Why does nutrition advice change?

Nutrition information seems to change daily, leaving most consumers confused. Can sugar harm your heart? Are eggs in or out? Is caffeine good or bad?

The media leap to publicize the latest study, contributing to the confusion. Unfortunately, news stories do not usually investigate the limitations of the research or explain the complexity of the findings. There are a few reasons why the outcomes of nutrition research can be misunderstood or flawed.

We cannot isolate a nutrient’s effect

In the past, nutrition research emphasized the role of a single nutrient acting as a magic bullet to miraculously prevent disease or the sole agent responsible for the development of disease.

We can get so focused on the health benefits of a certain vitamin or phytochemical that we miss an important point:  Different components in a single food can work together to benefit our health, and so can components in different foods eaten together. This is referred to as “food synergy.”

One example of how different nutrients and components in food work together is the pairing of broccoli with tomatoes. In a study published in 2004 in the Journal of Nutrition, prostate tumors grew much less in rats fed tomatoes and broccoli than in rats who ate diets containing broccoli alone or tomatoes alone, or diets that contained cancer-fighting substances (like lycopene) that had been isolated from tomatoes or broccoli.

The bottom line:  A lycopene supplement may not hurt, but the whole tomato will probably help more.  And a tomato eaten with broccoli may be even better. Nutritional relationships are complex and it seems that Mother Nature knew what she was doing when she created plant foods—the natural state is the best package.

Data is flawed

Data collection for nutrition studies is flawed because people do not report accurately in studies relying on this type of data.  We tend to underestimate what we eat, but even more fundamentally, we don’t remember what we ate to report it back.

Additionally when we eat out, we don’t know what ingredients were in the food or how it was prepared. As Marion Nestle, a prominent nutritionist says in her book Food Politics, “The most intellectually demanding challenge in the field of nutrition is to determine food intake.”

Finally, in studies comparing one diet to another, it is not always possible to control what people eat. In a study comparing a group eating a low-fat diet to control group eating typical diet higher in fat, those in the low-fat group cheated and ended up eating a higher-fat diet than the researchers recorded, while those in the control group (normal diet) lowered their fat intake voluntary, perhaps because the study made them aware of it.  In the end, unbeknownst to the researchers, the two groups were not far apart in the amount of fat they were eating. Hence, it was not surprising the “low-fat diet” group didn’t show any health benefits.

Genetics play a role

Another surprising variable in nutritional research is genetic difference among the participants studied. These differences can impact how individuals digest and use nutrients in food. Sometimes, when a study of a nutrient shows a difference only in a small number of people, it could be due to individual metabolic differences. We cannot isolate the metabolism of a food from the entire makeup of the person eating it.

While individual studies may give different data about a particular nutrient, the value of a healthy diet is not in doubt. Repeatedly, studies show good food choices have a positive impact on health and poor diets have negative long-term effects.

Let food be your medicine, to deliver the nutrients you need to perform, maintain function, and fight disease.  American diets that mimic the USDA’s “My Plate” have a lower incidence of major chronic diseases. To look for well-founded nutrition information, visit www.nih.gov and www.eatright.org.

For additional tips, visit www.choosemyplate.gov.

To learn more about nutrition services at Anne Arundel Medical Center, visit AskAAMC.org/nutrition.

Caldwell Shackelford Photo3

By Ann Caldwell and Maureen Shackelford, nutritionists and registered dietitians at Anne Arundel Medical Center. To reach them call 443-481-5555.

Originally published Nov. 16, 2015. Last updated Jan. 23, 2019.

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