How does metabolism change when eating a very low calorie diet?
We put this to Giles Yeo, from MRC Metabolic Diseases Unit...
Giles - Well, let me see if I understand the question. I mean the biggest influence on your metabolic rate is still going to be you size. So the larger you are, the higher your metabolic rate, oddly enough, and the smaller you are the lower your metabolic rate, so thereís that. However, what happens when you lose weight, and you lose a lot of weight, your body (your brain in particular) does not like that. And so what it does is it tries everything it can to stop you from losing weight and one of the things it does is to slow down, ever so slightly, your metabolic rate and, also, increase your food intake to try and make you gain the weight back.
Chris - But does that persist indefinitely? So, if I lost a lot weight, and I changed my lifestyle, would my brain for the next 55 years still be trying to get me back to the state I was in before I lost weight or would it slowly adapt and learn that the new slim me was the way I wanted to be?
Giles - Well, Iíll give you the depressing answer first. The depressing answer, as far as it has been measured. Now you can imagine trying to do that in a human being is pretty tough. But all of the experiments that have been done over a couple of years, where theyíve held someone down at a specific weight after having lost, unfortunately your brain, certainly through that time tries to pull you back up to that weight that you once were.
Chris - Thereís going to be a lot of sorry people out there now, isnít there?
Kat - I have heard that itís really hard to do these kinds of studies because people lose weight and then they just put it back on again. Very, very sad!