Ryan, 61, has tried low-carb, low-fat, the 'dry sherry diet', the boiled egg diet, Weight Watchers, "everything".

"While I managed to lose weight, I always put it back on and then a few more kilos," says Ryan.

Her experience is common among the 63 per cent of Australian adults who are overweight or obese; 95 per cent can lose the weight, but they can't keep it off. In fact, they often end up heavier than when they started.

It is a problem Dr Nick Fuller, from the University of Sydney's Charles Perkins Centre, has sought to address in over a decade of work as an obesity researcher and specialist.

"The reason the scales keep going up is because we are tuned to a set body weight – a weight that the body feels most comfortable being," Fuller explains.

When we take our bodies out of that comfort zone by restricting energy through dieting, our body works to counteract the weight loss, slowing down our metabolism, activating our hunger hormones and, when we return to normal eating, storing a little extra fat to "survive the next starvation (otherwise known as a diet)". 

Some obesity experts prescribe medications to suppress the hormonal response, but Fuller believes there is another way.

In an approach he has called Interval Weight Loss, Fuller says we can avoid triggering the hormonal cascade by losing a small amount of weight – typically 2 to 2.5 kilograms – over the course of one month. The weight is then maintained for one month, giving the body and its 'set-point' time to adjust, before another weight-loss "interval" starts.

"To avoid disturbing the equilibrium too much you don't ideally want to lose much more than that, and then to negate all of the problems that often come with weight loss, you need to then maintain that weight for the next month to reset what is now your normal body weight before proceeding to lose weight again," Fuller explains. "If you continue to lose weight you will not succeed." 

The gradual, comparatively gentle process means there is no need to count calories or restrict food groups. Along with a focus on quality sleep and activity levels, interval weight-loss involves eating five small meals a day of whole foods, including carbohydrates, dairy, eggs, nuts, oil and even chocolate as well as vegetables and fruit.

Ryan was skeptical when she first learned of the approach; one that unlike everything else she had tried did not involve restriction or a constant focus on weight loss.

"I had quite a few robust discussions about me not wanting to actually follow what he was suggesting," she recalls. "The challenge for me was believing that this would work because nothing had before. In the beginning I wanted results immediately. He convinced me that was why I hadn't been successful for the previous 30 years." 

After fifteen months on the plan, Ryan lost the 20 kilograms she had been trying to lose. Eight years later, she has kept the weight off.

"I feel fantastic," she says. "I still make breakfast my largest meal of the day [as the plan recommends]. It forever changed my mindset about how you approach weight loss. Previously it was 'on Monday, I'm going to go on this massive diet and I can't eat this and I can't eat that and I can't go out for dinner and I can't do this'. That all changed and suddenly I wasn't on a diet and I was losing weight and most importantly, I was keeping it off."

Fuller believes its success is the fact that it is not a diet.

"It is a realistic lifestyle plan, individually tailored, and scientifically proven," he says. "It helps a person redefine their set body weight so they keep the weight off for good."

Interval Weight Loss by Dr Nick Fuller is out on Monday, September 4 in bookstores.

smh.com.au