Eat, Drink, and Be Healthy

by Walter Willett

  OUR HEALTH DEPENDS ON PLANTS

  The diet we eat today doesn’t look a thing like the diet our hunter-gatherer ancestors ate over hundreds of thousands of years. They probably relied on a wide variety of fruits and vegetables, scrabbling to pick and eat whatever edible morsels they could find. It is likely that, over time, humans became metabolically dependent on hundreds of compounds made by plants. These phytochemicals help detoxify the harmful substances found in plants; help some of our enzymes fight cancer, infection, and other cellular disruption; and work with others to repair damage to cells. So far, only a small number of these compounds have been labeled essential nutrients.

  “Vegetables and fruits contain the anticarcinogenic cocktail to which we are adapted,” noted cancer researcher John Potter once wrote. “We abandon it at our peril.”

  TOO MUCH OF A GOOD THING

  Could eating too much of some kinds of fruits or vegetables be bad for you? The answer is yes.

  Almost all essential nutrients can be toxic if you take in too much of them. That cautionary note likely applies to fruits and vegetables as well. Legendary biochemist Bruce Ames once pointed out that plants evolved to make chemicals that are toxic to insects and other animals that might eat them, or to ward off infections by bacteria, yeast, and other organisms.21 Many of these chemicals are natural carcinogens when tested, but, as Ames pointed out, we have evolved multiple detoxification mechanisms to protect us. It is possible that some of these plant-made agents will slip through our defenses. And we have also altered the chemical content of the foods we eat, especially fruits and vegetables, by selective breeding for many characteristics, such as sweetness, that could increase the natural carcinogens.

  Here are a few examples of potential harms:

  Too much spinach. This green leafy vegetable is a healthful, versatile plant. You can eat it raw in salads, use it as a bed for salmon, or sauté it as a side dish. But spinach is quite high in oxalates. The kidneys can turn these naturally occurring acids into kidney stones. The more oxalates consumed, the greater the risk of developing these painful stones.22 This doesn’t mean you should avoid spinach. But if you have had a kidney stone, it would make sense to limit spinach to a few times a week and rely on a wider variety of greens, most of which are lower in oxalates. You might also eat cheese or some other dairy food along with spinach, because these foods reduce the absorption of oxalates.

  Grapefruit juice. This popular juice contains potent compounds that alter the metabolism of many drugs. Depending on the drug, these changes can lead to too much or too little of the drug in the bloodstream (see “Juice” on page 174). If you take medications and you like to drink grapefruit juice or eat grapefruit, talk with your health care provider about possible interactions.

  Brussels sprouts. Many people like the edgy bitterness of this cruciferous vegetable. But this bitterness is sometimes a signal of potentially cancer-causing chemicals. In a pooled analysis of cohort studies, my colleagues and I saw a modest increase in pancreatic cancer among people consuming Brussels sprouts three times a week.23 In a separate analysis, high consumption of Brussels sprouts was also linked to a higher risk of developing high blood pressure.24 If you think about the unusual shape of the Brussels sprout, the tight packages of leaves that we eat emerge from the stalk, which would normally be covered with bark or spines for protection. The fragile sprouts don’t have anything like that, and so turn to a different defense mechanism: chemical warfare. Given what we’ve found, it makes sense to eat this vegetable not more than once a week while we wait for more data.

  As we dig more deeply into the roles of specific fruits and vegetables, I expect to see more of the unexpected. Plants may seem like simple organisms compared to animals, but their biology is complicated!

  PUTTING IT INTO PRACTICE

  There isn’t any magic daily number or combination of fruits and vegetables for optimal health. Instead, I offer two words of advice: “five” and “variety.” Keep in mind that potatoes and corn don’t count for the five-plus servings a day, and that you should count juice as only one fruit serving, even if you drink it two or three times a day.

  Aim for five. The five servings a day used as the goal for national programs turns out to have been a good choice. When it comes to cardiovascular disease and premature death, a large meta-analysis linked higher consumption of fruit and vegetables to a lower risk of dying from any cause. The biggest benefit came from hitting five servings a day.25 Eating more than five servings of vegetables and fruits a day is perfectly fine, but you don’t need to put that high on your priority list.

  In the DASH study described on page 156, the target of nine servings a day was definitely beneficial. But there’s no way to know if five or six or seven servings a day would have done the same thing.

  Eat for variety and for color. Getting five servings of fruits and vegetables a day is important, but variety matters too. On most days try to get at least one serving from each of the following fruit and vegetable categories:26

  • dark green, leafy vegetables

  • yellow or orange fruits and vegetables

  • red fruits and vegetables

  • legumes (beans) and peas

  • citrus fruits.

  Cook your tomatoes. Treat yourself to tomatoes: processed tomatoes or tomato products cooked in oil on most days. Tomatoes are rich in lycopene, a powerful antioxidant that has been linked with lower rates of prostate cancer and memory loss. Because lycopene is tightly bound inside cell walls, your body has a hard time extracting it from raw tomatoes. Cooking breaks down cell walls, and oil dissolves lycopene and helps shuttle it into the bloodstream.

