Editor's note: This popular story from the Daily Briefing's archives was republished on May 12, 2020.
When it comes to diet and weight loss, "even the experts still have widely divergent opinions," Gina Kolata reports for the New York Times. Kolata rounds up "a few certainties about dieting" as well as some of the many unknowns.
While diet studies often have conflicting results, Kolata writes there are a few well-grounded dieting and weight loss facts:
- The diet that works for someone else may not work for you. Experts can't say which diet is the best for weight loss, because people's bodies react to diets in different ways. "Most studies comparing diets have produced results" that show "no difference in weight loss between" groups on different diets "as long as the calorie intake was" the same. As a result, George Bray, an obesity researcher and professor at the Pennington Biomedical Research Center, advises that people "[e]at the diet [they] like and stay with it."
- The latest diet "fad" is nothing new (and so probably nothing magical). It's easy to get caught up in the latest diet trend, but it's also important to know that most of those diets are decades old. For example, Kolata writes low-carb diets were introduced in 1863, while calorie-restricting diets have been around for centuries.
- It's unreasonable to expect conclusive answers from diet studies. Most diet studies are short term (a year or less), which means researchers rarely know if subjects are able to maintain their diets and weight loss over over longer periods of time. As a result, most diet studies lead to "skepticism, argument, and debate," Kolata writes.
- Healthier diets don't always result in weight loss. Diets that revolve around calorie restriction will lead to weight loss, but diets that focus on healthy food consumption are not always low in calories, Kolata writes. The reverse is also true. "[S]ome diets simply are not healthy even if you are shedding pounds," Kolata writes. So how do you know if your current diet is considered "healthy?" Experts say most research supports diets that are high in unprocessed foods, fruits, and vegetables.
Given the limitations cited above, it's no surprise there are several unanswered questions in the diet and weight loss world. Kolata rounds up the four biggest unknowns in the field.
- Why do people have varying responses to diets? Genes might influence diet success, but scientists have been unable to determine whether genes determine a person's response to different diets, Kolata writes. Motivation could also be a factor. "One person may be mentally ready to diet, while another might make only a halfhearted effort," Kolata writes. Other experts think the body's response to carbs could also be a factor. However, studies on the subject have found conflicting results.
- Is there a diet that helps keep the weight off? Unfortunately, there's not yet a tried and proven way to keep weight off. In fact, Kolata reports, after weight loss, the body will lower its metabolic rate to try to regain the fat. David Ludwig of Boston Children's Hospital staged a study to see if low-carb diets help prevent weight gain, but the results failed to determine whether or not it was effective.
- Do sugary foods make people gain weight? While most researchers agree that sugary foods contribute to the obesity epidemic, they are unsure to what extent. And experts are hesitant to claim that sugary foods are more responsible for obesity than other foods like refined grains.
- Why has the obesity epidemic gotten worse? Society has seen a lot of changes, and it's unclear which have contributed to the obesity epidemic and to what extent, Kolata reports. Growing portion sizes, the popularity of restaurants and fast food, and snacking could contribute to societal obesity. Even the decline in smoking, a habit that's tied to lower body weight, could be a contributing factor, Kolata writes (Kolata, New York Times, 12/10/18).
Cheat sheet series: Evidence-based medicine 101
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