Fats are the absolute enemy of anyone trying to be slim, as they represent the most concentrated form in which surplus energy is stored. Eating fats means you are eating an animal’s energy reserves, which, in theory as in practice, improve your chances of increasing your weight.

There are two major sources of fats: animal and vegetable. Animal fat, found in a virtually pure state in lard, is very much present in pork products such as pâtés, salamis, sausages, hot dogs, and meat spreads. Lamb and mutton and certain poultry, such as goose and duck, have a plentiful supply. Beef is not as fatty, especially those cuts that can be grilled. Only ribs and the rib eye are really rich in fat. Butter, which comes from the creamy top of milk, is practically a pure fat. The fat content of heavy cream is around 36 percent. The five fish with the most fat, easily recognizable by their rich taste and blue skin, are sardines, tuna, salmon, mackerel, and herring. But remember that these fish are no fattier than ordinary steak, and the fat of coldwater fish is rich in omega-3 fatty acids, a known safeguard against cardiovascular disease.

Vegetable fats are, for the most part, represented by the long list of plant and nut oils and fruits such as avocado. Oil is even fattier than butter. Although some oils like olive, canola, or sunflower oils have nutritional qualities that have been proved to protect the heart and arteries, they all have the same caloric value and should be banned from any weight loss diet, avoided during the Second stage , and eaten sparingly during the final third stage.

Peanuts, walnuts, hazelnuts, pistachios, and macadamia nuts are snacks that are often eaten with a cocktail; their combination with alcohol greatly increases the calorie intake of the meal to follow.

For those who want to be slim, and in particular for those who are trying to lose weight, fats represent every danger possible.

Fats contain, by far, the most calories—9 calories per gram (more than double the calories in carbohydrates, which provide only 4 calories per gram).

Fats are very rich foods and so are rarely eaten alone. Oil, butter, and heavy cream are often associated with bread, starch, pasta, or salad dressings; the combination increases the overall calorie count considerably.

Fats are not assimilated as quickly as fast sugars, but they are

assimilated far more quickly than proteins, and thus their comparative energy contribution increases accordingly.

Fatty foods reduce our appetite only moderately, and snacking on them, rather than on proteins, does not reduce your desire for a large meal afterward or delay the time before you next feel hungry.

Finally, animal fats with high amounts of fatty acids—butter, sausages, dried meats, and fatty cheeses—pose a potential threat to the heart. For this reason, they cannot be consumed without restriction.