Weight loss is both fat and water...

I'm sure most people who have dieted at some point have heard "experts" say that especially in the early stages of a diet the body will lose a lot of water as well as body fat, meaning not all weight loss is fat, in some cases they says its mostly water. I'm not convinced that this is necessarily the case...

It turns out that the average persons body fat deposits are made up of about 15% water.

This maybe a gross misunderstanding of the facts but it would be logical to assume that as you use up stored body fat the underlying structure goes, including the water around it. Meaning for every pound of weight you lose on a diet 15% of that is water, the rest is fat. Obviously water has no calorific content, so does that mean that 1 pound of weight loss is not worth 3,500 calories but actually about 3,000 since 15% of it is water? (1 pound of body fat is equal to 3,500 calories.) I have no idea but this could explain why weight loss seems to be more than expected when calculating potential weight loss from the BMR and calories eaten. This is quite good news really.

I cannot see this as a problem, and I know some people have hang ups about actually losing fat as if it is more important than water. The reality of course is that the water here is stored WITH the fat, its not like you have pools of water located around the body. The body fat stores themselves contain the water, so when you lose fat you lose both together.

How then does the body just get rid of the water, and not the fat, as per the old story about losing mostly water when beginning a diet? Again, I have no idea but I cannot see this as plausible. Why would the body decide to off load only water from fat stores in the event of a reduction of food energy coming in, what purpose does that serve when the body should be looking to metabolise its saved energy to make up the shortfall? I don't buy it as it sounds like one of the "old wives" tales, like not eating late at night as it causes weight gain, which is of course not true.

From what I can see (taking it as a sceptical layman of course), the body's reaction to a downturn in energy coming in from food is to begin to use up stored fat reserves, that's a simple thing to understand and is totally accepted scientifically. Since these reserves include water in their structure when the fat is burned for energy the water is no longer required and is got rid of. The water loss is in line with fat loss, has to be. Now I understand some people can retain more water than others, so its possible they may have a higher ratio of fat to water but I would still imagine that when fat is burned, the fat and water are lost at the same rate.