Edited by Doctor Roberto Uliano
«Introduction to metabolism
DIET-INDUCED THERMOGENESIS (TID)
The thermal effect of food is defined as the amount of energy spent on digestion of food. It is made up of 2 components: a fixed thermogenesis and an optional one. Fixed thermogenesis is the energy that the organism spends on absorption. and the use of food. It depends a lot on the type of food eaten. Carbohydrates have a thermal effect of 7%, lipids of 3%, while proteins can even reach 35%. On average for a complete meal the effect food temperature is 10%. A meat-only meal induces a thermal effect of 30% of the caloric value of the meal. This is due - in addition to the work necessary to support digestion - to the energy expenditure of the liver engaged in protein synthesis and in the transformation of proteins into glucose. Thanks to the effect of proteins on TID, high-protein diets have recently become fashionable which, if on the one hand slightly increase metabolism, on the other can induce hepatic and renal fatigue with consequent states of edema. The thermal effect of the food is recorded one hour after the meal and can be performed by indirect calorimetry.
The optional thermogenesis is given by the energy expenditure due to the activation of the sympathetic nervous system following the ingestion of a meal.
Research indicates that obese people or people who tend to gain weight have a very blunt thermogenic response to food intake, causing the body to easily store fat. A half-hour walk after a meal can effectively increase TID.
ADAPTIVE THERMOGENESIS AND THERMOGENESIS
See also: Weight loss, yo-yo effect and adipose-specific thermogenesis
Thermogenesis is the process by which the body produces heat to keep the body temperature constant. To do this much of the energy taken in through food is converted into heat through particular organelles present in the cells: the mitochondria. When thermogenesis occurs. developed in climate change - especially when the cold arrives, in situations of stress or hyperalimentation - it is called adaptive thermogenesis. Adaptive thermogenesis is under the control of the sympathetic nervous system, which through some hormones such as catecholamines (in particular norepinephrine) induces an increase in heat production. Muscle and liver play a predominant role in this mechanism, but brown adipose tissue is also involved in a small part, which in the adult man is little represented (about 700 grams) compared to common body fat (white adipose tissue). found in the areas of perianal, pericervical, and heart fat, but represents about 14% of the basal metabolism.Thermogenesis occurs through certain proteins present in the mitochondria: the UCP.
Adaptive thermogenesis plays a key role in the genesis of obesity. Numerous studies indicate that a good percentage of the obese have a low thermogenesis compared to the norm. For these characteristics, new molecules are being studied to increase the thermogenesis of the obese. One of these, which is already on the market, it is sibutramine. This drug is marketed to reduce the sense of hunger, but it is also capable of increasing thermogenesis by counteracting the degradation of noradrenaline. The same effect is induced by "ephedrine in association with caffeine, which still today they are used under the counter as a slimming product despite having massive side effects. Other supplements with a slight thermogenetic effect are: green tea in association with caffeine, the Citrus arantium, whose thermogenetic properties have yet to be confirmed, and capsaicin, a very effective derivative of chili peppers but which not everyone can use for the gastric side effects it induces.
Thermogenesis, on the other hand, also plays an important role during weight loss. During caloric restrictions to lose weight, the body implements numerous compensations: the loss of lean mass and the decrease in diet-induced thermogenesis, adaptive thermogenesis and the secretion of thyroid hormones. This fine regulation is implemented by the body to conserve energy. This leads to a greater metabolic efficiency which in the subsequent re-feeding phase leads to a rapid recovery of adipose tissue in the initial phases and then subsequently of the lean mass. This means that the metabolism still remains low, and that there is a greater ease of gaining fat and regaining weight in greater quantities than the initial values (yo-yo effect). The good rule of thumb is to give a day and a half of freedom calorie per week is still very important for the characteristics of the metabolism.
At the epidemiological level it has been seen that the current living environments are extremely thermoneutral and this does not allow to produce that surplus of energy with a thermogenic effect that would allow a greater expenditure of energy.
ENERGY EXPENDITURE ASSOCIATED WITH THE "ACTIVITY"
it is defined as the energy expenditure of relationship life. It includes both the energy expenditure for planned physical exercise and an energy expenditure defined as N.E.A.T. (nonexercise activity thermogenesis). NEAT includes all the calories you burn by doing all those little daily gestures like tapping your fingers on the counter, walking while on the phone, jumping for joy, laughing, going down stairs, climbing stairs, walking, cooking, washing dishes , doing manual work etc.
This energy expenditure, over the last few decades has been increasingly decreasing and it is possible that it is one of the major causes of the rapid growth of overweight and obesity, together with the wide availability and availability of food. going to work, to work, to play and manual jobs were more, free time was not easily spent in front of the television or the computer.
Amateur sport, although important, weighs much less in terms of energy expenditure than NEAT. It is unlikely that sport is daily (unless it is competitive) and hardly lasts more than one "hour a day. A" daily hour in the gym costs an average of 200-300 Kcal per day, which can be offset by 100 g of bread. more. NEAT, on the other hand, can play a key role in maximizing energy expenditure. For example, an active job can make you spend up to 1500 Kcal per day compared to a sedentary job. Thin people, as well as anorexics, are familiar with this mechanism and are often identified as hyperactive. To increase NEAT it is necessary to identify a daily activity, pursue it and check if it is effective. For example, the possibility of walking to work or leaving the car before the workplace, or getting off a stop earlier, could be considered. substantial between an obese and a thin person is that the latter move more, for at least 2 hours a day.
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The measurement of daily energy expenditure must be carried out with suitable portable devices. One of these is the ARMBAND, a triceps band that is worn throughout the day. It is capable of recording movement, skin temperature, linear acceleration of the body, etc. The recorded data is then processed to identify if the physical activity time and quantity are adequate for the caloric intake. It is an excellent tool for understanding this important aspect of metabolism in depth.
