Energy and nutrients in foods

Man, in order to live and have the capacity to perform work, requires a continuous supply of energy, whether for physical activity, for muscular work, for the functioning of the nervous system and the heart, or for processes related to growth, tissue repair, reproduction and maintenance of body temperature.

How does the body obtain energy? The food we eat is responsible for supplying this energy to the body, obtaining this energy from the oxidation of carbohydrates, fats and proteins.

The amount of energy that originates when a food is totally oxidized or metabolized to produce carbon dioxide and water is called energy or caloric value. If we speak of kilocalories we can observe, in the table below, the average value that the oxidation of food acquires in the organism:

• 1 g of fat = 9 kcal

• 1 g protein = 4 kcal

• 1 g of carbohydrates = 4 kcal

• 1 g of fiber ? 2 kcal

All foods, in varying amounts according to their different macronutrient content (carbohydrates, fats and proteins), are potential sources of energy. For example: foods rich in fats are more caloric than those containing essentially carbohydrates or proteins.

Even alcohol, which is not a nutrient, provides metabolically usable energy (with a yield of 7 kcal/g) when consumed in moderate amounts (less than 30 g ethanol/day). Vitamins, minerals and water are not considered energy sources.

Food as an energetic and nutritional contribution: For the preparation of diets it is of vital importance to know the nutritional composition of foods and the different groups in which they are classified, as this will be of great help when choosing the foods and menus that will form part of the diet.

Every person will need to regularly consume a certain amount/quality of energy and about 50 nutrients that are stored in food, to maintain their health from a nutritional point of view. Due to the various adaptations that man has developed throughout his evolution, nowadays, he can use or consume a great variety of products or foods to obtain the necessary energy and nutrients.

According to the Spanish Food Code, foodstuffs are those substances or products of any nature which, due to their components, characteristics, preparation and state of preservation, are susceptible to be habitually and suitably used for normal human nutrition, as fruit or as dietary products in special cases of human nutrition.

It was previously mentioned that alcohol, despite not being a nutrient, provides metabolically usable energy, but it is important to note that exceeding the recommended consumption limit would cause adverse reactions.

The ingestion of alcohol on an empty stomach would cause it to be absorbed more rapidly, and since alcohol, once ingested, is distributed throughout the body's fluids and cells, it will result in blood alcohol levels (BAC) of about 0.750 g/l if 30 g of alcohol is consumed, an amount at which a person will feel euphoria, disinhibition and loss of reflexes.

Alcohol is metabolized mainly in the liver at a rate of 60-200 mg/kg body weight per hour. Women metabolize it less efficiently and because they have less body water, they will have a higher BAC after ingesting 30 g of alcohol. For this reason, some countries recommend an ethanol intake of ? 20 g/day.

Spices and condiments: spices, aromatic herbs and condiments such as salt, vinegar, etc., used to add or improve flavor and/or aroma, although they provide nutrients and above all numerous phytochemicals, have little nutritional value since they are ingested in very small quantities.

Vitamin losses: the different culinary processes to which foods are subjected to improve their hygienic and gastronomic quality modify their nutritional value. In some cases their nutritional value increases but in others it decreases, losing some of their nutrients.

Examples: Variable amounts of some vitamins, mainly water-soluble vitamins, may be lost during cooking. Minerals, although not destroyed by heat treatments, can be lost in the cooking water or in the liquids released by the meat.

In the case of water-soluble vitamins, the loss will vary according to the culinary process to which they are exposed: frying, baking, boiling, roasting, etc.

Fortification or enrichment of foods: these two terms are generally used synonymously and indicate that some nutrients have been added to a food or food product to restore or increase its nutritional value.

In some specialized techniques, such as the refining of flours and cereals in general, significant losses of minerals and vitamins are observed with respect to the content of the whole grain.

Also, the elimination of fat from many foods to reduce their caloric value leads to the loss of fat-soluble vitamins, such as a or d. Therefore, through fortification, the initial levels of nutrients lost during the handling of the food will be restored and even surpassed.

