Adipose tissue pathology, obesity classification and core clinical manifestations

Each fat cell contains 0.91–1.36 micrograms of lipid. When obesity occurs and progresses rapidly, only fat cell hypertrophy is generally observed. However, in cases of slow, long-term, and persistent obesity, both fat cells become hypertrophic and their number increases. The total number of fat cells in a normal person can increase from (2.68 ± 0.18) × 10¹⁰ to (7.70 ± 1.35) × 10¹⁰, a threefold increase. It is generally believed that fat cell hypertrophy and hyperplasia do not occur entirely concurrently in the occurrence and development of obesity, and normal women have more fat cells than men.

Obesity in the elderly without a prior history of obesity is primarily due to enlarged adipocytes. Adults with long-term severe obesity, in addition to enlarged adipocytes, also exhibit some degree of adipocyte proliferation. Those who are overweight at birth, significantly obese in infancy, or obese during puberty are likely to become obese in adulthood. In these adult obese individuals, enlarged and proliferating adipocytes coexist, demonstrating that the period of childhood obesity is crucial for the amount of adipocytes. This age group is more conducive to adipocyte proliferation than other age groups. Adipose tissue varies in color, distribution of blood vessels and nerves, and adipocyte structure.

Adipose tissue is generally classified into two types: white adipose tissue and brown adipose tissue. White adipose tissue is white or yellow in color, and its fat cells contain single lipid droplets the same size as the cells themselves; this is called monovesicular adipose tissue. Its blood vessels and nerves are not very developed, and most adipose tissue in the body belongs to this type. Brown adipose tissue contains many scattered small lipid droplets in its fat cells; this is called multivesicular adipose tissue. Its blood vessels and nerves are more abundant, but its distribution in the human body is limited, mainly found in the interscapular region, neck, armpits, mediastinum, and around the kidneys. Functionally, brown adipose tissue is a heat-generating organ.

When the body ingests food or is exposed to cold, the fat in brown adipose tissue burns, generating heat to meet the body's needs. This heat-generating tissue directly participates in the overall regulation of body heat, dissipating excess heat to the outside and maintaining a balance in energy metabolism. Studies have found that obese rats have reduced brown adipose tissue, which is replaced by white adipose tissue. When weight control is successful, the amount of brown adipose tissue in normally distributed areas increases, and white adipose tissue disappears. Obesity is classified. It is also classified according to etiology.

Simple obesity refers to obesity without any organic disease. This type of obesity accounts for more than 95% of all obesity cases and is the focus of clinical treatment. Simple obesity can be classified in several ways, including by degree of obesity (mild, moderate, and severe) and by fat distribution (generalized uniform obesity, central obesity, upper or lower body obesity, abdominal or gluteal obesity, etc.). Secondary obesity refers to obesity with a clear cause. It can also be classified according to obesity characteristics. Constitutional obesity is characterized by childhood obesity, with enlarged and hypertrophic fat cells distributed throughout the body; it is also called hypertrophic fat cell obesity or childhood-onset obesity.

Acquired obesity. Fat is mostly distributed in the trunk, and fat cells only enlarge without increasing in number. Most patients develop this condition after the age of 20-25 due to overnutrition and genetic factors; it is also known as simple hypertrophic fat cell obesity or adult-onset obesity. Clinical manifestations of obesity. Main manifestations. The clinical manifestations of obesity are excessive fat deposition throughout the body or in specific areas, resulting in mechanical damage and various diseases and metabolic changes, leading to a variety of symptoms. It can occur at any age, but is most common between 40 and 50 years old, and is also not uncommon in those over 60-70 years old.

In men, fat is primarily distributed in the neck, trunk, and abdomen, with less in the limbs; in women, it is mainly distributed in the abdomen, lower abdomen, buttocks, chest, and limbs. A newborn weighing over 3.5 kg, especially an overweight newborn whose mother has diabetes, should be considered a precursor to obesity. Overnutrition during childhood growth and development can lead to childhood obesity. Middle-aged women of childbearing age may experience varying degrees of obesity after two to three pregnancies and breastfeeding. Men over 40 and women after menopause often experience weight gain and varying degrees of obesity. Obesity is primarily characterized by the large accumulation of fat.

Depending on the distribution of fat, obesity can manifest as a "pear shape," where fat is mainly distributed in the buttocks, thighs, and groin; or an "apple shape," where fat is mainly distributed in the abdomen, especially the inner abdomen, sometimes referred to as "abdominal obesity." In men, fat is primarily distributed in the neck, trunk, and head, while in women it is mainly in the abdomen, lower abdomen, breasts, and buttocks. Common symptoms: Weight gain of 10%–20% above the standard weight usually does not cause noticeable symptoms. However, weight gain due to edema can cause noticeable symptoms such as eyelid swelling, difficulty clenching fists, and a feeling of heaviness in the lower limbs, even with a 10% increase in weight.

A range of clinical symptoms typically appear when a person's weight exceeds the standard by more than 30%. Moderate to severe obesity manifests as shortness of breath when climbing stairs, fatigue during physical labor, heat intolerance, excessive sweating, and varying degrees of lower limb edema. Some patients experience difficulty with daily activities such as bending over to put on shoes and socks, especially after a large meal when the abdomen is distended and bending forward is impossible. Weight-bearing joints are prone to degenerative changes and may experience pain. Prolonged excessive load on the spine can lead to proliferative spondylitis, manifesting as lower back and leg pain. Purple striae may appear on the skin, distributed on the outer buttocks, inner thighs, and lower abdomen; these are finer and pale redrulosic than those seen in Cushing's syndrome.

Excessive sweating leads to skin folds, erosion, dermatitis, and tinea. As obesity worsens, movement becomes difficult, and exertion causes shortness of breath and fatigue. Prolonged periods of sitting or lying still, or even excessive sleepiness, further promote obesity. Key symptoms include: Increased appetite: A large appetite and frequent hunger are both a cause and a significant symptom of obesity. Fatigue and drowsiness: The large amount of fat accumulated in the body creates an excessive burden, leading to decreased physical strength. Obese individuals require more energy and oxygen during activity than normal, hence their general dislike of exercise, drowsiness, and easy fatigue after even slight activity or physical labor.

Patients with relatively insufficient oxygen intake, coupled with inadequate alveolar ventilation, are prone to hypoxemia, which can easily lead to fatigue and drowsiness in obese patients. Furthermore, difficulty breathing can severely disrupt sleep, causing brief periods of apnea (sleep apnea), resulting in daytime sleepiness.