In 1992 the U.S. Department of Agriculture officially released the Food Guide Pyramid, which was intended to
help the American public make dietary choices that would maintain good health and reduce the risk of chronic disease. The
recommendations embodied in the pyramid soon became well known: people should minimize their consumption of fats and oils
but should eat six to 11 servings a day of foods rich in complex carbohydrates--bread, cereal, rice, pasta and so on. The
food pyramid also recommended generous amounts of vegetables (including potatoes, another plentiful source of complex carbohydrates),
fruit and dairy products, and at least two servings a day from the meat and beans group, which lumped together red meat with
poultry, fish, nuts, legumes and eggs.
Even when the pyramid was being developed, though, nutritionists
had long known that some types of fat are essential to health and can reduce the risk of cardiovascular disease. Furthermore,
scientists had found little evidence that a high intake of carbohydrates is beneficial. Since 1992 more and more research
has shown that the USDA pyramid is grossly flawed. By promoting the consumption of all complex carbohydrates and eschewing
all fats and oils, the pyramid provides misleading guidance. In short, not all fats are bad for you, and by no means are all
complex carbohydrates good for you. The USDA's Center for Nutrition Policy and Promotion is now reassessing the pyramid, but
this effort is not expected to be completed until 2004. In the meantime, we have drawn up a new pyramid that better reflects
the current understanding of the relation between diet and health. Studies indicate that adherence to the recommendations
in the revised pyramid can signif- icantly reduce the risk of cardiovascular disease for both men and women.
How did the original USDA pyramid go so wrong? In part, nutritionists fell victim to a desire to simplify their
dietary recommendations. Researchers had known for decades that saturated fat--found in abundance in red meat and dairy products--raises
cholesterol levels in the blood. High cholesterol levels, in turn, are associated with a high risk of coronary heart disease
(heart attacks and other ailments caused by the blockage of the arteries to the heart). In the 1960s controlled feeding studies,
in which the participants eat carefully prescribed diets for several weeks, substantiated that saturated fat increases cholesterol
levels. But the studies also showed that polyunsaturated fat--found in vegetable oils and fish--reduces cholesterol. Thus,
dietary advice during the 1960s and 1970s emphasized the replacement of saturated fat with polyunsaturated fat, not total
fat reduction. (The subsequent doubling of polyunsaturated fat consumption among Americans probably contributed greatly to
the halving of coronary heart disease rates in the U.S. during the 1970s and 1980s.)
OLD FOOD PYRAMID conceived by the U.S. Department
of Agriculture was intended to convey the message "Fat is bad" and its corollary "Carbs are good." These sweeping statements
are now being questioned.
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The notion that fat in
general is to be avoided stems mainly from observations that affluent Western countries have both high intakes of fat and
high rates of coronary heart disease. This correlation, however, is limited to saturated fat. Societies in which people eat
relatively large portions of monounsaturated and polyunsaturated fat tend to have lower rates of heart disease. On the Greek
island of Crete, for example, the traditional diet contained much olive oil (a rich source of monounsaturated fat) and fish
(a source of polyunsaturated fat). Although fat constituted 40 percent of the calories in this diet, the rate of heart disease
for those who followed it was lower than the rate for those who followed the traditional diets of Japan, in which fat made
up only 8 to 10 percent of the calories. Furthermore, international comparisons can be misleading: many negative influences
on health, such as smoking, physical inactivity and high amounts of body fat, are also correlated with Western affluence.
Unfortunately, many nutritionists decided it would be too
difficult to educate the public about these subtleties. Instead they put out a clear, simple message: "Fat is bad." Because
saturated fat represents about 40 percent of all fat consumed in the U.S., the rationale of the USDA was that advocating a
low-fat diet would naturally reduce the intake of saturated fat. This recommendation was soon reinforced by the food industry,
which began selling cookies, chips and other products that were low in fat but often high in sweeteners such as high-fructose
When the food pyramid was being developed, the typical American
got about 40 percent of his or her calories from fat, about 15 percent from protein and about 45 percent from carbohydrates.
