Harvard Enters the Fray
When the goals of human health and the agriculture sector clash, the best mediator may not be the government. So researchers like Walter Willett are stepping to the plate. As an engineer of several influential studies on health and nutrition, Willett has spent decades looking at how our diets affect our health. And now, he has posed a confident challenge to the USDA guidelines, dubbed the "Healthy Eating Pyramid."

Willett's pyramid has few features in common with its counterpart. The two designs share the same shape -- the foods we should eat less of share a small space at the top, and the foods that should be eaten regularly make up the broad base. And both pyramids recommend lots of fruits and vegetables.

But the similarities end there. Weight control (and Willett believes weight is best controlled through exercise, rather than strict caloric limits) makes up the base of Willett's pyramid, providing a common sense reminder that a good diet is necessary but not sufficient for good health.

The new pyramid also reduces what Willett believes is a dangerous reliance on carbohydrates and encourages consumers to choose the healthier options in all food groups. The Healthy Eating Pyramid builds on some fundamental science:

Not all fat is bad. Polyunsaturated and monounsaturated fats (found in vegetable-based oils and fish) improve the ratio of "good cholesterol" (LDL) to "bad cholesterol" (HDL). Not all carbohydrates are good. In fact, refined carbohydrates of the sort found in white rice and white bread, can be very quickly broken down to glucose -- increasing blood sugar levels more than whole grains do.

High intake of starch from refined grains and potatoes are associated with a high risk of type two diabetes and coronary heart disease. On the other hand, a greater intake of fiber is related to a lower risk of these illnesses.

*Red meat raises the risk of diabetes, heart disease, and colon cancer. Poultry and fish, conversely, contain less saturated fat and more unsaturated fat.

The result? A pyramid with a base of regular physical activity and weight control. The next layer up emphasizes whole-grain, high-fiber carbohydrates and healthy fats (like vegetable oils, avocados and nuts). Eating lots of fruits and vegetables is encouraged, along with moderate amounts of nuts and legumes. Fish, poultry and eggs are also OK. At the tip are some traditional nutritional losers, red meat and butter, alongside refined starches and sugars.

Willett's pyramid stands tall in the light of the latest research. As part of the sweeping Nurses' Health Study, which began in 1976 and continues today, Willett's group at Harvard have followed the eating habits of 140,000 people. Using the USDA's own scoring system -- called the Healthy Eating Index -- Willett's team scored how well each participant's diet followed the USDA recommendations. The researchers then developed a similar scoring system to measure how well each participant followed Willett's Healthy Eating Pyramid guidelines.

In December 2002, Willett's team reported that people who followed the new guidelines had significantly reduced risk of chronic disease, compared to people who followed USDA recommendations (see "Diet quality and major chronic disease risk..." in our bibliography). The women who adhered most closely to the USDA pyramid suffer 14 percent less heart disease than those who did not follow them. But women who had diets mirroring the Healthy Eating Pyramid showed a whopping 28 percent less heart disease than people who ate very differently.

Fat: Is the Debate Over?
When the USDA food pyramid was assembled, the average American got about 40 percent of his or her calories from fat, about 15 percent from protein, and about 45 percent from carbohydrates. The "fat is bad" mantra that pervaded popular culture in the 1990s was already out of favor with nutritionists. But the USDA pyramid's simplified advice may have helped maintain the status quo.

Fresh fruits and vegetables are generally nutritional bargains. Photo: Michigan Newswire.

"I don't think anyone is recommending a low-fat diet at this point," says Alice Lichtenstein, Director of Tufts University's Human Nutrition Research Center on Aging. The creators of the USDA food pyramid, she says, made a dangerous oversimplification when they combined all fats at the tip. Scientists had known for decades that saturated fat raises cholesterol levels in the blood. And high cholesterol levels are associated with a high risk of coronary heart disease, which can cause heart attacks and other illnesses that develop from blockage of arteries to the heart.

Studies in the 1960s showed this relationship, but they also showed that polyunsaturated fat reduces cholesterol. And societies in which people eat large amounts of monounsaturated and polyunsaturated fat have lower rates of heart disease. Think Greek: On the island of Crete, where diets contain large amounts of fish and olive oil, the rate of heart disease is lower than in Japan, where fats make up less than ten percent of the caloric intake of the average diet.

Standard dietary advice at that time was to replace saturated fat with polyunsaturated fat, and many researchers believe the halving of coronary heart disease rates in the U.S. during the 1970s and 1980s is a result of the subsequent shift in the American diet.

So why would the USDA endorse the "all fat is bad" canon decades later? In part to simplify, and in part to avoid singling out food products (like beef) that contain lots of unhealthy fats.

