle cuisine have been overshadowed by supersizing, and it isn’t uncommon to consume a meal that contains 1,500 to 2,000 calories, almost what you need for an entire day.

  This incredible access to food and the nearly unlimited variety of choices test the willpower of even the most sensible eater. When combined with too little physical activity, it’s a sure recipe for weight gain. And because weight control is the single most important factor in your good health after not smoking, overeating can pose serious health risks.

  FOR ENERGY, A CALORIE IS A CALORIE

  We eat food for two physiological reasons: to get energy and to get chemical building blocks. The amount of energy a particular food can deliver to mitochondria—the tiny engines that power your cells—is measured in calories. Technically, a food calorie is the amount of heat needed to raise the temperature of a liter of water (just over a quart) from 14.5° C to 15.5° C. Practically, a food calorie is about the amount of energy a 150-pound person burns each minute while sleeping.

  If you read diet books or keep up with health and nutrition news, you’ve probably heard a lot about “fat calories” or “carbohydrate calories.” The idea that fat calories are different from carbohydrate calories came from studies done under extreme conditions, such as consuming pure carbohydrate, protein, or fat. In these situations, the body converts dietary fat to body fat a bit more efficiently than it does carbohydrate or protein.

  In a normal diet, though, your body converts all carbohydrate, fat, and protein to energy at the same rate. When it comes just to generating energy, a calorie is a calorie. (Calories from trans fat may be an exception; more on that later.)

  This calorie blindness is the result of a neat solution to a vexing problem faced by some of earth’s early inhabitants: how to run a body on different fuels. Instead of having completely different intracellular systems for fats, carbohydrates, protein, alcohol, and the like, the cells in your body use one of two energy sources: glucose and fat. Much of what you eat is (or can be if needed) converted to the energy coin of the realm, a six-carbon sugar called glucose. When you eat, some of the glucose dumped into your bloodstream is used immediately by your cells. Some is linked into long chains, called glycogen, and stored in your muscles and liver. Any leftovers are converted to fat and squirreled away in special fat storage cells and padded in between muscles. If glucose is like cash in your pocket, ready to be spent when needed, glycogen is money in the bank, available with a bit of effort, and fat is money tied up in stocks or mutual funds. However, the conversion of glucose to fat is a one-way street: fat can’t be converted back to glucose. So while your cells typically run on glucose, when there isn’t enough, you can switch over to burning fats, either directly from the fat you eat or by withdrawing fat from storage in your body. Brain cells are an exception: they run on glucose only.

  CALORIE QUALITY MATTERS TOO

  While a calorie is ultimately a calorie on the cellular level, the foods you eat for calories can have an important effect on your health.

  The source of calories can influence how satisfied you feel after eating. Some foods, like an apple, can fill your stomach and leave you content for hours, while a can of soda with twice the calories will hardly ease your hunger. A good approach is to take in fewer calories by eating whole high-fiber foods like apples or carrots. In that way, the quality of your diet and the amount of food you consume are highly intertwined, improving both your weight and your long-term health.

  Another way in which “calories” may differ is highlighted in the book Always Hungry? by my colleague David Ludwig. He highlights a longstanding paradox: some people have hundreds of thousands of surplus calories stored as body fat and yet can be just as hungry as thin people. How is it that overweight and obese individuals aren’t able to draw from their stored calories when they are hungry instead of eating more? Ludwig offers evidence that a higher insulin level, stimulated mainly by eating rapidly digested and absorbed carbohydrates, is a key metabolic signal that shunts calories into storage as fat and keeps those calories locked up and inaccessible. That provides a rationale for following a diet with a lower glycemic load, which I describe in chapter six.

  While carrying too many pounds is a key threat to health, it’s important not to lose sight of the fact that diet affects health in many ways that aren’t related to weight. Those need to be factored into planning a diet for long-term weight control. For example, among women in the Nurses’ Health Study, low diet quality contributed as much to heart disease risk as excess weight.15

  DOES FIDDLING WITH THE FORM OF CALORIES HELP YOU LOSE WEIGHT?

  Almost any kind of diet can lead to weight loss, at least for a few months. Some of the most absurd diets ever published have their champions who will testify, complete with eight-by-ten glossy color photographs, that the diet helped them lose weight. That’s because even the oddest diet makes people pay attention to how much they are eating rather than eating willy-nilly throughout the day. This mindfulness is often enough to limit daily calories, the single most important key to controlling weight. It is aided and abetted by the monotony imposed by many of these diets and their inability to please the palate. Most fad diets fail in the long run. For that matter, so do many middle-of-the-road, commonsense diets.

  The ultimate diet is one that offers meals and snacks that rapidly make you feel pleasantly full (technically called satiety), delay the return of hunger pangs (technically called satiation), are pleasing and satisfying, meet your body’s needs for energy and nutrients, and work to prevent chronic disease. That’s a tall order. Countless books have been written claiming they’ll give you all or part of this dietary nirvana. Most promise far more than they deliver.

