This is interesting:
"Protein is an essential nutrient, and is vital to your health. It is used to build muscles, skin, hair and nails. However, many people put their health at risk by eating too much protein.
The typical American diet already provides plenty of protein and there is no point in adding any more, unlike fat cells, there is no place in the body to store protein so the excess is eliminated or is seen as fat rather than muscle.
So what you need to do is to consume just enough protein to allow your muscles to be healthy, perform work and grow. But how much is just enough?
You only use protein for about 15% of your energy use, the majority of energy comes from fats and carbohydrates. Exercising doesn't necessarily mean that you require more protein but more carbohydrates to stop your body breaking down protein and using that for energy.
Try to make sure that 70% of your protein comes from sources such as meat, fish, eggs or poultry. The complete protein provided by these foods combines with incomplete protein consumed from other food sources. So your body makes the best of all the protein that you consume."
From I'll Pump You Up.com
I guess therefore that this about a balance of protein, fat and carbs - I suspect I have been overdoing the protein a little bit, looking at my food diary. I need to make sure I eat a bit more salad + oily dressings and/or veg with butter, that kind of thing.