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Exercise can benefit metabolic health in obesity
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Adults with mild to severe obesity can obtain metabolic health benefits with physical activity and healthy fitness behaviors while remaining obese, study data show.
“The most important finding is that you cannot judge your patient’s fitness or health by simply looking at their body weight,” Jennifer L. Kuk, PhD, associate professor in the School of Kinesiology and Health Science at York University in Toronto, told Endocrine Today. “Your patients can be physically active and not lose weight, but it is likely still going to be beneficial for their health. It is important for you and your patient to disconnect success with only what you see on the scale.”
Kuk and colleagues evaluated data on 853 adults from the Wharton Medical Clinic to determine the relationships between fitness and metabolic risk factors in individuals with higher levels of obesity.
BMI levels were categorized as mild obesity (BMI 34.9 kg/m2), moderate obesity (BMI 35 kg/m2 to 39.9 kg/m2) and severe obesity (BMI 40 kg/m2). Age- and sex-specific VO2 max cutoffs were used to define fitness: unfit (< 20th percentile) or fit ( 20th percentile). Participants were divided into six groups based on fitness status and BMI: fit with mild obesity (n = 107; mean age, 51 years; 80.4% women), unfit with mild obesity (n = 151; mean age, 54.8 years; 75.5% women), fit with moderate obesity (n = 60; mean age, 43.9 years; 90% women), unfit with moderate obesity (n = 181; mean age, 53.5 years; 77.9% women), fit with severe obesity (n = 38; mean age, 44 years; 86.8% women) and unfit with severe obesity (n = 316; mean age, 48.5 years; 75% women).
Metabolic profiles were significantly worse in participants with severe obesity regardless of fitness compared with the fit with mild obesity group (P < .05) and the unfit with mild obesity group (P < .05).
Differences in waist circumference between the fitness groups were greater in men (P = .06) and women (P = .0005) in the higher obesity classes. Waist circumference differences reached significance only in women with moderate obesity (fit, 112.1 vs. unfit, 116.5 cm; P = .001) and severe obesity (fit, 119.6 cm vs. unfit, 129.2 cm; P < .0001).
Compared with the mild obesity group, regardless of fitness, the unfit moderate and severe obesity groups had increased RRs for preclinical hypertension, hypertriglyceridemia and hypoalphalipoproteinemia and prediabetes (P < .05).
“We are starting to realize that obesity and weight management is much more complicated and difficult than telling patients to eat less and move more,” Kuk said. “Better work is needed to understand the drivers to obesity-related metabolic conditions and how best to treat them once they are present. Part of that is recognizing that each patient will be unique in how they arrived at their condition, what their goals and circumstances are and how best to treat their condition.
“Part of the issue with obesity management is that we do not yet have the interventions to match the patient expectations for weight loss, and so clearly that is an issue that needs further research,” she said. “However, the other issue is that bias and discrimination that individuals with obesity face and how that may drive them to more drastic and potentially unhealthy weight-loss strategies. Work is also needed on how best to change public opinion on obesity.” – by Amber Cox
For more information:
Jennifer L. Kuk, PhD, can be reached at jennkuk@yorku.ca.
Disclosures: Kuk reports no relevant financial disclosures. One researcher reports he is the founder and an employee of the Wharton Medical Clinic.
Perspective
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Do and colleagues have compared metabolic parameters, such as blood pressure, glucose, triglycerides and HDL cholesterol, between individuals with low and high fitness defined by VO2 max. Furthermore, they have conducted these comparisons within three strata of obesity. It is not clear why the authors did not report data from patients with class I obesity (BMI 30 kg/m2 to 34.9 kg/m2) since there would have been substantial numbers within the study population of 853 patients with obesity followed at the Wharton Medical Clinic in Ontario, Canada. Nevertheless, the authors demonstrated that unfit patients had worse metabolic parameters than fit patients within the class II and class III obesity categories; however, significant differences between fit and unfit were not observed within the overweight category. The authors also found that unfit patients had greater waist circumferences than fit patients within both class II and class III obesity categories, but not within the overweight category. The authors conclude that physical fitness measured by VO2 max is an important determinant of metabolic health in obesity, and they contend that interventions designed to augment VO2 max could be clinically beneficial even in patients with moderate and severe obesity.
Two considerations are relevant to the optimal interpretation of these data. The first is that VO2 max measurements were normalized to total body weight, not fat free mass. The units of VO2 max are milliliters of oxygen consumed divided by kilogram of body weight per minute. Thus, with progressive obesity the volume of oxygen consumption gets divided by a greater denominator of total body weight. The maximum volume of oxygen cosumed was approximately 35 mL/kg body weight per minute in the fit patients across all BMI categories. That means that the fit severe obese were actually more physiologically fit than the fit overweight patients when the amount of oxygen consumed is normalized to fat free mass instead of total body weight. While this makes the data more difficult to interpret, it is still true that when comparing fit and unfit patients with overlapping weights within each of the class II and class III obesity categories, there were still significant differences in metabolic parameters.
The second consideration pertains to insulin resistance. In the course of these comparisons, metabolic traits were only worse when the waist circumference in the unfit patients was elevated compared with fit patients. Waist circumference is a marker of insulin resistance independent of BMI, which suggest that differences in inulin sensitivity are also at play as an explanation for observed differences in metabolic parameters. If VO2 max was a strong determinant of metabolic fitness, why were not metabolic traits improved in fit compared with unfit overweight patients even if waist circumferences were similar? VO2 max, BMI and insulin sensitivity can all vary to an extent independently from one another, and the data indicate that all three factors are playing a role in cardiometabolic disease.
In summary, it appears that VO2 max, BMI and insulin sensitivity are all exerting an effect to exacerbate cardiometabolic disease parameters among patients with obesity. However, the relative contribution of each of these processes cannot be ascertained by this study. Even so, the authors make a valid and important point that increments in physical activity that increase VO2 max would be expected to improve metabolic traits even in patients with severe obesity.
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