Adipose tissue can be found in a number of different places throughout the body. White adipose tissue is the most abundant type of fat in humans. It’s distributed within subcutaneous fat, visceral fat, and bone marrow fat.
Subcutaneous fat is found throughout the whole body, in the spaces between the skin and underlying muscles. Visceral fat is predominantly found around the organs in the abdominal cavity, such as the liver, intestines and kidneys, as well as in the peritoneum, which is a serous membrane that lines the outside of the abdominal organs. Visceral fat is more metabolically active than subcutaneous fat, meaning it breaks down stored fat more easily, releasing fatty acids into circulation. Due to its proximity, fatty acids travel to the liver through the portal vein, leading to an increase in liver fat known as hepatic steatosis or metabolic fatty liver disease (MAFLD).
White adipose tissue is also present in the bone marrow, a sponge-like tissue present in the central cavity of bones. In addition, white adipose tissue can be found in the pericardium surrounding the heart or cushioning other parts of the body, like the soles of the feet, eyeballs, and certain blood vessels.
Unlike white adipose tissue, brown adipose tissue, also known as brown fat, is mostly present during fetal life and in infants. In newborns, brown adipose tissue is mainly located on the back, along the upper half of the spine, in between the shoulders, and surrounding the kidneys. With age, the amount of brown fat decreases progressively. In adults, remaining brown fat deposits can be found surrounding the vertebrae, above the clavicles, in the upper back, and in the mediastinum, which is the central compartment of the thoracic cavity.
In healthy adults, adipose tissue usually comprises 20 to 25% of the total body weight. Nonetheless, the specific body fat percentage varies considerably amongst individuals, ranging from less than 10% to over 40% of the total body weight. Increased levels of adipose tissue have been associated with several health problems, including obesity, diabetes mellitus, and heart disease, among others.