The average diet is too high in protein, fats and sugar, too highly processed and refined, and too salt! It totally disrupts the natural mechanisms that tell us when we have eaten enough!
A healthy adult diet derives most of its energy from starchy foods, fruit and vegetables, with sufficient protein to provide for growth and repair of tissue.
The appetite mechanisms work on starch meals and they work on protein meals to ensure the delicate balance between the food we need and the food we eat. Unfortunately for eaters of the average diet, the appetite mechanisms do not work on the fat content of refined and processed foods. Even a small imbalance can result in a steady increase in weight and the laying down of body fat. It can also result in the eating disorders of anorexia and bulimia.
If you base meals on wholemeal and whole grain starches and potatoes and don't add extra fats and sugar to the diet, the natural appetite mechanisms can return to control how much we eat, without the need for us to make a deliberate effort to control body weight.
Some energy is needed just to stay alive. A sleeping man requires 0.3 MJ/hour just to maintain the life processes and any waking activity that allows the body to rest completely uses slightly more energy. Sitting up at a desk to work will use 0.42MJ/hour. Light domestic work, washing and dressing, about 0.75MJ/hour. Active physical work in carrying loads and using shovels or other manual labour can rise to 1MJ/hour. Similar energy levels are required by sports activities but the particularly high energy requirements of games such as squash at 2MJ/hour can only be sustained for a short time.
A lighter and fitter person will require slightly less energy for the same amount of exercise and, on average, a woman requires slightly less energy than a man for the same work.