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Sources of Calories: Carbohydrates, Fats and Proteins
Sources of Calories: Carbohydrates, Fats and Proteins

Sources of Calories: Carbohydrates, Fats and Proteins

Date: September 23, 2021

Carbohydrates (including fiber), fats and proteins are the main sources of energy for the body because they provide the necessary fuel for body heat and functioning of the body. Their potential energy is expressed in calories, a term that indicates the amount of chemical energy that can be released in the form of heat when food is metabolized. As a result, high-energy foods are also high in calories, while low-energy foods have fewer calories. Fats provide approximately nine calories per gram, carbohydrates and proteins approximately four.


Carbohydrates are the main energy generator for all body functions, especially for the brain and central nervous system and for muscle exercise.
They are necessary to promote digestion and assimilation of foods and, with the exception of milk, they are exclusively of vegetable origin. Carbohydrates contain the same number of calories per gram as protein and less than half the calories as fat.
Carbohydrates are composed of carbon, hydrogen and oxygen, which provide us with readily available calories, producing heat in the body when carbon in the body joins oxygen in the bloodstream. They also help regulate the metabolism of proteins and fats, as fats need carbohydrates to be broken down in the liver.

All sugars and starches are carbohydrates. Sugars are divided into two categories. Simple carbohydrates are the three easily digestible monosaccharides (simple sugars made up of one molecule), and disaccharides (double linked sugars in pairs made up of two monosaccharide molecules) which require more complex digestion. Complex carbohydrates are starch and glycogen; these are polysaccharides composed of different glucose chains.
Fibers, which do not play an active role in energy production and are largely undigested, are composed of the polysaccharides cellulose, gum, pectin, hemicellulose and mucilage and are therefore classified as carbohydrates. Lignin, which behaves like a fiber but is not a polysaccharide, is no longer classified as a fiber. Simple sugars, or monosaccharides, are glucose or blood sugar, fructose, the sweetest sugar found in fruit, and galactose (which is released only during digestion) found in milk sugar. The liver converts the monosaccharides fructose and galactose into glucose.
The sugars, or disaccharides, are lactose, which is divided into its two monosaccharide components glucose and galactose; maltose, present in beer malt and plant sprouts, is split into two single glucose molecules; and sucrose (beet or sugar cane table sugar) which is split into the monosaccharide molecules of glucose or fructose. Honey, a disaccharide, is broken down like white sugar, except that honey also contains minimal amounts of some vitamins and minerals.
Complex carbohydrates (starches) to be broken down into simple sugars and subsequently into glucose to be absorbed, require a prolonged enzymatic action. These starches are composed of many different combinations of glucose chain molecules. Many types of rice, grains and potatoes are built from these units while other polysaccharide chains are fibers.
Some of the processed glucose is used as fuel by the tissues of the brain, nervous system and muscles. The rest of the glucose from carbohydrates is converted into glycogen and stored in a layer of fat under the skin and throughout the body as an energy store. When these fat stores are converted into glucose and used as fuel for the body, weight loss results.
Carbohydrates deficient in essential vitamins, minerals and fiber are referred to as "empty calories". Excessive consumption of starches and sweets, such as cookies, candies, cakes, snacks, can exclude other nutrients from the diet and cause nutrient deficiencies and obesity.
Carbohydrate snacks based on sugars and starches provide the body with energy almost instantly because they cause an immediate rise in blood sugar. However, the blood sugar level drops quickly again, creating a strong need for sweet foods and sometimes stnacness, dizziness, nervousness and headaches.
Refined foods like white flour, white sugar, and polished rice are deficient in B vitamins and other nutrients. If the B vitamins are absent, the combustion of carbohydrates cannot take place and disorders such as indigestion, heartburn and nausea can occur. Excessive consumption of these refined foods will accentuate any deficiency of B vitamins already present in the individual. Unrefined whole carbohydrates such as grains, legumes, fruits and vegetables are the only foods that are not associated with any deadly disease. Research has shown that a diet low in complex carbohydrates gives positive results in the case of ailments such as heart failure, high blood precision, anemia, kidney dysfunction, cancer and dental caries.


