CHAPTER 6. Physical activity, sedentary behaviour, and obesity Michael Leitzmann Insufficient levels of daily physical utes per week of moderate-intensity a particular threshold. Despite this activity play a potentially major role in physical activity for overweight or issue, some have operationalized contributing to the obesity epidemic obese adults to improve their health, the definition of weight maintenance that currently affects both developed and 200–300 minutes per week for as a change of ≤ 5 lb (≤ 2.3 kg) [4] and developing countries. Therefore, long-term weight loss [1]. Moder- or < 3% of body weight [5], with a physical activity has become a vital ate-intensity activities are those that weight change of > 5% considered part of public health strategies for require 3–6 times as much energy as to be clinically significant [5]. prevention of weight gain, for weight sitting quietly. In 2002, the Institute of This chapter discusses whether loss, and for prevention of weight Medicine of the National Academies physical activity is effective for pre- regain after weight loss. In fact, vir- recommended 60 minutes per day of vention of weight gain, for weight tually all public health agencies and moderate-intensity physical activity loss, and for prevention of weight re- scientific organizations recommend for prevention of unhealthful weight gain after weight loss. This chapter physical activity as part of weight gain [2]. In 2003, the International focuses primarily on adults. management, including but not limit- Association for the Study of Obesity ed to the World Health Organization advocated 40–50 minutes per day Physical activity and prevention (WHO), the United States Centers of moderate-intensity physical ac- of weight gain for Disease Control and Prevention tivity for prevention of obesity, and (CDC), the National Heart, Lung, and 60–90 minutes per day for prevention Primary prevention of obesity begins Blood Institute, the American Heart of weight regain in formerly obese with weight maintenance, not weight 6 CHAPTER Association, the American College individuals [3]. reduction. Long-term observation- of Sports Medicine (ACSM), and the Setting definitions for clinical- al studies of physical activity in re- World Obesity Federation, as well ly significant weight loss has been lation to weight maintenance fairly as several national and regional challenging, in part because health consistently show a relationship guidelines. gains related to weight maintenance between the two. For example, the In 2001, the ACSM issued guide- or weight loss probably operate under prospective Harvard cohorts showed lines recommending at least 150 min- a continuum and are not based on that women and men who reported Chapter 6. Physical activity, sedentary behaviour, and obesity 43 increasing their recreational activity the effect of isolated physical activi- body mass, and therefore it leads to a levels by 23.2 metabolic equivalent ty on weight loss among overweight more desirable effect on overall body (MET)-hours per week (top quin- and obese individuals from random- composition [12]. tile) gained 1.76 lb less (0.8 kg less) ized clinical trials and reported that Moreover, physical activity of within the next 4 years of follow-up 120–240 minutes per week of aero- high intensity leads to more pro- than those who decreased their ac- bic exercise at intensities of 40–85% nounced weight loss than physical tivity levels by 16.3 MET-hours per of maximum heart rate were relat- activity of lower intensity. This is in- week (bottom quintile) [6]. One MET ed to weighted mean differences dicated by pooled data on a compar- is defined as the ratio of the energy in weight of −1.6 kg (95% confidence ison of high-intensity versus low-in- consumed during a specific activity interval [CI], −1.64 to −1.56 kg) for tensity exercise without changes in to the energy consumed while sitting 6-month programmes and −1.7 kg diet during 3.5–12-month periods −1 −1 quietly (3.5 mL O2 kg min ). Sim- (95% CI,−2.29 to −1.11 kg) for 12-month in 317 subjects from four trials, in ilarly, the 15-year Coronary Artery programmes. The authors concluded which the high-intensity-exercise Risk Development in Young Adults that isolated aerobic exercise is not group showed a reduction in weight (CARDIA) Study reported that each an effective weight-loss therapy but of −1.5 kg (95% CI, −2.3 to −0.7 kg) 0.5 hour per day of walking, the most may be effective in conjunction with compared with the low-intensity- popular type of recreational activity diets [10]. exercise group [11]. among adults, was associated with Most recommendations from pub- According to the 2009 ACSM po- 0.15 kg/year less weight gain in men lic health organizations and govern- sition paper, physical activity demon- and 0.29 kg/year less