18.2: Foods are Not Sources of Single Nutrients

Thinking about foods in terms of single nutrients, rather than groups, is a popular way of looking at nutrition in our society, and one which has been carefully fostered by commercial interests. They promote foods that are identified with certain glamorized nutrients.

For example, almost everyone knows that citrus is a good source of vitamin C. So a message used in advertising is that an orange-colored powder which contains vitamin C may be mixed with water and substituted for orange juice. Many consumers don’t realize that other nutrients (e.g., folate) also found in orange juice are absent from this product. In fact, informed consumers know that they don’t have to rely on citrus fruits for their vitamin C. They might get the recommended amount from a number of lesser sources during any given day—possibly a banana, some lettuce, a few cherries, some string beans.

Understanding Foods in Groups

In looking at food composition tables, we see a pattern: Animal flesh—whether beef, chicken, or fish—tends to be high in protein. Fruits, vegetables, and whole grains are generally rich in fiber, vitamins, and certain minerals. Milk is a good source of calcium, riboflavin, and protein. By grouping foods according to this pattern, and recommending numbers of servings from each group, scientists have come up with a simple guide for getting enough of the essential nutrients.

Such a food-group method of diet planning has been set up by the U.S. Department of Agriculture (USDA). In the 1940s, it was the “Basic Seven”—foods were placed in seven groups, each of which was chosen to furnish certain nutrients. This system proved too cumbersome. It was hard for school children and adults alike to get a clear view of seven different food groups, together with the recommended number of servings for each.

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Originally, the USDA grouped foods to plan crops for the needs of the population.

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The concept was periodically modified, most recently to the MyPlate eating guide of five food groups (see Fig. 18-2). This guide is more personalized and interactive: ChooseMyPlate.gov Enter your age, gender, weight, height, and level of physical activity to get an estimate of your calorie needs, the recommended amounts of each food group, and the suggested limits to sodium, saturated fat, and added sugars.

How can our magnificent array of food and the variety of nutrient needs be reduced so simply to a few food groups? A key assumption in selecting a healthful diet by using the food-group method is that from day to day and season to season, we will select differently from each of these groups, so that over a period of time, the nutrient values of many different foods will be balanced to a desirable average.

For this to happen, variety is important. We are assured of some variety by selecting foods from each of the food groups, but it’s also important to choose a variety of foods within each food group.

It should be emphasized that each food is unique in its nutritional profile. For example, if one eats a serving of beef instead of pork, one takes in less thiamin, since pork happens to be an especially rich source. Similarly, one sort of apple or orange, nut or bean differs nutritively from others.

At first glance, the numbers of recommended portions for the Vegetables, Fruits, and Grains Groups may seem high, but the portion sizes are small. For example, ½ cup of spaghetti or rice is 1 Grain portion; it’s not unusual to eat 1½ cups of rice or pasta (3 Grain portions).

What Makes the Guide Work—Or Not Work?

Let’s examine the Vegetables Group for a moment, as an example of how the food-group concept works. Your personalized MyPlate plan might recommend that you eat 2½ portions of vegetables/day. (1 portion = 1 cup cooked or raw vegetables, or 2 cups leafy salad greens).

Most of us don’t eat this many. (Some of us don’t regularly eat any vegetables at all.) Instead of a lot of vegetables, we tend to eat a lot of high-fat/ low-fiber foods, such as meat, cheese, and pastries. This is partly why the American diet tends to be low in fiber and high in calories and fat. The MyPlate eating guide aims to improve this.

Vegetables and fruits are generally low in fat and calories and high in fiber, vitamins, minerals, and phytochemicals (“plant chemicals”). Lycopene, for example, is a phytochemical in tomatoes that may reduce the risk of some cancers. Eating the recommended portions of vegetables—and fruits, grains, protein, and dairy—generally improves our diets. In other words, the food-group method would help nutritionally if it were regularly used.

Figure 18-2: MyPlate Eating Guide

On the other hand, there are flaws in the system. And these flaws suggest the need for nutrition knowledge and planning beyond food groups. For one, there are now thousands of convenience foods in which “basic foods” are combined. How do you place pizza, or chicken-pot pie, or taco salad, in food groups? In many instances, small amounts from various food groups may be present, but not enough to constitute a portion of any one group. But small amounts add up.

Consider a slice of pepperoni pizza. Pepperoni contributes to the Protein Group, but it’s a high-fat meat in a small amount. The crust may be suitable as a portion from the Grains Group (though it’s unlikely to be made from whole grain), and the cheese may scrape through as a portion from the Dairy Group. But what of the tomato sauce? It isn’t a whole vegetable serving, but partial servings can add up over the day.

The MyPlate guide isn’t ideal, but it does steer us towards meeting our nutrient needs. It’s less helpful in steering us away from excesses that may have a bearing on our risk of chronic disease.

Reducing Risk of Chronic Disease

There’s substantial information on how diet affects the risk of such diseases as heart disease, type-2 diabetes, chronic liver disease, and some cancers. We’ve discussed many of these relationships in earlier chapters.

Unfortunately, we’re bombarded with advice from many diverse sources, including advertisements, food labels, diet and health books and websites, sports and fitness magazines, and social media, not all of which is based on scientific evidence. Often, the advice is tied in with products for sale. This—together with a steady stream of news reports of studies that often seem in conflict—can leave us bewildered. What’s the consensus of our nutrition experts?

Dietary Guidelines for Americans

The Dietary Guidelines Advisory Committee, established jointly by the U.S. Department of Agriculture and U.S. Department of Health and Human Services, issues a set of Dietary Guidelines for Americans.¹ These guidelines are directed toward reducing the risk of chronic disease.

Originally published in 1980, they are revised every five years to reflect new scientific knowledge. The 2020-2025 guidelines emphasize concern with increasing prevalence of obesity in children and adults and subsequent increases in chronic diseases like diabetes and heart disease.

Dietary habits are hard to change, so a healthy dietary pattern should start early in life. For example, children younger than age 2 should avoid foods and beverages with added sugar; starting at age 2, added sugar should be limited to less than 10% of total calories. For the complete guidelines, go to DietaryGuidelines.gov

Other Dietary Advice

Many organizations, including the American Heart Association heart.org, American Cancer Society cancer.org, and American Diabetes Association diabetes.org, make dietary recommendations concerning chronic disease. It’s reassuring that the experts from these various groups have come up with remarkably similar recommendations (see Table 18-1), most of them covered by the MyPlate guide and the Dietary Guidelines for Americans.