Nutritionists did not want to suggest eating more protein, because many sources of protein (red meat, for example) are also
heavy in saturated fat. So the "Fat is bad" mantra led to the corollary "Carbs are good." Dietary guidelines from the American
Heart Association and other groups recommended that people get at least half their calories from carbohydrates and no more
than 30 percent from fat. This 30 percent limit has become so entrenched among nutritionists that even the sophisticated observer
could be forgiven for thinking that many studies must show that individuals with that level of fat intake enjoyed better health
than those with higher levels. But no study has demonstrated long-term health benefits that can be directly attributed to
a low-fat diet. The 30 percent limit on fat was essentially drawn from thin air.
The wisdom of this direction became even more questionable
after researchers found that the two main cholesterol-carrying chemicals--low-density lipoprotein (LDL), popularly known as
"bad cholesterol," and high-density lipoprotein (HDL), known as "good cholesterol"--have very different effects on the risk
of coronary heart disease. Increasing the ratio of LDL to HDL in the blood raises the risk, whereas decreasing the ratio lowers
it. By the early 1990s controlled feeding studies had shown that when a person replaces calories from saturated fat with an
equal amount of calories from carbohydrates the levels of LDL and total cholesterol fall, but the level of HDL also falls.
Because the ratio of LDL to HDL does not change, there is only a small reduction in the person's risk of heart disease. Moreover,
the switch to carbohydrates boosts the blood levels of triglycerides, the component molecules of fat, probably because of
effects on the body's endocrine system. High triglyceride levels are also associated with a high risk of heart disease.
The effects are more grievous when a person switches from either monounsaturated or polyunsaturated fat to carbohydrates.
LDL levels rise and HDL levels drop, making the cholesterol ratio worse. In contrast, replacing saturated fat with either
monounsaturated or polyunsaturated fat improves this ratio and would be expected to reduce heart disease. The only fats that
are significantly more deleterious than carbohydrates are the trans-unsaturated fatty acids; these are produced by the partial
hydrogenation of liquid vegetable oil, which causes it to solidify. Found in many margarines, baked goods and fried foods,
trans fats are uniquely bad for you because they raise LDL and triglycerides while reducing HDL.
INTERNATIONAL COMPARISONS reveal that total
fat intake is a poor indicator of heart disease risk. What is important is the type of fat consumed. In regions where saturated
fats traditionally made up much of the diet (for example, eastern Finland), rates of heart disease were much higher than in
areas where monounsaturated fats were prevalent (such as the Greek island of Crete). Crete's Mediterranean diet, based on
olive oil, was even better for the heart than the low-fat traditional diet of Japan.
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The Big Picture
To evaluate fully the health effects
of diet, though, one must look beyond cholesterol ratios and triglyceride levels. The foods we eat can cause heart disease
through many other pathways, including raising blood pressure or boosting the tendency of blood to clot. And other foods can
prevent heart disease in surprising ways; for instance, omega-3 fatty acids (found in fish and some plant oils) can reduce
the likelihood of ventricular fibrillation, a heart rhythm disturbance that causes sudden death.
The ideal method for assessing all these adverse and beneficial
effects would be to conduct large-scale trials in which individuals are randomly assigned to one diet or another and followed
for many years. Because of practical constraints and cost, few such studies have been conducted, and most of these have focused
on patients who already suffer from heart disease. Though limited, these studies have supported the benefits of replacing
saturated fat with polyunsaturated fat, but not with carbohydrates.
The best alternative is to conduct large epidemiological
studies in which the diets of many people are periodically assessed and the participants are monitored for the development
of heart disease and other conditions. One of the best-known examples of this research is the Nurses' Health Study, which
was begun in 1976 to evaluate the effects of oral contraceptives but was soon extended to nutrition as well. Our group at
Harvard University has followed nearly 90,000 women in this study who first completed detailed questionnaires on diet in 1980,
as well as more than 50,000 men who were enrolled in the Health Professionals Follow-Up Study in 1986.
After adjusting the analysis to account for smoking, physical
activity and other recognized risk factors, we found that a participant's risk of heart disease was strongly influenced by
the type of dietary fat consumed. Eating trans fat increased the risk substantially, and eating saturated fat increased it
slightly. In contrast, eating monounsaturated and polyunsaturated fats decreased the risk--just as the controlled feeding
studies predicted. Because these two effects counterbalanced each other, higher overall consumption of fat did not lead to
higher rates of coronary heart disease. This finding reinforced a 1989 report by the National Academy of Sciences that concluded
that total fat intake alone was not associated with heart disease risk.