Refined sugars, which are relatively nutrient-free but high in calories, can be replaced.
For example, an orange with its natural sugars has the same calories as a tablespoon of white sugar, but the difference is in the amount of valuable nutrients present in the fruit's pulp and fiber. Natural sugars are present in many fruits and vegetables.

Carbohydrates can be synthesized in the body starting from some amino acids and the glycerol component of fats, and therefore the National Research Council (USA) does not establish a precise requirement.
However, most experts agree that carbohydrates should account for 55 to 60% of the calories in the diet. For most people, the minimum quantity is 100g, 125g is sufficient and 300g is the ideal dose for everyone.
Desserts such as cookies, cakes and candies should not exceed 10% of your daily calorie intake. It is believed that 25% of the total energy currently consumed is in the form of sugar.

Diversity in baseline matebolism, activity level, height and weight will affect the amount of carbohydrates the body needs. A total lack of carbohydrates, however, can produce ketosis, toxic compounds that can cause brain damage, low energy, depression, apathy and the depletion of essential proteins in the body.

In low-carb diets, where protein is burned for energy, the kidneys can be overworked trying to quickly rid the body of toxins. Large quantities of water are required to stabilize this process. In a balanced diet, fat burned is previously stored fat, not protein. These fat stores burn more effectively, which benefits the whole body.


Carbohydrate foods are the only source of non-nutritive fiber which is a polysaccharide and is part of the carbohydrate family. The walls of foods of plant origin are composed of fibers, present in the peel of fruit and vegetables and which are mostly indigestible for humans. Their contribution to energy production is minimal; however, in a high-fiber diet they can contribute up to 15% of energy production.
However, we must be careful because excessive consumption of fiber can cause deficiencies. In this case, the vitamins and minerals combine with the fibers and are excreted before the body can absorb them.

Dietary fibers have a particular chemical structure, can be broken down by bacterial enzymes and are water soluble. Human enzymes cannot break down fibers, with the exception of hemicellulose, which is digested by bacteria in the large intestine.


The greatest positive impact of dietary fiber is on the colon, the last part of the gastrointestinal tract, where diseases such as cancer or diverticulitis can develop. Dietary fibers exercise the intestinal muscles so that they remain healthy and toned and helps this part of the digestive tract move smoothly and evacuate regularly. Wheat bran is considered to be one of the best fibers for softening stool, as long as the larger parts are ingested. Foods rich in fiber satisfy the appetite and increase the volume of food along the intestine. Fibers such as pectin and guar which form a gel in contact with water lengthen the transit time along the intestine, while insoluble fibers (cellulose) shorten it.

Fiber can play a positive role in ailments such as overweight or obesity, constipation and diarrhea, hemorrhoids, appendicitis, diverticulitis, colon cancer, increased blood fat, cardiovascular disorders and diabetes.

The consumption of purified fibers such as cellulose may not give the same benefits as the consumption of the same substance present in a food such as whole wheat.

Wheat bran, which is mostly cellulose, does not lower cholesterol, while oat bran and apple pectin lower it.


