Subcutaneous adipose tissue (SAT) is the layer of fat located directly beneath the skin. It is composed of fat-storing cells called adipocytes, which are held within a framework of loose connective tissue. As the deepest layer of the skin, it sits on top of muscle and bone, forming a continuous sheet found in varying thicknesses over most of its surfaces.
Primary Functions of Subcutaneous Fat
One of the primary purposes of subcutaneous adipose tissue is to serve as the body’s energy depot. When caloric intake exceeds immediate energy needs, the body converts the excess into lipids, which are then stored within the adipocytes. This stored fat can be mobilized and broken down to provide energy during periods of fasting or increased physical demand.
Beyond energy storage, this tissue layer provides thermal insulation for the body. By acting as a barrier between the internal organs and the external environment, it helps to slow the loss of heat and maintain a stable core body temperature.
Subcutaneous fat also functions as a protective cushion for the body’s underlying structures. It pads muscles, bones, and delicate organs, absorbing shock and reducing the risk of injury from impacts. Special connective tissue within the layer also helps attach the skin to the muscles and bones below it.
Finally, subcutaneous fat is an active endocrine organ that synthesizes and secretes various hormones and signaling molecules. These substances are released into the bloodstream and travel to other parts of the body, where they participate in regulating a wide range of physiological processes. This communicative function connects SAT to the broader metabolic and inflammatory systems of the body, influencing overall health.
Distinguishing Subcutaneous and Visceral Fat
A primary distinction between subcutaneous and visceral fat is their location. Subcutaneous fat is the tissue found just beneath the skin, often described as the “pinchable” fat that can be physically grasped. This placement separates it from the deeper structures of the body.
Visceral fat, in contrast, is located deep within the abdominal cavity, where it cannot be seen or easily measured from the outside. It fills the spaces between major internal organs such as the liver and intestines. Its proximity to the portal vein means that substances it releases can travel directly to the liver, influencing metabolic processes.
The two types of fat also differ significantly in their metabolic activity. Visceral fat is more metabolically active, meaning it breaks down and releases its components into the bloodstream more readily. This tissue has a higher density of blood vessels and inflammatory cells compared to subcutaneous fat, and its secretions can promote inflammation.
These differences in location and activity lead to distinct associations with health outcomes. High levels of visceral fat are strongly linked to an increased risk of developing metabolic syndrome, type 2 diabetes, and cardiovascular diseases. The inflammatory substances released by visceral fat can interfere with normal insulin function. While excessive accumulation of any fat is not ideal, subcutaneous fat is considered less detrimental than excess visceral fat.
Metabolic Role in Health
Subcutaneous adipose tissue is a highly active participant in the body’s endocrine system, producing hormones that regulate metabolism. One hormone it secretes is leptin, which plays a part in appetite control. Leptin signals to the brain to suppress hunger and increase energy expenditure when fat stores are sufficient.
Another hormone produced by subcutaneous fat is adiponectin. This protein helps to improve the body’s sensitivity to insulin, allowing cells to more effectively absorb glucose from the bloodstream. Higher levels of adiponectin are associated with a lower risk of developing type 2 diabetes.
Healthy subcutaneous tissue can effectively store excess fatty acids, preventing them from accumulating in other tissues like the liver and muscle where they can cause dysfunction. This capacity to safely “buffer” lipids is a protective metabolic function. It contributes to maintaining insulin sensitivity and overall metabolic stability.
When subcutaneous fat accumulates excessively, it can become dysfunctional. The fat cells may become enlarged and stressed, leading to a state of chronic, low-grade inflammation. In this state, the tissue releases more pro-inflammatory molecules and fewer beneficial ones like adiponectin, which can contribute to systemic insulin resistance.
Factors Influencing Subcutaneous Fat Levels
The amount and distribution of subcutaneous adipose tissue are significantly shaped by genetic predispositions. Heredity influences an individual’s baseline number of fat cells and where those cells are most likely to accumulate. These genetic factors can determine whether a person is more inclined to store fat in the upper or lower body, contributing to natural variations in body shape among different people.
Hormones also play a major part in dictating fat distribution patterns. Estrogen, for example, tends to promote fat storage in the hips, thighs, and buttocks. Testosterone, on the other hand, encourages fat storage around the abdomen, as does the stress hormone cortisol.
Lifestyle choices, particularly diet and physical activity, have a direct impact on the overall volume of subcutaneous fat. A consistent caloric surplus leads to the expansion of fat stores. Conversely, regular exercise and a balanced diet can help manage these fat levels by promoting the use of stored lipids for fuel.
Finally, the process of aging brings about natural changes in both the amount and location of subcutaneous fat. As people get older, metabolic rates tend to slow, and there is often a redistribution of fat from just under the skin to deeper, visceral stores. For women, the decline in estrogen after menopause often leads to a shift in fat storage from the lower body to the abdomen.