Changes in adipocytes, abnormal lipid metabolism, and imbalance in energy metabolism

33. What changes occur in fat cells that cause weight gain in the human body?

Obesity, in terms of fat cells, is determined by two factors: (1) mainly by congenital genetic factors, with fat cells increasing in number during infancy and early childhood through cell division; (2) acquired factors related to food intake and expenditure, due to the increase in fat cell volume.

The increase in the size of human fat cells is mainly determined by the amount of food intake and energy consumption.

Normal human fat cells are typically 67–98 micrometers in size and contain about 0.6 micrograms of fat.

If food intake is large and energy consumption is low, the volume of fat cells can double, reaching 127-134 micrometers, and the fat content can reach 0.91-1.50 micrograms.

The fat cells of an adult have an unlimited capacity.

If fat cells grow too large to accommodate the deposited fat during infancy, new fat cells will divide to take over the task. Therefore, human fat is a storage facility, and the degree of obesity is limitless.

Fat cells can increase or decrease in size and can proliferate, making them very active.

Gaining weight is easy, but losing weight is also possible.

Generally speaking, mild to moderate obesity in teenagers, or middle-aged obese individuals without a history of childhood obesity, is mainly caused by hypertrophic fat cells and tissue proliferation. Obesity in the elderly is mainly due to hypertrophic fat cells, and these individuals are relatively easier to lose weight in.

34. What are the causes of abnormal lipid metabolism in obesity?

Obese patients not only have an increase in fat cell tissue, but also a significant increase in blood lipids, especially triglycerides, free fatty acids and cholesterol levels, which are often higher than normal, and often lead to varying degrees of cardiovascular and cerebrovascular diseases.

The causes of hyperlipidemia are not due to a single factor, and the mechanisms are quite complex.

(1) Dietary factors: Obese people consume more calories than they need, with an increased proportion of fats, which is one of the causes of hyperlipidemia.

A survey conducted in Beijing on the fat intake of urban residents and farmers showed that in 1982, it increased by 0.65 to 1.2 times compared to 1959, and was 10 times higher than that of the Japanese.

(Table content has been deleted)

(2) Genetic factors: Obese patients with a family history of obesity often have hyperlipidemia, and even those with normal weight in the family may have hyperlipidemia.

35. What is the relationship between obesity and energy metabolism?

Traditional views hold that the main cause of obesity is overeating.

Recent studies have shown that obesity is a congenital condition.

Obese patients have a low energy metabolism rate due to genetic reasons, which leads to obesity.

The food we ingest must be digested and absorbed to be converted into bioenergy, which is then supplied to the whole body to sustain life.

This transformation is called "energy metabolism".

The energy substances provided by food in energy metabolism are mainly protein, fat, and carbohydrates (also known as grains), which are called the three major nutrients.

After conversion, about 50% of the energy is converted into body heat to maintain body temperature, and the other 50% is converted into chemical energy to meet the life needs of various tissue cells.

When the energy produced by ingested nutrients is roughly equal to the energy actually consumed by the body, it is called metabolic balance; when the energy intake exceeds the energy required for consumption, it is a positive balance, and the excess is converted into fat for storage; when the energy intake is insufficient to meet the energy needs, the body breaks down fat from fat stores to provide energy, which is a negative balance.

Under normal circumstances, obese people have a positive energy balance, meaning they consume more energy and consume less, because obese people often eat more and are less active.

Many studies have been conducted on this topic, but the conclusions are still inconsistent.

Some researchers have conducted comparative observations on the activity levels of normal-weight children and obese children, and found that obese children do indeed have less activity levels than children of normal weight. However, when their respective weights in kilograms are converted into the activity load, the two are similar.

Other studies have reported that among subjects with a family history of obesity, even those of normal weight had a lower capacity for thermogenesis after eating than those without a family history of obesity.

In real life, it is true that some overweight people are more active than thin people, while some thin people eat more than overweight people.

It is evident that the same amount of food intake produces different metabolic effects in different people, which involves individual differences in food digestion, absorption, and energy conversion.

The same amount of exercise consumes different amounts of energy in different people, suggesting that different people utilize nutrients at different rates.

Nevertheless, for an individual, the function of being addicted should be relatively constant.

Obesity is a result of a positive metabolic balance.