Shockingly it's because all those foods that are the kiss of death for female bodybuilders diets - high glycaemic index such as white bread, crisps and chips – are genuinely addictive. Like addictive in the Class-A drug sense!
Researchers have found that unhealthy food triggered the same brain mechanisms which are key to other addictions such as heroin, cocaine and cigarettes.
Eating highly processed carbohydrates can cause excess hunger and stimulate brain regions involved in reward and cravings, according to the study.
The study, published in the American Journal of Clinical Nutrition, investigated how food intake is regulated by dopamine-containing pleasure centres in the brain.
Study leader Dr David Ludwig, of Boston Children’s Hospital in the United States, said: 'Beyond reward and craving, this part of the brain is also linked to substance abuse and dependence, which raises the question as to whether certain foods might be addictive.'
To examine the link, researchers measured blood glucose levels and hunger, while also using MRI scanning to observe brain activity during the crucial four-hour period after a meal, which influences eating behaviour at the next meal.
Evaluating patients in such a time frame is one novel aspect of the study, whereas previous studies have evaluated patients with an MRI soon after eating.
Twelve overweight or obese men ate test meals designed as milkshakes with the same calories, taste and sweetness.
The two milkshakes were essentially the same; the only difference was that one contained rapidly digesting - high-glycaemic index - carbohydrates, and the other slowly digesting - low-glycaemic index - carbs.
After the participants consumed the high-glycaemic index milkshake, they experienced an initial surge in blood sugar levels, followed by sharp crash four hours later.
This decrease in blood glucose was associated with excessive hunger and intense activation of the nucleus accumbens, a critical brain region involved in addictive behaviour.
Previous studies of food addiction have compared patient reactions to drastically different types of foods, such as high-calorie cheesecake versus boiled vegetables.
Another novel aspect of the new study is how a specific dietary factor that is distinct from calories or sweetness, could alter brain function and promote overeating.
Dr Ludwig said: 'These findings suggest that limiting high-glycaemic index carbohydrates like white bread and potatoes could help obese individuals reduce cravings and control the urge to overeat.'
Though the concept of food addiction remains controversial, the findings suggest that more interventional and observational studies be done.
Dr Ludwig said additional research will hopefully inform clinicians about the subjective experience of food addiction, and how they can potentially treat obese patients and regulate their weight.