Main Links of the Functional Nutrition System
The maintenance of energy and plastic balance in the body is ensured by two main pathways:
- External link. This is the primary way to meet metabolic demands under normal conditions. The external link represents a complex chain of behavioral and physiological reactions: formation of feeding motivation, selective appetite, food-seeking behavior, direct food intake, and digestive processing within the gastrointestinal tract.
- Internal link. This is activated during forced or voluntary food deprivation. It provides endogenous nutrition—maintaining an optimal pool of nutrients by utilizing the body's own tissue reserves. This is accompanied by a downregulation of metabolic processes, regulated by hormones of the pituitary gland, thyroid gland, pancreas, and other endocrine glands.
Mechanisms of Endogenous Nutrition
If external food intake ceases, the body triggers two main survival mechanisms aimed at mobilizing internal resources.
1. Utilization of Nutrient Depots ("Autoinjection") This process, described by the physiologist V.N. Boldyrev, involves the release of nutrients from tissues directly into the bloodstream. Notably, this process is closely timed with periods of so-called "hunger motor activity" of the stomach. The circulation of substances occurs in a closed loop:
- Release of reserves from tissues into the bloodstream.
- Transition from the blood into the gastrointestinal lumen.
- Processing of the released substances by digestive juice enzymes.
- Reabsorption into the blood in an adequate, easily digestible form.
2. Redistribution of Nutrients This mechanism, studied by I.P. Razenkov, involves a strict redistribution of resources within the starving organism. Nutrients are withdrawn from organs less critical for basic survival (primarily skeletal muscle) and directed to the most vital consumers—the heart and brain. The transport pathway is analogous: substances pass from muscles into the blood, undergo processing in the gastrointestinal tract, and return to the blood to nourish vital centers.
Exogenous Nutrition and Pathophysiology of Overeating
Under normal conditions, the body functions via exogenous nutrition—the intake of food from external sources. The sensation of hunger begins to form as early as 3–4 hours after the last meal.
Here, the evolutionary principle of "preemptive feeding" comes into play. A person consumes food under the influence of hunger, despite the absence of a real deficit, while existing endogenous reserves would more than suffice for 20–30 days of autonomous operation.
With guaranteed and constant access to food, this principle becomes hazardous. Unjustified preemptive eating leads to severe pathophysiological consequences:
- Development of overweight and obesity.
- A sharp increase in the prevalence and severity of cardiovascular diseases.
- A significant reduction in overall life expectancy.
Clinical Application: Therapeutic Fasting
Understanding the mechanisms of the internal self-regulation link formed the basis of therapeutic fasting. It relies on the physiological ability of the body to alter (decrease) the intensity of metabolic processes in tissues, particularly in the brain.
- Neurotic disorders and obsessive-compulsive states.
- Cardiac rhythm disorders and arterial hypertension.
- Peptic ulcer disease of the gastrointestinal tract.
- Various "functional" disorders of body systems.
Individual variability in survival during fasting is high—ranging from 5–10 to 60 days, but on average, the safe reserve is 20–30 days, making short-term therapeutic fasting physiologically justified.