Dietary guidelines form the American Heart Association recommended that people get half their calories from carbohydrates and no more than 30 percent from fat, although Willett points out that no studies have shown that there are long-term health benefits associated with a low-fat diet. "The 30 percent limit on fat was essentially drawn from thin air," he wrote earlier this year.

In the Nurses' study, researchers found that eating trans fat increased the risk of heart disease substantially, and eating saturated fat increased it slightly. Eating monounsaturated and polyunsaturated fats decreased the risk.

Possibly the worst consequence of a low-fat diet is the often resulting reliance on carbohydrates. By the time the USDA food pyramid was being developed, studies had shown that when a person replaces calories from saturated fat with an equal amount of calories from carbohydrates, the levels of bad cholesterol and total cholesterol fall, but the level of good cholesterol also falls. The ratio does not change, so there is only a small reduction in heart disease risk. What's more, the change to carb-heavy meals boosts the blood levels of triglycerides (which, when put together in long chains, make fat). Not surprisingly, high triglyceride levels are associated with a high heart disease risk.

Even worse, Willett points out, is a diet that switches from healthy fats to carbohydrates. In this case, bad cholesterol levels rise and good cholesterol levels drop, worsening the ratio. Willett recommends reverting to the old advice. Replace saturated fats with monounsaturated or polyunsaturated fats, he says, and your cholesterol balance will tip in favor of good health.

Both Willett and Lichtenstein recommend shying away from what is perhaps the most insidious fat: trans fat. Found in margarines and fried foods, trans fats raise bad cholesterol and triglycerides while reducing good cholesterol.

And those low-carb, high-protein diets? Even if lean meats are substituted for the more popular saturated fat-laden bacon and burgers, you'd have to eat a lot of vegetables to get enough fiber. An easier route, and one that can be just as low (or lower) in calories, is to balance lean meats with high-fiber whole grains, Willett says.

Jointly with the Harvard School of Public Health and other institutions, Oldways published these "healthy eating pyramids," a set of dietary guides based on the global dietary traditions most closely associated with good health. ©2000 Oldways Preservation & Exchange Trust.

A Pyramid for Every Person?
Willett concedes that his pyramid is designed for the average American diet. What about the millions of Americans -- vegans, diabetics, lactose-intolerants, chocoholics -- who require more specialized advice? Some critics have even charged that the USDA pyramid amounts to "nutritional racism" -- after all, as many as 90 percent of Asian-Americans, and 70 percent of African-Americans, have difficulty digesting the lactose in milk products. Yet the traditional pyramid suggests a healthy diet must include two to three servings of milk or dairy products per day.

Thankfully, scores of nutritionists are working on alternatives. Chances are, there's a pyramid for most anybody. Lichtenstein has been working on a pyramid designed for people over 70. And while her version has many similarities to Willett's, it also takes into account the special nutritional requirements gained with age.

"The dairy group specifically says low-fat or non-fat dairy products," Lichtenstein notes. "Whole milk is nutrient-dense but has a lot of saturated fats." Elderly people can get the needed calcium and protein from low-fat products while reducing overall saturated fat.

Since many older Americans need more fiber, Lichtenstein included a fiber icon in the 70-plus pyramid. "It's supposed to remind people that you get more fiber if you choose whole grain products instead of refined grains, or if you eat an orange instead of drinking orange juice," she says.

The Oldways Preservation and Exchange Trust has devised pyramids for the Mediterranean diet, the Latin American diet, the Asian diet, and the vegetarian diet. All include daily physical activity at the base and emphasize whole grains and healthy fats over refined grains and saturated or trans fats. But each is designed with the lifestyles, dietary preferences (and limitations) of different groups of people.

The Mayo Clinic's Healthy Weight Pyramid emphasizes eating foods with low energy density. Image courtesy the Mayo Clinic.

And in response to the thriving obesity epidemic in the U.S., the renowned Mayo Clinic has issued a Healthy Weight Pyramid designed to encourage weight loss, weight maintenance, and long-term health. Its focus is on foods, like fleshy vegetables and lean meats, that have relatively low calorie densities. The idea here is that you get full on fluff -- water and fiber, for example -- without sacrificing nutrients.

Such pyramids are only valuable, Lichtenstein notes, if people pay attention to them. And in truth, no one can say whether that's the case.

"Before we all come up with different versions of the pyramid, we really need to learn more about what would help people," she says. "I think we don't know enough about what motivates people to make healthier food choices. The current pyramid is one of the most recognized nutrition tools available but I'm not sure people are using it."

Read the fine print on nutrition labels, and you'll see that serving sizes often differ from those endorsed by the USDA - and its Food Guide Pyramid. Image: NIH.

We'd like our diet deliberations to end there, but they don't. Meet the persistent problem of portion size.

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