Good for you, bad for you—or just good?
As professors of human nutrition at Washington State University, Shelley McGuire and Kathy Beerman are always being asked what they eat. At the grocery store, acquaintances have been known to peer into their grocery carts or to try to discreetly hide their own carts.
For the record, McGuire enjoys drinking whole milk. Beerman eats bagels and cream cheese. They don’t care what’s in your shopping cart, and they don’t want to be food police, judging foods good or bad.
“It’s not a judgment I feel comfortable making,” says Beerman. “People should keep health in mind when they eat, but that is a personal decision. Eat the cookie, enjoy it, and let’s move on.”
Maintaining the balance
The science of nutrition is relatively new, and researchers in the discipline have struggled with maintaining a scientific balance in telling us what should be on our plates. The field started in the early 1900s, when scientists began making connections between nutritional deficiencies and diseases. The emphasis was on how to prevent such diseases as scurvy or rickets, which are caused by vitamin deficiencies. Early dietary recommendations derived from an effort to establish what kinds of rations were best for soldiers. In addition to helping to avoid nutrient-deficiency diseases, the recommendations encouraged consumption of the greatest number of calories to ward off malnutrition. An early food pyramid, actually a circle, recommended eating from the following food groups: milk, ice cream, and cheese; butter and fortified margarine; and citrus fruit, tomatoes, and raw cabbage.
By the 1970s, people were living longer, and food was often fortified with vitamins. Diseases such as cancer and heart disease began to gain prominence, and the emphasis in nutrition science changed from preventing nutritional deficiencies to preventing diet-related disease.
The food pyramid
In a recent article in Scientific American, Walter Willett and Meir Stampfer, of the Harvard School of Public Health, argue that the effort to simplify nutrition science has led to flawed dietary recommendations. For instance, the fact that people in industrialized countries eat lots of saturated fats and tend to have a lot of coronary heart disease led to recommendations that we should keep fats to a minimum in our diet, hence their position at the tip-top of the pyramid, the most recent of which was developed in 1992. The pyramid, though, does not distinguish between what science says are the more beneficial unsaturated fats and the more harmful saturated fats found in meat and butter.
Simplifying the science led people to thinking that fat was bad and that carbohydrates were therefore good. Willett and Stampfer argue that no evidence exists to show that people who follow the food pyramid are healthier or live longer. In fact, one epidemiological study showed that after controlling for the effects of exercise and smoking, people who came close to following the food pyramid were no healthier than those who didn’t.
The problem with dietary recommendations is that they haven’t necessarily been based on sound science, says McGuire. People pay close attention to the very personal issue of food and want answers. But science doesn’t necessarily move in an accommodatingly linear way.
The result is that a little science can turn easily into dogma. Even when science later changes course and comes to a different conclusion, it’s hard to re-educate the public.
The problem is often compounded by government agencies and regulations. For instance, one entire government agency, part of the National Institutes of Health, exists solely to battle cholesterol. What happens, McGuire wonders, when we find out that dietary cholesterol isn’t our enemy?
New text, new approach
For their part, McGuire and Beerman are trying to take a balanced approach with a new textbook on nutrition. The challenges of the field require that the new text be more integrated and multidisciplinary than those of the past.
The book, to be published in 2007 by Thomson Wadsworth Publishing, is meant for the approximately 25,000 students who make their way annually through McGuire’s or Beerman’s introductory nutrition class and other courses like it nationwide. These courses, designed for students trying to fulfill their bioscience requirements, require no prerequisites, so most of the students have little science background. At the same time, the text is intended for use in the more scientifically rigorous nutrition course offered to health-related majors, such as those in exercise physiology, nursing, pre-physical therapy, dietetics, and pre-med.
As the science of nutrition has changed in recent years to encompass a variety of research in fields ranging from immunology to biochemistry, textbook authors have generally responded by generalizing and removing some of the specific science. Classic texts were organized by nutrients, with chapters on protein, fats, carbohydrates, and minerals. They also reflected science’s early discoveries that lack of a particular nutrient causes a certain disease. Diabetes was therefore discussed in the chapter on glucose, osteoporosis in the chapter on calcium, and heart disease in the chapter on fats.
But just as nutrition has come to encompass many scientific fields, researchers have increasingly found that one nutrient, or the lack of it, doesn’t necessarily cause disease. Many diseases, such as osteoporosis, heart disease, and cancer, have been found to be related to a variety of factors in the diet.
“How nutrients act together can influence the risk of developing disease,” says McGuire.
In their book, McGuire and Beerman first introduce students to the scientific process, then introduce nutrients and human physiology. A more detailed study of the different types of nutrients follows. The heart of the book is an integrated approach to the study of diseases, including how obesity, heart disease, cancer, and bone health are related to nutrition and diet.
In some ways, McGuire and Beerman wish they could just tie one nutrient with its most closely associated disease.
“It would be easier to do that way,” says McGuire.
Kathy Beerman is currently studying the effect of soy milk on postmenopausal health.
Shelley McGuire studies fat in human breast milk and how it is influenced by diet.