Every day we have to meet our calorie expenses by getting food. Carbohydrates, proteins and fats are energy sources needed to stay active.
“Nothing is lost, nothing is created, everything is transformed,” said the famous chemist Antoine Lavoisier. Energy is the transformation of matter into heat, light or movement.
Where does the Body take its Energy?
Energy is found in many forms: chemical, electrical, thermal, mechanical and nuclear. For the human machine, every molecule that enters into the composition of food contains chemical energy called “calorie”. These calories come from carbohydrates, proteins and lipids which, once digested, form reserves. From these reserves, the cells produce adenosine triphosphate (ATP), which is used as a source of energy to perform all kinds of work. Without ATP, our heart does not beat, our legs do not run, the food is no longer digested and our brain stops working.
Grease: a Reservoir of Energy
We do not think of it like that, but in the average man (70 kg, 1.73 m), 100,000 calories are stored in the fatty tissue! Its muscles represent 25,000 calories, mostly in the form of protein, while 600 calories of sugars are stored in the liver and muscles in the form of glycogen. Fat is therefore the adaptation of the most effective body to conserve energy. The proof: theoretically, a person of normal weight can survive a fast of two months thanks to his reserves of energy, whereas an obese could survive nearly one year!
During prolonged fasting, however, the body could not use the energy stored in the muscles without causing organ function problems. It is therefore necessary to avoid this state of deprivation by eating in a varied and balanced way to provide the body with the essential energy for its proper functioning. Health Canada also publishes dietary reference intakes to guide consumers in their choice of the type of calories to be consumed in the form of carbohydrates, proteins or fats.
The Essence of the Brain: Carbohydrates
Except for meat, poultry and fish, all foods contain different kinds of carbohydrates such as starch, lactose, glucose, fructose, etc. Fiber is also part of the carbohydrate family. However, since they are not digested, they do not contribute to energy intake. Digested carbohydrates are transformed into glucose, a simple sugar. The glucose is then transported in the blood to the cells for energy production in the form of ATP, just as gasoline is transported to the engine in order to operate a car.
Sugar is a fast energy that requires little processing. The brain loves it. Each gram of carbohydrate provides four calories. According to current recommendations, 45% to 65% of calories should come from carbohydrates, or at least 130 grams per day. But the brain, this great boss of the body, requisitions them all. In a state of fasting, carbohydrate reserves are quickly exhausted. When there is no more sugar, the brain feeds on ketone bodies, substances produced when using fat stores as a source of energy. In this case, you may experience fatigue, loss of appetite and nausea.
The only glucose reserve is in the liver and muscles, and it is stored there as glycogen. When the amount of carbohydrate consumed is too large and the reserve capacity is exceeded, the sugar is then converted into fat and then stored in the adipose tissue. Weird, but true! Too much sugar does not provide more sugar, but only fat.
Protein Serving the Muscles
Proteins are found mainly in meat, fish, legumes, nuts, milk, cheese, yogurt, etc. After being digested in the stomach and intestine, they are cut into small particles called amino acids. Imagine a protein like a big pearl necklace, each pearl being an amino acid. Amino acids can be converted to glucose to provide energy, but their main role is to maintain functional organs. Proteins are needed to build all tissues, from muscles to skin, from hair to antibodies. They form the fibers of the wall of the organs and the muscles that make the heart beat. Proteins are also the basic elements of hormones, responsible for several metabolic functions. They represent about 16% of body weight.
Metabolic functions are optimized when 10% to 35% of energy comes from proteins. An adult must consume 0.8 g of protein per kilogram of his daily weight, ie 56 g for a 70 kg man. Like sugar, protein provides four calories per gram and, when the intake is too high, the excess accumulates as fat – just next to that produced by excess sugar. Exercise and pathologies increase protein requirements: the athlete puts his muscles, which ask for more, to a severe test; the patient, in turn, needs proteins to regenerate his tissues; this is easily understood in the case of a large burnt, for example.
Fat: Muscle Food
Whether saturated, monounsaturated or polyunsaturated, fats each have a primary role to play. They form the membrane of cells and participate in certain functions of the nervous system. They also allow the absorption of so-called fat-soluble vitamins (A, D, E and K). Trans fat, invented by the food industry, does not have a vital role. Since saturated and monounsaturated fats can be synthesized by the body, only polyunsaturated fats, such as omega-3 and omega-6, are essential in the diet. These fats, among others, are found in fish and vegetable oils such as canola or olive oil. Muscle feeds mostly on fat. Because dietary intake often exceeds metabolic requirements, fat is stored in adipose tissue and is used to form ATP for fasting or prolonged exercise.
Balancing sugars and fat
The harmful effects of saturated and trans fats on health have been widely publicized. But a diet low in fat and high in carbohydrates also increases the risk of cardiovascular disease. Balance is therefore essential: from 20% to 35% of the energy should come from lipids. Women should consume a minimum of 1.1 g of omega-3 and 12 g of omega-6 per day and men of 1.6 g and 17 g respectively. One gram of fat provides nine calories, more than double the amount of one gram of carbohydrate or protein. Fat is therefore the most concentrated energy source of food.