Scientists may have uncovered why diets backfire, new research suggests.
Slimmers feel hungrier and have a stronger desire to eat up to two years after losing weight, a study found.
Among obese people who lose nearly 10 per cent of their body weight, their ‘thermostats reset’ to increase the impulse to eat, which the researchers believe may once have been an evolutionary advantage to protect against famine.
For people carrying too much weight, ‘hunger hormones’ may be harder to ignore as they become ‘deaf’ to signals that they are full, the scientists add.
The researchers, from the Norwegian University of Science and Technology, wrote: ‘Patients with severe obesity will, therefore, have to deal with increased hunger in the long term.’
Obesity affects up to 40 per cent of adults in the US and around 25 per cent in the UK.
Slimmers feel hungrier and have a stronger desire to eat up to two years after losing weight
How the research was carried out
The researchers analysed 35 severely obese adults who underwent a two-year weight-loss plan focusing on diet and exercise.
The study’s participants spent several weeks in a wooded retreat where they were given dietary advice and exercise coaching.
Every six months from the start of the study to two years later, the researchers analysed how hungry the participants were before, and three hours after, their meals, as well as how much food they planned to eat.
The researchers also assessed the participants’ circulating hormone levels to determine how they responded to the prospect of a meal or after just eating one.
After one year, the participants returned to the retreat to learn how to maintain their weight loss.
‘Patients with obesity will have to deal with increased hunger’
After four weeks, the participants lost on average 3.5 per cent of their body weight.
Their appetite-boosting hormones also rose rapidly, which the researchers put down to increased exercise.
Despite these rising hormone levels, the participants did not report increased hunger or desire to eat but instead felt fuller sooner when eating.
After a year on the programme, the participants lost around 7.4 per cent of their body weight but reported a significant increase in hunger and a desire to eat, alongside reduced fullness after meals.
Although after two years on the weight-loss plan the participants had mostly kept the pounds off, they continued to report increasing levels of hunger, as well as reduced fullness when eating.
The researchers wrote: ‘Patients with severe obesity will, therefore, have to deal with increased hunger in the long term.’
The findings were published in the American Journal of Physiology-Endocrinology and Metabolism.