Subcutaneous fat mass (SAT) is the adipose tissue stored directly beneath the skin, serving as the body’s primary long-term energy reserve. Subcutaneous fat mass is a significant component of overall body composition. Although fat tissue has often been viewed negatively, it is an active and necessary organ that performs numerous functions important for maintaining health and metabolic balance. The distribution and quantity of this tissue play a role in an individual’s health profile.
Defining Subcutaneous Fat and Its Location
Subcutaneous fat is anatomically positioned in the hypodermis, the innermost layer of the skin situated directly beneath the dermis and epidermis. This layer consists mainly of loose connective tissue, which includes a high concentration of adipocytes, or fat cells. The subcutaneous tissue also contains larger blood vessels and nerves that pass through it on their way to the dermis.
This fat layer is the most abundant type in the body, typically accounting for about 90% of total body fat. It is the soft, palpable fat that can be grasped or pinched in areas like the abdomen, thighs, and hips. The thickness and distribution of this layer vary significantly among individuals, influenced by genetics, sex, age, and nutritional status.
Distinguishing Subcutaneous Fat from Visceral Fat
Distinguishing subcutaneous fat (SAT) from visceral fat (VAT) is necessary for understanding health implications. SAT is located just beneath the skin, while VAT is stored deeper within the abdominal cavity, surrounding internal organs such as the liver and intestines. This difference in location is responsible for their contrasting metabolic characteristics.
Subcutaneous fat is generally considered metabolically benign or even protective, especially the fat stored in the lower body (gluteofemoral region). This tissue acts as a storage depot for excess energy, preventing fat from accumulating in organs like the liver and muscle, a phenomenon known as ectopic fat storage. This protective role may contribute to better insulin sensitivity.
Visceral fat, in contrast, is highly active metabolically and is associated with increased health risks. Because VAT drains directly into the liver via the portal vein, it releases fatty acids and signaling molecules that directly affect liver function. This direct access to the liver is believed to contribute to insulin resistance, chronic low-grade inflammation, and a higher risk of conditions like type 2 diabetes and cardiovascular disease.
Biological Roles of Subcutaneous Fat
Subcutaneous fat acts as a mechanical cushion, absorbing shock and protecting underlying structures like muscles, bones, and internal organs from physical impact. This padding is noticeable in areas exposed to frequent pressure, such as the hands and buttocks.
The tissue also plays a role in thermal insulation, helping the body regulate its temperature and maintain a stable internal climate. The layer of fat beneath the skin minimizes heat loss and protects against extreme temperatures.
Furthermore, subcutaneous fat is a dynamic endocrine organ that actively participates in metabolic regulation by producing and secreting various hormones. These hormones include leptin, which regulates appetite, and adiponectin, which improves insulin sensitivity and has anti-inflammatory properties. A sufficient amount of healthy subcutaneous fat is necessary for maintaining whole-body energy balance.
Methods for Assessing Body Fat Distribution
Accurately quantifying subcutaneous fat mass and its distribution is necessary in clinical and research settings. One accessible and inexpensive method is the use of skinfold calipers. This technique involves measuring the thickness of the skin and underlying subcutaneous fat at specific anatomical sites, such as the triceps and suprailiac regions. The measurements are then used in prediction equations to estimate total body fat percentage.
More advanced imaging techniques provide highly accurate measurements that can differentiate between SAT and VAT. Dual-Energy X-ray Absorptiometry (DEXA) scans measure total fat mass, lean mass, and bone density. While effective for total body fat, DEXA is less precise for distinguishing deep fat depots compared to cross-sectional imaging.
Computed Tomography (CT) and Magnetic Resonance Imaging (MRI) are considered the gold standard for precisely quantifying both subcutaneous and visceral fat. These techniques provide detailed images that allow researchers to segment the abdominal area into SAT and VAT compartments, offering a clear picture of fat distribution. While highly accurate, CT and MRI are more expensive and less available for routine use.