Losing weight is not easy. Not at all. But keeping it off is even harder. This is not new knowledge, but it is only recently that we have started to find out why it’s so hard to keep it off. Last year, I was working with some colleagues on a meta-analysis that evaluated different strategies for keeping weight off after a period of rapid weight loss using a very low calorie diet (<1000 kcal/d). We evaluated different types of diets (low GI, high protein, and so on) and supplements, exercise and finally anti-obesity drugs.
What we found was pretty depressing: none of the strategies were very effective at helping people keep the weight off. This much we were able to conclusively prove.
This got me thinking about how the body defends against weight loss. I concluded that there are at least three types of primary defenses against weight loss, all of them powerful and hard to dodge for anyone wanting to lose weight long-term. Moreover, the defenses operate according to the rubber band principle: the more weight you lose, the more defense activation, and hence weight regain, you are likely to experience.
First, once weight loss occurs the body will increase circulation of appetite increasing hormones and peptides, such as ghrelin (increases hunger) and leptin (increases satiety). Sure, you can override this cognitively, at least for a while, but you are basically swimming upstream from now on. It’s doable, just not very easy.
The second line of defense is called adaptive thermogenesis. This means that your body goes into calorie saving mode once you have shed some weight, and you will now burn a lot fewer calories during both rest and exercise. This reduction in metabolism is a lot lower that what we would normally expect as a result of having a lighter body.
The third line of defense is behavioral relapse into old habits. Some habits are formed early in life and are manifested in the brain. By losing weight you needed to change your old eating and exercise habits and form new ones. But those “highways” in the brain didn’t just go away, they are still there. And we are indeed creatures of habit, and after a period of fighting those first two defenses, those old habits can easily make a comeback when you feel tired and stressed.
And there also appear to be more defenses, not least psychological and emotional ones. One such example is that many overweight individuals identify with having extra pounds, usually established already in childhood. This means that they are used to a looking heavier than others. Once they lose weight, some individuals will struggle to identify with their new appearance, and consciously or not, they can can feel uncomfortable and regain for that reason, no matter how much they want to appear thinner.
My suspicion is that children who grow up overweight will have a harder time losing weight that adult-onset weight gainers for this very reason, since adult-gainers do not identify with being overweight to nearly the same extent.
The highly visual nature of obesity could in fact be one of the reasons it is so hard to treat long-term, at least with current reactive methods, such as drugs, diets and exericse.
I can understand if you feel a bit depressed reading this but in order to make real progress we have to understand why we have been failing for so long. Now we at least know a bit more about what does not work and why. I say that is at least partial progress. Real tangible progress will happen when we find methods that do not trigger these defenses in the same way or perhaps even avoid them altogether.
If you feel particularly nerdy and want to read the meta-analysis we did, please see Johansson K, Neovius M, Hemmingsson E. Effects of anti-obesity drugs, diet and exercise on weight loss maintenance after a very low-calorie diet or low-calorie diet: a systematic review and meta-analysis of randomized controlled trials. Am J Clin Nutr 2014;99:14-23. This paper was published open-access meaning that there is no fee for downloading it.
Ps. I will be holidaying for 2 weeks now, have a great summer everyone! Ds.