What Does the Research Say on Weight Loss and Health?

What’s your take on the research evidence saying that weight loss is necessary for good health? I know that the Health at Every Size community claims that the association of obesity with poor health outcomes is likely caused by weight cycling and medical bias rather than fat, and that health-promoting behaviors make a difference independent of weight loss, but it’s so rare to find a doctor who believes this. When doctors nag you to lose weight, where does this fall in the spectrum of sound vs. unsound medical advice?
—Anonymous

What doctors are likely reacting to in this situation is a body mass index (BMI) in the overweight (25 to 29.9 kilograms per square meter) or obese (30 or more kg/m2) range. BMI is simply an equation that relates weight and height. It was developed as a tool for clinical research and is used because height and weight are taken at nearly every doctor’s visit. However, it was never really intended to be applied to individuals. Rather BMI is a way to track weight trends among populations.

Additionally, studies relating weight and health problems such as hypertension and diabetes show association, not causation. The interplay between genetics, epigenetics (changes in how our genes are expressed that can be inherited or changed by our environment), body size, and disease are poorly understood. You can imagine, it would be impossible to randomize study participants to have different BMIs and then see if they develop new health problems, even if you could get an ethics board to approve it (you could not).

To complicate matters further, studies have not typically distinguished between subjects who have overweight and obesity but good metabolic health — no high blood pressure, blood sugar issues, heart disease, fatty liver disease, or changes in cholesterol levels. But a meta-analysis of patients with a BMI of greater than 25 who did not have any metabolic disease and were considered physically fit did not show an increased risk of mortality.

The best evidence for weight loss is in improving existing health concerns like prediabetes and diabetes. Those studies that do show a benefit of weight loss show a benefit with a decrease of as little as 5% to 15% of body weight. In the DiRECT trial, 46% of patients with Type 2 diabetes put their diabetes in remission with weight loss in this range.

In my practice, I advocate a more holistic approach, promoting healthy lifestyle choices and fitness — I recommend 150 minutes of moderate-intensity exercise and two strength-training sessions per week. When weight loss is warranted to address existing health issues, the goal of weight loss does not need to be a “healthy” BMI, but rather improvement in measures of overall health, including blood pressure, blood sugar, liver enzymes, and cholesterol.