Fats - or lipids, their chemical name - represent the dietary source of maximum concentration of energy. There are three types of lipids: triglycerides, phospholipids and sterols.
When oxidized, they provide more than double the calories per gram provided by carbohydrates and proteins. In fact, one gram of fat produces about nine calories. Fats provide about 60% of the body's energy needs at rest. The importance of fats is vital to the body, but if taken in excessive quantities they can become a problem. The diet should be planned to include essential quantities and avoid excesses that can lead to health problems in the future.
Over time, nature creates a reserve of energy that is always available for our needs. One of these reserves is the fat stored in the liver and muscles in the form of glycogen. When needed, enzymes break down glycogen into glucose, ready to work for the body. Another reserve is the fat stored under the skin layers throughout the body and used when the liver supplies are depleted. Unlike the liver, the body can store an unlimited amount of fat which can serve as energy for all the cells in the body until the reserves are exhausted. The substances that give the fats the different flavor, consistency and melting point are the "fatty acids". When energy-producing nutrients store their fats, they become fatty acids. They are the most obvious form of fat in both the diet and the body. They are found in meats, for example under the skin of poultry and in the fatty parts of red meats, and on soups and sometimes on pizzas. The fat that accumulates in the body and makes us look plump is made up of triglycerides (three fatty acids attached to a glycerol). There are different combinations of triglycerides and each animal species has its own characteristics. Animals raised for slaughter can be fed with different types of food which will determine the greater or lesser hardness of their fats.
Fatty acids have two differences: chain length and saturation. The length of the chains is related to absorption while saturation refers to saturated or unsaturated fatty acids. In fats from fish or vegetables, there are points missing in the chemical bonds and fatty acids are called unsaturated, a definition which, on food labels, is abbreviated to UFA. When the missing point is only one, the fatty acids are called monounsaturated and the abbreviation is MFA, if instead the missing points are two we speak of polyunsaturated fats or PUFA.
Unsaturated or soft (short-chain) fatty acids, including monounsaturated and polyunsaturated fatty acids, are usually liquid at room temperature and are generally of vegetable origin, are extracted from fruits, nuts or seeds (corn, canola, safflower, sunflower, olives , etc.). Saturated (long-chain) fatty acids are solid at room temperature and, with the exception of coconut and palm oils, are generally of animal origin. In margarines, vegetable fats have been subjected to a process called "hydrogenation", in which unsaturated oils are transformed into solid fats. These fats are then referred to as "trans" fatty acids. Other sources of saturated fat are milk derivatives, eggs and cheeses.
There are three "essential" fatty acids. The human body can synthesize all the fatty acids it needs from carbohydrates, fats and proteins from food, with the exception of linoleic, linolenic and arachidonic acids. These polyunsaturated fatty acids cannot be produced by the breakdown of other substances in the body; they must be provided by the power supply and are therefore called essential. They are necessary for normal growth and for the health of the blood, arteries and nerves. Arachidonic acid can be synthesized from linoleic acid when it is supplied to the body by the diet.
Linolenic acid is part of the family of polyunsaturated fatty acids known as omega 3 fatty acids, and is found mainly in fish and flaxseed oil. Experts conduct research on the role of omega 3s on growth and development, vision, tumor development, blood clotting, arthritis, heart disease and hypertension. Omega 3 acids keep skin and other tissues young and healthy by preventing dryness and exfoliation. Fish with dark meats and linseed oil contain good amounts.
Linoleic acid is an omega 6 fatty acid and we find it in products that come from the earth, such as plant seeds and in oils produced from seeds. Vegetable fats such as corn, safflower or soybean oil contain another percentage of linoleic acid. Researchers have long known the importance of fatty acids from the omega 6 family. These essential fatty acids are necessary for the transport and breakdown of cholesterol. Both omegas should be taken together as their balance is essential. Rapeseed oil is the one that has the best balance of the two acids.
If a supplement is taken that contains only one of the two acids it can create a deficiency in the other. The deficiencies of these acids are however rare, because we can find them in many different foods.
The second category of fats are phospholipids; they too, like triglycerides, have a glycerol structure. Among the members of this category, the best known is lecithin. These fatty acids have only two chains of fatty acids attached to them (as for lecithin, there is a third, choline) and form a fundamental component of the cell membrane. They are valuable nutrients, essential for life. Lecithin can be produced by the liver, so it is not an essential nutrient. Lecithin has been found to lower excessive cholesterol levels in some individuals.
The third category of fats are sterols, the most famous of which is cholesterol, which also include vitamin D and the sex hormone testosterone. Sterols are large, complex molecules made up of interconnected carbon rings that are essential for sexuality. Cholesterol is an essential substance for health. It is a normal component of most tissues in the body, especially those of the brain, nervous system, liver and blood. Over nine-tenths of cholesterol ends up in cells where they perform vital structural and metabolic functions. Unused parts can be harmful to some individuals, which is why foods containing high-cholesterol animal fats should be avoided.
Foods that contain other types of cholesterol, such as liver and eggs, would appear to be less harmful, but should be consumed in moderation, especially by those with family members with coronary heart disease and those with high LDL cholesterol levels.
Each body treats cholesterol differently. Measuring the two types is important for finding out your personal level.
Some of the cholesterol is transformed into substances such as vitamin D and the rest has three purposes: to aid digestion and assimilation of fats (in the form of bile in the liver); circulate in the body for structural maintenance of cells, and be packaged in lipoproteins. There are two types of lipoproteins: the good type (HDL) which promotes the elimination of cholesterol and the bad type (LDL) which in large quantities forms clots in the arteries and exposes the vascular system to the risk of numerous ailments and diseases. Like lecithin, cholesterol can be produced by the body (2.8g per day) whether it is ingested or not and is therefore not an essential nutrient. Only 25% of the cholesterol in the blood comes from food. The raw materials from which the liver produces cholesterol are carbohydrates and fats.
In addition to providing energy and valuable nutrients to the body, fats act as transporters of the fat-soluble vitamins, A, D, E, and K. Eliminating fat from the diet also eliminates these vitamins. By promoting the assimilation of vitamin D, fats help supply calcium to tissues in the body, particularly bones and teeth. Fats are also important for the conversion of carotene into vitamin A. Fat deposits surround, protect and maintain organs such as the heart and liver in place. The hard deposits present under the kidneys protect them from impacts. The mammary glands in the breast are also protected by a layer of fat. A layer of fat insulates the body from changes in ambient temperature and maintains body heat while giving shape to our body. Fats prolong the digestive process by slowing down the secretions of hydrochloric acid from the stomach. This way they create a prolonged feeling of fullness after a meal.

