2. These same individuals also seem to be at the same relative risk of diabetes and cardiovascular disease as equally healthy, but lean individuals.
3. Nevertheless, despite being metabolically healthy, some evidence suggests that excess weight may put such obese individuals at risk for early mortality due to other, non-metabolic, factors.
4. This latter point would imply that all obese individuals should be encouraged to lose weight, despite their metabolic health. This, in fact, is in line with guidelines developed by leading health authorities which currently recommend weight reduction as the primary treatment strategy for all obese patients, regardless of metabolic health. However, as we learned yesterday, weight loss via caloric restriction among metabolically healthy obese may actually result in a deterioration in insulin sensitivity, thereby increasing risk of developing type-2 diabetes.
Now, as most of you know, when a completely counter-intuitive finding like this comes along, where even the study authors fail to come up with a plausible mechanism, it is up to other researchers to follow up with additional research to either corroborate or refute this original finding.
Because I am personally drawn to paradoxical and counterintuitive findings in science, I was very intrigued by the findings of Karelis and colleagues and decided to follow up their study, but include a few variations:
a) Since the study of Karelis et al. only used female subjects, we wanted to ensure this wasn’t due to a gender effect and thus included both men and women.
b) Additionally, to test the possibility that their finding was driven only by modality of weight loss (caloric restriction, in their case) we employed a number of weight loss interventions (diet alone, exercise alone, and the combination of diet and exercise).
c) Finally, while the original study only looked at insulin sensitivity, we decided to assess changes in other variables of interest (body composition, blood lipids, glucose and insulin levels, etc.).
In our study, which has just been published in the prestigious journal, Diabetes Care, a total of 63 metabolically-healthy obese men and women and 43 metabolically-unhealthy obese men and women participated in 3-6 months of exercise and/or diet weight-loss intervention.
And what did we find?
First, body weight, waist circumference, and total and abdominal fat mass were significantly reduced in all subjects – regardless of gender, modality of weight loss, and metabolic status.
Second, in contrast to the findings of Karelis et al., insulin sensitivity IMPROVED after weight loss in both the metabolically-healthy (by about 20%) and metabolically-unhealthy obese individuals. However, the improvement was greater in the metabolically-unhealthy subjects. See figure below.
Importantly, this improvement was similar across all weight loss modalities. In other words, dietary caloric restriction did not have a unique negative effect on insulin sensitivity.
Finally, while the metabolically-unhealthy obese individuals also showed improvement in numerous other outcomes (triglycerides, fasting glucose and insulin, HDL-cholesterol, and total cholesterol), a reduction in fasting insulin was the only other metabolic improvement among the metabolically-healthy obese. This latter finding is not surprising given the normal baseline levels of most metabolic risk factors among metabolically-healthy obese individuals. That is, since they were healthy to begin with – they can only get so much healthier after weight loss (ceiling effect).
Thus, we found no evidence of deterioration in metabolic profile among metabolically-obese individuals who lost weight via a lifestyle intervention.
While limited health care resources dictate the need to prioritize high-risk obese individuals for aggressive treatment, to imply that obese individuals who are metabolically healthy should not lose weight may not be the most appropriate public health message. Such a public health message may be particularly misguided at a time when the prevalence of obesity continues to increase, despite a greater public awareness of the benefits of weight loss. In this context, our findings reinforce current recommendations which suggest that all obese individuals should be encouraged to lose 5-10% body weight.
Although a fair number of obese individuals may have a perfect metabolic profile, it appears they may still experience negative consequences of their excess weight. Furthermore, weight loss achieved via lifestyle intervention appears to still bring about some metabolic benefit among previously healthy obese individuals (it certainly doesn’t seem to harm health). Given the numerous non-metabolic benefits of weight loss (mobility, joint problems, psychological status, sexual function, etc.), all obese individuals have something to gain from a modest 5-10% weight loss.
Have a wonderful weekend,
References and Further Reading:
Janiszewski, P., & Ross, R. (2010). Effects of Weight Loss Among Metabolically Healthy Obese Men and Women Diabetes Care, 33 (9), 1957-1959 DOI: 10.2337/dc10-0547