In-depth analysis of obesity: from body fat measurement to differential diagnosis of complex types

Total body fat accounts for approximately 15% of body weight in men and 22% in women. Obesity is defined as having more than 25% of body fat in men and more than 30-35% in women. Measuring subcutaneous fat thickness can be used as an auxiliary diagnostic method for obesity-this is done using a special skin fold caliper. For naturally lean individuals, the subcutaneous fat thickness under the shoulder blades should not exceed 14 mm; for naturally stocky individuals, it should not exceed 23 mm; the average subcutaneous fat thickness for a person of normal build at age 25 is 12.4 mm; a thickness exceeding 14 mm indicates obesity.

X-ray imaging or ultrasound can also be used to measure the thickness of subcutaneous fat, but these examinations are rarely performed in China at present. With the development of medical science and the improvement of diagnostic technology, it is now possible to determine the number and size of fat cells. The number of fat cells in a normal middle-aged person is about 3.1 billion, while the number of fat cells in an extremely obese person can reach 10 to 12 billion, which is 3 to 4 times that of a normal person.

Although obesity is a common sign of endocrine-metabolic disorders, the vast majority are caused by constitutional factors and overeating. After making a diagnosis, further differentiation of the cause and type is necessary. (I) Simple obesity: Fat distribution is widespread, appetite is good, glucose tolerance is slightly impaired, and blood lipids (total lipids, triglycerides, free fatty acids, cholesterol, etc.) may be elevated. A few may have similar manifestations to Cushing's syndrome, such as hypertension, impaired glucose tolerance, amenorrhea or oligomenorrhea, acne, hirsutism, and striae. However, simple obesity does not present with central obesity, thin skin, plethora, purpura, and typical purple striae; X-ray examination shows no enlargement of the sella turcica or significant osteoporosis; the low-dose dexamethasone test is positive, and blood cortisol levels are not high. These characteristics can differentiate it from Cushing's syndrome.

(II) Water Retention Obesity: This is relatively common, especially in middle-aged and menopausal women, and less common in men. This type of obesity develops rapidly, with weight gain of 10-15 kg or more within a few days or 1-2 years. The obesity is unevenly distributed and accompanied by edema. Fat is mainly distributed in the legs, thighs, buttocks, abdomen, and breasts, while the back is not significantly affected. The increase and decrease in weight and edema show a clear pattern, generally more pronounced in the afternoon than in the morning, aggravated by fatigue or exercise, and relieved by rest and lying down. The average weight gain in a normal person is 0.4 kg in the evening compared to the morning, but in those with water retention obesity, it averages 1.5 kg. Due to increased body fluid, symptoms such as headache, irritability, and depression are common. The cause of edema may be insufficient sympathetic nerve excitation when standing, leading to relatively insufficient blood supply to the brain. This, through the reflex action of volume receptors, causes increased aldosterone secretion, resulting in water retention and water retention obesity.

(III) Cushing's syndrome: Fat distribution shows central obesity, mainly manifested as obesity in the face, neck, chest, and abdomen; purple striae on the limbs; increased hair growth; sexual dysfunction; amenorrhea; positive dexamethasone test; increased urinary 17-hydroxycorticosteroid and 17-ketosteroid excretion; and elevated blood cortisol levels. (IV) Hypothyroidism-related obesity: Not true obesity, but mainly characterized by a bloated appearance due to myxedema. Basal metabolic rate, blood thyroxine levels, serum protein-bound iodine, thyroid 131 iodine uptake rate, and serum T₃ and T₄ are all decreased, but cholesterol and triglycerides are increased. Other less common types of obesity can be diagnosed through a comprehensive analysis of medical history, physical examination, and laboratory tests.

Advances in medical science have led to obesity no longer being seen as a symbol of health. However, many people remain unaware of the harm obesity poses to human health, believing that "being a little overweight is okay" and adopting an indifferent attitude. The harmful effects of obesity on human health have been confirmed by numerous studies. It is estimated that approximately one-third of people have reduced life expectancy due to being overweight or obese. While cancer treatment can extend average lifespan by two years, treatment for obesity can extend it by four years. Statistics on common diseases causing human death have revealed significant differences in mortality rates between obese and normal-weight individuals.

Diseases such as diabetes, cirrhosis, appendicitis, and gallstones cause a mortality rate 2.06 to 3.83 times higher in obese individuals than in those of normal weight. Chronic nephritis, cerebral hemorrhage, coronary heart disease, and acute accidents cause a mortality rate 1.31 to 1.91 times higher than in those of normal weight. If everyone could maintain a normal weight, the mortality rate from coronary heart disease would be reduced by 35%. Mortality increases with weight. For example, in the 40-49 age group, those exceeding their ideal weight by more than 30% have an average mortality rate of 42% for men and 36% for women, demonstrating a significantly higher mortality rate among obese individuals compared to those of normal weight.