Edited by Doctor Roberto Uliano
Many times we hear it said: "I gain weight even with a simple glass of" water "or:" that person can eat whatever he wants without gaining weight. "In some cases these statements, when viewed from the metabolic point of view, have a background of In fact, in 1983 a study published in "Metabolism" showed that obese and overweight people have a metabolism unable to give an adequate response during and after meals. The defect, according to this study, affects the part of the metabolism that it has the function of keeping the body weight constant, through the dissipation of the energy introduced with food through heat. We try to understand the causes through the knowledge of metabolism.
Metabolism indicates the energy expenditure that the organism has to face to carry out all its physiological and daily functions. It consists of a basal metabolism, a thermogenic metabolism and a metabolism by activity.
The basal metabolism represents the minimum energy expenditure for the survival of the organism. It constitutes 65-75% of the total metabolism, of which 50% is involved in the management of body temperature. The basal metabolism decreases by about 2-3% each decay of life, due to the decrease in cellular activities and the decrease in lean mass. Its variations among individuals depend mainly on the musculature, the body surface, the lean mass (all that is not adipose tissue), the circulating hormone levels and genetics. Women have a lower basal metabolic rate than men (5-10% less), due to the lower amount of lean mass and the greater amount of adipose tissue.
Thermogenetic metabolism is the ability of cells to produce heat. It is represented by a mandatory part, for maintaining the body temperature at 37 ° C, and an optional part triggered for the production of heat following changes in the ambient temperature. One aspect of thermogenesis is that induced by the diet (TID). It consists of two variants, the obligatory one due to the amount of energy expended for digestion, the absorption and use of food, and the optional one, determined by the ingestion of a meal, whose function is essential for dissipation. of energy, in the form of heat, when the caloric intake exceeds the needs of the organism. This ancestral mechanism is very important to keep body weight constant over time.
The last metabolic mechanism is the energy expenditure linked to the activity, defined as the energy expenditure of the relationship life. It includes both the energy expenditure for planned physical exercise such as sport, and an energy expenditure, defined as NEAT (nonexercise activity thermogenesis), which affects all the calories that are burned with those small daily gestures, such as walking, descending and climbing. stairs, cooking, washing dishes, doing manual work, etc.
Resuming the study published in "Metabolism" it is stated that the metabolic response following "food intake or" exposure to cold (as we have seen defined optional thermogenesis), is less important in the obese than in normal weight people. This study has shown, for the first time, that in the obese there is a greater conservation of energy and a lower energy expenditure following external stimuli. Further studies have defined that the cause of the problem is the optional part of thermogenesis, which does not manages to do its duty with respect to the reason for which it was created.
How to diagnose metabolic defects?
There is a substantial difference between estimating and measuring metabolism. The estimate is made through relatively accurate mathematical formulas, which based on weight, height or the calculation of the body surface give an estimate of the basal metabolic rate. These mathematical formulas are different and each different according to the subject evaluated (obese, normal weight, children , adolescents, elderly). All the formulas, however, give an error of 10-30% with respect to the real individual value. The error increases if the estimate is made in subjects who are already on a diet or who have already lost weight (a cause of the change in the state of hydration of the organism).
Further information: online calculates the indicative basal metabolic rate of obese subjects.
The actual measurement can be accurately performed through indirect calorimetry, a fast and non-invasive reference method. It consists in measuring the consumption of oxygen and carbon dioxide exhaled by the subject, in a certain time interval. On the basis of the recorded data, the basal energy metabolism is then deduced. The actual measurement of metabolism lays the foundation for a correct nutritional program. In fact, eating a diet far below one's metabolism induces a loss of lean mass, resulting in a decrease or block of the metabolism itself. Under these conditions, weight loss is more likely to stop very soon.
To identify thermogenic defects or the causes of slow weight loss, it is possible to measure the metabolism after having eaten a meal, in order to check whether the body responds to an external stimulus such as the introduction of food.
The measurement of daily energy expenditure must be carried out with special portable devices. One of these is the Armband, a triceps band that is worn throughout the day. This device is capable of recording movement, skin temperature, linear acceleration of the body, etc. The recorded data is then processed to identify if the time of physical activity and its quantity are adequate for caloric intake. It is a great tool for learning about the lifestyle of obese people.
What are the causes of the metabolic defect
Obesity and overweight are caused by a caloric imbalance between the energy introduced through food and the daily energy expenditure. There is evidence that the obese have low levels of physical activity and that the caloric intake is often higher than the average of people, but in many cases the excess fat is not explained only by these two variables, which suggests that there are other pawns at stake. In these cases, physiological, hormonal and metabolic insights are necessary. metabolic view exists, SO we have seen, a greater ability of the obese to store energy in the form of fat. The hormonal and metabolic terrain of these people is often complicated by an unfavorable genetic predisposition. In fact, there are gene variants in the population that allow the individual to store fat more effectively and gene variants that determine a lower thermogenic efficiency in dissipating energy in the form of heat (FTO, Beta and Alpha adrenergic polymorphisms).
What to do then? Identifying the metabolic defect in these cases allows greater effectiveness of intervention and personalized treatment. In fact, it is possible to improve the pathological picture through personalized interventions on the diet and lifestyle, capable of increasing metabolic efficiency.
Ultimately, it is likely that an obese will never become a shiloutte, but nevertheless can achieve a normal and healthy weight through targeted intervention.
Bibliography: Segal KR, Gutin B. “thermic effects of food and exercise in lean and obese women”. Metabolism 1983; 32: 581
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