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The facts on fasting

The concept of intermittent fasting is everywhere, but is it sensible? Sage60 talks to the founder of this kind of fasting about how and why it works.

“Intermittent fasting” is a phrase oft heard these days, as if it’s new and novel. In fact, everyone does it every day.

“Fasting has been used for thousands of years,” says Jason Fung, the Toronto-based nephrologist (kidney doctor) who recommends intermittent fasting in his two books The Obesity Code and The Diabetes Code, and on his website “It’s in the Bible. Fasting is considered healthy from all of antiquity — the ancient Romans did it, the ancient Greeks did it and every religion does it.”

Doctors routinely advise patients to fast, Fung says, “when you have to do surgery, when you have to do an ultrasound, when you have to do a colonoscopy, when you have to do bloodwork.

“Fasting is not something cruel and unusual,” Fung says. He advises patients to use fasting to help lose weight, maintain a healthy weight and naturally reverse the effects of Type 2 diabetes.

“Fasting is something you're supposed to be doing every day,” he says. “That’s the word, breakfast — the meal that breaks your fast. Sometimes you eat and you store calories, and sometimes you don't eat and you use those calories. If you continue to eat all the time and never fast it's like a one-way valve. The energy, the calories, are going to go in, but they're never going to come out, because you're never allowing your body to use (the energy).”

In recent decades, obesity rates have climbed, along with the rates of Type 2 diabetes, heart disease and other health issues that are often obesity-related. Fung tracks these changes with the slow shift in eating habits and routine.

Prior to the 1970s, he says, “people would finish eating by 6:30 at night” and typically eat nothing for 14 hours until breaking the fast with their morning meal. Mothers told their children to not snack after school because “you’ll spoil your dinner.” Naughty children were sometimes sent to bed without dinner. It was all fasting, he says. “Everybody did it without thinking about it.”

Over recent decades, the snack-food industry has poured money into marketing that has tried “to convince us that we had to eat all the time,” Fung says. “Snacking was basically an indulgence, not something that was good for you. We sort of lost sight of a lot of what was healthy and what was unhealthy.”

Fung’s plan for intermittent fasting is simple, and it’s not  a temporary weight-loss diet.

“Fasting is not really dieting, it’s really just part of the natural cycle of eating and fasting,” he says. “It's basically trying to flip the switch in where your body is getting its energy from. Is your body going to get energy from the food, or is it going to get it from its own stores? Everybody thinks of it as a diet, because it has the same sort of end, which is weight loss, but it's got a different purpose to it entirely.

“There's a lot of misinformation, but, like I said, it's nothing that hasn't been done for thousands of years.”

Being a doctor, he does advise readers to eat healthily, and offers guidance in his books and on his website, but his focus is on not what you eat, but when you eat.

Fasting might be overnight — a popular method is to eat only between 11 a.m. and 6 p.m. or 7 p.m., for example. (An informal survey of people who are routinely fasting in this way finds no reports of undue hunger, nor other complaints.)

Fasting is generally safe for seniors, though Fung advises older people on medications to consult their doctor before fasting.

“Fasting is not really dieting, it’s really just part of the natural cycle of eating and fasting...It's basically trying to flip the switch in where your body is getting its energy from. ”

Jason Fung 

He also recommends that older people start slowly, in case there are other health issues. He suggests eliminating snacks, and gradually working up to fasts of 16 or 18 hours before attempting longer durations. “You might be hungry, but that's not particularly dangerous.”

Fung says fasting is a key to regulating levels of insulin, a sort of “nutrient sensor” in the body. When insulin levels drop, the body senses that no food is coming in and instead of storing energy as fat and blood sugar, it takes energy from those existing stores.

“That’s basically all that's happening in your body,” he says.

“It's no different than sleeping and waking. You don't want to sleep all the time, you don't want to wake up all the time. There's a balance there. Same thing with feeding and fasting, you should feed sometimes, and you should fast. Any time you're not eating, you’re fasting. It's just the natural balance. It’s not that there's anything magical about it, it’s just part of the natural cycle.”

He sees the need, and the results, in his practice as a kidney specialist.

“Mostly, it was that I needed people to lose weight, because I see a lot of diabetics and diabetes is actually a reversible disease. If you reverse it, then you don't get the kidney disease. That’s why I was very interested in promoting fasting.”

About the author

Peter Simpson is an Ottawa-based writer and editor.