The term fortification would then be applied in those situations in which a certain nutrient is added to a food that it did not originally have. The addition of iodine to table salt is a good example of fortification.

It is vitally important to choose the right food and the nutrients to be added. Milk, for example, would be a good choice for fortifying certain nutrients, especially those intended for children. Cereals are also a good example, as they are used as a vehicle for water-soluble vitamins and minerals.

¨light¨ or light products: nowadays we are facing a new food culture where the use of the so-called ¨light¨ or light products has increased. The ¨light¨ products (of low or reduced caloric value, mainly intended to control body weight), are those in which some of their components or ingredients have been eliminated or reduced, affecting such reduction, fundamentally, to their caloric value. Here are some examples:

• Calorie reduction is achieved by replacing sugars with acaloric sweeteners (as in the case of soft drinks or jams); by totally or partially eliminating the fat from the food, mainly in dairy products; or by reducing the alcohol content, as in beer.

• Reducing fat translates into lower energy content. This can be seen in the reduced fat content of whole, semi-skimmed and skimmed milk where semi-skimmed milk contains 1.5 percent fat and skimmed milk less than 1 percent fat, while whole milk contains about 3.5 percent fat.

• The elimination of fat, in addition to reducing calories, also implies the reduction of cholesterol and the loss of vitamins such as d, e or vitamin a. This should not be considered a cause for concern since it is common practice in many countries to enrich skimmed products with these vitamins.

• It is important to know that there is no difference with respect to other nutrients since the calcium or protein content is practically the same in any of the three types. In short, skimmed dairy products have a very low caloric value and therefore contain a higher concentration of nutrients, which is very useful for those people who wish to lose weight or who, due to illness, etc., want to reduce fat and/or energy consumption.

Nutritional quality in the elaboration of the diet:

• Energy: to maintain a stable weight the diet must provide a certain amount of energy. A good way to know if we are consuming the right amount of calories is to control the weight. If over a month, for example, our weight does not change, it means that we are consuming the energy we need. An increase in weight indicates that we are eating more than we need.
• Nutrient density or amount of nutrient per 1000 kcal of the diet: The higher the nutrient density, the better the quality of the diet. The high fat and simple carbohydrate content of many diets can dilute their nutrient density.

How to measure the energy of food: The energy of food is measured in kilocalories, this energy is acquired from nutrients product to complex reactions that occur in our body. There is no direct relation between the weight of an organ and the need for a certain amount of energy, rather the requirements depend on whether the organ or system is working or not.

Carbohydrates provide 4 kcal per gram, this means that 1 gram of carbohydrates provides 4 kcal. Proteins contribute 4 kcal/g and lipids, 9 kcal/g.

Nutritional balance:

• To achieve nutritional balance you must: Ingest the necessary energy, without excesses or deficits: each person is different, so energy needs will depend on factors such as age, sex, height, weight, physical activity and basal metabolism. Special situations such as pregnancy, illness, medication, climate, etc. will also have an influence. Although there are complicated formulas for its calculation, the total daily energy needs are estimated between 25-30 kcal/kg weight for an adult person.
• To achieve nutritional balance, it is necessary to: Choose the correct ratio of nutrients: total daily energy should be achieved through macronutrients in the following proportion:

• " Carbohydrates: 55-60% of total daily energy.

• "Proteins: 10-15% of the total energy.

• " Fats: 25-30% of the total energy.

Of these:

• " 18-20% monounsaturated fat.

• "5-7% polyunsaturated fat.

• "Less than 10% saturated fat.

• "Along with this, it is necessary to take into account the contribution of vitamins, fiber, minerals and water.

It is important to note that the proportions may vary depending on pathologies or specific needs.

Distribute the intake during the day: 3-5 meals a day are usually recommended, distributing the food according to the needs of our activity:

• "Breakfast should provide 25% of daily energy.

• "Lunch, 35%.

• "Dinner, 15%.

• "To them, we would increase two lighter intakes, the mid-morning lunch, by 15% and the afternoon snack, 10%.

• "In selected cases, an afternoon snack could be recommended, depending on specific pathologies or atypical schedules.