weight gain in ment agencies use both physical ac- strates a dose–response relationship women, with stronger associations tivity and dietary energy restriction for with weight loss, such that < 150 min- noted among those with a larger weight loss. Weight-loss programmes utes per week of moderate-intensi- baseline weight [7]. Taken togeth- vary considerably with respect to the ty physical activity yields minimal er, these long-term epidemiological amount of physical activity used and weight loss, > 150 minutes per week investigations indicate that moder- the level of energy restriction imposed, of moderate-intensity physical activ- ate-intensity physical activity is as- with a greater energy deficit yielding ity results in weight loss of 2–3 kg, sociated with prevention of weight a more pronounced weight loss. Ev- and 225–420 minutes per week of gain. A 2009 position paper from idence suggests that dietary energy moderate-intensity physical activity the ACSM stated that 150–250 min- restriction combined with physical leads to weight loss of 5–7.5 kg [8]. utes per week of moderate-intensity activity results in greater weight loss In addition to the effect of physical physical activity is effective to prevent than dietary energy restriction alone. activity on weight loss, regular exer- weight gain [8]. For example, a Cochrane review cise yields numerous health benefits involving 1049 subjects from 14 trials independent of weight loss, such as Physical activity and weight loss with follow-up of 3–12 months com- improvements in insulin action, blood pared exercise plus diet versus diet lipids, endothelial function, haemo- A negative energy balance brought alone and reported a weight loss of static factors, and blood pressure about by physical activity will lead to −1.1 kg (95% CI, −1.5 to −0.6 kg) in [13]. weight loss, with a greater negative the exercise-plus-diet group versus energy balance resulting in a more the diet-only group [11]. Similarly, Physical activity and prevention pronounced weight loss. Directed pooling the data from 452 subjects of weight regain after weight research on the long-term effect of from five trials yielded a reduction in loss physical activity on weight loss has body mass index (BMI) of −0.4 kg/ been sparse. A 12-month random- m2 (95% CI, −0.7 to −0.1 kg/m2) in Most people are able to lose weight ized controlled trial found a cumu- the exercise-plus-diet group versus but have considerable difficulty lative weight loss of 1.8 kg in men the diet-only group [11]. Physical ac- maintaining weight loss. Physical and 1.4 kg in women for those engag- tivity and dietary energy restriction activity is widely endorsed as being ing in moderate to vigorous activity yield comparable weight loss if they indispensable for long-term weight for 60 minutes per day, 6 days per offer similar amounts of negative maintenance [1] and is frequently week [9]. By comparison, sedentary energy balance. Importantly, energy referred to as a stable predictor of controls gained 0.1 kg (men) and 0.7 kg restriction combined with exercise weight maintenance after weight loss (women) during that period. A recent training is more effective than en- [14]. The evidence for maintenance systematic review and meta-analysis ergy restriction alone for increasing of weight loss is far less abundant examined the available evidence on loss of fat mass and preserving lean than that for initiation of weight loss. 44 A recent systematic review and Intervention studies have consis- Few studies have examined the meta-analysis of randomized con- tently found no effect of resistance effects of resistance exercise on trolled trials on long-term mainte- exercise on reducing body weight [8] prevention of weight gain. One ran- nance of weight loss reported that the or visceral adipose tissue [18]. The domized trial assessed the efficacy combination of physical activity and combination of resistance and aero- of a 2-year strength programme in dietary energy restriction resulted bic exercise may enhance loss of fat 164 overweight and obese pre- in a difference of −1.56 kg (95% CI, mass compared with resistance ex- menopausal women and reported −2.27 to −0.86 kg) in weight regain ercise alone. A recent meta-analysis decreased percentage of body fat compared with controls at 12 months of 15 trials with 741 participants com- (2-year change of −3.68% ± 0.99% [15]. There was no evidence of ef- pared the effect of 2.5–6 months of vs −0.14% ± 1.04% in controls) and fectiveness for interventions involv- aerobic training and resistance train- attenuated intra-abdominal fat (2- ing physical activity only. An earlier ing on weight loss in overweight and year change of 7.05% ± 5.07% vs systematic review that also included obese subjects and reported that com- 21.36% ± 5.34% in controls) [20].