What Is A Healthy Diet?

by Wei Perng, PhD

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Last week, I met with a prospective Master’s student wrapping up her B.S. in Nutritional Sciences. She told me about her background in nutrition, her laboratory training, and her desire to conduct nutrition-related research in human populations. I asked her whether there was a particular focus area that piqued her interest and she said, “I feel as though there isn’t a lot known regarding what a healthy diet is supposed to look like for normal people. I’d like to look into that.”

This caught me off guard, especially because the overarching goal of nutrition research is to characterize healthy diets in order to promote health, both for individuals and the broader population. As I thought more about our conversation, it occurred to me that perhaps the issue isn’t a lack of research on what constitutes a healthy diet, but rather that our views on this topic are constantly changing due to new research, and that translating and disseminating those findings to a lay audience is challenging.

The Original Food Pyramid (1992)

Our ever-changing knowledge of a healthy diet. Throughout elementary and middle school, I remember seeing the Food Pyramid prominently displayed on the cafeteria walls. This guide recommended daily servings sizes for 5 major food groups: grains, vegetables, fruits, dairy, and meat/poultry/fish/eggs/nuts. These recommendations were based on dietary guidelines from the 1980s that were designed to combat heart disease, the #1 killer in the U.S. at the time. Epidemiological studies from the 1940s and 50s, like the Seven Countries Study, had identified sodium, cholesterol, saturated fats, and trans fats as culprits.

Despite following the Food Pyramid guidelines for a decade, heart disease rates continued to rise, and by 2000 Americans were consuming approximately 45% more grain products than in the early 1970s. The majority of grains consumed were refined carbohydrates, which quickly break down into glucose, causing the body to release insulin and promote fat storage (see my previous blog post). Very soon, studies linking refined carbohydrates to obesity, diabetes, and cardiovascular disease began to surface (e.g., Liu et al. AJCN 2000; Mann EJCN 2007).

In 2005, the Food Pyramid was flipped on its side to show colorful vertical wedges of the 5 food groups, with the width of the band corresponding with the recommended quantity. The biggest difference between the 1992 and 2005 Food Pyramids was the slightly larger focus on fats (the yellow sliver next to the red “Fruits” wedge), more specific serving sizes, and recommendations to choose lean meats and whole grains over fried or fatty meats and refined grains, respectively. The new pyramid also included a stick figure running up a set of stairs as a reminder of the importance of physical activity.

The Modified Food Pyramid (2005)

Unfortunately, many consumers found this depiction to be confusing, and many others – myself included - were never actually exposed to this version of the Pyramid.

In 2010, the U.S. Department of Agriculture and the Department of Health and Human Services implemented an overhaul of the dietary guidelines. They replaced the Food Pyramid with the Food Plate, which encourages people to dedicate half of their diet to fruits and vegetables, while emphasizing smaller portions over all. Unlike the Food Pyramids, which emphasized specific servings of each food group, the Food Plate shows the relative proportions of food groups on a plate.

The Food Plate (2010)

Nutrition experts at the Harvard School of Public Health subsequently modified the Food Plate, known as the Healthy Eating Plate, to include healthy fats like olive and canola oil, as well as recommendations to choose non-sweetened beverages over sugary ones.

Difficulty in disseminating knowledge to the general public. With the different food guides that have emerged during a 20-year timeframe (and even more versions if you start from the very beginning of the USDA Food Guide history), it’s not difficult to see why people are confused about what a healthy diet looks like. A recent article in the New York Times showed findings from a survey that asked nutritionists and a representative sample of the American electorate what foods are considered “healthy.”  Some foods, such as kale, apples, and oatmeal, were considered healthy by everyone, while other items like French fries and cookies were universally unhealthy. However, there were also several discrepancies. Ordinary Americans -- but not nutritionists -- considered granola bars, frozen yogurt, and meal replacement shakes healthy. At the other end of the spectrum, tofu, sushi, hummus, wine, and shrimp were rated as healthy by nutritionists but not by the public. One reason for these discrepancies may be that the public’s perception of “healthy” is subject to current trends and marketing schemes. For example, granola bars are often stocked with health foods, with sweeping claims on dietary fiber and antioxidants, despite the fact that they often contain as much or more sugar than cookies.

What can be done?

1.   Nutrition education. For starters, it is important not to skimp on nutrition education during primary education, as healthy habits start young.

2.   Nutrition counseling as part of routine health check-ups. Routine well-child, well-woman, and prenatal visits provide excellent avenues for health care providers to provide materials and touch base with their patients on healthful food choices.

3.   Conscious efforts to disseminate research findings to the lay community. Greater efforts to relay research findings to the general public. News releases, popular press articles, and community events are all examples of viable ways to disseminate scientific knowledge to the lay community.