Publicity about the recently released results from the Women's Health Initiative (WHI) on lowfat diets is a good example of the confusion the media causes when headlines seem to contradict earlier research results and common sense. Some of the media reports on the WHI study said that lowfat diets have no effect on disease risk. Such gross oversimplifications may capture the reader's attention, but they too often undermine a person's determination to practice healthier eating and living habits.
Part of the problem is that people now know that their diet and lifestyle habits have a major impact on their health. Consequently, we want answers on how to live more healthfully. It's frustrating to hear "we don't know yet." But it is a mistake to take the most recent reported study as the sole authoritative source of knowledge. If you do, you may think that health advice is constantly changing when new reports appear. True scientific progress doesn't come in single giant leaps. It's more like putting a puzzle together, one piece at a time.
Different types of studies have different strengths and weaknesses. Laboratory and animal studies help us to see how a potential dietary influence, like a vitamin or phytochemical, might work. But these studies don't show if it will work that way in people. Randomized controlled studies provide answers on the short-term effects of dietary or lifestyle practices in humans, but they don't tell us whether people can achieve the same results on their own. Large epidemiological studies try to track people's diets and health outcomes years later, but they depend on how accurately people can remember and record what and how much they really ate or did. Other studies can describe what happens when people are given instructions to follow a certain diet or exercise routine, but they can't determine what the diet or routine can really do.
Furthermore, we don't eat single foods or nutrients. Our food choices interact inside our bodies, and it's not easy to tell what part of the diet is responsible for what effect. Conclusions can also change drastically, if factors like weight, exercise, smoking, family history and supplement use are either accounted for in analyses or overlooked. In addition, studies of a few months or even years can't fully answer questions about health problems like cancer and heart disease that develop over 10 to 20 years or more.
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To use science as a guide to healthy living, think like a scientist. Don't expect black-and-white answers that label a food "good" or "bad." Your whole diet almost always matters more. Realize that when a study shows no effect, it doesn't mean there isn't one. Variables like too short a study time, inaccurate data collection, or too few people observed may have influenced the results. Consequently, never make changes in your eating or lifestyle based on the results of one study. Consider the weight of evidence from many different kinds of studies. Lastly, remember that any change can have multiple effects on your health good or bad. For example, losing excess weight will boost your overall health.
Science can't yet explain in detail why a healthy diet and lifestyle work. But we have a good idea of what habits best promote health. First, eat a mostly plant-based diet in reasonable portions with limited amounts of saturated fat. Second, limit your salt and alcohol intake, if you choose to drink at all. Third, exercise regularly and maintain a healthy weight. These are excellent habits that should bring you a variety of health benefits.