Body weight regulation

Total calories are more important than any single macronutrient. 

Regulatory systems such as neurochemicals, body-fat stores, protein mass, and hormones play a role in regulating intake and weight. Short-term regulation governs consumption of food from meal to meal. Short-term controls are concerned primarily with factors governing hunger, appetite, and satiety. Satiety is associated with the postprandial state when excess food is being stored. Hunger is associated with the postabsorptive state when those stores are being mobilized. Physical triggers for hunger are much stronger than those for satiety, and it is easier to override the signals for satiety.

Healthy younger and older men of normal weight consume a typical diet and perform usual activities. When overfeeding or underfeeding interventions were made, the younger men exhibited spontaneous under eating or overeating to alter body weight accordingly. The older men don’t have the same responsiveness to change in caloric intake. Older persons are more vulnerable to unexplained weight losses or gains because of their inability to control spontaneous short-term changes in food intake. Age alone should not preclude weight loss treatment in older adults. Careful evaluation of risks and benefits is needed.

Long-term regulation is controlled by the availability of adipose stores and hormone responses. Long-term regulation seems to involve a feedback mechanism in which a signal from the adipose mass is released when normal body composition is disturbed, as when weight loss occurs. 

Fat storage in not obese adults appears to be regulated in a manner that preserves a specific body weight. In humans deliberate efforts to starve or overfeed are followed by a rapid return to the original body weight, as though the latter constitutes a ‘set point’ that is amenable to physiologic influences. That is why some forms of obesity are the result of an abnormally established set point. Body weight remains remarkably stable despite variations, possibly from internal regulatory mechanisms that are genetically determined.

Some studies suggest that body weight can be displaced only temporarily and that resting metabolic rate lowers, resulting in body weight response to weight loss. Other studies do not show an adaptive metabolic response to weight loss. Instead, a transient reduction in energy expenditure is observed with energy restriction that normalizes on return to energy balance conditions.

The resting metabolic rate explains 60% to 70% of total energy expenditure. Since most of us do more than sleep 24 hours a day, our daily calorie needs will be higher than our resting metabolic rate. Resting metabolic rate (RMR) declines with age and with restriction of energy intake. When the body is suddenly deprived of adequate energy, such as with involuntary or deliberate starvation or semi starvation, the RMR adapts to conserve energy against an unpredictable future by dropping rapidly, by as much as 15% in 2 weeks. When adequate food intake is restored, the RMR returns to baseline levels. Under nutrition impairs digestive function and aggravates the nutritional state.

Persons, who do not restrict calories, require an increasing amount of physical activity to maintain body weight. All activities counts. Not exercise activity thermogenesis is the energy expended for everything that is not sleeping, eating, or sports like exercise. In includes all activities that expend energy such as going to work, typing, doing yard work, toe-tapping. A sedentary lifestyle may be of profound importance in obesity. To reserve obesity, individual strategies should be developed to promote standing and ambulating time by 2.5 hours per day and also reengineer work, school, and home environments to render active living the option of choice.

To lose weight at a healthy rate people need to be between their minimum calories (calorie intake calculation) and maintenance calories. The best way to reach ideal weight is to add some physical activity into each day and make healthier food choices.