  Diets usually fiddle with the form of calories by focusing on one particular dietary villain or hero. The most common ones are fat, carbohydrates, protein, the glycemic index, and energy density.

  LOW-FAT DIETS AREN’T THE ANSWER

  A common though absolutely false thread that runs through many diets is the idea that fat in food makes fat in the body. Limit “fat calories,” so the thinking goes, and you’ll be able to control your weight. Although there’s a pleasant symm
etry to that logic, there’s no good evidence linking dietary fat with excess weight. In fact, there’s plenty of evidence showing that a higher percentage of calories from fat doesn’t lead to gaining weight or being overweight and the evidence is tending in the opposite direction.

  That’s why the Harvard Healthy Eating Pyramid and Healthy Eating Plate don’t ban fats. Instead, they treat fats as important nutritional factors in your diet. I cover what fats to choose and how much to eat in chapter five.

  To be sure, some countries with high fat intake have many overweight people. In the United States, for example, the average person gets about one-third of his or her daily calories from fat (a relatively high percentage), and almost two-thirds of the population is overweight or obese. But not long ago in parts of South Africa, where 60 percent of people were overweight, fat contributed barely one-quarter of calories. In other words, factors other than dietary fat influence overweight and obesity.

  I am not trying to absolve dietary fat or downplay its potential contributions to weight or weight gain. Dietary fat affects energy, fat stores, and weight. But there is no evidence that calories from fat contribute more to weight gain than calories from carbohydrates or other sources.

  But if you balance the number of calories you eat with the number of calories you burn, especially if part of the burn comes from exercise, then you won’t gain weight on a diet that has 35 percent, 40 percent, or more calories from fat. And if you are eating the right kinds of fat, you will help protect yourself from heart disease and other chronic conditions.

  A LOW-CARB DIET MAY HELP

  For years, mainstream nutrition experts dismissed Dr. Robert Atkins’s carbohydrate-shunning diet as an unhealthy fad. How in the world could a high-protein, high-fat, low-carbohydrate diet help with weight loss when everyone knew that fat was a dietary demon? Once the Atkins diet got its day in court—the court of careful scientific testing—the good doctor was proven to have a decent case, at least in part.

  The low-carb idea isn’t new. In the mid-1800s, the aforementioned William Banting, an obese British undertaker, happened on a low-carbohydrate diet. He tried it for a few months and watched with delight as the pounds slipped away without the gnawing hunger and cravings that other diets had caused him. Banting’s Letter on Corpulence, Addressed to the Public, written in 1863,16 became so popular that people began using the term “to bant” in place of “to diet.”

  Eating chicken, beef, fish, beans, and other high-protein foods that are the staples of low-carb diets slow the movement of food from the stomach to the small intestine. Slower stomach emptying means you feel full longer and it takes longer to get hungry. Second, protein’s gentle, steady effect on blood sugar smooths out the blood sugar–insulin roller coaster caused by the digestion of rapidly digested carbohydrates like white bread, white rice, or a baked potato (see “Why Carbohydrates Matter” on page 112 and can stretch the time between hunger pangs.

  Are bunless burgers the key to weight loss? Some solid studies, like the Dietary Intervention Randomized Controlled Trial (DIRECT) trial I describe on page 56, indicate that low-carb diets can help overweight people shed pounds. Low-carb diets like the Atkins diet seem to be easier to stick with than low-fat diets and, contrary to experts’ warnings, generally don’t cause harmful changes in blood cholesterol even when they contain fairly high amounts of fat, although that depends on the type and source of fat.

  One concern in the nutrition community about low-carb, high-protein diets was that eating a lot of protein would be bad for the bones. The digestion of protein creates acid. Generating too much acid could, in theory, force the body to pull calcium from bone to neutralize it. But that doesn’t appear to be the case.

  High protein intake can also put extra demands on the kidneys. This probably isn’t an issue for most people, but it may pose problems for those with mild kidney disease. People with high blood pressure are often in this category.

  But eating unlimited amounts of beef, sausage, butter, and cheese, as promoted by the original Atkins diet, isn’t a good idea for overall good health. There are better ways to cut back on unhealthy carbs. Eating more nuts, beans, soy foods, fish, poultry, nonstarchy fruits and vegetables, whole grains, and vegetable oils, as recommended by the Healthy Eating Pyramid and Healthy Eating Plate, can work for weight control even as it reduces the risks of heart disease, diabetes, and several cancers. Even Atkins was heading in that direction before his untimely death in 2003, as his final book had shifted toward this version of a low-carbohydrate diet.

  LOW-GLYCEMIC DIETS MAY BE AN EXCELLENT OPTION

  When you eat a carbohydrate-rich food like bread or rice, your blood sugar rises. How much it rises depends on the food, how much of it you eat, how much insulin your body produces in response to it, and if (or how much) you are resistant to the effects of insulin. White bread, cornflakes, and other highly processed carbohydrates, as well as white potatoes, trigger large, rapid increases in blood sugar (glucose). Intact or minimally processed grains, beans, and most fruits and vegetables generate smaller, slower increases (see chapter six).

