The food and drink we consume in our daily diet provides the energy and nutrients we need to stay healthy and energetic. Our personal calorie needs vary according to our weight, age, gender and activity level, but on average women need approximately 2000 calories a day to maintain their energy balance and keep their weight stable, while men need around 2500.
The energy content of stored body fat is about 3500 calories, so a 500 calorie deficit is needed each day in order to lose one pound. The safest way to create an energy deficit is by reducing calorie intake and at the same time increasing energy expenditure / exercise.
FAT - There are 9 calories in each gram of fat. As all fat contains 9 calories per gram, the type of fat you eat is irrelevant from a weight loss viewpoint. However, from a health viewpoint it is important to reduce your intake of animal fats and replace them with vegetable fats/oils.
The Good: Unsaturated Fats are divided into monounsaturated fats and polyunsaturated fats, and both types are thought to have beneficial effects on cholesterol levels. Monounsaturated fats help lower LDL (bad) cholesterol while also boosting HDL (good) cholesterol. Polyunsaturated fats are often a good source of omega-3 fatty acids, found mostly in cold-water fish, nuts, oils and seeds, and also in dark leafy greens, flaxseed oils and some vegetable oils. The Bad: Saturated Fats are the artery-clogging saturated fats from meat and dairy products. These fats are solid at room temperature. Saturated fats not only clog our arteries, they also directly raise total and LDL (bad) cholesterol levels. Avoid them as much as possible. Cookies, pies, mousses, cheesecakes, croissants, French fries, mashed potatoes, any type of meat consumed with skin (except fish), meat by-products, pork, butter and vegetable oil... you can find more info here.
CARBOHYDRATES - There are under 4 calories in each gram of carbohydrates (3.75 calories). Choose carbs with a low glycemic index rating: most fruits and vegetables (except potatoes and watermelon), grainy breads, pasta, legumes/pulses, milk, yogurt, (some cheeses, nuts), fructose. These low-GI carbs take longer to digest and help maintain stable blood glucose levels. Carbs which are high on the glycemic index (eg. refined sugary foods) contain more 'empty' calories - i.e. non-nutritious calories and can upset blood glucose levels, which may disrupt our appetite mechanism and trigger food cravings. These products are following corn flakes, rice krispies, baked potatoes, watermelon, croissants, white bread, extruded breakfast cereals, most white rice's (e.g. jasmine).
PROTEINS - There are under 4 calories in each gram of protein. Although protein is essential for good health, it is better to lower your intake of animal protein (e.g. from cheese and meat) and increase your intake of vegetable protein (e.g. from beans, soybeans, lentils, nuts.) From a health viewpoint, over-consumption of protein is not recommended and may cause health problems. If you are trying to lose weight, it is best to eat a diet which is low in animal fat, high in healthy (low glycemic index) carbohydrates with modest amounts of protein and about 1200 calories.