Fats are beneficial for other reasons as well. Natural oils give a healthy complexion and nourish the scalp so that it can grow shiny hair. Our muscles work thanks to the fat present between the fibers which represents a constant reserve of energy.
Excessive fat consumption leads to the storage of abnormal amounts of cholesterol throughout the body, which can cause atherosclerosis. Currently, all doctors recommend avoiding excess saturated fat and cholesterol. Many diseases are linked to excessive fat intake or being overweight. If more calories are consumed than the body needs, body weight increases and with it the risk of obesity, diabetes, hypertension, cancer and possibly other diseases and disorders. Furthermore, excessive fat consumption causes abnormally slow digestion and assimilation and thus leads to indigestion.
Although fat deficiency is rarely found in humans, it also implies a deficiency of fat-soluble vitamins. A deficiency in fatty acids can cause eczema or other skin disorders. Severe fat deficiency could lead to severe growth retardation. If a carbohydrate deficiency is accompanied by a lack of water in the diet, or if there is kidney dysfunction, fats are not fully metabolized and can become toxic to the body.
Fatty or fatty foods should be kept in covered containers, out of direct light and in a cool place to prevent rancidity caused by oxidation. Some protection from rancidity is provided by vitamin E, a naturally occurring fat-soluble antioxidant vitamin found in many foods and can become toxic to the body.
Dietary prescriptions recommend that total fat intake does not exceed 30% of the daily dietary intake. Saturated fats should not exceed 10%, unsaturated and polyunsaturated fats not less than 10%, and monounsaturated fats the remaining 10%. As far as cholesterol is concerned, it is normally suggested not to exceed 300mg per day; however this amount varies from person to person. Foods that contain linoleic and linolenic acid should also be included in the diet.


