After introducing the concept of the metabolically healthy obese phenotype earlier this week, we have covered the risk of chronic disease as well as mortality among this large proportion of obese individuals who despite their excess weight remain metabolically healthy. Today we look at the effect of weight loss among such individuals.
While countless epidemiological studies have shown that as you move from a normal weight (BMI = 18.5-24.9 kg/m2) towards overweight (BMI = 25-29.9kg/m2) and obesity (BMI ≥ 30kg/m2) the risk of many diseases increases exponentially, it is also true that approximately 25% of obese individuals are metabolically healthy despite their excess weight. These individuals are also at no greater risk of chronic diseases such as diabetes and cardiovascular disease than their lean counterparts. However, as we learned yesterday, despite being metabolically-healthy obese individuals may still be at greater risk of mortality.
This latter point would indicate that despite suggestions to the contrary, all obese individuals, regardless of their metabolic status should be counseled to lose some weight.
But should they? What if weight-loss among otherwise healthy obese individuals actually makes them unhealthy?
According to a paradoxical study by Karelis and colleagues, otherwise healthy obese women who lose weight via dieting may actually WORSEN their metabolic profile.
In the study, a sample of obese women were divided into either metabolically healthy (20 women) or metabolically at-risk (24 women) based on their level of insulin sensitivity (a marker of diabetes risk – the more insulin sensitive, the better) as measured using the euglycemic-hyperinsulinemic clamp procedure. These women then underwent 6 months of a medically supervised dietary weight loss program consisting of approximately 500-800 calorie reduction in daily food intake.
After the intervention all women lost a significant amount of body weight (approximately 6-7%).
More interestingly, however, while the metabolically at-risk obese women showed a 26% increase in their level of insulin sensitivity, the insulin sensitivity of the metabolically healthy obese women actually deteriorated by 13%!
In other words, by losing weight those obese women who were originally metabolically healthy may have actually increased their risk of diabetes.
This finding is very unexpected, and as of yet has not been corroborated by another study. Nevertheless, it does raise the very intriguing possibility that weight-loss among otherwise healthy obese women may not only unnecessary but, in fact, counter-productive.
This finding falls broadly in line with a recommendation paper by Drs. Arya Sharma and Robert Kushner published in the International Journal of Obesity earlier this year. In that paper the authors proposed a novel obesity classification system which not only assesses weight, but also health complications of excess weight. Germane to the above discussion, Sharma and Kushner recommend that among obese individuals who have “no apparent obesity-related risk-factors” the goal of patient management should be to simply avoid further weight gain, or maintain current weight, rather than to induce weight loss. (To read Dr. Sharma’s full discussion of the new classification system please visit his blog here.)
In essence, the idea that healthy obese individuals may not have much to benefit from weight loss, metabolically speaking, is not that surprising – they are healthy to begin with! However, whether weight-loss may actually be ill-advised for healthy obese individuals needs to be investigated by future studies – until a counter-intuitive finding such as this one is corroborated, many remain doubtful (including me). For example, it remains unknown whether exercise-induced weight loss among healthy obese individuals could also result in metabolic detriment (doubtful). Additionally, we have currently no idea if the above finding also holds true among men.
No idea, until tomorrow, that is.
Tune in tomorrow to read about a study I did during my PhD work in an attempt to resolve this issue.
References and Further Reading:
Karelis, A., Messier, V., Brochu, M., & Rabasa-Lhoret, R. (2008). Metabolically healthy but obese women: effect of an energy-restricted diet Diabetologia, 51 (9),