  Fresh is best. Eat several servings of fresh, uncooked fruits and vegetables each week because cooking damages or destroys some important phytochemicals. Vitamin C and folic acid, for example, are sensitive to heat. Otherwise, the physical state of the fruits and vegetables you eat doesn’t much matter. Frozen fruits and vegetables are nearly as good as fresh ones and may even be more nutritious than “fresh” fruits and vegetables that have been stored for weeks or months under conditions that prevent ripening. Canned fruits and vegetables are usually fine, although many come loaded with salt and added sugar.

  THE SPUD IS A DUD

  As I have said earlier, potatoes and corn don’t deserve to be called vegetables in the nutritional sense. Sure, they meet the minimum requirements—they are plants, after all—but the resemblance ends there. When it comes to healthy eating, it’s best to think of potatoes and corn as starches like rice and pasta, since they deliver mostly easily digested starch.

  Fresh Fruits and Vegetables

  * * *

  The freshest produce is what you grow yourself and pick just before you eat it. You don’t need a farm plot or a big suburban backyard to do this. My backyard is only about 40 feet by 20 feet. Yet in that space, not far from busy Harvard Square, my wife and I have a peach tree that yields several bushels of fruit a year, a pear tree, raspberries that bear fruit in both June and October, blueberries, four varieties of grapes, and herbs. We used to grow tomatoes, cucumbers, and greens, but the fruit trees have made the space too shady, so we visit farmers’ markets for these vegetables. Our garden gives us something fresh, tasty, and healthy for at least four months of the year.

  The average American consumes more than 100 pounds of potatoes a year,27 making the spud the most popular “vegetable” in America. (Compare that with about 10 pounds of carrots and 8 pounds of broccoli per person.) Because potatoes are such a huge commodity, they have received special treatment from the USDA and from politicians.

  The potato is one of several starchy vegetables mentioned by name in the Dietary Guidelines for Americans. The USDA has said that batter-coated frozen potatoes—the ones used to make french fries—can be classified as a fresh vegetable.

  Congress even promoted potatoes a few years back when senators from Maine, Idaho, and other potato-growing states, backed by the National Potato C
ouncil, added potatoes to the list of vegetables that could be bought with vouchers from the federal Special Supplemental Nutrition Program for Women, Infants, and Children (WIC). The 2014 omnibus appropriations bill directed the USDA to allow all varieties of fresh, whole, or cut vegetables to be part of the WIC program, which included white potatoes and french fries. That’s just one more example of promoting agribusiness over health.

  More than two hundred studies have shown that people who eat plenty of fruits and vegetables decrease their odds of having heart attacks or strokes, of developing a variety of cancers, or of suffering from constipation or other digestive problems. Yet the same body of evidence shows that potatoes don’t contribute to this benefit and may even contribute to poor health. Here are just two examples:

  In the analysis of long-term weight that I described on page 158, eating fruits in general and vegetables with high fiber and low glycemic load was related to low weight gain over a twenty-four-year period. Eating starchy vegetables such as potatoes, corn, and peas was linked to greater weight gain.

  High blood pressure afflicts millions of Americans, putting them at risk of having a stroke and developing cardiovascular disease. Potatoes are a good source of potassium, which can help reduce blood pressure. They also have a high glycemic load (see page 118), which can boost blood pressure and increase the risk of diabetes. We have shown that higher consumption of potatoes is linked to the development of type 2 diabetes, especially when compared with the same number of servings from whole grains.28

  Juice and Smoothies: No Recipe for Health

  * * *

  Eating fruits and vegetables is unquestionably good for health. Pulverizing them into juices and smoothies isn’t, for two key reasons:

  You will consume extra calories. Ordinary servings of fruits and vegetables tend to be relatively low in calories. Turning them, especially fruits, into juice or smoothies almost always adds calories. Take orange juice as an example. Eating a medium-size navel orange gives you about 12 grams of sugar. A cup of orange juice gives you more than twice that amount of sugar, because you end up drinking the juice from more oranges than you would eat. We also tend to absorb calories more quickly from juice than from whole fruits, because the sugar is locked up inside of cells, which slows down their release into the bloodstream.

  You can overdo it. Kale became a miracle food, lionized by celebrities such as Gwyneth Paltrow, Kevin Bacon, and Bette Midler. This green, leafy vegetable is rich in vitamins K, A, and C, delivers fiber, and more. It is great in salads and soups, and when sautéed makes a wonderful side dish. If a little bit is good, more is better, right? Sadly, no. As a member of the Cruciferae family, kale contains chemicals that can block the formation of thyroid hormone, which helps regulate an individual’s metabolism. Consuming too much kale—hard to do when eating the vegetable but easy to do when drinking kale smoothies—can cause the thyroid gland to slow its production of thyroid hormone. This condition, known as hypothyroidism, can cause symptoms that range from fatigue and increased sensitivity to cold to weight gain, muscle aches and stiffness, thinning hair, depression, and memory loss.

  It’s best to eat fruits and vegetables the way they grow, not concentrated into juice and smoothies.

