Caloric Restriction With or Without Exercise: The Fitness versus Fatness Debate

From Medicine and Science in Sports and Exercise®

D. Enette Larson-Meyer; Leanne Redman; Leonie K. Heilbronn; Corby K. Martin; Eric Ravussin

Abstract
There is a debate over the independent effects of aerobic fitness and body fatness on mortality and disease risks.

Purpose: To determine whether a 25% energy deficit that produces equal change in body fatness leads to greater cardiometabolic benefits when aerobic exercise is included.

Methods: Thirty-six overweight participants (16 males/20 females) (39 ± 1 yr; 82 ± 2 kg; body mass index = 27.8 ± 0.3 kg·m2, mean ± SEM) were randomized to one of three groups (n = 12 for each) for a 6-month intervention: control (CO, weight-maintenance diet), caloric restriction (CR, 25% reduction in energy intake), or caloric restriction plus aerobic exercise (CR + EX, 12.5% reduction in energy intake plus 12.5% increase in exercise energy expenditure). Food was provided during weeks 1-12 and 22-24. Changes in fat mass, visceral fat, V·O2peak (graded treadmill test), muscular strength (isokinetic knee extension/flexion), blood lipids, blood pressure, and insulin sensitivity/secretion were compared.

Results: As expected, V·O2peak was significantly improved after 6 months of intervention in CR + EX only (22 ± 5% vs 7 ± 5% in CR and −5 ± 3% in CO), whereas isokinetic muscular strength did not change. There was no difference in the losses of weight, fat mass, or visceral fat and changes in systolic blood pressure (BP) between the intervention groups. However, only CR + EX had a significant decrease in diastolic BP (−5 ± 3% vs −2 ± 2% in CR and −1 ± 2% in CO), in low-density lipoprotein (LDL) cholesterol (−13 ± 4% vs −6 ± 3% in CR and 2 ± 4% in CO), and a significant increase in insulin sensitivity (66 ± 22% vs 40 ± 20% in CR and 1 ± 11% in CO).

Conclusions: Despite similar effect on fat losses, combining CR with exercise increased aerobic fitness in parallel with improved insulin sensitivity, LDL cholesterol, and diastolic BP. The results lend support for inclusion of an exercise component in weight loss programs to improve metabolic fitness.

Introduction
Numerous studies have linked increased adiposity[17,32] and reduced physical activity[17] and/or fitness[32,35] to increased risk of cardiovascular disease (CVD) and overall mortality. However, because of the strong link between physical fitness-particularly of aerobic nature-and reduced prevalence of obesity,[35,38] there is debate about the potential independent effects of aerobic fitness and adiposity (i.e., fatness) on CVD and metabolic health risk factors. For example, it is generally recognized that the benefits of increased physical activity on CVD risks include decreased platelet aggregation, enhanced fibrinolysis, decreased susceptibility to malignant ventricular arrhythmias, improved endothelial function, and myocardial oxygen delivery, along with reduced obesity.[12] The detriments of increased fatness, on the other hand, include increased renin-angiotensin system activation,[10] low-grade inflammation,[2,39] and chronic oxidative stress[20] which result in reduced nitric oxide availability, increased vascular tone and arterial stiffening, and increased systolic and pulse pressures.[8,29] Furthermore, both fatness and poor fitness are linked with insulin resistance, elevated blood pressure, and elevated total and low-density lipoprotein (LDL) cholesterol concentrations,[12] all of which improve with weight loss and enhanced fitness. These links are of course complicated by the strong negative relation between fitness and fatness.

Although several large studies[18] including the Nurses Health Study[17] and the Lipid Research Clinic Study[32] have provided evidence supporting independent contributions of both decreased physical activity/fitness and increased fatness on mortality, there are several reports predominately from Blair's group[4,5,23,33,34] suggesting that aerobic fitness can negate the adverse effects of fatness on mortality.[4,33,34] Such results have often been interpreted that reducing fatness is not necessary in light of adequate fitness.[24] The majority of previous studies, however, have been criticized for inclusion of mostly relatively young healthy white individuals rather than a more ethnically representative sample of aging individuals.[38] In contrast, analysis from the Look AHEAD (Action for Health in Diabetes) Trial in a large ethnically diverse sample of overweight individuals with type 2 diabetes found that both fitness and fatness are related to CVD risk factors, but that the strength of the association for fitness versus fatness was different for different risk factors.[38] These results along with a few other trials[3,19] suggest that both fitness and reduced fatness are important for reducing overall morbidity and mortality.

An interesting question still up for debate is whether improvements in fitness or fatness independently alter risk factors for CVD and the metabolic syndrome, particularly during caloric restriction (CR). Prolonged CR increases life span in rodents and other shorter-lived animal species,[36] but the addition of exercise improves average life span but not maximal life span.[16] In humans, CR has been shown to impact several biomarkers of longevity including fasting insulin concentration, body core temperature,[14] DNA damage,[14] and markers of atherosclerosis.[9] It is, however, not known if in a prospective design, the addition of exercise training will yield extra health benefit in the face of similar weight and fat loss. In other words, does CR with or without exercise result in different improvements in cardiometabolic risk factors which could ultimately improve longevity? The purpose of this analysis was to determine whether a deficit by energy restriction or energy restriction plus aerobic exercise that produces equal change in fatness[26] leads to greater cardiometabolic benefits when exercise is included.

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