Along with water, proteins are the most abundant substances in the body. They are very important for maintaining good health and vitality and are essential for the growth and development of the body. All tissues, bones and nerves are mostly made up of proteins. Protein is the main source of building material for muscles, blood, skin, hair, nails and internal organs, including the heart and brain. An important protein, collagen, participates in the formation of scar tissue, constitutes the protein base of the teeth and the material of which the ligaments and tendons are made and strengthens the walls of the arteries.
In addition to being the major source of building material for the body, proteins are also a source of heat and energy as they provide four calories per gram. However, this energy function is not exercised when the diet includes enough fat and carbohydrates.

Muscles and other vital protein tissues can be used for energy in the absence of other sources. Likewise, excess protein not used for tissue building or energy can be converted by the liver and stored as fat in the body's tissues for later use as energy.

Some hormones are proteins, especially thyroid hormone and insulin, which control various body functions such as growth, sexual development and metabolic rate. Protein also helps prevent blood and tissues from becoming too acidic or too alkaline (proteins such as albumin in the plasma prevent imbalances in the blood). With the help of some minerals, proteins also help regulate the water balance in the body.
Other important proteins are enzymes, substances necessary for basic life mechanisms, and antibodies, which help protect us against foreign substances such as viruses, bacteria and other disease-carrying agents.
In addition, proteins are important in the formation of milk during training and in the blood clotting process. Some proteins in the body, called transport proteins, take nutrients and other molecules and transport them in and out of cells. They transport fats, fat-soluble vitamins, water-soluble vitamins and minerals to all cells throughout the body. Other proteins move nutrients from one organ to another. An example is the hemoglobin protein, which carries oxygen from the lungs to the cells of other organs.
During digestion, the long protein molecules are broken down into simpler units called "amino acids". Amino acids are necessary for the synthesis of organic proteins and for other building blocks of tissues. Amino acids are the basic units of which proteins are made up and the final product of protein digestion. The body requires about 22 different types of amino acids in precise configurations to form human proteins. Of these, 13 amino acids can be produced by the human body, while nine, called "essential amino acids" must be supplied by the diet. These are: methionine, threonine, tryptophan, leucine, isoleucine, lysine, valine, phenylalanine and histidine.
Histidine, an essential amino acid for children, has been added to the list of essential amino acids for adults. Sometimes a non-essential amino acid can become essential due to illness or trauma (very intense stress). Glutamine could be part of these amino acids, in the case of a very sick person. The body loses protein in the event of stress such as surgery, bleeding, injury or prolonged illness. In these cases it is necessary to consume more protein to rebuild or replace the tissues that no longer function well.
For proper protein synthesis for the body, all essential amino acids must be present simultaneously in the proper proportions. If a single amino acid is deficient or absent, even if only temporarily, the synthesis of proteins will be reduced or will stop completely. The result is that the utilization of all amino acids is reduced to the same proportions as the amino acid which is scarce or missing.
When a food contains all the essential amino acids it is called a "complete protein". Foods that lack essential amino acids or have minimal amounts of them are called "incomplete proteins". Most meats and dairy products are full protein foods, while jelly is not. Most vegetables and fruits are incomplete protein foods. To get a complete protein meal, from incomplete protein foods, you have to combine the various elements carefully, so that those lacking an essential amino acid are accompanied by others that contain it.
Vegetarian diets can be programmed to contain all proteins. To have a complete protein content, beans can be associated with corn, nuts, rice, seeds and wheat; brown rice can also be associated with the same foods. Peanut butter and jam bread is a complete protein food, provided it is made with whole grain bread. The quantities you will find below are those of a right combination of high quality amino acids: valine, 48g; phenylalanine and tyrosine, 73g; leucine, 70g; sulfur-based amino acids, 26g; lysine, 51g; threonine, 85g; tryptophan, 11g; Isoleucine, 42g; and histidine, 17g (see food composition tables). These essential amino acids can be taken in the form of food supplements but should not be ingested with milk or other high protein foods because they would have the same receptors. It is suggested that you use juices or other liquids instead.
