Obesity is not a simple aesthetic alteration, but a real pathology that increases the risk of many serious diseases, reducing expectations and quality of life. The increase in morbidity associated with severe overweight is mediated by endocrine and metabolic alterations favored by a sedentary lifestyle and an incorrect lifestyle. Also in this context, physical activity is the ideal means to promote weight loss, maintain the weight achieved and oppose these dangerous hormonal modifications.
Endocrine changes related to obesity
GH: the obese subject produces less GH than a normal-weight individual. Although the basal values are within the norm, the secretory peaks are less frequent and the total production is therefore lower.
Exercise is already in itself a powerful stimulus for GH secretion.
The response of this hormone becomes maximum during anaerobic exercises with high lactic acid production. However, a significant increase in plasma GH levels is already observed for low intensity exercises (50% of VO2max) which are certainly more suitable for the obese subject.
Thyroid hormones: the plasma levels of T4 (inactive form) are normal, but increases the turnover of T3 (active form). The increased production of thyroid hormones is therefore readily neutralized by the increased disposal speed.
These hormones are the main regulators of body metabolism. In the case of hypothyroidism (reduced production of T3 and T4) the basal metabolic rate is reduced by 40%; on the contrary a hyperthyroid subject has an accelerated body metabolism, up to 25-50% higher than the norm.
In some cases obesity is caused precisely by reduced thyroid function. Physical activity, for its part, cannot do much to bring the situation back to normal. However, regular exercise, regardless of the presence or absence of thyroid abnormalities, tends to increase metabolism, increasing muscle mass and improving overall metabolic activity.
Endorphins: basal plasma levels are within the norm, but the circadian rhythm disappears and there is little response to secretory stimuli. These hormones have a powerful analgesic and exciting activity; their action is comparable to that of morphine.
Physical activity is a powerful stimulus for the secretion of endorphins and this explains the sense of well-being and fulfillment that, despite the profuse fatigue, appears at the end of a physical exercise.
ACTH and cortisol: the circadian rhythm is preserved, but increases the turnover. Cortisol, produced in response to the pituitary hormone ACTH, has district effects as it stimulates the development of subcutaneous adipose tissue in the trunk and abdomen. Although during endurance sports activity increases cortisol secretion, exercise does not significantly affect basal plasma levels.
Gonadal axis: in the male the plasma levels of testosterone and of some proteins delegated to its transport decrease (SHBG). While free testosterone levels are still normal, on the other hand, obese people have slightly higher levels of estrogen. In fact, an enzyme called aromatase that converts testosterone into estradiol is concentrated in the adipose tissue.
Estrogens are typically female hormones able to influence the bodily distribution of adipose tissue concentrating it above all in the thighs and buttocks.
In women, obesity correlates to menarche (appearance of the first menstrual flow) early with frequent cycle disorders and a greater tendency to follicular atresia. Hirsutism and polycystic ovaries are frequent.
Insulin: the risk of developing type II diabetes mellitus is double for each 20% weight increase compared to the norm.
In the obese subject the appearance of diabetes is linked to the insulin resistance that precedes it. In this first phase, a veritable antechamber of diabetes, the binding capacity of insulin decreases, due to a decrease in the number and affinity of membrane receptors. Because of the difficulties that glucose encounters when passing from the circulatory stream to the tissues, the blood sugar level increases. Despite the high blood glucose concentration the cells are hungry because only a small portion of it can reach them. This lack of glucose at the cellular level stimulates the liver to produce it again and to release further quantities into the circulation. In this way we enter a vicious circle from which the body tries to escape by increasing the production and secretion of insulin. Arriving at a limit point, the pancreatic cells responsible for the production of this hormone undergo, due to too much work, a functional decline, opening the doors of diabetes.
Considering that about 80% of the ingested glucose is used by the muscle, we can guess the role of physical exercise in preventing diabetes. Regular aerobic activity improves cellular glucose utilization and enhances insulin action, significantly reducing the risk of developing type 2 diabetes mellitus.
Physical exercise also improves blood lipid structure and cardiovascular function, reducing the risk of cardiovascular disease. At the same time there is a reduction in the risk of developing certain cancers (colon cancer) and an overall improvement in mood (sport reduces the appearance of depression and anxiety associated with overweight).
Exercise prescription and obesity
Physical activity is a valid support to caloric restriction which, in the absence of its contribution, fails in the vast majority of cases. The same obese should realize that his severe overweight is the direct consequence of reduced physical activity.
Some say that the increased appetite induced by the exercise ends up opposing weight loss. In reality, as we saw in the first part of this article, physical activity triggers a series of endocrine and metabolic changes, which can promote weight loss regardless of the calorie content of the diet. Obviously an immoderate intake of food is opposed to weight loss, however it is good not to impose excessive caloric restrictions, difficult to bear both physically and psychologically.
The energy expenditure related to the exercise is maximum for typically aerobic activities such as cycling, walking, endurance swimming or cross-country skiing. These sports disciplines are also particularly suitable for overweight individuals, as they do not subject the skeletal and cardiovascular systems to the typical stresses of anaerobic sports.
The choice of physical activity is very important not only from the purely metabolic point of view but also from the psychological one. Forcing a subject to perform an activity that he does not like means increasing his repudiation of something he already perceives as hostile and frustrating. For the same reason it is good to avoid situations that may create embarrassment, highlighting instead the progress, even modest, made in the sport practiced.
Finally, we must not forget that, despite appearances, an obese subject, even at a young age, could be a carrier of pathologies that require special precautions. A thorough investigation of the client's medical profile is therefore a must. Dialogue and collaboration with other professional figures (psychologist, doctor, dietician etc.) is also very important.
