Fat Distribution and Health Risks: Unveiling Why "Apple-Shaped" Obesity Is More Likely to Lead to Various Chronic Diseases
(III) Distribution of body fat
Depending on where fat accumulates, obese individuals exhibit different body shapes, broadly categorized into two types, figuratively known as apple-shaped and pear-shaped. Apple-shaped refers to a large waist with fat accumulation under the skin of the abdomen and around the abdominal organs, while pear-shaped refers to fat accumulation in the buttocks and thighs. Men are primarily apple-shaped when obese, while women are more likely to be pear-shaped. The location of fat accumulation is controlled by hormones. In men, testosterone causes fat to accumulate in the abdomen, while in women, estrogen causes fat to remain in the buttocks and thighs. After menopause, the effects of estrogen weaken, and fat shifts back to the abdomen, resulting in a large belly.
From an aesthetic point of view, neither apple-shaped nor pear-shaped obesity is considered attractive. From a health perspective, apple-shaped obesity, characterized by abdominal fat accumulation, poses a greater health risk. This type of abdominal obesity, also known as central obesity, is more closely linked to the development of various chronic diseases. Researchers at West China Hospital in my country conducted a study on the body fat distribution characteristics of over 300 volunteers and found that the body fat distribution of obese people in China differs from that in Europe and America, exhibiting a characteristic of central obesity. Under the same body mass index, Chinese obese individuals have a higher body fat percentage than those with generalized obesity.
Why is abdominal fat accumulation more harmful? First, abdominal fat metabolism is more active, with a higher fat breakdown rate, producing more free fatty acids that enter the bloodstream. Second, because abdominal fat resides in the abdominal cavity, the large amounts of free fatty acids produced by the lipolysis of mast cells directly enter the hepatic portal system, stimulating hepatic gluconeogenesis and triglyceride synthesis. Increased abdominal fat is the primary cause of insulin resistance.
(iv) The relationship between insulin resistance and various chronic diseases
Insulin resistance is a major cause of many adult metabolic disorders, such as type 2 diabetes, hypertension, and dyslipidemia. When cells become resistant to insulin, glucose from the blood struggles to enter the cells. To maintain normal blood glucose levels, insulin secretion increases compensatorily, leading to hyperinsulinemia. Over time, pancreatic beta cells become overworked and their function gradually declines, resulting in insufficient insulin production to lower blood glucose levels to the normal range. This leads to diabetes.
Compensatory hyperinsulinemia caused by insulin resistance is also a major cause of hypertension. Elevated blood insulin levels act on the renal tubules, increasing sodium reabsorption and leading to water and sodium retention. Simultaneously, it enhances sympathetic nerve excitability, causing increased heart rate and cardiac output, directly promoting hypertension. Compensatory excess insulin secretion also increases triglyceride synthesis, raising low-density lipoprotein cholesterol (bad cholesterol) and lowering high-density lipoprotein cholesterol (good cholesterol) levels. Lipids deposit on the arterial walls, forming plaques that narrow the lumen, increasing the risk of coronary heart disease and stroke.
Measurement of body fat and definition of overweight and obesity
(I) Methods for measuring body fat
1. Human body density method (also known as underwater weighing method)
It is the "gold standard" for measuring body fat. Human fat tissue has a lower specific gravity than non-fat tissue. When a person is weighed underwater, based on Archimedes' principle of buoyancy, the volume and density can be calculated using a formula to determine the body fat percentage. This method yields relatively accurate results, but the equipment used is inconvenient to carry and the operation is complex, making it unsuitable for routine clinical use.
2. Computed Tomography (CT)
Scanning at the umbilicus level to calculate the visceral fat area is the most accurate method for diagnosing abdominal obesity, allowing for separate measurement of subcutaneous and visceral fat. However, the procedure is complex and requires expensive equipment, limiting its widespread use. 3. Bioelectrical impedance analysis (BIA) is based on the high electrical impedance of adipose tissue, allowing for indirect calculation of the proportion of body fat through the body's conductivity. This method is relatively simple and fast, and is currently widely used in field investigations.
body mass index method
Body Mass Index (BMI) is currently recognized as the simplest and most practical anthropometric indicator for estimating obesity levels. It is a value based on height and weight to determine the amount of body fat (degree of obesity). The specific calculation formula is as follows: BMI = weight (kg) / height (m)². For example, a middle-aged man who is 1.75 meters tall and weighs 78 kg would have a BMI of 78 / 1.75² = 25.5 (overweight).