This confused me for a while. The fact is that most diets "work" to the extent that reducing calorific intake to less than the energy expended will over time lead to weight loss.

Low fat has the seductive feel of the holy grail. It is true that a fat gram is 9 calories and a carbohydrate gram or a protein gram is only four. It then seems a good idea to reduce the fat as you should get "more for your money". Couple this with the demonising of fat as being bad for you, lumping all fats together, and claims that it is the sure way to a heart attack, and you have a powerfull perception in peoples minds. This is reinforced when you lose weight on a low fat diet.

But there are a number of problems. The first is sustainability. In other words what happens when you stop dieting. Most low fat diets are not diets for life, they are bland and involve considerable self control because the carbohydrate and lower protein does not give the appetite suppressant qualities of low carb. When you stop dieting the body regains weight, often to a higher level than before. So you diet again and it "works" but maybe just a little slower this time. This is the classic yo yo that we have all been through.

The second problem is that low fat diets restrict protein. Protein and fat are not neatly divided into seperate compartments. You cannot just eat the protein out of an egg, and no matter how much trimming you cannot take all the fat out of meat.

This lack of protein, brings into play Nat's point in that if you deny muscle their special food - protein, muscle will diminish. Muscle weighs much more than fat and is much harder to put back. So in the yo yo scenario, you lose muscle but you put back fat. This is because it is the carbohydrate that stimulates Insulin that promotes the creation of fat. Fat itself is biologically neutral it does not make you fat.

The third problem is that the low fat message is insidous, it makes you scared of all fat. People stop eating eggs and dairy, they refuse to use oil for cooking. This means that all the good oils, and the omega 3 that they contain become the baby that is thrown out with the bath water! People deride junk food like hamburger and fries. They say it is the fat making you fat. In fact it is the potato not the frying, it is the bun not the burger that is the problem.

It is also true that for most going on a "low fat/low calorie diet" will lower the total carbohydrate intake.

The fourth problem is that to create low fat products and alternatives, sometimes the alternatives are less healthy than the natural fat product. Additives and flavour are added or completely substituted with things like soy.

You could also ask the flip side of you question, ....Why is it with the growth in low fat products, the western world is getting larger?

The reason is that not everyone is on a diet but they want to be healthy and as stated before the fat lobby is very good at getting under your skin. You are persuaded to take the low fat skimmed milk off the shelf, you will pick up the supermaket " healthy" range. You will buy the kids the low fat potato chips and think you are doing the right thing. But take out the fat and you have a higher level of carbohydrate. Slowly slowly the nation gets fatter.