Dietary Differences Masked by Averages

As the rates of obesity and related health problems, such as type 2 diabetes, continue to rise, the quality of our diets is being increasingly scrutinized by health professionals in both the public and private sectors. The diets of different sociodemographic groups are of particular interest to public health officials because of the disparities among these groups in terms of incidence of certain diseases, like obesity. With better knowledge of the dietary differences associated with gender, education, income, race, and ethnicity, public health officials can identify groups that are particularly vulnerable to poor health and devise appropriate strategies.

Looking at average intakes of dietary components such as fats, cholesterol, and calories across sociodemographic groups shows that the richer, more educated segments of society have better diets, on average, than the poorer and less educated groups. Similarly, the quality of diets tends to increase with age. But assessing dietary differences by comparing average intakes can be misleading. In fact, for many nutrients and other dietary components, most groups meet the intake levels recommended by health authorities. Comparing dietary differences between groups at different intake levels—that is, between the light, moderate, and heavy eaters in these groups—provides a clearer perspective on disparities in diet quality.

High intakes of saturated fats tend to raise blood cholesterol, a risk factor for heart disease. On average, men with less than a high school education consume 2 grams more of saturated fat per day than men with at least some college education. Because 2 grams of saturated fat is about 6 percent of a 21-50 year old male’s recommended daily limit of 32 grams, this difference is not so alarming. What tips the balance is the difference in saturated fat intakes between the heavy eaters in the two education groups. Among the heavy eaters—those in the top 10 percent of intake levels (90th percentile or higher)—men with less than a high school education consume 7 grams or more additional saturated fat per day than do men with some college education. For women, the average difference does give a good indication of the difference in saturated fat intake by education level across the range of intakes. After adjusting for other socioeconomic characteristics, Black men and women consume more cholesterol per day on average than White men and women. The picture is more alarming at higher intake levels where the gap widens for both men and women.

This is a sobering message for nutritionists, dietitians, and other public health professionals. Judging disparities in diet quality based on average intakes alone may be misleading. Many of the disparities in the intakes of energy, fats, and cholesterol are more extreme at the higher, unhealthful levels. Closing these gaps in dietary quality may pose a greater challenge than we realize.