You are here
November 6, 2019
The Challenges of Communicating about Nutrition Research
By Alison Brown, Ph.D., M.S. and Charlotte Pratt, Ph.D., M.S., RD
National Heart, Lung, and Blood Institute
Communicating nutrition research findings accurately can be a challenge. The nutrition field is constantly evolving. With new studies published daily, we are bombarded with nutrition messages that may seem contradictory at times. One moment, breaking news reveals that nutrient X lowers your risk for disease. The next, a major story might say the opposite. So how do you keep yourself from writing contradictory stories from one week to the next?
Here’s one recent example from the Annals of Internal Medicine. It recommends “that adults continue current unprocessed red meat and processed meat consumption.” These findings contradict conclusions in the U.S. Dietary Guidelines for Americans and other dietary guidance from non-governmental bodies such as the American Heart Association, which advise that most Americans should reduce their intake of red and processed meat. How can different analyses reach such different conclusions?
Imagine all the variations in your diet over the past day, or year, or over your lifetime. Then consider how long it takes to see changes in your body when you change your diet. Nutritional behaviors are complex and variable—even for the same person on the same day. But outcomes are often only meaningful over the long-term.
There are both practical and cost limitations to conducting nutrition studies in people. Many studies, like the one above, are based primarily on observation rather than experimentation. Observational studies can’t directly control for all relevant factors in nutrition—that is, all the variables that go into what, when, and how you eat. (For more, see Understanding Clinical Studies.)
It’s important to consider these “confounding” factors when you’re writing about nutrition research.
What is confounding?
Confounding can be considered a mixing of effects. The effects of a study intervention (e.g., a nutrient) on a given health outcome are mixed in with the effects of an additional factor (or set of factors). That can make it difficult to tease out cause and effect. For example, some studies have found that moderate alcohol consumption is associated with lower risk for cardiovascular disease and type 2 diabetes. But it’s unclear if the lower risk can be fully attributed to alcohol itself, or if it’s due to confounding factors. For example, a Finnish study found that moderate drinkers ate more fish than non-drinkers. That, rather than the alcohol, could be what reduced their risk for cardiovascular disease.
In an observational study, researchers can statistically adjust for some confounding factors. However, some confounding factors may be unknown, unmeasured, or incorrectly defined. It’s crucial for nutrition communicators to present this nuance when writing about nutrition research.
What are some potential confounding factors?
Lifestyle and behavior can be confounding factors in nutrition research. People who eat healthier tend to also have other healthy lifestyle behaviors. They often meet recommended levels of physical activity and sleep. On the other hand, those who eat unhealthy may also have other unhealthy habits. For example, people who eat a lot of fried food may also be more likely to lead a sedentary lifestyle or have diseases or conditions like diabetes or hypertension.
Nutrients themselves can also be confounding factors. Nutrients are essential for health, and nutrient supplements can play an important role in preventing deficiencies—for example, vitamin C supplements for scurvy and iron supplements for anemia. But in many rigorous studies, nutrient supplements have had no effects when tested for complex, chronic health conditions, such as cancer, heart disease, or diabetes. That’s probably because people eat food, not nutrients. Nutrient supplements may lack those unknown nutrients that make particular foods healthy. Different foods and nutrient components (e.g., phytochemicals from fruit and vegetables) can also interact to achieve different effects.
Thus, in nutrition and chronic disease prevention research, it’s often wise to report on studies that focus on ‘diet’ (a cumulation of multiple food components), ‘diet quality’ and ‘dietary patterns’ (e.g., the DASH eating plan) instead of specific nutrients alone (e.g., salt, sugar).
Even though they are not always practical, controlled feeding trials provide an ideal setting for evaluating the effect of a dietary exposure or treatment. In such a trial, a dietary intervention (e.g., supplement or particular dietary pattern) is randomly assigned to study participants. Other factors are controlled, giving researchers greater confidence that any observed effects are due to the intervention. Participants are typically expected to adhere to a controlled diet by consuming all foods provided in a research kitchen. However, these kinds of studies can be costly and are often short-term, with a relatively small number of participants.
Randomized controlled trials are the gold standard for demonstrating cause and effect in medical research, including research on nutrition. Observational studies are most useful for finding associations and generating hypotheses. In developing nutrition recommendations like the U.S. Dietary Guidelines, experts weigh evidence from both observational studies and randomized controlled trials; however, greater weight is placed on trials because they generally have better control over confounding.
If a hot new study conflicts with the Guidelines, ask yourself why.