In Chinese adults, visceral adipose tissue shows higher expression of TNF-alpha and TLR4 mRNA than subcutaneous adipose tissue in obese individuals, whereas subcutaneous adipose tissue shows higher expression of TNF-alpha and TLR4 mRNA than visceral adipose tissue in lean individuals, indicating that depot-specific inflammatory gene regulation differs by obesity status.

In obese people, fat cells around the organs release more fatty acids, which turn on a protein called TLR4. This triggers a chain reaction inside the cells that turns on genes making inflammatory signals like TNF-alpha. At the same time, the same fat cells make more of an enzyme that creates active cortisol, which further boosts inflammation and fat growth. Together, these two pathways make the belly fat much more inflamed than the fat under the skin. In lean people, this doesn't happen — fatty acids stay low, TLR4 stays quiet, and cortisol doesn't pile up, so the fat under the skin ends up more inflamed than the belly fat.