Article
Why and how to prescribe exercise: Overcoming the barriers
To help patients start exercising and stay with it, clinicians should start by writing a prescription.
Although exercise is probably less effective than diet in reducing weight, most studies show that adding it to a diet regimen will increase the weight loss.1,2 Guidelines from the American Heart Association, American College of Cardiology, and Obesity Society recommend a comprehensive lifestyle program that includes a low-calorie diet as well as an increase in physical activity.3
Here, we review the many benefits of exercise for obese patients, not only in terms of weight loss, but also its positive cardiovascular and metabolic effects. Then we discuss how to motivate and prescribe exercise for this challenging group.
EXERCISE IMPROVES WEIGHT LOSS
Increasing energy expenditure by exercising can mobilize and burn stored fat and thus lead to weight loss.4
Typically, with no changes in caloric intake, exercising 60 minutes at low intensity most days of the week will remove up to 0.5 lb per week.5 Exercising harder for longer will take off more weight, up to 3 lb per week.1,6 Some practitioners believe that the total volume of exercise (frequency multiplied by time) is more important than the intensity in determining the amount of weight loss.2,7,8
Ross et al9 randomized 101 obese men to try to lose weight by exercising at a low to moderate intensity, to try to lose weight by dieting, to exercise without the goal of losing weight, or to do nothing (the control group). About half the participants declined or dropped out, but 52 completed the trial. The weight-loss-through-exercise group had lost approximately 15 lb by 12 weeks; the diet group lost a similar amount. Total body fat, visceral fat, and abdominal obesity were all reduced with both diet- and exercise-induced weight loss.
In a study in 130 severely obese adults, after 6 months of high-intensity physical activity for a mean duration of 71 minutes per week, those on an exercise-and-diet regimen lost an average of 24 lb, compared with 18 lb with diet alone.10
Another trial involved obese patients who were instructed to jog the equivalent of 20 miles (32.2 km) a week, with no restriction on caloric intake.11 They lost only 2.9 kg (6.5 lb) over 8 months. Increased food intake explained this minimal weight loss.
In an analysis of 20 studies, exercise-only interventions of 4 months or less resulted in a mean weekly weight loss of 0.4 lb (0.2 kg), with a total loss of about 5 lb (2.3 kg).12
A systematic review of 15 studies noted that aerobic exercise for 3 months or more resulted in a significant reduction in visceral adipose tissue in overweight men and women as measured by computed tomography.13
Effects that different types of exercise have on weight loss
In a study of 119 sedentary adults who were overweight or obese and who were randomized to aerobic, resistance, or combined aerobic-resistance training over 8 months, those involved in aerobic or combined aerobic and resistance training had the greatest reduction in total body and fat mass.14 Given that the combined aerobic-resistance training program required twice the time commitment of the aerobic-alone program, the authors suggested that the most efficient manner of reducing body and fat mass is aerobic training alone.14 In contrast, if the goal is to increase lean muscle mass rather than lose weight and fat, then resistance training would be preferred.14
A meta-analysis confirmed the benefit of aerobic exercise, which resulted in significantly more loss in weight (1.2 kg, 2.6 lb), waist circumference (1.57 cm), and fat mass (1.2 kg, 2.6 lb) than resistance training.15 However, combined aerobic and resistance training was even better, with significantly more weight loss (2.0 kg, 4.4 lb) and fat mass reduction (1.9 kg, 4.2 lb).15
In summary, aerobic and combined aerobic-resistance training appear to be more effective for weight management in obese people than resistance training alone.
ADDITIONAL BENEFITS OF EXERCISE
Increasing regular physical activity through structured exercise has the additional benefits of improving physical fitness, flexibility, mobility, and cardiovascular health.16,17
Even before patients lose a significant amount of weight (eg, 10%), low-intensity exercise such as walking 30 to 60 minutes most days of the week will rapidly improve cardiorespiratory fitness and have positive effects on cardiovascular risk factors such as hypertension, elevated blood glucose, and dyslipidemia.18,19 Aerobic exercise and resistance training also reduce chronic inflammation, which is a strong indicator of future disease, especially in obese patients who have high levels of inflammatory biomarkers.20,21
Even if he or she does not lose much weight, an obese exercising person with good cardiorespiratory fitness has lower cardiovascular risk than a person who is not obese but is poorly conditioned.22
Exercise lowers blood pressure
Overactivity of the sympathetic nervous system is thought to account for over 50% of all cases of hypertension.23 Obesity in concert with diabetes is characterized by sympathetic overactivity and progressive loss of cardiac parasympathetic activity.24 Cardiac autonomic neuropathy is an underestimated risk factor for the increased cardiovascular morbidity and mortality associated with obesity and diabetes, and physical exercise may promote restoration of cardioprotective autonomic modulation in the heart.24
Several studies have shown that aerobic endurance exercise lowers blood pressure in patients with hypertension, and reduction in sympathetic neural activity has been reported as one of the main mechanisms explaining this effect.23 Another mechanism is endothelium-mediated vasodilation: even a single exercise session may increase the bioavailability of nitric oxide and decrease postexercise blood pressure.25
Different types of exercise have been shown to have different effects on blood pressure.
