A new study in Cell Metabolism about the benefits of a low-protein diet has some media outlets reporting that a high protein diet is as harmful as smoking. I have been asked by several people to comment on this study, so here is my take.
The study asked subjects to recall what they had eaten in the last 24 hours; that information was then used to establish a dietary pattern that represents how they eat year-round. This is problematic for two reasons. First, the 24-hour recall may or may not accurately represent an individual’s true eating patterns. Second, association does not make for causation–this study explores dietary choices but does not consider all the additional lifestyle factors that account for 95% of the risk of developing chronic disease. These lifestyle factors include foods consumed, foods not consumed, exposure to toxins (such as cigarettes), activity level, socioeconomic status, social and family relationships, physical activity level, and stress. To know what impact animal protein has on mortality, we need to do a randomized prospective trial that controls for these lifestyle factors.
A prospective study starts with an intervention and then follows the subject for a specific period of time after that intervention. For example, the epidemiologic evidence had suggested that taking estrogen after menopause protected the bones, the heart, and the brain. The evidence was very strong, so physicians began prescribing estrogen to post-menopausal women. Yet after the prospective trials for postmenopausal estrogen began, they had to be stopped early because the estrogen group had more heart attacks. So why did the epidemiologic evidence indicate that women taking estrogen did better on so many fronts than the women who did not take estrogen? It turns out that the women who took estrogen in the epidemiologic studies were in a higher socioeconomic class. They had more money, were more likely to exercise, and were more likely to be closer to ideal body weight. In short, it was other lifestyle factors that were influencing risk for health and disease. It is critical that we remember that epidemiologic data that show association is not the same as data that show causation. Rather, the epidemiologic data raise interesting questions or hypotheses that need to be tested prospectively. To understand causation, it is far more useful to look at a prospective study that uses randomized controls, such as “Flavonoid-rich fruit and vegetables improve microvascular reactivity and inflammatory status in men at risk of cardiovascular disease.” In this trial, subjects were randomized and then the intervention group was given 6 servings of vegetables and berries a day. Numerous biologic assessments were made of blood vessel function in both the group that had the intervention as well as the control group that continued their usual eating pattern. The intervention group had healthier measures on many fronts. Researchers were able to conclude that consuming 6 or more servings of vegetables and berries improved blood vessel health and many biologic markers of risk for heart disease. Note that the WAHLS™ Diet plans use 9 servings of vegetables and berries.
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