This scientiﬁc uncertainty is not overly surprising given that humans eat so many different foods. For any individual, the health effects of diets are modulated by genetics but also by education and income levels, job satisfaction, physical ﬁtness, and the use of cigarettes or alcohol. To simplify this situation, researchers typically examine the effects of single dietary components one by one.
Studies focusing on one nutrient in isolation have worked splendidly to explain symptoms caused by deﬁciencies of vitamins or minerals. But this approach is less useful for chronic conditions such as coronary heart disease and diabetes that are caused by the interaction of dietary, genetic, behavioral and social factors. If nutrition science seems puzzling, it is because researchers typically examine single nutrients detached from food itself, foods separate from diets, and risk factors apart from other behaviors. This kind of research is “reductive” in that it attributes health effects to the consumption of one nutrient or food when it is the overall dietary pattern that really counts most.
For chronic diseases, single nutrients usually alter risk by amounts too small to measure except through large, costly population studies. As seen recently in the Women’s Health Initiative, a clinical trial that examined the effects of low-fat diets on heart disease and cancer, participants were unable to stick with the restrictive dietary protocols. Because humans cannot be caged and fed measured formulas, the diets of experimental and control study groups tend to converge, making differences indistinguishable over the long run—even with fancy statistics.
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Marion Nestle is Paulette Goddard Professor in the department of nutrition, food studies and public health and professor of sociology at New York University. She received a Ph.D. in molecular biology and an M.P.H. in public health nutrition from the University of California, Berkeley. Nestle’s research focuses on scientiﬁc and social factors that inﬂuence food choices and recommendations. She is author of Food Politics (2002, revised 2007), Safe Food (2003) and What to Eat (2006). She also writes a popular nutrition blog, Food Politics.
Reprinted with permission. Copyright © 2007 by Scientific American, a division of Nature America, Inc. All rights reserved. For more information about the issue, go to: http://www.scientificamerican.com/article.cfm?id=eating-made-simple