But what about illnesses besides coronary heart disease?
High rates of breast, colon and prostate cancers in affluent Western countries have led to the belief that the consumption
of fat, particularly animal fat, may be a risk factor. But large epidemiological studies have shown little evidence that total
fat consumption or intakes of specific types of fat during midlife affect the risks of breast or colon cancer. Some studies
have indicated that prostate cancer and the consumption of animal fat may be associated, but reassuringly there is no suggestion
that vegetable oils increase any cancer risk. Indeed, some studies have suggested that vegetable oils may slightly reduce
such risks. Thus, it is reasonable to make decisions about dietary fat on the basis of its effects on cardiovascular disease,
Finally, one must consider the impact of fat consumption on obesity, the most serious nutritional problem in
the U.S. Obesity is a major risk factor for several diseases, including type 2 diabetes (also called adult-onset diabetes),
coronary heart disease, and cancers of the breast, colon, kidney and esophagus. Many nutritionists believe that eating fat
can contribute to weight gain because fat contains more calories per gram than protein or carbohydrates. Also, the process
of storing dietary fat in the body may be more efficient than the conversion of carbohydrates to body fat. But recent controlled
feeding studies have shown that these considerations are not practically important. The best way to avoid obesity is to limit
your total calories, not just the fat calories. So the critical issue is whether the fat composition of a diet can influence
one's ability to control caloric intake. In other words, does eating fat leave you more or less hungry than eating protein
or carbohydrates? There are various theories about why one diet should be better than another, but few long-term studies have
been done. In randomized trials, individuals assigned to low-fat diets tend to lose a few pounds during the first months but
then regain the weight. In studies lasting a year or longer, low-fat diets have consistently not led to greater weight loss.
A rapid increase in blood sugar stimulates a large release
of insulin, the hormone that directs glucose to the muscles and liver. As a result, blood sugar plummets, sometimes even going
below the baseline. High levels of glucose and insulin can have negative effects on cardiovascular health, raising triglycerides
and lowering HDL (the good cholesterol). The precipitous decline in glucose can also lead to more hunger after a carbohydrate-rich
meal and thus contribute to overeating and obesity.
In our epidemiological studies, we have found that a high
intake of starch from refined grains and potatoes is associated with a high risk of type 2 diabetes and coronary heart disease.
Conversely, a greater intake of fiber is related to a lower risk of these illnesses. Interestingly, though, the consumption
of fiber did not lower the risk of colon cancer, as had been hypothesized earlier.
Overweight, inactive people can become resistant to insulin's effects and therefore require more of the hormone
to regulate their blood sugar. Recent evidence indicates that the adverse metabolic response to carbohydrates is substantially
worse among people who already have insulin resistance. This finding may account for the ability of peasant farmers in Asia
and elsewhere, who are extremely lean and active, to consume large amounts of refined carbohydrates without experiencing diabetes
or heart disease, whereas the same diet in a more sedentary population can have devastating effects.
Eat Your Veggies
High intake of fruits and vegetables is perhaps the least controversial aspect of the food pyramid.
A reduction in cancer risk has been a widely promoted benefit. But most of the evidence for this benefit has come from case-control
studies, in which patients with cancer and selected control subjects are asked about their earlier diets. These retrospective
studies are susceptible to numerous biases, and recent findings from large prospective studies (including our own) have tended
to show little relation between overall fruit and vegetable consumption and cancer incidence. (Specific nutrients in fruits
and vegetables may offer benefits, though; for instance, the folic acid in green leafy vegetables may reduce the risk of colon
cancer, and the lycopene found in tomatoes may lower the risk of prostate cancer.)
The best way to avoid obesity is to LIMIT YOUR TOTAL CALORIES, not just the fat calories.
The real value of eating fruits and vegetables may be in
reducing the risk of cardiovascular disease. Folic acid and potassium appear to contribute to this effect, which has been
seen in several epidemiological studies. Inadequate consumption of folic acid is responsible for higher risks of serious birth
defects as well, and low intake of lutein, a pigment in green leafy vegetables, has been associated with greater risks of
cataracts and degeneration of the retina. Fruits and vegetables are also the primary source of many vitamins needed for good
health. Thus, there are good reasons to consume the recommended five servings a day, even if doing so has little impact on
cancer risk. The inclusion of potatoes as a vegetable in the USDA pyramid has little justification, however; being mainly
starch, potatoes do not confer the benefits seen for other vegetables.
