A breakthrough experiment has shown that it takes 12 months of dieting before the body’s chemicals change and a new weight can be maintained permanently.
Scientists have in the past found that dieting triggers a backlash from the body. Hunger-causing hormones surge and cells begin to stash more calories into fat, leading many to return to their old weight once the diet is finished.
Now it appears that these powerful defence mechanisms can be overcome. Researchers in Denmark have found that obese people who had shed an eighth of their weight on an intensive diet and then kept it off for a year saw dramatic changes in the chemicals governing their appetites.
Signe Sorensen Torekov, associate professor of biomedical sciences at the University of Copenhagen, says the study demonstrated that it was possible to defeat the body’s natural resistance to losing weight.
‘It’s very difficult to fight the hunger,’ she says. ‘It’s like a drug you’re fighting against. This would have been an excellent mechanism 50 years ago, but the problem now is that we have so much food available that we can eat all the time.
‘We were able to show that if you’re able to keep your weight down for a year, then it shifts and it becomes easier.’ The effect relies on three molecules. After a meal, increases in two hormones called GLP-1 and PYY rein in appetite. Ghrelin, a hunger hormone, dwindles as the food is digested and its sugar enters the bloodstream. For many overweight and obese, these compounds conspire to keep them hungry for longer.
The Danish scientists put 20 obese adults on an exacting diet of powdered shakes and soups for eight weeks so that each lost an average of 12.5kg. Over the following 12 months they stayed on a tough eating plan to help them stick to their new weight.
After the year, the researchers found that their participants’ bodies were much better at dampening their appetites after a meal, ramping up the hunger-curbing hormones.
After a 600-calorie energy drink they produced 65 per cent more GLP-1 than they did before the weight loss programme, indicating that they were more sated. Dr Torekov says the obese patients had in effect changed their ‘set points’ – the weight their bodies strive to maintain.
Fiona Gribble, professor of endocrine physiology at the University of Cambridge, says the findings showed that keeping weight off could become easier if people persevered, although the changes might also be down to moving away from a fatty diet. ‘I think it’s very good news,’ she says.
However, Giles Yeo, a hunger hormone expert also at Cambridge, says that without comparable results for a group of obese people who had tried and failed to keep the weight off, it was impossible to be sure the method worked. ‘The real answer is that your body will fight forever in order to stay the same weight. The gut hormone levels are interesting, but you need to be looking at how the brain responds as well.
‘At the moment, everything tells us that the brain will continue fighting and trying to get you to put the weight back on until the day you die. A recovering alcoholic is an alcoholic for life: in a similar way, an obese person who is no longer obese will always be an obese person on the inside, so to speak.’
Dr Yeo says it might be more effective to give obese people doses of a fat cell-derived hormone called leptin, which appears to trick the brain into thinking you’ve eaten more than you have. Early trial data suggests this helps the overweight to consume fewer calories.
The study is published in the European Journal of Endocrinology.
When fat people say that they cannot help overeating, they may be right. A part of the brain involved in weighing up choices was thinner in obese people, suggesting that they have more difficulty overcoming subconscious urges, scientists said.
Blaming a lack of willpower is simplistic, but bans on muffins at cafés, snack ads and other temptations could be the best way to fight obesity, the researchers say.
Paul Fletcher, professor of health neuroscience at the University of Cambridge, who carried out the study whose results were published in the International Journal of Obesity, says: ‘You can educate people and get them to value healthy foods but something seems to happen when food is actually there. It’s almost a Pavlovian impact that overcomes their best intention.’