  To directly evaluate the overall impact of eating potatoes on blood pressure in a contemporary population of Americans, we turned to data from the Nurses’ Health Studies and the Health Professionals Follow-Up Study. Participants on the higher end of the potato-consumption spectrum—baked, boiled, and mashed, and fried—were more likely to have developed high blood pressure.29

  The trade-off of risks and benefits for potatoes, corn, and other starchy vegetables depends on other aspects of diet and lifestyle, especially physical activity. My grandfather was a dairy farmer in Michigan. He was active from sunup to sundown and was as lean as the rails that bordered his fields. He ate potatoes and ate them often. But he was able to tolerate their glycemic load in a way most sedentary Americans can’t today.

  I’m invoking solid evidence when I recommend that most people not eat potatoes often and turn instead to nonstarchy vegetables like carrots, broccoli, and spinach.

  CHAPTER NINE

  * * *

  You Are What You Drink

  “TO YOUR HEALTH.” THAT TRADITIONAL toast captures an essential nugget of nutrition information: what and how much you drink is just as important to your health as what and how much you eat.

  More than half of your body weight is made up of a briny fluid that is similar to the oceans that nurtured primordial life. This fluid bathes, cushions, and lubricates your cells, tissues, and organs. It gives cells their shape and provides their substance. And it forms the watery highways that transport nutrients, wastes, hormones, and other substances throughout your body.

  When it comes to fluids, the constant struggle for survival can be reduced to this: you dry, you die. Your skin, kidneys, nasal passages, and several hormones work together to keep the fluid part of you from drifting off into the air. But preventing water loss isn’t enough. You need to take in enough fluid to carry out a variety of critical metabolic tasks—things like making urine to flush away toxic by-products of digestion and metabolism, maintaining blood volume, and preventing body salts from getting too concentrated, as well as replenishing whatever water you lose.

  The average person uses about a milliliter of fluid for every calorie burned. That’s about 64 ounces for a 2,000-calorie-a-day diet. Exactly how much fluid you need to take in each day depends on you. Your needs are partly genetically programmed and largely determined by diet, the environment, and activity.

  • Diet. If you eat lots of fruits and vegetables, which are mostly water, you may not need to drink as much as someone who eats a lot of meat, bread, or salt. In western Tanzania, people drink much less water than elsewhere in the world because they satisfy much of their daily fluid needs by eating water-rich cooked bananas, which make up a large part of the diet.

  • Environment/weather. When the temperature is perfectly comfortable, you lose about 64 ounces of water a day through your skin, the moist air you exhale, and urine. When it’s “too darn hot,” as Ella Fitzgerald croons, you lose even more. You can also lose extra fluid in the winter, when the relative humidity plummets and the dry air draws water out of your skin.

  Do You Need to Drink Eight 8-Ounce Glasses of Water a Day?

  * * *

  You may have heard or read that you need to drink eight 8-ounce glasses of water a day. That’s a medical myth, one of those “facts” that is repeated so often it gains the ring of truth.1 Where it came from no one really knows. One possible source is the physiological requirement that burning 2,000 calories’ worth of food a day requires about 64 ounces of water. Another is a 1945 report by the National Food and Nutrition Board (under the National Academies of Sciences, Engineering, and Medicine) that included this recommendation: “A suitable allowance of water for adults is 2.5 liters daily in most instances.”2 Two point five liters is a little more than eight 8-ounce glasses. If that’s the source, the next sentence in the report—“Most of this quantity is contained in prepared foods”—has been overlooked or ignored. Recommendations from the same board in 2004 raised the bar to about fifteen 8-ounce glasses of water for men and eleven for women, with more needed during strenuous activity.3

  Some of the fluid your body needs comes from your food. If you eat a lot of fruits, vegetables, and soups, you don’t need to drink as much as someone who eats “drier” foods. The rest comes from what you drink. Water is your best bet, but coffee, tea, juice, soda, sports drinks, beer, and other water-based beverages can also resupply the water you lose.

  • Activity. The more active you are, the more fluid you need. When your muscles burn glucose, they generate heat. As you sit and read these words, some of that heat helps keep your body temperature near 98.6°F. Start scraping old wallpaper off a wall or running around a track and you quickly make more heat than you need. This extra heat must be vente
d or you literally risk cooking the temperature-sensitive proteins that make you you. That’s what sweat does. As sweat forms on your skin and evaporates, it carries heat away from your body. When you are giving your body a real workout, you can lose up to a quart (32 ounces) of fluid an hour.

  Because your body doesn’t have an easy-to-read gauge that tells you when your fluid level is low, several rules of thumb are often offered: Drink when you are thirsty. Drink before you are thirsty. Drink enough so your urine is consistently clear or pale yellow rather than bright or dark yellow. None of these are great guides.

  By the time you feel thirsty, your fluid level can already be low. That’s especially true when you are working or playing hard and losing water quickly. Aging tends to uncouple the sense of thirst from the body’s fluid level, and many older people become dehydrated without realizing it. Urine color is influenced by what you eat and some vitamin supplements.