Continuous dieting is the age-old way of losing weight. But limiting food intake every day slows the metabolism, which often results in weight loss tapering off — the “famine response”. Hungry dieters are left frustrated and ready to give up the seemingly never-ending dieting grind.
On-off diets, or intermittent diets, can trick the body into skipping the usual adaptive response to conventional dieting. They can make it psychologically easier to stick with diet regimes by incorporating regular off-diet breaks.
Intermittent dieters eat less (on some diets substantially less) food for a short time, then switch to eating normally, and then back. The idea is that the body doesn’t have the time to become accustomed to the diet or kick in the famine response and slow the metabolism. The metabolism is jolted into working at the normal rate through the short, sharp bursts of dieting.
A more extreme type of intermittent dieting is occasional water fasting (consuming nothing except water) for a short period every month or so; or five-day diets that mimic water fasting, undertaken a few times a year.
These fasting regimes don’t only offer weight loss: some experts believe they can provide other therapeutic benefits, such as fighting inflammation, reducing blood sugar levels and stimulating autophagy, a natural clean-out of the body’s damaged cells. Water fasting — eating nothing and drinking only water — is incredibly difficult for the ordinary person, so now there are kits that experts claim can stimulate the body to mimic the response to a five-day water-only fast.
The Western world is looking for more effective ways to lose weight: better ways of dealing with the increasingly alarming trajectory of obesity and weight-related disease in adults and adolescents. It has been a long, hard road, especially in the spiritual home of fast food, the US.
Australians, too, are getting fatter. Each year, the average weight of Australian adults increases by 1kg. Carrying too much weight can lead to a huge range of health issues: problems with blood pressure and the heart, with weight-bearing joints such as knees and ankles, with diabetes and some cancers. Numerous studies have shown, by way of contrast, that staying slim, or even a little underweight, can help lead to longer, healthier lives.
Last year Nuala Byrne, head of the school of health sciences at the University of Tasmania, led a study looking at a two weeks on, two weeks off diet, also based on the principle of evading the body’s adaptive metabolic and behaviour responses to long-term continuous dieting.
A fortnight of moderate dieting (eating about one-third less than usual), was followed by a week of normal eating — keeping the body in balance, getting neither fatter nor thinner.
The study, published in the International Journal of Obesity, demonstrated that not only was the intermittent diet more effective than conventional dieting but the results seemed to last longer after the dieting trial had ended.
“We’ve been interested to understand how you can get better bang for your buck,” Byrne says. “In our two weeks on, two weeks off study, we actually did find markedly greater weight loss in the intermittent dieting group. We’re interested to find out why that might be.”
Humans, she notes, have evolved to feast in good times to store energy and live through the bad times. But when the good times just keep coming, as they have for most of the West for many decades, the body’s fat stores can become dangerous.
However, Byrne adds: “If we weren’t able to eat excessively when food was available and store that energy, we wouldn’t have survived as species.”
Keeping weight low is a huge positive for health and longevity, she says, but at the same time modern Australians are constantly confronted with an increasing range of tasty, calorie-rich foods.
Amanda Salis, professor of obesity research at the University of Sydney, was a co-researcher on Byrne’s study. She notes the two weeks on, two weeks off diet wasn’t a particularly difficult regime for the participants, requiring only a moderate reduction in calories during the calorie-restriction weeks.
The results of the trial were surprisingly good, she says, noting that the 5:2 intermittent diets didn’t show the expected avoidance of the famine reaction. Although dieters often found them easier to stick to, the rate of weight loss was no different from that of conventional diets.
“We don’t know why that is,” she says. “It may be that five days isn’t enough time for the body to get back into energy balance.”
Dieters on the 5:2 trials may have had dieting front of mind to too great an extent, and so consciously or subconsciously restricted their kilojoule intake to a degree even on the days when it wasn’t required. The body then continues to believe it is dealing with famine and reacts accordingly, slowing the body’s metabolism and the rate of weight loss.
Michael Thomsen, a naturopath and businessman based in Hobart, is particularly enthusiastic about the health benefits of fasting: so enthusiastic that he plans to import from the US a packaged diet that supposedly mimics fasting, promoting weight loss as well as a general clean-out of the body’s damaged cells.
Developed by a respected US biogerontologist and cell biologist at the University of Southern California, Valter Longo, the ProLon diet comes in cardboard boxes; the dieting person eats the contents of the boxes, and absolutely nothing else, for five days.
It may sound like dubious fast-buck quackery (a one-week kit costs $330), but Longo does not personally profit from the diet (the patent is held by the university) and results of his studies have been published in respected academic journals.
The packaged diet apparently has been carefully designed to be appetising, to feel relatively filling and, most important, to trick the body into thinking it’s fasting, Thomsen says. It consists of precise amounts of various food elements and supplements.
Across five days on this diet, the body gets rid of damaged cells and creates a surge of new stem cells, he says, possibly helping to prevent or reduce the likelihood of chronic disease.
“Most of the research so far has been in healthy people,” Thomsen adds. “Now it’s been so successful that the research is moving into people with diseases.”
He hopes to obtain Therapeutic Goods Administration approval for the packaged ProLon diet soon and expects it be available in Australia by early next year.
Australian academics, including Salis, have seen a published academic paper recording the results of the ProLon diet in a rodent trial as well as preliminary results of the diet in a small trial in humans, and they see it as reputable.
“They looked at what happens in the body when a person goes on a fast, and they looked at certain biomarkers, including hormones, and they aimed for a diet with a nutritional composition that would induce a similar biological response,” Salis says. The paper notes that more work was needed in humans, she adds, but “certainly the results looked promising”.