This is one of the most common questions that I get. For people who’ve been steeped in diet culture – even if they’ve personally had the experiences of short term weight loss, long term weight regain, and yo yo dieting – it can be really difficult to believe that successful long-term weight loss is something that almost never happens. That’s certainly how I felt when I first started to read through the research. I had a really tough time believing that the idea that I could and should become thin to be healthy – which was promoted and sold to me more aggressively than any other concept or product in my life – was not only not based on research, but actually directly contraindicated by it.
The issue here is two-fold. First even if we believed that weight loss would improve health (though Mann and Tomiyama 2013 suggests that it doesn’t) there isn’t a single study in existence where more than a tiny fraction of people were able to achieve long term weight loss using any method. Statistically the most common outcome of intentional weight loss attempts (whether they are “diets” or “lifestyle changes” or any thing else that is an attempt to manipulate body size through diet and/or exercise) is weight regain. The thing that seems to cause the most confusion is that almost everyone loses weight short term, and we mistakenly believe that if we can lose weight short term then we can lose weight long term and maintain that weight loss.
The truth is that the vast majority of people regain their weight and the majority gain more than they lost (see Mann and Tomiyama 2007) So even if we think that being fat is a problem, given the current research, recommending weight loss is the worst advice we can give. Weight loss simply does not meet the ethical requirements of evidence based medicine since we don’t have any evidence that suggests that it will work for more than a tiny percentage of people and we don’t have any evidence that is able to link decreased weight to better health, controlling for behaviors. In fact when people decrease weight without changing behavior (as in the case of liposuction for example) we don’t see changes in health.
In fact, what we see over and over is that when people change their behavior, their health often improves and often they lose weight short term. We then inexplicably credit the weight loss with the improved health rather than crediting the behaviors. When studies control for behavior we find that people of different sizes with the same behaviors have the same health hazard ratios and risks of all cause mortality (see Wei et al, Matheson et. al, and the Cooper Institute Longitudinal Studies to start.)
Given the fact that we have no evidence that supports a weight loss intervention either for change in body size or a change in health, but we have a great deal of evidence for increased health through behaviors regardless of starting weight or weight change associated with the behaviors, the ethics of evidence-based medicine require that we prescribe healthy behaviors to those interested in improving their health, or that if we give a weight loss intervention we practice informed consent and let them know that almost everyone who attempts that intervention has the exact opposite of the intended result, and that we have no evidence that, even if the person is in the tiny minority who succeed, their health will be improved.
We should also be very clear that neither health nor healthy habits are an obligation – nobody owes anybody health or healthy habits by any definition. Everyone gets to choose how they prioritize their health and what path they want to take to get there. Also, regardless of habits, health is never guaranteed and never entirely within our control. Finally health is not a barometer of worthiness, and our health isn’t anybody else’s business unless we make it their business.
People are allowed to disagree with this, but let’s not pretend that disbelief, however indignant or authentic or well meaning, is the same thing as evidence-based conclusions. The idea of weight loss creating health is what I call a Galileo Issue – it’s widely believed, fervently supported, it’s heresy to suggest that it’s not true, and yet it is not supported by evidence. We have to start basing our interventions on evidence over “everyone knows” if we hope to actually give people accurate information.
UPDATE: Awhile ago I told you that a screenwriter had written a screenplay based on my time dancing. Well, you know that game where you try to decide who should get to play you in a movie about your life? That game just got very real for me. The screenplay has been optioned and, per one of the members of the team “we are going to make the hell out of this movie!” And it all started with a connection made by a blog reader (Thanks TS!) It’s super exciting, and a little weird, and super exciting. I’ll keep you updated as there are more details!
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