Another flaw in the USDA pyramid is its failure to recognize
the important health differences between red meat (beef, pork and lamb) and the other foods in the meat and beans group (poultry,
fish, legumes, nuts and eggs). High consumption of red meat has been associated with an increased risk of coronary heart disease,
probably because of its high content of saturated fat and cholesterol. Red meat also raises the risk of type 2 diabetes and
colon cancer. The elevated risk of colon cancer may be related in part to the carcinogens produced during cooking and the
chemicals found in processed meats such as salami and bologna.
HEALTH EFFECTS of the recommendations
in the revised food pyramid were gauged by studying disease rates among 67,271 women in the Nurses' Health Study and 38,615
men in the Health Professionals Follow-up Study. Women and men in the fifth quintile (the 20 percent whose diets were closest
to the pyramid's recommendations) had significantly lower rates of cardiovascular disease than those in the first quintile
(the 20 percent who strayed the most from the pyramid). The dietary recommendations had no significant effect on cancer risk,
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Now let's look at the health effects
of carbohydrates. Complex carbohydrates consist of long chains of sugar units such as glucose and fructose; sugars contain
only one or two units. Because of concerns that sugars offer nothing but "empty calories"--that is, no vitamins, minerals
or other nutrients--complex carbohydrates form the base of the USDA food pyramid. But refined carbohydrates, such as white
bread and white rice, can be very quickly broken down to glucose, the primary fuel for the body. The refining process produces
an easily absorbed form of starch--which is defined as glucose molecules bound together--and also removes many vitamins and
minerals and fiber. Thus, these carbohydrates increase glucose levels in the blood more than whole grains do. (Whole grains
have not been milled into fine flour.)
Or consider potatoes. Eating a boiled potato raises blood
sugar levels higher than eating the same amount of calories from table sugar. Because potatoes are mostly starch, they can
be rapidly metabolized to glucose. In contrast, table sugar (sucrose) is a disaccharide consisting of one molecule of glucose
and one molecule of fructose. Fructose takes longer to convert to glucose, hence the slower rise in blood glucose levels.
Poultry and fish, in contrast, contain less saturated fat
and more unsaturated fat than red meat does. Fish is a rich source of the essential omega-3 fatty acids as well. Not surprisingly,
studies have shown that people who replace red meat with chicken and fish have a lower risk of coronary heart disease and
colon cancer. Eggs are high in cholesterol, but consumption of up to one a day does not appear to have adverse effects on
heart disease risk (except among diabetics), probably because the effects of a slightly higher cholesterol level are counterbalanced
by other nutritional benefits. Many people have avoided nuts because of their high fat content, but the fat in nuts, including
peanuts, is mainly unsaturated, and walnuts in particular are a good source of omega-3 fatty acids. Controlled feeding studies
show that nuts improve blood cholesterol ratios, and epidemiological studies indicate that they lower the risk of heart disease
and diabetes. Also, people who eat nuts are actually less likely to be obese; perhaps because nuts are more satisfying to
the appetite, eating them seems to have the effect of significantly reducing the intake of other foods.
Yet another concern regarding the USDA pyramid is that it
promotes overconsumption of dairy products, recommending the equivalent of two or three glasses of milk a day. This advice
is usually justified by dairy's calcium content, which is believed to prevent osteoporosis and bone fractures. But the highest
rates of fractures are found in countries with high dairy consumption, and large prospective studies have not shown a lower
risk of fractures among those who eat plenty of dairy products. Calcium is an essential nutrient, but the requirements for
bone health have probably been overstated. What is more, we cannot assume that high dairy consumption is safe: in several
studies, men who consumed large amounts of dairy products experienced an increased risk of prostate cancer, and in some studies,
women with high intakes had elevated rates of ovarian cancer. Although fat was initially assumed to be the responsible factor,
this has not been supported in more detailed analyses. High calcium intake itself seemed most clearly related to the risk
of prostate cancer.
Men and women eating in accordance with THE NEW PYRAMID had a lower risk of major chronic disease.
More research is needed to determine the health effects
of dairy products, but at the moment it seems imprudent to recommend high consumption. Most adults who are following a good
overall diet can get the necessary amount of calcium by consuming the equivalent of one glass of milk a day. Under certain
circumstances, such as after menopause, people may need more calcium than usual, but it can be obtained at lower cost and
without saturated fat or calories by taking a supplement.
