Cortisol is a hormone that is essential for human life. It is released in response to stressors on the body, and has an integral role in our metabolism, including keeping our blood sugars from going low when fasting (eg overnight). Cortisol also stimulates fat cells to grow and mature, particularly the fat cells around the organs (called visceral fat).
Some people who struggle with excess weight may be more sensitive to the effects of cortisol, resulting in a higher tendency to accumulate fat around the organs, called visceral fat. This visceral fat is much more dangerous to health than the fat that collects under the skin (called subcutaneous fat), as it is the visceral fat that is associated with a higher risk of metabolic complications such as diabetes, high blood pressure, and heart disease.
If cortisol is actually being overproduced, this can lead to a lower resting metabolic rate because it leads to a breakdown in muscle mass (muscle mass is an important determinant of resting metabolic rate – read more about this here). Cortisol also stimulates hunger, resulting in increased desire for highly saturated fat and sweet foods in particular.
During stress, cortisol is released and snacking often increases, but it’s unclear whether the increased snacking is due to the cortisol increase or the stress itself. This stress can be psychological stress, but also physical stress such as untreated obstructive sleep apnea.
While pathologic overproduction of cortisol by an adrenal or pituitary gland tumour is rare (called Cushing’s syndrome), it is likely that stress (psychological or physical) may contribute to differences in cortisol production, which may in turn have an effect on body weight.
So, understanding cortisol physiology teaches us that managing both psychological and physical stressors are key to successful weight management.