The FastDay Forum

In reply to a tweet from someone who asked Dr Mosley why it was she didn't seem to have lost much weight, although her clothes were fitting her better, he replied "initially you lose mix of fat and water. Then just fat, but water goes back on. So you may be losing fat but not weight."

I'm not sure I understand this. Surely fat weighs something - well, of course it does - so what does he mean? Am I being totally thick or being blinded by science? I'm interested to know the answer because I haven't lost much weight either, though I have lost a good two and a half inches of my waist since the end of September.

[carorees]

I don't understand why that would be the case but I'll try to find out. However, it's true that several people have found the same thing has happened!

I'd really appreciate that!

[carorees]

Ok, so it seems that as the fat cells shrink as we burn up the fat they contain, they also lose water, so we lose fat and water. Then, it also seems that in overweight people the amount of water held in the cells (I presume adipose cells but I couldn't work that out exactly) is higher than in normal weight people, while the proportion of water carried outside the cells is lower and that as fat is lost, the proportion of water carried outside the cells increases, which I am guessing means the total body water goes back up again like Dr M said.

I did a PubMed search for "weight loss AND fat AND muscle AND water AND changes" which brought up a load of papers discussing how best to measure these changes. It seems that the accuracy of the current methods is not certain. However, my explanation above is what I concluded by looking at some recent papers on weight loss and measuring body composition. I might be wrong though! If my conclusions are correct, I would guess that the water drop/increase is likely to be smaller in people who are less overweight.

Not sure I really understand that, but thanks anyway. I am not very good at understanding Science as much as I'd love to!

[carorees]

Well I didn't understand it too well either as I've never written about this area of medicine before so I probably explained it badly!

Basically, it looks like he might be right in some people at least...not very helpful I know!

This topic interests me. My weight is now back where it was this time last year but my waist has shrunk. Am not overly concerned as weight loss isn't my goal but am interested to know of any scientific explanation. Worth also pointing out that I do a good level of exercise bike riding 50-100 miles a week and swim (distance plus sprints) 3x pw including fast days. I also go overboard with confectionary consumption on feed days.

[carorees]

Skippy, did you see my post in science watch about resting metabolic rate decreasing disproportionately with weight loss? Don't know how much weight you lost but it might be relevant!

if you lose fat from one place it may be hiding out somewhere else, or you may have added muscle through exercise that is reducing the apparent weight loss skippy ?