Basal metabolism is the rate of energy expenditure per unit of time. The correctness of its measurement requires a strict set of criteria. These include being in a physically and psychologically calm state, a thermally neutral environment, and a post-absorbing state.
Description
Heat production in the body is known as thermogenesis. It can be measured to determine the amount of energy expended. Basal metabolism decreases with age. It can also be increased by building muscle mass. Diseases, diet, stress levels, environmental temperature all affect overall energy expenditure.
Calculation methods
Accurate calculation of basal metabolic rate requires that the person's sympathetic nervous system is not stimulated. It can be measured by gas analysis using direct or indirect calorimetry.
You can also calculate your basal metabolic rate using an equation using age, sex, height, and weight. Studies using both methods provide evidence of validityrespiratory quotient, which measures the intrinsic composition and utilization of carbohydrates, fats, and proteins as they are converted into units of energy substrate.
Phenotypic Flexibility
Basal metabolism is a flexible trait. It can be reversibly adjusted within the body. For example, lower temperatures usually result in higher metabolic rates. There are two models that explain how basal metabolism changes with temperature: the Variable Maximum Model (VMM) and the Variable Fractional Model (VFM).
PMM claims that the metabolic rate increases during the cold season. PFM says basal metabolic rate is a constant.
Research
Early work by scientists J. Arthur Harris and Francis G. Benedict showed that approximate metabolic values can be derived using body surface area (calculated from height and weight), age, and sex. This takes into account oxygen and carbon dioxide indicators taken from calorimetry.
By eliminating the sex differences that arise from the accumulation of adipose tissue by expressing the metabolic rate per unit of "fat-free" body weight, the calculation value of the basal metabolic rate (BMR) between the sexes is essentially the same.
Physiology
The main organ responsible for regulating metabolism is the hypothalamus. It forms part of the side wallsthird ventricle of the brain. The main functions of the hypothalamus:
- Control and integration of the activity of the autonomic nervous system (ANS). It regulates the contraction of the heart muscle and the secretion of many endocrine organs (thyroid gland).
- Regulation of feelings of rage and aggression.
- Control body temperature.
- Regulating food intake.
The center of nutrition (hunger) is responsible for the sensations that make a person look for food. With enough nutrition, leptin levels become high. The saturation center is stimulated. Impulses are sent that block the feeling of hunger. If there is not enough food, ghrelin levels rise. Receptors of the hypothalamus are irritated. There is a feeling of hunger.
The thirst center works in a similar way. The increased osmotic pressure of the extracellular fluid stimulates the cells of the hypothalamus. If the thirst is satisfied, the pressure will decrease. These functions form a survival mechanism that forces a person to maintain bodily processes as measured by basal metabolic rate.
Write parameters
Basal Metabolism Formulas were first published in the early twentieth century. They used the following concepts:
- P - total heat production at full rest;
- m - mass (kg);
- h - height (cm);
- a - age (years).
One of the popular estimation methods is the Harris-Benedict formula:
- for women: UBM=665 + (9.6 × m) + (1.8 × h) - (4.7 ×a);
- for men: BMR=66 + (13.7 × m) + (5 × h) - (6.8 × a).
Why calculate?
Basal metabolic rate can be used to gain, lose, or maintain weight. Knowing how many calories are burned, you can calculate how much to consume. For example:
- Eat and burn equal amounts of calories to maintain weight;
- to recruit - consumption must exceed combustion;
- to lose less calories than you burn.
How to calculate calories
The next step after estimating basal metabolic rate is to calculate lifestyle calories:
- Seated. Without physical activity. Multiply BMR by 1, 2.
- Slightly active. Doing light exercise 1-3 times a week. Multiply UBM by 1, 375.
- Moderately active. Physical activity 3-5 times in seven days. UBM times 1.55.
- Active. Up to seven workouts per week. Multiply BMR by 1, 725.
- Hard work. Constant physical activity. UBM times 1, 9.
The formula would be more accurate if it included body composition, weight history and other factors.
Reasons for individual differences
In Scotland, a basal metabolic rate study was conducted in 150 adults. The indicators ranged from 1020 to 2500 kcal/day. The researchers calculated that 62.4% of this variation was due to differences in "fat-free mass." Other reasons included body fat(6.8%), age (1.8%), and experimental error (2.1%). The rest of the variation (26.6%) was unexplained. She was not affected by gender or tissue size in high-energy organs such as the brain.
Biochemistry
The increase in postprandial thermogenesis in basal metabolism occurs depending on the composition of the food consumed. Almost 70% of the total human energy consumption is associated with life support processes that occur in the body. Approximately 20% of energy expenditure comes from physical activity. About 10% - for the digestion of food. These processes require the consumption of oxygen with coenzymes. This gives energy to survive and expel carbon dioxide.
Most of the energy the body spends on maintaining the required level of fluid in the tissues. About one tenth is devoted to mechanical work (breathing, digestion and heartbeat).
The breakdown of large molecules into smaller ones is catabolism (for example, the breakdown of proteins into amino acids). Anabolism is the process of their creation (proteins are converted into amino acids). Metabolism is the result of these reactions.
Heartbeat hypothesis
In 1925, Raymond Pearl proposed that lifespan is inversely related to basal metabolic rate. Support for this theory comes from the fact that large animals have longer life spans. This hypothesis has been supported by several new studies linking lower basal levelsmetabolism with an increase in the life cycle in the animal kingdom, including humans. Calorie restriction and lowering thyroid hormone levels have been associated with higher longevity in animals.
However, the ratio of total daily energy expenditure to metabolic rate at rest can vary from 1.6 to 8.0 in different mammalian species.
With allometric scaling, maximum potential lifespan is directly related to metabolic rate.
Medical aspects
A person's metabolism depends on his activity and physical condition. Decreasing food intake usually reduces its rate. The body tries to conserve energy. Studies show that a low-calorie diet (less than 800 calories per day) reduces the rate of metabolic processes by more than 10 percent. Menopause and disease also affect metabolism.
