Exercise Shown to Beat Out Dieting for Reducing Obesity Risks

Weight loss through dieting has been the principal approach to reducing the elevated mortality and chronic health risks of obese individuals. However, emerging research suggests that physical fitness may play a more important role in managing obesity-related health risks, even without weight loss.

Obesity (defined as a Body Mass Index [BMI] of 30.0 or higher) in the United States has reached epidemic proportions, with one in five children and more than one in three adults struggling with obesity. The condition disproportionately affects minorities and the less educated. Outside the US, obesity has doubled in more than 70 countries since 1980.

Obesity can lead to a myriad of chronic health diseases, including type 2 diabetes, heart disease, chronic pain, and some cancers, and costs the US healthcare system $147 billion a year.

Unfortunately, weight loss is difficult to achieve and even harder to maintain. Over the past 40 years, while Americans have increasingly tried to lose weight, obesity in the country has tripled. Repeated weight-loss efforts are associated with weight cycling (i.e., losing weight and regaining it over and over again). In a Journal of Obesity & Metabolic Syndrome article that examined obesity and weight cycling studies, the author concludes that weight cycling may increase the risk of cardiovascular events and other negative health consequences.   

If it is so difficult to keep weight off, what are overweight and obese individuals to do to reduce their mortality risk?

Researchers set out to address the mortality-risk reduction of intentional weight loss compared to increasing physical activity (PA) or cardiorespiratory fitness (CRF), as well as the impact of weight loss vs. PA on cardiovascular disease markers and published their findings in iScience. 

CRF refers to the body's ability to supply oxygen to the muscles during sustained physical activity. It is measured as the maximum rate of oxygen consumption during exercise of increasing intensity. However, unlike BMI, CRF is difficult and time consuming for practitioners to measure and there are no universally accepted definitions of “fit” and “unfit.”

The researchers noted that results of studies of intentional weight loss (e.g., weight loss from dieting, liposuction, or bariatric surgery) and mortality risk were either inconsistent or inconclusive. However, an examination of data from a number of independent studies showed that increasing either PA or CRF is associated with significant reductions in all-cause and cardiovascular mortality risk.

From meta-analysis of the influence of CRF on the BMI-mortality relationship, the researchers observed that unfit individuals (i.e., low CRF) had a ∼2–2.5 times greater risk of all-cause mortality regardless of BMI. Importantly, unfit normal-weight individuals could be at a higher risk of all-cause mortality than obese individuals. Therefore, physical fitness may be more important to reducing the risks of obesity than weight loss alone.

With few exceptions, researchers noted that increasing PA is associated with a ∼15–50% reduction in all-cause mortality and a ∼15–40% reduction in cardiovascular mortality or events. As an individual improves their CRF (i.e., moving from unfit or low fit to higher fitness), the reduction in all-cause mortality is 30–60% and reduction in cardiovascular mortality is 42–52%. Therefore, overweight and obese adults would benefit the most from strategies to increase PA, which could also increase CRF.

The researchers also looked at studies of weight loss as compared to PA on cardiovascular disease markers such as blood pressure, glycemic control, blood lipids, and vascular function. Analysis of the studies showed that the improvements in the cardiometabolic risk markers from weight loss are generally no greater than exercise without a specific weight-loss target. Ectopic (body) fat, including visceral abdominal fat and fat stores in the liver and other lean tissues, is associated with higher mortality and cardiovascular and other health risks, especially in sedentary obese individuals. Although exercise training typically does not lead to significant reductions in total body fat, it can significantly reduce ectopic fat. This may be the reason exercise is associated with improvements in cardiometabolic risk profiles with little, if any, weight loss. 

The researchers concluded that the weight-centric approach to obesity treatment and prevention has been largely ineffective. A weight-neutral approach with a focus on increasing physical activity and improving CRF (the so-called “fat-but-fit” approach) may be as, or more, effective than a weight-loss-centered approach in reducing the mortality and health risks associated with obesity. Such an approach also could avoid the physical and mental pitfalls of weight cycling.