Fat
Overview
Fat is a major energy storage source in living organisms and a component of cell membranes and hormones, performing important physiological functions in the human body. Adipose tissue is responsible for maintaining energy homeostasis, temperature regulation, protecting internal organs, and secreting various signaling molecules. However, excessive fat accumulation acts as a key factor causing obesity and metabolic diseases.
Main Content
Types and Functions of Adipose Tissue
The human body contains three main types of adipose tissue: white adipose tissue (WAT), brown adipose tissue (BAT), and beige adipose tissue. White adipose tissue primarily stores energy in the form of triglycerides; when adipocytes enlarge and proliferate, it accumulates as visceral fat. Brown adipose tissue is rich in mitochondria and participates in non-shivering thermogenesis that generates heat, and is present in newborns and some adults. Beige adipose tissue exists within white adipose tissue and is a plastic cell type that acquires brown-adipocyte-like functions in response to certain stimuli (cold, exercise), and has recently become a major subject of metabolic research.
Adipose tissue is not merely a storage organ but an endocrine organ, secreting adipokines such as leptin and adiponectin to influence appetite regulation, insulin sensitivity, and inflammatory responses. Subcutaneous fat plays roles in insulation and cushioning against external impact, while visceral fat supports the spaces between internal organs.
Types and Metabolism of Dietary Fat
Dietary fat is classified by fatty acid structure into saturated fat, unsaturated fat, and trans fat. Saturated fat is found mainly in animal fats, and excessive intake increases blood LDL cholesterol. Unsaturated fat is divided into monounsaturated fat (olive oil, avocado) and polyunsaturated fat (omega-3 and omega-6 from fatty fish, nuts), and is known to be beneficial for cardiovascular health. Trans fat is produced during partial hydrogenation and is dangerous fat that raises LDL while lowering HDL. During digestion, fat is broken down by bile and lipases into free fatty acids and monoglycerides, then absorbed and transported through lymphatic vessels in chylomicrons.
Fat and Health Diseases
Excessive abdominal fat (visceral fat) increases the risk of metabolic syndrome, type 2 diabetes, hypertension, dyslipidemia, and cardiovascular disease. Conversely, an appropriate body fat percentage is essential for immune function and hormonal balance; in women, being underweight increases the risk of amenorrhea and osteoporosis. Non-alcoholic fatty liver disease occurs when fat excessively accumulates in liver cells, and its prevalence is increasing across countries. Recent research in personalized nutrition emphasizes that, more than the total amount of fat, fatty acid composition and timing of intake have greater effects on health.
Regulatory Mechanisms of Fat Accumulation
The storage hormone insulin promotes fat synthesis in adipocytes and suppresses fat breakdown. In contrast, glucagon and catecholamines activate hormone-sensitive lipase to break down fat. Genetic factors (e.g., FTO gene variants), epigenetic changes, and gut microbiota composition also influence fat accumulation. Recently, the remodeling processes of adipocytes themselves—adipocyte death, angiogenesis, and fibrosis—have been highlighted as key factors determining the complications of obesity.
Latest Trends
In 2024–2025, glucagon-like peptide-1 (GLP-1) receptor agonists have emerged as the standard for obesity treatment, drawing renewed attention to the physiological understanding of adipose tissue. In particular, the concept of “healthy expansion”—beyond simple weight loss—has arisen, and research is actively being conducted on controlling adipocyte size and promoting vascularization. Non-pharmacological strategies to activate brown fat (cold adaptation, exercise) and the effects of brown-fat-derived metabolites on insulin sensitivity are being validated in clinical settings. In addition, anti-inflammatory therapies that block the pathways by which inflammatory signaling from adipose tissue immune cells (e.g., macrophages) leads to systemic disease are in early clinical trials, and drug delivery systems targeting the adipose microenvironment are being studied. Among dietary fats, evidence has accumulated for the primary prevention of cardiovascular disease using the anti-inflammatory effects of omega-3 fatty acids; in 2025, the European Society of Cardiology guidelines proposed a new atherogenic index (e.g., the ω-3/ω-6 ratio) assessing fat quality, indicating that nutritional approaches are also evolving.
Related Topics
- [[Obesity]]
- [[Cholesterol]]
- [[Protein]]
- [[Carbohydrate]]
- [[Metabolic syndrome]]