I was reading through my RSS feeds today (oh google reader, what will I do without you) and came across a post by another statistician who had written up some studies she had read recently. I’m going to pull an entire section, including quotes from the study, because it’s important.
Diets don’t work
This one is called “Medicare’s Search for Effective Obesity Treatments: Diets Are Not the Answer” and it was written in 2006 by Traci Mann, A. Janet Tomiyama, Erika Westling, Ann-Marie Lew,Barbra Samuels, and Jason Chatman.
Here’s the abstract:
The prevalence of obesity and its associated health problems have increased sharply in the past 2 decades. New revisions to Medicare policy will allow funding for obesity treatments of proven efﬁcacy. The authors review studies of the long-term outcomes of calorie-restricting diets to assess whether dieting is an effective treatment for obesity. These studies show that one third to two thirds of dieters regain more weight than they lost on their diets, and these studies likely underestimate the extent to which dieting is counterproductive because of several methodological problems, all of which bias the studies toward showing successful weight loss maintenance. In addition, the studies do not provide consistent evidence that dieting results in signiﬁcant health improvements, regardless of weight change. In sum, there is little support for the notion that diets lead to lasting weight loss or health beneﬁts.
There are two things I love about this paper (commenters please take note).
First, since the goal was to understand whether something would be covered under Medicare, the point of the paper is to understand whether a treatment for obesity is effective for the general population, and not for a given individual. Because obesity is considered an illness but not a disease, there’s a pretty high bar for which treatments are considered effective.
Second, I love the way the researchers combed through the existing literature in dieting and explained the systematic bias that exists – the way the studies exclude people for whom dieting doesn’t work, the way they allow biased statistics in, and more. I’m pretty sure this systematic bias is due to the fact that many studies are paid for by commercial dieting plans. That and because people just want positive results. In any case, it’s super refreshing to see a paper written that isn’t telling you misleading stuff you want to hear. Here’s an excerpt:
Of note, studies always report the percentage of participants who manage to keep off some percentage of the lost weight, but only a subset reported on participants for whom the diet was counterproductive, even though this percentage is typically larger than the percentage who kept off substantial weight.
Even more problematic is that most researchers also subtract additional categories of participants from their original study totals (and their data analyses), and excluding these categories does not just make the follow-up rate appear higher than it actually was, but it also typically makes the diet appear more successful than it was. These additional categories of exclusions include participants who did not lose sufﬁcient amounts of weight during the study, participants who left substantial portions of questionnaires blank, participants who had participated in a similar diet before, participants who refused to participate in earlier follow-ups for the study, participants who did not return calls, and participants who had gastric bypass surgeries (or other types of surgery) to induce weight loss subsequent to the study. One study reported excluding two participants from analyses because “inclusion of the two patients strongly skewed the results against weight loss maintenance” (Walsh & Flynn, 1995, p. 232).
These types of exclusions can lead to follow-up reports on fractured samples. For example, one study enrolled 426 participants in a diet program (Anderson, Vichitbandra, Qian, & Kryscio, 1999) and then excluded all but 154 participants from analysis for a variety of the reasons reported above. Researchers obtained follow-up weights for 112 of those 154 participants at their ﬁrst time point and therefore reported a follow-up rate of 73%, even though only 26% of the original participants were included in the follow-up. In addition, the article is a long-term follow-up study, but the ﬁnal four follow-up points only include from 15 to 42 participants each, a tiny fraction of the original sample size.
They also found evidence that dieting can be a leading indicator of major weight gain:
Among female adolescents who dieted, the risk for obesity onset over the four years was over three times that for nondieters.
I was put on my first diet at age 12; it was actually a hospital run behavior modification program where I had to go and get weight with other overweigh adolescents every week for a while. Thing is, I wasn’t particularly heavy. I was certainly a solidly built girl, but if I’d been a boy they would have been signing me up for the football team and talking about how I would make a great linebacker some day.
My first major diet “success” resulted in a loss of 50lbs and landed me in the hospital. I gained the weight back and then some.
My second major diet “success” was with phen-fen, because of which I now need to get EKGs on a regular basis for the rest of my life. I gained it all back and more
My third major diet “success” resulted in a loss of 60lbs, and two minor mental illnesses; exercise bulimia (you can’t eat unless you burn off at least that many calories exercising) and OCD (counting calories to an obsessive level). I gained it all back again, thankfully no more.
I am not explicitly dieting right now, because as the article above quite clearly states, diets don’t work. I am not exercising to earn the right to eat. I ride my bike to work to keep my heart healthy.
If I could go back to that 12 year old girl, I would tell her how much LOVE the freedom and power of riding my bike. Not talk about food. Not put her down. Just talk about how this was finally an exercise I could enjoy. It took me until my 30s to find it.
But I hate the current “conversation” (really shaming of fat people, no dialogue to be had) around weight and childhood obesity. People who are thin behave as though it’s the easiest thing in the world; just stop sitting on the sofa eating bon bons and you, too, will be skinny. I had a dear friend who could just skip desert for a couple of weeks and drop 5-10 lbs. He couldn’t understand why it was so hard.
But don’t you think, given the shame and prejudice overweight people face in our society, that if it WERE that easy we would have all done it by now?
There is nothing morally wrong with me that leads to my weight. I do not lack will power; in fact I have far more drive and self control than most people I know. But our bodies are complex and each is unique. We do not all respond the same way to… well pretty much anything. I can, and have, followed what the mainstream tells me the rules of dieting are. And those rules have failed; as the study above suggests.
When are we going to realize that shame and one-size-fits-all solutions are not healthy for anyone involved?