Adipose tissue is often reduced to a simple accumulation of fat that one would like to get rid of, for aesthetic reasons. Far from being a passive entity, this adipose tissue is nevertheless an organ in its own right, fulfilling important physiological functions.

Adipose tissue is made up mainly of fat cells, adipocytes, of which there are different types. There are thus two main types of adipose tissue:

• le white adipose tissue (or white fat), consists of white adipocytes, triglycerides, fibroblasts, macrophages, blood and endothelial cells and preadipocytes. In adults, this white adipose tissue represents 15 to 20% by weight. A distinction is made between white subcutaneous adipose tissue and white visceral adipose tissue. The first is located under the skin, in the superficial and deep layers. It is distributed over the whole body, but with different areas of concentration depending on the sex: in the stomach and shoulders in men, below the belt at the level of the thighs, hips and buttocks in men. wife. This adipose tissue is indeed used to nourish the fetus in the event of restriction of caloric intake during pregnancy. This localization gradually disappears at menopause, promoting abdominal distribution. The visceral white adipose tissue, or intraperitoneal, is located in the abdomen, behind the abdominal muscles. It represents 5 to 20% of total adipose tissue depending on the person. It is involved in all metabolic activities and is particularly sensitive to insulin.
• le adipose tissue brown (or brown fat) is made up of brown adipocytes. In humans, it is mainly present in the fetus and newborn.

Adipose tissue is an organ in its own right that performs different functions within the body depending on the type of skin tissue.

An energetic role

The white adipose tissue, and particularly the subcutaneous, thus constitutes the most important energy reserve of the organism. Following the process of lipogenesis, energy is stored there in the form of triglycerides, which will serve as an energy source when the carbohydrate reserves are depleted.

An endocrine function

White adipocytes secrete hormones directly linked to the central nervous system. They secrete in particular adipokines such as leptin, often qualified as “the hormone of satiety”. In connection with the hypothalamus, it indeed regulates appetite. Adipocytes also secrete pro-or anti-inflammatory cytokines, estrogens, prostaglandins and other hormones. These hormones play a decisive role in regulating the energy balance.

A role of thermoregulation

Brown fatty tissue is a source of heat. According to a 2014 study, it would also be able to burn calories.

A role of support and mechanical protection

Adipose tissue protects mechanically stressed areas of the body, such as the arch of the foot, the buttocks. It also helps support the organs.

obesity

With their large capacity for storing fat in the form of triglycerides, adipocytes absorb energy surpluses. The adipose tissue then increases, both by increasing the size of the adipocytes and by multiplying their number. However, an excessive accumulation of adipose tissue is at the origin of obesity, moreover defined by the WHO (World Health Organization) as “an abnormal or excessive accumulation of adipose tissue representing a danger to health” .

Clinically, there are two types of obesity depending on the location of the adipose tissue:

• abdominal obesity, with adipose tissue concentrated on the stomach. We speak of abdominal obesity in the presence of a waist circumference greater than 94 cm in men and 80 in women.
• gynoid obesity, with adipose tissue concentrated on the buttocks, hips, thighs.

This distinction is not only aesthetic. It is important for health because depending on its location, excess adipose tissue will not have the same consequences, especially on the metabolic and cardiovascular levels. Abdominal obesity, also known as visceral obesity, is thus considered to be the most harmful to health. Unlike subcutaneous adipose tissue, visceral adipose tissue is in fact an important cardiovascular risk factor and predictor of the onset of diabetes and / or dyslipidemia.

Metabolic syndrome

Metabolic syndrome, sometimes called syndrome X, is not a disease but a collection of physiological and biochemical disorders. According to the International Diabetes Federation (IDF), a person has metabolic syndrome when they have abdominal obesity and at least two of the following factors:

• a high level of triglycerides: greater than or equal to 1,7 mmol / L, i.e. the equivalent of 150 mg / dL)
• low HDL cholesterol (“good” cholesterol): less than 1,03 mmol / L (40 mg / dL) in men, 1,29 mmol / L (50 mg / dL) in women
• arterial hypertension: blood pressure greater than or equal to 130 mmHg for systolic blood pressure and 85 mmHg for diastolic blood pressure
• high fasting blood glucose levels: greater than or equal to or greater than 5,6 mmol / L (100 mg / L).

The metabolic syndrome can eventually lead to many complications: type 2 diabetes, cardio-vascular diseases.

It is now clearly established that there is a strong link between the importance of abdominal adipose tissue and various abnormalities associated with metabolic syndrome. This abdominal adipose tissue in fact secretes hormones – leptin, prostaglandins, angiotensinogen and angiotensin II, adiponectin, resistin – directly involved in the occurrence of metabolic and cardiovascular complications.

Lipodystrophies

Lipodystrophies include a set of rare congenital or acquired diseases (partial lipodystrophic syndrome of Dunnigan, lipodystrophies of Barraquer and Simons, etc.) characterized by a generalized or partial absence of adipose tissue, more or less associated with an hypertrophy of this adipose tissue in certain areas. ‘other body areas. These distribution abnormalities lead to a metabolic syndrome with insulin resistance.

Management of obesity

Multidisciplinary care – nutritional monitoring, regular practice of an adapted physical activity, psycho-cognitive-behavioral approach, even drug treatment (Orlistat) – is the basis of the management of obesity. If this fails, bariatric surgery may be considered.

Management of metabolic syndrome

There is currently no drug treatment to cure the metabolic syndrome. The management is based both on that of the cause of the syndrome – abdominal obesity – with weight loss, and the manifestations of the syndrome – hypercholesterolemia, diabetes, hypertension – with drug treatment and hygiene rules. life.

Adipose tissue autografting

The adipose tissue autograft is used in cosmetic and reconstructive surgery to restore natural volumes in the event of congenital malformations, trauma, aging or ablative surgery (removal of the breast in the event of breast cancer in particular).

The technique used, called Coleman (Structural Fat Graft), follows 3 stages: the adipose tissue is first removed by mechanical liposuction or manual aspiration with a syringe, most often in the upper abdomen, the lower part of the body. abdomen, inner thighs, outer thighs, flanks or knees. It is then treated by centrifusion to keep only the adipocytes, then reinjected.

Liposuction

A cosmetic surgery technique, liposuction removes localized excess fat by aspiration. Under anesthesia, blunt cannulas are inserted through tiny incisions. Thanks to negative pressure, the fat cells are then sucked out. Liposuction can be performed on different areas of adipose tissue localization: saddlebags of course but also arms, ankles, calves, knees, thighs, abdomen, hips and even on the double chin and oval of the face. However, this technique does not replace a rebalancing of food and the practice of regular physical activity to lose weight.

Calculating BMI

The body mass index, or BMI, is used to assess body size and diagnose states of thinness or obesity. It is calculated with the following formula: weight in kilograms divided by height, in meters, squared.

• 10 to 15,9 is considered “severe thinness”
• 16 to 18,4 is considered “thin”
• 18,5 to 24,9 is considered “normal”
• 25 to 29,9 is considered “overweight”
• 30 to 39,9 is considered “obese”
• 40 and over is considered “severe obesity”.

However, this index has limits: it does not indicate the distribution of adipose tissue.

Bioimpedance

Bioimpedance analysis, or body composition analysis, involves sending a weak, harmless electrical signal through the body. This signal passes through water retained in muscle tissue, while it meets resistance when it passes through fatty tissue. This resistance (called “impedance”) is then analyzed and allows the calculation of the body composition of an individual according to his sex, his size and his age.

Metabolic MRI

Metabolic MRI with measurement of intraperitoneal and abdominal fat is used in certain diagnoses of lipodystrophies.