Peter Janiszewski at Obesity Panacea has posted a fascinating series on the issue of people who are obese but metabolically healthy. We worry about rising rates of obesity because obesity increases the risk for health problems like diabetes and cardiovascular disease — but what if that’s not universally true? And if it turns out that some obese people aren’t at an increased risk of chronic diseases, should they still be urged to lose weight?
The first post in the series introduces the definitions of “obese” and “metabolically healthy”:
To date, 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 ≥ 30 kg/m2) the risk of many diseases increases exponentially.
… Today it is believed that approximately 25-30% of obese individuals ¬remain metabolically healthy (normal blood glucose, blood lipids, blood pressure, and cytokine profile) despite their excess weight.
Janiszewski notes that there are no established criteria for “metabolically healthy,” so studies using different criteria may find different percentages of the obese population to meet this description. It’s also good to keep in mind that while the BMI cutoffs are useful for studying population health (e.g., tracking the percentage of the population with BMIs of 30+), they’re not necessarily the best indicator for determining whether any given individual is at an ideal weight (e.g., athletes may have high BMIs because they have lots of muscle mass, not because they have high body-fat percentages).
With those caveats in mind, what does research tell us about the health of obese individuals with different metabolic health status?
In the second post, Janiszewski describes two studies that divided research subjects into groups based on their BMI categories and the presence or absence of metabolic syndrome. Researchers tracked their subjects for more than a decade and recorded the development of diabetes and cardiovascular disease. Both studies found that subjects who were overweight or obese were not at increased risk for developing CVD; one found no increased risk for diabetes, and the other found obesity in the absence of metabolic abnormalities to be “a relatively weak risk factor” for developing diabetes.
From those two studies, it sounds like an overweight or obese person might be able to stave off health problems by remaining metabolically healthy. Exercise is a great way to reduce the risk of developing metabolic syndrome – so, as some put it, fitness may be just as important fatness.
The third post raises a caution for those of us who might feel justified in hitting the doughnuts after a vigorous workout. Janiszewski talks to researchers Jennifer Kuk and Christopher Ardern, whose study (published recently in Diabetes Care) looked at death rates among the overweight and obese and found that death rates are higher for obese individuals, regardless of whether they’re metabolically healthy or not. (Kuk also notes that they used a more strict definition of “metabolically normal,” which suggests that only about 6% of obese individuals are metabolically healthy.) Kuk reports on what they found about causes of death:
80% of the deaths in the metabolically-healthy obese were due to cancer and ‘other’ causes. Other causes are likely traumatic injuries, which highlights an important point. Obese individuals are less likely to survive a trauma as compared to normal weight individuals despite similar injuries. This is related to longer transport times due to their higher body weight, and difficulty assessing and treating the injuries due to their increased size. Further, they are less likely to see their physicians regularly, which may be in part why cancer is generally diagnosed in obese individuals at later stages. Thus, this study fits in line with the idea that these individuals are not more likely to develop these metabolic diseases, but still die from other causes.
Based on this research, it does sound like everyone who’s obese should be advised to lose weight. But, Janiszewski asks, what if weight loss can actually be detrimental to health? His fourth post describes a study that followed obese women, 20 of whom were metabolically healthy and 24 of whom were deemed metabolically at-risk based on their insulin sensitivity (sensitivity to insulin is good). After a six-month medically supervised weight loss period, in which all women lost significant amounts of body weight, researchers evaluated subjects’ insulin sensitivity. The metabolically at-risk group showed a 26% increase in insulin sensitivity – but, the counter-intuitive finding was that insulin sensitivity in the metabolically healthy subjects actually dropped 13%. This surprising finding has yet to be corroborated, Janiszewski reports, and I’d like to see a study with a larger sample size take on this issue.
Janiszewski’s fifth post describes a study he and his colleagues conducted (which has just been published in Diabetes Care) to examine this same question with a somewhat different study design. They looked at both women and men, used different weight loss intervention (diet alone, exercise alone, and both), and assessed changes in body composition, blood lipids, and other variables. Their 63 metabolically healthy obese subjects and 43 metabolically unhealthy obese subjects engaged in their assigned interventions for 3-6 months. They actually found that insulin sensitivity improved in both groups, and the improvement was similar for the groups using different interventions.
Janiszewski reaches a familiar conclusion: “All obese individuals have something to gain from a modest 5-10% weight loss.” Given that so many people try and fail to achieve sustainable weight loss, though, it’s also helpful to see that regular exercise can reduce the risk of metabolic syndrome and, consequently, the risk of cardiovascular disease and perhaps diabetes. That risk reduction might not translate to longer lives, but it can certainly improve quality of life.
The whole series is well worth a read; you can start here with Part 1.