John DiTraglia MD
Why is it so hard to lose weight? The main reason is that if you lose weight you get tired and hungry and miserable. That is the psychological part of weight loss. But another conspiracy against weight loss is physiologic. Your metabolism decreases if you lose weight. That makes it harder to lose more weight and easier to put it back on. There are many ways this could happen and it’s kind of complicated and difficult to study.
Resting energy expenditure (REE) goes down and activity energy expenditure goes down if you lose weight. Activity energy expenditure and maybe REE, go down even more if you “get in shape.” Resting energy expenditure, the energy you burn while you’re doing nothing, decreases if you lose weight because that weight is no longer there to burn calories. Your resting energy expenditure is dependent on how much of you there is, especially the fat-free part of you. Another possible conspiracy would be if your REE goes down even more than would be predicted by the loss of your fat mass and fat-free mass.
A few weeks ago we reported on a study of this question that found that while you are losing weight the body fights back physiologically more than is accounted for by the weight loss but that once you stabilize, if you stabilize, at a reduced weight, the decrease in REE is explained entirely by the reduced body mass.
Another examination of this issue was published recently in the journal Obesity. (1) These authors from Toronto and Ottawa examined data from 2,977 subjects from dozens of published studies. They found that before those subjects lost weight their fat mass and fat-free mass explained 77 percent of their REE and that after they lost weight 79 percent. No difference. So it is not a conspiracy, or at least this small part of why it is so hard to lose weight is not part of the conspiracy. Maybe more interesting from this information is what about the other 20 plus percent of REE whether you lose weight or not? What explains that?
In the end the only way to find out what is going to happen to you is count your calories and watch the scale.
1. Schwartz, et al. Greater than predicted decrease in resting energy expenditure and weight loss: Results from a systematic review. Obesity 2012;20:2307-10.