Role of Physical Activity for Weight Loss

Energy balance is a process through which the body attempts to establish homeostasis. Most individuals spend much of their lives in the same weight range without daily focus on caloric intake and output. The two parts of the equation for weight maintenance are energy intake (eating and drinking) versus energy output (nonexercise thermogenesis + exercise). To achieve weight loss, the American Diabetes Association (ADA) (1), American Academy of Clinical Endocrinologists (AACE) (2), and National Academy of Nutrition and Dietetics (3) all recommend exercise as an integral part of any weight loss program. Physical activity and exercise are often used interchangeably. However, correctly defined, physical activity is all movement that creates energy expenditure, whereas exercise is planned, structured physical activity (1).

Research supports the importance of exercise in relationship to improved cardiovascular fitness, insulin sensitivity, glycemic control of type 2 diabetes, blood pressure, and depression scores (1), but does exercise itself contribute to weight loss and maintenance efforts?

The questions addressed in this article are: Does exercise in and of itself improve weight loss efforts outside of dietary restriction? Is there a difference between aerobic training and resistance training in achieving weight loss or weight maintenance? What are the potential explanations for less weight loss than predicted with exercise? When weight loss is achieved through any weight loss intervention program, does exercise contribute to the maintenance of that weight loss?

Does Exercise in and of Itself Improve Weight Loss Efforts?

Many outcomes data have been reported from research studies that have examined exercise alone, exercise plus dietary restriction, or dietary restriction alone to determine strategies for weight loss. The challenge over time is to accurately monitor both sides of the equation as individuals interact in their daily lives.

A systematic review of studies with a minimum of 1-year follow-up (4) suggested that subjects who used exercise alone for weight reduction experienced minimal weight loss. There are two questions that need clarification: 1) Does the drive for homeostasis require greater bouts of exercise than previously recommended to contribute to weight loss? 2) Do individuals compensate for exercise by either eating more or reducing their nonexercise activity thermogenesis?

Thirty-six overweight participants were assigned to either exercise plus calorie restriction or calorie restriction alone to determine whether exercise enhanced weight loss efforts. The calorie deficit remained constant during the 6-month trial. Ten percent weight loss was achieved over 6 months in both interventions without a statistically significant difference in the percentage loss of body fat. However, the exercise group had the added benefit of improved aerobic fitness (5).

In a randomized, controlled trial of 52 obese men (BMI 31.3 ± 2.0 kg/m2), Ross et al. (6) demonstrated a body weight decrease of 7.5 kg over 3 months in the exercise-only group (16 men) that was comparable to that of the calorie-restricted group. Duration of exercise was based on the goal of a daily 700-calorie energy expenditure (∼60 min/day), suggesting that performing exercise greater than the minimum national recommendations for health of 150 min/week may be required to achieve clinically meaningful weight loss.

Donnelly et al. (7) demonstrated weight loss with exercise alone in a group of 141 overweight or obese (BMI 31 kg/m2) men and women in the Midwest Exercise Trial 2. Exercise was supervised for 10 months with an exercise calorie-equivalent reduction of either 400 or 600 calories 5 days per week and a completion rate of 65%. In the completion group, weight losses were 3.9 ± 4.9 and 5.2 ± 5.6 kg, respectively. This demonstrated a clinically significant weight loss for both men and women. However, the amount of activity to achieve this weight loss was again greater than the general exercise recommendations for health.

Weiss et al. (8) demonstrated not only effective weight loss (7% over 16.8 weeks) with exercise alone, but also preservation of lean body mass (LBM) and improvement of maximal oxygen consumption (VO2max) when compared to weight loss with a comparable energy deficit through calorie restriction alone; the latter resulted in both a loss of LBM and a decrease in VO2max. In addition, as with other studies that have demonstrated weight loss with exercise, the amount of exercise was substantial at 7.4 ± 0.5 hours/week.

Longer bouts of exercise have demonstrated a greater contribution to weight loss, both in controlled research trials and through self-reported information collected by the National Weight Control Registry (NWCR) (9–11). The NWCR has reported that 94% of individuals in the registry reported including exercise in their weight loss program (9); weight loss was greater in the group with the greatest physical activity, but this group also reported more dietary restraint (10), and only 1% of participants reported exercise alone for weight loss (11).

Most, but not all, study data indicate that exercise alone plays a very small role in weight loss. A joint position statement of the American College of Sports Medicine and the ADA (12) states that the “recommended levels of PA [physical activity] may help produce weight loss. However, up to 60 min/day may be required when relying on exercise alone for weight loss.”

The 2016 AACE and the AmericanCollege of Endocrinology comprehensive clinical practice guidelines for medical care of patients with obesity (13) include an evidence recommendation for “aerobic training of ≥150 min/week of moderate intensity, with better outcomes with increasing amounts and intensity of exercise.”