Studies have shown that dieting comes with an effect on psychological wellbeing. Famous early studies within the 20th century on men that were deprived of food for periods of months on low-calorie regimes did find that they became more fixated on food for instance. Professor Peter Rogers from the University of Bristol is an expert in food and behaviour. He states that individuals who slim down, just to regain everything, are opening themselves as much as periods of elation followed by disappointment and dejection. 'There are lots of unrealistic expectations. It takes considerably longer than people want to shed extra pounds safely and maintain it. Obviously, there are lots of individual variations, but yo-yo dieting may affect self-esteem.

People can and do feel irritable when their blood sugar levels start to drop, (a phenomenon referred to as hanger or 'hunger anger') since the mental abilities are dependent on glucose to do its job, but Professor Rogers is sceptical about the link between dieting and quantity of a feel-good hormone serotonin within the brain. 'The link is unclear and we don't fully realize if dieting leads to neurochemical changes which affect mood.'