Specific dynamic action of food (SDA)
Any food intake is accompanied by an increase in energy expenditure, which is called the specific dynamic action of food. This process is triggered by afferent signals from oral and gastric receptors directed to the hunger center. Interestingly, heat production increases even during sham feeding, when food does not enter the stomach.
Different nutrients elicit responses of varying strength:
- Proteins produce the most powerful effect. They increase energy expenditure by 30–40%. This process starts 1.5–2 hours later and lasts up to 7–8 hours.
- Carbohydrates lead to a more modest increase of 4–6%, with the effect lasting 2–3 hours.
- Fats increase energy expenditure only negligibly.
Balanced diet
The concept of a balanced diet is based on three main pillars:
- Physiological compliance: the composition of ingested food must strictly match the body's current demands.
- Energy balance: the caloric value of the diet (adjusted for assimilation efficiency) must equal total energy expenditure. The energy expenditure formula includes basal metabolism, the specific dynamic action of food, and the cost of physical work.
- Macronutrient balance: proteins, fats, and carbohydrates should relate by weight as 1:2:4, and by caloric value as 15%, 30%, and 55%, respectively.
Theory of adequate nutrition
In addition to the classical approach, A.M. Ugolev put forward the theory of adequate nutrition (trophotropic theory). It shifts the focus to the subtle mechanisms of the digestive tract.
Its key provisions:
- Food must replenish the molecular composition of the digestive enzyme systems.
- Normal progression of both cavitary and membrane (surface) digestion must be ensured.
- Absorbed nutrients must strictly correspond to the body's current requirements (adequate resorption).
- Enormous importance is attached to the normal intestinal microflora.
This theory explains why, in genetic or acquired enzyme defects (fermentopathies), familiar foods become harmful. For example, milk ceases to be adequate food in case of lactase deficiency.
Components of a wholesome diet
Simply counting calories is not enough to build a proper diet. Nutrient quality is crucial:
- Proteins must have an optimal ratio of dispensable and indispensable amino acids.
- The fat profile requires fatty acids with varying degrees of saturation.
- The carbohydrate portion must be diverse and necessarily include ballast substances (dietary fibers such as pectin and cellulose).
- Micronutrients (vitamins and minerals) are regulated taking into account age, gender, energy expenditure, as well as season and climate.
Briefly: answers to topical questions
Which substances are classified as ballast carbohydrates (dietary fiber)?
Ballast carbohydrates (dietary fiber) include cellulose, hemicellulose, and pectic substances.
Sources also indicate that bacterial enzymes of the intestinal microflora break down cellulose, hemicellulose, and pectins that are not digested in the small intestine.
By what percentage do fats increase energy expenditure through the specific dynamic action of food?
The exact percentage increase in energy expenditure for fats is not specified in the sources: fats cause a negligible increase in energy expenditure due to the specific dynamic action of food.
For comparison, proteins increase energy expenditure by 30–40%, and carbohydrates by 4–6%.
What are the physiological functions of ballast substances (dietary fibers) in the gastrointestinal tract?
In the gastrointestinal tract, ballast substances enhance motor function and can also act as demineralizing factors.
Main effects of dietary fiber:
- Enhanced motility — a positive effect associated with increased motor function of the gastrointestinal tract, which is used to prevent constipation.
- Demineralizing action — ballast substances can reduce the absorption of minerals.
- Digestive function of microflora — bacterial enzymes in the large intestine break down fibers that are not digested in the small intestine.
It is easy to remember the Protein:Fat:Carbohydrate ratio by weight using powers of two: 2^0 (1) : 2^1 (2) : 2^2 (4).
Class and exam questions
What constitutes the total energy expenditure of the body?
Total energy expenditure consists of the basal metabolic rate, the specific dynamic action of food, and energy spent on physical work.
Which nutrient stimulates thermogenesis the most after eating?
Proteins cause the maximum increase in energy expenditure—they raise energy expenditure by 30–40%.
What role do bacteria play in Ugolev's theory?
In the trophotropic theory of adequate nutrition, the intestinal microbiota is viewed as a vital participant in digestion, without which normal nutrient assimilation is impossible.
What else to study on this topic
- Functions of nutrition (plastic and energetic)
- M.N. Shaternikov's contribution to the science of nutrition
- Specialized nutrition for specific groups according to A.A. Pokrovsky
- Principles of nutritional standard setting
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