by Lisa Ellis
Potatoes, white bread and most pastas are bad, some fats are good, calcium isn't as important as you think, and the U.S. government's supposedly authoritative food pyramid is just plain wrong.
So says "Eat, Drink, and Be Healthy" (Simon & Schuster, August 2001), Harvard Medical School's entry into the bewildering debate over diet and nutrition. The book contends that the U.S. Department of Agriculture's widely reproduced Food Guide Pyramid whose largest component is grain products such as bread and pasta is "built on shaky scientific ground" and distorted by the department's mission to promote agriculture, especially dairy and grain farming.
Instead, Harvard offers the Healthy Eating Pyramid, a guide that author Walter Willett, M.D., Dr. P.H., says should help people navigate through the confusing tangle of diet advice because it is based on decades of accumulated research, not just one or two studies.
In summary, it recommends sharply restricting red meat, potatoes and refined grain products such as white bread; limiting dairy products to one or two servings a day; replacing unhealthy saturated fat with healthier unsaturated vegetable oils; and emphasizing whole grains, fruits and vegetables.
"This book represents an effort to pull together the best available evidence on how diet influences health. Unfortunately, that hasn't been done very often," says Dr. Willett, a professor of medicine at Harvard Medical School and chairman of nutrition at the Harvard School of Public Health. He also is one of the principal investigators of the Harvard-based Nurses' Health Study, one of the largest long-term health studies in the United States.
The USDA pyramid, first published in 1992, ignored the evidence at that time, and subsequent studies have made it even more outdated, Dr. Willett says. (A USDA spokesperson, Jackie Haven, declines comment, saying: "The department has a longstanding policy of not commenting on diet books.")
"There's an inherent problem with the USDA creating the pyramid," Dr. Willett says. "The economic interests are so strong and beef and dairy are the most powerful that I think it's impossible for the USDA to say that people should limit red meat consumption or limit dairy products to one or two servings a day. It's very difficult for them to be objective, so it's probably the worst possible agency to do the pyramid."
Citing both positive and negative research findings about most categories of food and nutrients, the Healthy Eating Pyramid reshuffles the ingredients into a new structure to guide daily eating. Several of the recommendations directly challenge those of the USDA pyramid.
- The Healthy Eating Pyramid puts red meat, butter, potatoes, sweets, white bread, white rice, ordinary pasta and other refined grain products into a tiny compartment at the top, labeled "Use Sparingly."
- The broad foundation of the new pyramid the foods intended to provide the largest portion of daily calories consists of whole-grain foods, such as brown rice and whole-wheat bread, and vegetable oils such as olive and canola. In the USDA pyramid, all grain products are in one category, and people are urged to eat six to 11 servings a day, the most of any food group. The USDA recommends only limited use of all oils, fats and sweets.
- Both pyramids put fruits and vegetables in the middle. The new guide divides protein into categories, emphasizing nuts and legumes, followed by fish, poultry and eggs. It says that adults need only one to two servings of calcium-rich foods not necessarily dairy products or a calcium supplement each day.
- The Healthy Eating Pyramid, which is geared toward adults, also recommends a daily multivitamin "for insurance" and allows alcohol "in moderation" for people who have no history of addiction, depression or certain other medical problems.
Underpinning the entire new pyramid is a lifestyle that includes regular exercise, weight control and awareness of where your calories are coming from.
"You need to pay attention to all forms of calories, fat calories and carbohydrate calories," Dr. Willett says, because all calories can make you gain weight. "If there are unhealthy fats, think about ways to substitute healthy for unhealthy fats." People who are already on low-fat diets might be better off replacing some carbohydrates such as white bread or pasta with healthy fats such as olive oil, he says.
Dr. Willett acknowledges that nutrition research can be confusing when the public hears about it one study at a time. This is because the research unfolds in a rhythm that is "more a cha-cha two steps forward and one step back than a straight-ahead march," he writes. "...Like dropping stones into 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 book, which includes recipes and menus, offers a chapter on how to interpret nutrition research, and it identifies some questions about the health effects of certain foods as still unsettled.
But it states that the evidence is settled enough on these points:
- Refined grains such as white bread and rice should be eaten only in small quantities. These grains are broken down quickly into glucose (sugar), which is followed by a release of insulin so the body can use the glucose for fuel, then quick hunger pangs as the glucose level drops. The digestion of potatoes is similar, although they are now the number one vegetable consumed in the United States. "A constant and heavy demand on the pancreas to make insulin appears to be a key ingredient for adult-onset diabetes ... especially when paired with lack of exercise."
- Whole grains, especially if they are intact or coarsely ground, avert the glucose roller-coaster effect because they are digested much more slowly. They provide more nutrients than refined grains and may help protect against diabetes, heart disease and several forms of cancer.
- "Some fats are good for you, and it is important to include these good fats in your diet." Specifically, eating unsaturated fats found in most vegetable oils, nuts and fatty fish instead of saturated fats such as butter and animal fats can reduce low-density lipoproteins ("bad" cholesterol) and help to protect against coronary heart disease, erratic heartbeats and blood clots. Trans-fatty acids, found in many hard margarines and baked goods containing partially hydrogenated vegetable oils, should be avoided because they increase the risk of heart disease. Research connects excess weight, not overall fat consumption, to some forms of cancer, and people on low-fat, high-carbohydrate diets tend to regain the weight.
- It is not clear how much calcium people need. Worldwide, consumption varies, and countries with average higher calcium intake tend to have higher rates of hip fractures. There is little proof that boosting calcium to currently recommended levels will prevent fractures, the principal complication of osteoporosis, the "brittle bones" disease that is found mostly in older women. But exercise, certain medications, Vitamins D and K and sometimes hormone replacement can help to prevent fractures. There is some evidence that high levels of calcium may be associated with prostate and ovarian cancers.
- Protein itself does not appear to be related to rates of heart disease, cancer or diabetes, and it is digested slowly so it does not trigger sharp increases in blood sugar. Red meat should be restricted because it tends to include more saturated fat than other protein sources.
- Eating many and varied fruits and vegetables can decrease the risk of heart attack or stroke, protect against many forms of cancer, lower blood pressure, and guard against certain intestinal and eye diseases. Variety is important, because these foods include many micronutrients whose value scientists still are discovering. A vitamin pill is recommended only as insurance, not a substitute. A glass of fruit juice can add nutritional value to a diet, but consuming more than a glass per day can contribute to excessive calories.
Dr. Willett, whose family have been Michigan dairy farmers for generations, acknowledges that children need more calcium than adults, but probably not a lot more. "If the child really likes milk, having two or three glasses a day is OK, but I wouldn't beat them over the head to drink milk," he says. One- or two-percent milk is best for children under age 5, who need the calories, he says.
The recommendations of the book are likely to be controversial in some circles, Dr. Willett says, but he thinks it is time people acknowledge that the weight of evidence justifies changing the conventional wisdom about healthy eating.
"I think within the nutrition community there are a lot of people who would acknowledge there are problems with the [USDA] dietary pyramid but are reluctant to admit it," he says. "There's this sense that we must be consistent no matter what the evidence says, and that gets us into trouble ... But a tremendous number of people have tried the pyramid for weight reduction and found that it failed."