Gaining fitness has been shown to reduce the risk of heart disease and early death significantly more than losing weight.

According to an intriguing new study of the links between fitness, weight, heart health, and longevity, exercise is more important than weight loss for improved health and a longer life span, especially if you are overweight or obese. Obese persons who develop fitness rather than lose weight or diet have a decreased risk of heart disease and premature death, according to the study, which looked at the outcomes of hundreds of prior studies of weight loss and exercises in men and women.

The study adds to the growing body of data showing most of us may be healthy at any weight if we are also physically active.

I've written a lot in this column on the science of exercise and weight loss, and a lot of it is depressing if your objective is to lose weight. People who begin to exercise rarely lose much, if any, weight unless they simultaneously significantly reduce their food intake, according to previous research. In general, exercise burns far too few calories to help with weight loss. We also have a tendency to make up for part of the sparse caloric expenditure from exercise by eating more afterward, moving less, or inadvertently reducing our bodies' metabolic operations to minimize overall daily energy expenditure.

Glenn Gaesser, an exercise physiology professor at Arizona State University in Phoenix, is well-versed in the shortcomings of fat-burning regimens. He has spent decades researching the impact of physical activity on individuals's body compositions, metabolisms, and endurance, with a particular focus on obese people. Much of his previous research has demonstrated the futility of weight-loss regimens. For example, in a 2015 experiment he directed, 81 inactive, overweight women began a new regimen of walking for 30 minutes three times a week. A couple of them had lost weight after 12 weeks, but 55 of them had gained weight.

However, in other studies from Dr. Gaesser's lab, overweight and obese people with significant health problems, such as high blood pressure, poor cholesterol profiles, or insulin resistance, a marker for Type 2 diabetes, showed significant improvements in those conditions after they began exercising, regardless of whether or not they lost weight. Following these findings, Dr. Gaesser began to question if exercise may help overweight people maintain good metabolic health, regardless of their body mass, and potentially live as long as slim people — or even longer if the thin people were out of shape.

He and his colleague Siddhartha Angadi, an education and kinesiology professor at the University of Virginia in Charlottesville, began searching research databases for previous studies on nutrition, exercise, fitness, metabolic health, and lifespan. They were particularly interested in meta-analyses, which pool and evaluate data from numerous previous studies, allowing researchers to examine the outcomes of far more people than most individual weight loss or exercise studies, which are typically small-scale.

More than 200 relevant meta-analyses and individual studies were found. Then they set out to explore what all of this research, which included tens of thousands of men and women, the vast majority of whom were obese, had to say about the relative benefits of decreasing weight or getting in shape for enhancing metabolisms and longevity. In other words, scientists wanted to know whether decreasing weight or getting up and moving is better for someone who is overweight.

They discovered that the competition was not close. "When comparing head-to-head, the magnitude of benefit from improving fitness was considerably bigger than the size of benefit from lowering weight," Dr. Gaesser said.

The studies they reference suggest that sedentary, obese men and women who start exercising and improving their fitness can reduce their risk of early death by up to 30% or more, even if their weight does not change. According to Dr. Gaesser, this improvement puts them at a lower risk of early mortality than persons who are regarded to be of normal weight but out of shape.

On the other hand, if obese persons lose weight via dieting (rather than disease), their chance of dying young lowers by roughly 16 percent on average, though not in all studies. According to some of the studies cited in the new analysis, weight loss among obese adults had no effect on mortality risks.