Proteins, in order to perform their functions, must be digestible and of good quality. These proteins are called high quality proteins. Among the best we find the egg, which represents a precious protein food in those countries where proteins are scarce. Egg yolk contains a large amount of cholesterol which, if consumed in excessive doses, can be harmful; however the type of cholesterol contained in the egg is less harmful than that present in animal fats. It is a food to be consumed in moderation. Soy proteins are complete proteins of vegetable origin, qualitatively equal to those of animal origin and do not contain cholesterol.
Protein, whatever its quality, is not used effectively and does not aid growth without the help of carbohydrates and fats, nutrients that give us energy. When the body breaks down its own proteins to meet its energy needs, a shortage is created. Kwashiorkor and marasma are two serious diseases caused by protein deficiency.
Kwashiorkor is an urgent need for protein-rich foods when the only foods available are free of it. It is a disease that mainly affects newly weaned babies and those who go through periods of rapid growth. It is not only proteins that are lacking, zinc and all other nutrients are also lacking. The children's bodies are swollen from edema and the liver is enlarged. This disease is not linked to particular populations or cultures: it is present all over the world (see Kwashiorkor in Part V).
Marasma is mainly caused by hunger. In the event of marasma, it is not only the proteins that are lacking, there is a complete lack of food. The victims of the marasma (6-18 months) are more than their age, have a sickly appearance and are skin and bones. Their bodies lack the accumulations of fat that protect them from the cold. This disease is present in overpopulated areas, and in rural populations where there is a lack of food for children.
Stunted growth, which often goes unnoticed, may be an indication of a lack of protein among children in modern countries. Other symptoms are hair loss or hair color, joint swelling and weakening of muscles, including the heart muscle.
In adults, protein deficiency can lead to lack of vigor, depression, weakness, and poor resistance to infection. Antibodies do not work as they should and this leads to poor wound healing and slow healing from disease.
An excessive consumption of proteins does not give advantages, on the contrary it exposes to certain risks. Foods rich in animal protein are often fatty and can contribute to obesity and all related risks. Some studies have shown a link between high-meat diets and colon cancer. The greater the amount of protein in the diet, the less the amount of fruit, grains and vegetables. Diets high in protein promote the elimination of calcium and deplete the bones of minerals.
Excessive consumption of protein can also cause an imbalance in the body's fluids.
The minimum daily protein requirement - the minimum amount of amino acids to be consumed for optimal growth and good health in adults - is 0.8g of high quality protein per pound of body weight proportional to height. The National Research Council (USA) suggests consuming 1g of protein for every kilo of body weight.
These quantities change according to the condition, conformation and activity level of each individual. The data that is taken into account when planning a diet are usually based on the recommended dietary doses. About 15% of the substances taken in a day should be protein, the right amount varies between the recommended dietary dose and twice that dose. The recommended amount of protein below takes into account the differences between individuals living in the United States at a normal level of stress.
For babies from 0 to 6 months with a weight of 6 kg the quantity is 13 g; from 6 months to a year with a weight of 9 kg is 18 g; from one to three years with a weight of 14 kg is 23 g; from 4 to 6 years with a weight of 20 kg is 30 g; and from 7 to 10 years with a weight of 28 kg is 34 g. For females, aged 11 to 14, with a weight of 45 kg, the quantity is 45 g; from 15 to 18 years with a weight of 54 kg, 46 g; from 19 to 22, with a weight of 54 kg, 44 g; from 23 to 50, with a weight of 54 kg, 44 g; over 50 years and with a weight up to 54 kg, the quantity remains 44 g. For males, aged 11 to 14, with a weight of 45 kg it is 45 g; from 15 to 18, with a weight of 65 kg is 56 g; from 19 to 22 with a weight of 70 kg is 56 g; from 23 to 50, with a weight of 70 kg is 56 g; over 50 years and with a weight up to 70 kg the quantity remains 56 g. Pregnant women should add 30g and breastfeeding women 20g.

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