A Healthier Pyramid
Although the usda's food pyramid has become an icon of nutrition over the past decade, until
recently no studies had evaluated the health of individuals who followed its guidelines. It very likely has some benefits,
especially from a high intake of fruits and vegetables. And a decrease in total fat intake would tend to reduce the consumption
of harmful saturated and trans fats. But the pyramid could also lead people to eat fewer of the healthy unsaturated fats and
more refined starches, so the benefits might be negated by the harm.
To evaluate the overall impact, we used the Healthy Eating
Index (HEI), a score developed by the USDA to measure adherence to the pyramid and its accompanying dietary guidelines in
federal nutrition programs. From the data collected in our large epidemiological studies, we calculated each participant's
HEI score and then examined the relation of these scores to subsequent risk of major chronic disease (defined as heart attack,
stroke, cancer or nontraumatic death from any cause). When we compared people in the same age groups, women and men with the
highest HEI scores did have a lower risk of major chronic disease. But these individuals also smoked less, exercised more
and had generally healthier lifestyles than the other participants. After adjusting for these variables, we found that participants
with the highest HEI scores did not experience significantly better overall health outcomes. As predicted, the pyramid's harms
counterbalanced its benefits.
Because the goal of the pyramid was a worthy one--to encourage
healthy dietary choices--we have tried to develop an alternative derived from the best available knowledge. Our revised pyramid
emphasizes weight control through exercising daily and avoiding an excessive total intake of calories. This pyramid recommends
that the bulk of one's diet should consist of healthy fats (liquid vegetable oils such as olive, canola, soy, corn, sunflower
and peanut) and healthy carbohydrates (whole grain foods such as whole wheat bread, oatmeal and brown rice). If both the fats
and carbohydrates in your diet are healthy, you probably do not have to worry too much about the percentages of total calories
coming from each. Vegetables and fruits should also be eaten in abundance. Moderate amounts of healthy sources of protein
(nuts, legumes, fish, poultry and eggs) are encouraged, but dairy consumption should be limited to one to two servings a day.
The revised pyramid recommends minimizing the consumption of red meat, butter, refined grains (including white bread, white
rice and white pasta), potatoes and sugar.
Trans fat does not appear at all in the pyramid, because
it has no place in a healthy diet. A multiple vitamin is suggested for most people, and moderate alcohol consumption can be
a worthwhile option (if not contraindicated by specific health conditions or medications). This last recommendation comes
with a caveat: drinking no alcohol is clearly better than drinking too much. But more and more studies are showing the benefits
of moderate alcohol consumption (in any form: wine, beer or spirits) to the cardiovascular system.
Can we show that our pyramid is healthier than the USDA's? We created a new Healthy Eating Index that measured
how closely a person's diet followed our recommendations. Applying this revised index to our epidemiological studies, we found
that men and women who were eating in accordance with the new pyramid had a lower risk of major chronic disease. This benefit
resulted almost entirely from significant reductions in the risk of cardiovascular disease--up to 30 percent for women and
40 percent for men. Following the new pyramid's guidelines did not, however, lower the risk of cancer. Weight control and
physical activity, rather than specific food choices, are associated with a reduced risk of many cancers.
Of course, uncertainties
still cloud our understanding of the relation between diet and health. More research is needed to examine the role of dairy
products, the health effects of specific fruits and vegetables, the risks and benefits of vitamin supplements, and the long-term
effects of diet during childhood and early adult life. The interaction of dietary factors with genetic predisposition should
also be investigated, although its importance remains to be determined.
Another challenge will be to ensure that the information
about nutrition given to the public is based strictly on scientific evidence. The USDA may not be the best government agency
to develop objective nutritional guidelines, because it may be too closely linked to the agricultural industry. The food pyramid
should be rebuilt in a setting that is well insulated from political and economic interests.
Walter C. Willett and Meir J. Stampfer are professors of epidemiology and nutrition at the Harvard School of
Public Health. Willett chairs the school's department of nutrition, and Stampfer heads the department of epidemiology. Willett
and Stampfer are also professors of medicine at Harvard Medical School. Both of them practice what they preach by eating well
and exercising regularly.