Waist circumference and visceral obesity

The presence and characteristics of fat in the human body are considered relevant in the relationship between food, energy intake, and energy outburst. Regarding the adipose tissue, it is useful to clarify that it is divided in white adipose tissue (WAT) and brown adipose tissue (BAT). The most significant difference between the two is the fact that in the WAT there is a progressive accumulation of fat, whereas the BAT is used by our body for the energy outburst.

When the food intake exceeds our energy expenditure, our body accumulates fat via WAT: the main goal of a new approach to nutrition must be, together with physical activity, to re-balance our fat with less WAT and more BAT. Together with increased waist circumference, the WAT tends to put the patient in a dangerous position, with an increased cardiovascular and cancer risk. Nonetheless, recent specific nutritional patterns clarified that it is easier to reduce the WAT compared to the subcutaneous adipose tissue (SAT).

By functioning as a fat depot, WAT prevents lipotoxicity, a detrimental process deter-mined by excess of FFAs that can alter cell membrane structure and functions, creating aninflammatory environment, which finally leads to cell dysfunction and death. In obesity state, lipotoxicity has been found to contribute to increase macrophage infiltration into adipose tissue, insulin resistance, and hepatic steatosis.

When SAT maximum expansibility (maximum hypertrophy of pre-existing adipocytes and failure in adipogenesis) is achieved, calories surplus, due to excess energy intake and/or reduced energy expenditure, accumulates as fat in VAT, leading to its expansion. A marker of this ectopic fat accumulation in humans is the increased abdominal obesity, measure via waist circumference, a more reliable biomarker than BMI, which may lead to some methodological bias.

Firstly, BMI is only a ratio of weight to height and does not distinguish fat mass from lean body mass or among SAT and VAT, nor apple- from pear-shaped body. Secondly, the timing and method of BMI assessment seem to be critical.
Indeed, waist Circumference is measured horizontally midway in the distance of the superior iliac crest and the lower margin of the last rib, so far it better reflects deep visceral adiposity. According to the International Diabetes Federation definition, essential criteria to diagnose Metabolic Syndrome is adiposity assessed by WC.

Interestingly, physical activity and diet are still the most important weapons to modify the composition of our adipose tissue.