Aerobic training has been shown to reduce systolic blood pressure by 5.2 to 11.0 mm Hg and diastolic blood pressure by 3.0 to 7.7 mm Hg.26
The hypotensive effect of endurance aerobic training is probably mediated at least in part by a reduction in systemic vascular resistance through decreased activity of the sympathetic and renin-angiotensin systems and through improved insulin sensitivity.26 Other factors that may be involved include improved endothelium-dependent vasodilation, enhanced baroreceptor sensitivity, and arterial compliance.26
Dynamic resistance exercise has less of an effect than aerobic exercise, but it has been shown to reduce systolic blood pressure by 0.5 to 4.8 mm Hg and diastolic blood pressure by 0.5 to 4.1 mm Hg.26
In a meta-analysis of studies of resistance training lasting more than 1 month in healthy adults age 18 and older, the authors noted that resistance training induced a significant blood pressure reduction in 28 normotensive or prehypertensive study groups (–3.9/–3.9 mm Hg), whereas the reduction was not significant for the five hypertensive study groups.27
Isometric resistance exercise has been associated with small cardiovascular benefits, but has been shown to reduce systolic blood pressure by 10.5 to 16.5 mm Hg and diastolic blood pressure by 0.62 to 16.4 mm Hg.26
Exercise improves type 2 diabetes
Regular physical activity improves glycemic control and can prevent or delay the onset of type 2 diabetes mellitus.28 Furthermore, physical activity positively affects lipid levels, lowers blood pressure, reduces the rate of cardiovascular events, and restores quality of life in patients with type 2 diabetes.24,29
A meta-analysis of the effect of supervised exercise in adults with type 2 diabetes found that structured exercise achieved the following:
- Lowered systolic blood pressure by 2.42 mm Hg (95% confidence interval 0.45–4.39)
- Lowered diastolic blood pressure by 2.23 mm Hg (1.25–3.21)
- Raised the level of high-density lipoprotein cholesterol by 0.04 mmol/L (0.02–0.07)
- Lowered the level of low-density lipoprotein cholesterol by 0.16 mmol/L (0.01–0.30).30
The metabolic stress from physical exercise can increase oxidation of carbohydrates during exercise, increase postexercise consumption of oxygen (which can increase the rate of fat oxidation during recovery periods after exercise), improve glucose tolerance and insulin sensitivity, and reduce glycemia for 2 to 72 hours depending on the intensity and duration of the exercise.25
Exercise lowers the Framingham risk score
Exercise improves several of the risk factors for coronary artery disease used in calculating the Framingham risk score—ie, systolic blood pressure, total cholesterol, and high-density lipoprotein cholesterol—and thus can significantly lower this number. (It is important to remember that the Framingham score is a surrogate end point of cardiovascular risk that may correlate with a real clinical end point but does not necessarily have a guaranteed relationship.)
In a study of a 12-week exercise program in middle-aged women (ages 40–55), treadmill running for 30 minutes a day 3 days a week significantly reduced 10-year cardiovascular risk scores: 10-year risk 2.2% vs 4.3% in the nonexercising group.31 Others have also shown that enhanced levels of fitness are associated with lower 10-year Framingham risk estimates.32
A study of 31 healthy sedentary adults ages 50 to 65 who were randomized to an unsupervised but pedometer-monitored home-based walking program of 30 minutes of brisk walking 5 days a week noted significant reductions in systolic and diastolic blood pressure and stroke risk, and increased functional capacity in the walking group at 12 weeks.33 Thus, the Framingham risk scores were significantly lower in the exercising group than in with the control group.33
Given that overweight and obese patients who are starting to exercise may find jogging or running daunting, it should also be noted that three brisk 10-minute walks a day are at least as effective as one continuous 30-minute walk in reducing cardiovascular risk in previously sedentary people.34
SETTING ‘SMART’ GOALS
Because obese adults typically do not comply well with prescriptions for exercise, it is important to educate them about its benefits and to provide tools such as perceived exertion scales so they can monitor their exercise, document their performance, and chart their progress; smartphone apps can also be helpful.35 Supervised exercise may improve compliance and results.36 Initially, personal trainers are excellent for starting a habit change, but they are expensive. Virtual trainers are now available and cost far less.37
People do not become obese overnight.They gain weight over a long time. Likewise, weight reduction takes time if done in a sustainable and healthy manner. Thus, SMART goals—specific, measurable, attainable, realistic, timely—should be set to sustain the self-discipline required.
