Eating well during the week and splurging on chips and ice-cream on the weekend may seem like the ideal way to keep your weight and health under control, but this yo-yo approach to eating can be just as damaging to a person's health as a diet consistently made up of junk food, a new study reveals.
Three days of consuming foods high in fat and sugar – despite eating healthy foods the other four days – was enough to dramatically change the gut bacteria in rats so that it was the same as obese rats whose diet was constantly made up of junk food.
And rats who were in the cycled eating program consumed 30 per cent more energy than those who were eating healthily all the time. This expanded energy-intake swung drastically the other way after the rats went back to a healthy diet, they ate half as much food as their counterparts.
The study was led by Professor Margaret Morris, the Head of Pharmacology at University of New South Wales, and published in medical journal, Molecular Nutrition and Food, this week.
Professor Morris said even if someone is eating well during the week, they could be undoing all that good work by indulging on sweets and deep-fried food for a couple of days.
"Coming off and on this diet did do something to body weight," Professor Morris said. "It's quite relevant to our society, where many people have an alternating diet."
The study focus on gut microbiota, which are tiny cells found in the stomach. There are about 100 trillion microbial cells, which influence how humans metabolise food, and on nutrition and immune function. Disruption to that microbiota in the gut has been linked with gastrointestinal conditions such as obesity and inflammatory bowel disease.
Two groups of rats were studied over 16 weeks, one group which consumed a healthy diet every day, and the other which experienced a mixture of healthy and junk foods.
The rats who consumed high-kilojoule food for three days had access to healthy food at the same time, but chose not to eat it.
"The findings indicate that intermittent exposure to junk food three days a week is sufficient to extensively shift the gut microbiota towards the pattern seen in obese rats consuming the diet continuously," Professor Morris said.
"A reduction in the diversity of the gut's microbiota (bacteria) and a loss of some of the beneficial biota is clearly not a good thing for health."
The experiment mirrors some popular diets and eating advice, such as the 80/20 diet, which encourages followers to eat healthy foods 80 per cent of the time, and indulge 20 per cent.
Yo-yo dieting is common throughout the Western world, with many conflicting eating plans advocating certain certain foods, eliminating others and eating certain foods on certain days.
Lucinda Hancock, chief executive of Nutrition Australia Vic, said it was not sensible for anyone to eat junk food for three days a week and reiterated the organisation's message of healthy eating.
"The most immediate changes we should all make for better health are to eat more vegetables, eat more high-fibre wholegrains, and cut back on foods and drinks that are high in sugar, salt and saturated fat," she said.
"You don't have to cut them out entirely, but we definitely recommend having them only occasionally and in small amounts."