Thyroid and hormonal imbalances, hormone shifts during pregnancy and a slow metabolism all contribute to fat that's hard to move. A common hormonal imbalance is polycystic ovary syndrome (PCOS), which affects one in every five women in the UK (according to the NHS). There are four main symptoms of PCOS: irregular periods, ovaries becoming enlarged and containing fluid-filled sacs, unwanted hair growth and weight gain. Acne, especially on or around the chin area, is another common symptom of PCOS.

Another widespread hormonal imbalance is when the thyroid gland does not produce enough thyroid hormones, called hypothyroidism. Thyroid hormones are instrumental in regulating the metabolism, and if there are not enough of them being produced in the body, metabolism slows. This makes weight gain easier and stubborn fat harder to shift.

Cortisol (the stress hormone) is a very important hormone, and its overproduction (due to stressful lifestyles) can lead to weight gain and the build up of stubborn fat. People who are stressed and anxious, moreover, may turn to food as a coping mechanism.

Other common factors resulting in the build up of stubborn fat include: the ageing process (where muscle mass tends to become less), diabetes treatment, steroid treatment and excess tiredness.