  Easily digested foods that cause sharp spikes in blood sugar also stimulate a matching production of insulin. The more insulin dumped into the bloodstream, the faster glucose is removed. A sudden drop in glucose, along with other hormonal changes, generates new hunger signals.

  In an elegant study involving a dozen overweight boys at Boston Children’s Hospital, those who ate specially prepared breakfasts enriched with easily digested carbohydrates snacked almost twice as much during the morning as those who ate breakfasts that delivered the same number of calories but included more slowly digested carbohydrates.17

  The glycemic index and glycemic load (see page 118) measure how different foods affect blood sugar. People with diabetes have been using the glycemic index and glycemic load for years to plan meals and snacks that cause the smallest possible increases in blood sugar. These measures have become popular dieting tools. Both offer useful guides for choosing carbohydrates.

  You don’t need to religiously follow glycemic index and glycemic load tables in planning meals or snacks. There are simpler rules of thumb: Don’t eat highly processed sources of carbohydrates such as breads, pastries, cereals, crackers, and other foods made with white flour; white rice; and sugar-sweetened beverages. Instead, eat more intact grains and foods made from them, in addition to fruits, vegetables, and beans.

  ENERGY DENSITY ISN’T A RELIABLE GUIDE

  Several popular diet books claim foods that deliver relatively few calories per mouthful, like soup or baked squash, fill you up faster than foods that pack more calories, like meat or nuts, and so help you lose weight. This concept is called energy density. Apples, potatoes, cooked rice, and lettuce have low energy densities, largely because they are mostly water. Nuts, bagels, cookies, Wasa bread, and other dry, high-fiber foods have high energy densities.

  As a concept, energy density doesn’t necessary help when it comes to dieting. Some foods with low energy densities, like white bread and white potatoes, do nothing for weight loss and plenty for weight gain, while some high-energy-density foods, like nuts and olive oil, can help control weight.

  The strongest evidence against using energy density to control weight comes from the PREDIMED trial I mentioned earlier. In this trial, several thousand people did not gain weight even though they supplemented a Mediterranean-type diet with extra olive oil or nuts, two of the most energy-dense foods we know.

  HEALTHY EATING AIDS WEIGHT LOSS

  As I mentioned earlier, there’s a solid connection between healthy eating and weight loss. Strong evidence showing that healthy eating contributes to weight loss comes from the Nurses’ Health Study, the Nurses’ Health Study II, and the Health Professionals Follow-Up Study. My colleagues and I looked at consumption of specific foods in relation to changes in weight over twenty-four years among 120,877 women and men in these cohorts who were not initially overweight.18 The foods linked to greater we
ight gain included:

  • soda (overall, the most important food or beverage for weight gain because it was consumed so often)

  • potatoes in all forms

  • red meat

  • refined grains

  • sweets

  • fruit juice.

  Foods related to less weight gain included:

  • vegetables

  • fruits

  • whole grains

  • nuts

  • yogurt.

  Milk (both whole and low-fat) and diet soda weren’t appreciably linked to weight gain.

  Unless you believe in magic, it shouldn’t come as a surprise that no single food or beverage accounted for a large change in weight. But when we added up the contributions of these foods and beverages and others, diet quality had a large effect on weight gain. Interestingly, the pattern of foods related to the least weight gain corresponded quite closely with a Mediterranean-type diet and one matching our Alternative Healthy Eating Index, both of which are linked to long-term good health and weight loss or weight control.

  GO MEDITERRANEAN

  The most impressive evidence for the benefit of a Mediterranean-type diet on long-term weight control comes from the Dietary Intervention Randomized Controlled Trial (DIRECT). In this trial, 322 moderately obese men and women were randomly assigned to one of three diets: a low-fat diet with about 1,500 calories a day for women and 1,800 a day for men; a Mediterranean-type diet with the same calorie targets; and a low-carbohydrate diet with no calorie target but an aim to provide only 20 grams of carbohydrate a day for the first two months, then gradually increasing to a maximum of 120 grams a day.

  Among the participants who finished the two-year trial, those who followed the low-fat diet lost an average of 7 pounds, those following the Mediterranean diet lost about 10 pounds, and those on the low-carb diet lost 12 pounds. The healthiest changes in cholesterol levels were seen in the low-carb and Mediterranean groups, while the healthiest change in blood sugar was seen in the Mediterranean group.19 When the researchers checked in with the participants four years after the trial had stopped, those originally in the low-fat group had regained all the weight they had lost, while those in the Mediterranean-diet group had maintained their weight loss; the low-carbohydrate group was in between. Favorable metabolic changes had also persisted in the Mediterranean diet group.20