A new year, another kerfuffle among experts over the existence of that most elusive of human phenotypes: the person who is both obese and healthy.
Two new studies use widely divergent measures and time frames to explore the oft-observed link between carrying too much fat and developing metabolic disturbance. But the two appear to converge on three general conclusions:
1) The possibility of being both obese and healthy is real.
2) It is the exception, and not the rule.
3) If you're fat and healthy today, time is not necessarily on your side.
One study, published last week in the Journal of Clinical Investigation, finds the glass half full: In a small but meticulously chosen group of healthy obese people, even a controlled run-up in weight did not knock metabolic function off-course.
The other study finds the glass half empty: in a Research Letter to be posted online Tuesday in the Journal of the American College of Cardiology, researchers who followed British functionaries for two decades found that just over half of those who were obese but metabolically healthy at the outset had become metabolically unhealthy by the end. (On a more positive note, 38% remained obese but healthy.)
The results suggest that, for most who are obese, metabolic health -- should they enjoy it -- is but a way-station on the road to type 2 diabetes and its elevated risk of heart attack and stroke. "The natural course of healthy obesity is progression to metabolic deterioration," wrote the authors of the JACC article.
But the latest research does more than caution those carrying a lot of extra fat against procrastination: It also begins to identify factors that appear to provide protection against the development of diabetes and cardiovascular disease in the obese.
Chief among the protective factors identified by one of the studies was the absence of significant fat accumulated in an obese person's liver, said Dr. Samuel Klein of Washington University in St. Louis, senior author of the article that appeared last week in the Journal of Clinical Investigation. Klein and a team of investigators led by Dr. Elisa Fabbrini used levels of fat in the liver to create two groups of obese subjects, defining those with fatty liver above the 10% level as "metabolically unhealthy" at the outset and those with less than 5.6% as metabolically intact.
The researchers then put both groups -- 10 and eight subjects, respectively -- on a controlled fast-food diet that added 1,000 calories a day to their intake and resulted in a weight gain equivalent to about 6% of their starting weight (say, 12 lbs. for a 200-lb. subject).
A battery of tests gauging metabolic function showed that the obese subjects whose livers were free of major liver deposits from the start could gain such weight without significant change in their muscles' and organs' sensitivity to insulin, or increase in their blood pressure or triglyceride levels.
Their livers did become fattier, which suggests that, with continued weight gain over time, these subjects, too, might become unhealthy.
Obese subjects whose livers started out fatty, by contrast, responded to their moderate weight gain with higher blood pressure, an increase in insulin insensitivity, rising triglycerides, and a boost in their levels of "very-low density lipoproteins," which are strongly linked to cardiovascular disease risk.
Finding the factor that spelled the difference between healthy and unhealthy obesity could help physicians identify which obese patients most need to lose weight if they are to head off heart attack or stroke. And, in time, said Klein, it may point to therapies "to break that link" between obesity and metabolic diseases such as type 2 diabetes.
That may be particularly important in light of the discouraging statistics on long-term weight loss -- statistics reflected in the study of British civil servants: of 1,128 subjects who were deemed to be non-obese and healthy at the study's outset, 177 (nearly 16%) had become obese 20 years later, and 101 of those had developed a combination of conditions -- high blood pressure, metabolic disturbance, worrisome cholesterol levels -- that moved them to the "unhealthy" column. Of 181 subjects who started the study in the obese category, only 32 had lost enough weight 20 years later to exit the obese column, and nearly half of those remained unhealthy.