When we talk about diet, we are talking about the set of food substances that a person habitually takes (it has a broader sense than the use that is often given to this word when it refers only to a weight loss diet). That is to say, what type and what quantity of food we take.
With what we have said so far, we can already imagine that the diet has to be varied and balanced. Varied so that it contains all these different types of nutrients, and balanced so that they are present in the right proportions. In addition, the total calories (energy) we ingest must be equal to the total calories we consume.
As far as energy is concerned, there has to be a balance between the fuel we provide to our body (the energy that food can give us is measured in calories) and the energy we expend (with our physical activity, our vital needs, such as breathing, circulation, etc.). If we eat fewer calories than we expend, we lose weight; if we eat more calories than we expend, our body will accumulate them in the form of fat or adipose tissue and we will put on weight. And there are no exceptions. It is a balance and there must be a balance. It is true that there are people who need to eat little, because they immediately put on weight, and others who, even if they eat enough, do not put on weight. It depends on what each one eats, on what each one absorbs, on how the body uses the nutrients and also on the physical activity carried out. The fact of doing little physical activity obviously makes it easier for a person to put on weight than someone who does a lot of exercise. But it doesn’t fail: by lowering your intake, you lose weight. It is also true that some hormonal alterations, some medications or some brain injuries alter the metabolism or the sensation of hunger-satiety and favor that some people gain weight, and that control is more difficult. But, however we are, no one is able to put on weight without eating (or drinking, because sugary drinks are a great help to overweight!)
A first important point is, therefore, that we should not eat very energetic products, especially those that are not nutritionally useful for us. For example, refined sugars, industrial pastries and sugary soft drinks have more useless substances for our body than useful ones, but they also provide energy that either accumulates in the form of fat, or we will have to exercise so much to metabolize them that it does not pay off.
So that the diet is varied and balanced, we have to know a little what the foods contain, what type of nutrients they contribute. The main groups of nutrients are:
- Carbohydrates or carbohydrates: they are the most abundant nutrients in foods of vegetable origin. Their main function is to provide immediate energy. There are compound carbohydrates (potatoes, legumes, cereals…) and simple carbohydrates (found in sugar, honey, fruit, cakes, jam…). They are absorbed very differently and some provide us with interesting nutrients (fruit, when eaten raw, provides us with a large amount of necessary vitamins…), but others do not. If we eat too many carbohydrates, the body transforms them and is able to store them as fat.
- Fats or lipids: they are an important source of energy (they are the most caloric per unit weight), can be stored to provide energy when needed and also have a plastic component (for example, cell membranes are mostly made up of cholesterol, which is a lipid). There are polyunsaturated (the ‘good’ ones) and saturated (‘bad’) ones, with very different properties. There are fats in egg yolk (cholesterol), in oil, mixed with meat proteins, in butter… There are essential fatty acids, that is to say, that we must necessarily provide with food because our body cannot synthesize them.
- Proteins: they are essentially building material and especially important in periods of growth, when there are wounds (for example, when there are large bedsores or pressure ulcers, a supplementary supply of proteins is required). They are necessary for the production of hormones and many products essential for the proper functioning of the body. Proteins are mainly found in meat, fish, egg whites, milk and its derivatives and, in smaller quantities but of high nutritional quality, in legumes (lentils, chickpeas, etc.) and in some cereals. Proteins are made up of small pieces called amino acids. The amino acids that we must necessarily provide from outside because our body does not know how to synthesize them are the essential amino acids.
Apart from these three large groups of nutrients – carbohydrates, lipids and proteins – there are other foods that are equally important but which we need in much smaller quantities: vitamins and minerals. Vitamins are chemical compounds, generally complex, which have in common that in surprisingly small quantities they are essential for the functioning of the organism. Their absence can lead to potentially serious diseases, but their presence, even in small quantities, can solve the problem. There are fat-soluble vitamins (D, A, E, K), and they are found in vegetables, dairy products, liver… They are essential, but if taken in excess they can be toxic. And there are water-soluble vitamins: group B vitamins (found in meat, offal, legumes, cereals, dairy products, eggs and liver) and vitamin C (in citrus fruits, green leafy vegetables…).
A large amount of vitamins A and C are present in fruits. Some vitamins are easily denatured at high temperatures, so it is not the same to eat a cooked fruit than raw. An apple in a fresh fruit salad does not provide the same amount of vitamins as a baked apple. It is important to eat fresh, uncooked fruit or vegetables (tomatoes, carrots) every day. The best way to obtain vitamins is by way of the variety of foods we eat daily. Vitamin supplements should only be prescribed by a doctor and in very specific cases, because although the word vitamin suggests health, some, in excess, can be toxic.
Minerals are inorganic substances that are also present in food. We are not able to synthesize them from other compounds, so, like some amino acids, fatty acids or vitamins, we have to obtain them through food. The essential minerals in nutrition total up to 26 (calcium, phosphorus, iodine, iron, potassium…). Most of them are regulators, but others, such as calcium, have an important structural function. We cannot talk about each of them, but in the case at hand, it is important to insist on the need to take sufficient calcium so that the bones are well mineralized. When there is no standing, the tendency to osteoporosis is important and probably inevitable, but we can minimize it, among other things, by taking sufficient calcium (with the presence of vitamin D). Calcium is best absorbed from milk and its derivatives. Salmon and sardines, among others, also contain calcium.
Iron is needed for the manufacture of red blood cells. Lentils and spinach are famous for containing iron, and they do contain iron, but red meat contains much more. Iron can also be found in egg yolks, liver, salmon, peas, broccoli, etc.
Sodium (which is present mainly in salt) is involved in many processes, including the nervous and muscular system. In fact, a large number of foods contain it intrinsically, but we tend to supplement food with salt more than is necessary.
Salt, moreover, is addictive, and the commercial companies know it (in the advertisement for potato chips we are told: ‘you can’t eat just one!’). For some people this excess of salt is harmful because it raises their blood pressure or favors fluid retention. But we should also know that not all people with hypertension are sensitive to the removal of sodium from the diet, therefore, not all hypertensive patients should be recommended to follow a low-salt diet.