Energy consumption and balance: food dynamics, activity and heredity
② Specific Dynamics of Food The specific dynamics of food, also known as the thermic effect of food, refers to the increased energy metabolism in the body after food intake, resulting in a greater loss of heat energy compared to before eating. This additional increase in energy metabolism caused by food intake is called the specific dynamics of food. The specific dynamics of food are generally considered to be due to the energy expenditure caused by the digestion of food.
The three major nutrients in food have different specific dynamic effects (SDE). Protein has the strongest SDA, accounting for about 30% of the body's energy production; carbohydrates are next, accounting for about 5% to 6%; and fat has the least, accounting for about 4% to 5%. When eating a mixed diet, the additional energy expenditure caused by SDA is approximately 628 to 837 kJ (150 to 200 kcal), equivalent to 10% of the basal metabolic rate.
③ Resting metabolic rate: The sum of basal metabolic rate and energy expenditure from the specific dynamic action of food is the resting metabolic rate, which is relative to energy expenditure during physical activity. For an individual, the resting metabolic rate is relatively constant.
④ The energy expenditure during physical activity is opposite to the metabolic rate during rest. The energy requirement during physical activity is variable and greatly depends on the intensity and duration of the activity. Generally speaking, the greater the intensity of the labor, the longer the duration, and the less skilled the worker, the more energy is consumed.
Using the lowest energy-consuming basal metabolic rate of 1.0, a comparison of the energy consumption of some common daily activities in women reveals that people who are frequently active and engage in high-intensity activities consume significantly more energy in the same amount of time than those who are rarely active (see table below).
Metabolic coefficients of women at different intensities of activity (FAO et al., 1985)
Activity content metabolic coefficient Activity content metabolic coefficient Activity content metabolic coefficient
Basal metabolism 1.0, Room cleaning 2.2, Seeding 4.0
Reading while lying down 1.1 Taking care of children 2.2 Drawing well water 4.1
Sitting quietly watching TV 1.2 Taking a walk 2.4 Digging holes to plant trees 4.3
Sewing clothes 1.4 Walking slowly 3.0 Digging 4.6
Peeling potatoes 1.4 Washing clothes 3.0 Slowly hiking uphill 4.6
Office work: 1.7; Normal walking speed: 3.4; Brisk uphill walking: 6.6
Winnowing grain 1.7; Cleaning the yard 3.5
(3) Factors affecting thermal energy balance
Theoretically, if a person consumes too much energy (eating too much) while expending less energy (lower metabolic rate at rest, reduced physical activity), it will lead to excess energy. However, the factors causing this change are extremely complex. There are innate genetic factors as well as acquired factors. Acquired factors, also known as environmental factors, include dietary structure, lifestyle, physical activity and exercise, psychological factors, social factors, diseases, and medications. These factors can all cause an imbalance in energy metabolism and are important causes of obesity.
**26. Is obesity related to genetic factors?**
Obesity has a hereditary component. Heredity refers to the transmission of traits from parents or other ancestors to offspring. The relationship between genetic factors and obesity has long been recognized by the medical community. Studies have shown that heredity not only affects the amount and distribution of body fat, but also influences factors such as energy intake, basal metabolic rate, physical activity habits, and nutrient utilization.
(1) Incidence of obesity as a genetic trait
Studies have shown that when one or both parents are obese, the incidence of obesity in their children is significantly higher. A large-scale population survey conducted by American scholars found that among adolescents aged 10-19, the obesity rate was approximately 35%-45% if one parent was obese; and as high as 70%-80% if both parents were obese. In contrast, the obesity rate was only 10% if both parents were thin or of normal build.
The above data indicates that obesity exhibits a clear familial aggregation, but in many cases, congenital genetic factors and acquired environmental factors are intertwined and difficult to separate. Different scholars have used Body Mass Index (BMI) to assess the heritability of obesity with significant differences (ranging from 0% to 90%), leading some to remain skeptical about the importance of genetics. Recent twin and adopted child studies have provided strong evidence for the role of genetic factors. In identical twin populations, one group grew up in the same environment after birth, while the other group lived in different regions; the incidence of obesity was very similar in both groups. In the latter case, because identical brothers (or sisters) grew up in different environments, the influence of environmental factors was largely excluded. Adoption studies found no significant relationship between the weight of adopted children and their adoptive parents, but a close correlation with the weight of their biological parents. These experimental results suggest that obesity is related to genetic factors.
(2) Genetic factors and body type
The role of genetic factors is not only reflected in the amount of fat in the whole body, but also in the local distribution of fat in the body.
Recent studies have found a close correlation between the distribution of localized fat and certain diseases affecting human health, such as diabetes and cardiovascular disease. The familial similarities in body fat distribution have also been further investigated. Sally et al. measured 173 pairs of identical twins and 118 pairs of dizygotic male twins, finding that the heritability of subscapular skinfold thickness was as high as 77%. Further research indicates that girls are generally more influenced by body type inheritance than boys.
(3) Genetics and Energy Intake
Energy and nutrient intake exhibits familial characteristics. Strong similarities are observed not only between spouses but also between parents and children. Several studies on twins have demonstrated this characteristic, which is more pronounced in monozygotic twins. Since monozygotic twins spend more time together and eat more often than dizygotic twins, the influence of shared environmental factors cannot be ruled out.
A study from the Quebec Family Research Institute shows that total energy intake across generations is almost unaffected by genetic factors, but heritability increases significantly when the intake ratios of carbohydrates, fats, and proteins are calculated separately. Assuming that the intake ratios of the three macronutrients are indicators of food choices, this result suggests that food choices are also regulated by genetic factors.
(4) Heredity and Energy Consumption
When calorie intake remains constant, reducing calorie expenditure leads to excess calorie expenditure, resulting in weight gain and even obesity. Therefore, individual differences in calorie expenditure are essential considerations when studying the genetic effects of obesity. Calorie expenditure factors are quite complex, including: basal or resting metabolic rate, the specific dynamic action of food, and calorie expenditure during physical exercise and other physical activities.