The Fat Trap (NYT pop review):
Overweight individuals in Western nations (and, increasingly, beyond
) face interpersonal and institutional stigma for their bodies*
. Oftentimes, these stigmas are predicated on the belief that being overweight is a moral failure
, that being overweight is usually a result of laziness, decadence, and/or characterlogical poor impulse control. However, an emerging consensus among obesity researchers points toward strong, common physiological and individual genetic factors
as causative for heightened BMIs in the modern world and the general failure of dieting to produce BMI outcomes. A recent study in the New England Journal of Medicine (paywalled)
adds to this body of evidence, suggesting that chemical messengers held to contribute to altered "efficient" metabolism and increased hunger in the wake of low-calorie dieting are (on average) significantly elevated up to a full year (if not longer) following a substantial drop in weight from dieting.>
Caloric restriction as in dieting has been consistently shown both to decrease basal and activity-induced energy expenditure, leptin, and cholecystokinin and to increase levels of ghrelin and hunger, all of which likely contribute to weight regain. Reductions in energy expenditure have been displayed to persist for up to a year
. This paper is the first to suggest that not only reduced energy expenditure but also deleterious hormonal changes persist far after initial weight loss has taken place. Subjects were originally overweight to obese, had participated in a liquid diet weight-loss plan under medical supervision over a ten-week period and were provided with weight-maintenance advice and nutritional counseling during a 1-year follow-up. On average, subjects did manage to keep some (though not all) of the weight off (avg. -7.9kg, though less when including intention-to-treat group of individuals who did not successfully complete the first weight-loss phase of the study).
These results may help to explain the common finding that most people who diet fail to maintain, regaining some, all, or more weight,
(both paywalled) Some, however, keep their goals, frequently through sustained lifestyle changes
including near-daily exercise, dietary changes (e.g. portion control, wholesale elimination of certain food-groups), and weekly-to-daily weight monitoring
. (Though there is nothing approaching a consensus as to what extent the ability to effect these changes is independent of socioeconomic class, employment, daily time burden, personal history, and the biological factors in question.)
Some additional points and related articles (summarized well in the main link):
- Having lost at least 5kg through dieting in the past may be associated later in life with higher BMI above and beyond the influences of initial BMI and genetic interactions.
- On a population level, BMI may be anywhere from around 40% to 80% inheritable
for modern humans, the latter being the same inheritability as height. Genetic factors appear to influence not just energy intake and reward from eating, but also to what extent caloric content is retained as fat and the efficiency of general metabolism. At least individual 32 genetic loci have been associated with risk for being overweight or obese
, with some possibly operating in a linearly additive manner to explain variance in BMI. One of the most well-studied genetic polymorphisms (FTO: the fat mass and obesity-associated protein) predisposing to higher BMIs is present with at least one gene copy in roughly 65% of the Caucasian and African-American population
, with less prevalence (27-44%) in Asian-American populations.
- Identical twins tend to either over-gain or under-gain weight relative to caloric intake at similar rates in response to controlled overfeeding.
(They also tend toward similar body-weight distribution gain in response to said overfeeding.) Similarly, identical twins show large amounts of homogeneity within pairs in terms of weight loss and metabolic efficiency
* (Such stigma, in fact, may be rather counteproductive
if encouraging weight-loss is the goal of the stigmatizers.)