Losing weight with intermittent fasting: What to know

That's where people only eat during limited windows of time each day and then abstain from food or fast the rest of the day.

Fasting plans vary but are typically between four and twelve hours.

The most popular model is the 8- and 16-hour program, where a person can eat for eight hours and then fasts for 16 hours.

"You're not limiting your calories per day, you're just limiting the time you're eating," said Dr. Christopher Hine, Principal Researcher studying dietary interventions including intermittent fasting at the Cleveland Clinic Lerner Research Institute.

After more than a decade of research, Dr. Hine says they're already documenting promising results. 

"What we've seen is prior to surgery caloric restriction is quite beneficial," he said, "The outcomes are better, there's better organ function and less moods. Going into the stress of the surgery less is more."

He says fasting stimulates a process called autophagy which could also prevent serious disorders and illnesses including diabetes, high cholesterol and cancer; possibly slowing and/or reverse aging increasing a person's lifespan and health span.

"Autophagy is basically where a cell starts eating parts of its own like waste products or maybe misfolded proteins which could lead to Parkinson's or Alzheimer's disease," he said, "Intermittent Fasting is going to stimulate the burning of fat, it's going to slow protein synthesis so that's a potential mechanism of preventing cancer, also slows the growth of malignant cells, and stimulates stress response so you become more resistant to stress."

Toni Griswold wasn't sick or having surgery.

The registered nurse with a degree in nutrition who is in her 50s just wanted to lose a few pounds. She turned to intermittent fasting when all of the traditional diets failed to produce results.

"I couldn't look in the mirror, like omg is that even me," she said, "I'd lose like 15-pounds then I would gain 5-pounds, it was that classic yo yo."  

Until she tried the 8/16-hour intermittent fasting schedule. 

Over the course of a year, she lost 50 pounds and has kept it off. 

"Yea it, it's remarkable and just everything improved, just everything!"

There are countless other testimonials online but recently the American Heart Association released a study that said time restricted eating "may be associated with an increased risk of cardiovascular disease and mortality compared with eating 12-16 hours per day."

The study, funded by The National Key Research and Development Program of China and The National Natural Science Foundation of China says 20-thousand adults on an 8-hour time restricted eating schedule suffered a 91% higher risk of death from cardiovascular disease.

But Cleveland Clinic Cardiologist Dr. Heba Wassif questions that data.

"It caught my attention, but there were many caveats when I looked a bit closer. We don't know what the nature of the diet these participants had. For all we know, it could've been 8-hours of McDonald's. Until we have more information, I'd be very cautious about the long-term outcomes of patients," said Dr. Wassif.

In a press release, the Heart Association also said that the study did not necessarily reflect their "policy or position" and that they "could not guarantee as to their accuracy or reliability."

Dr. Hine declined to comment on the study at this time because the findings haven't been published in a peer reviewed journal, but he said it is always important to speak with your physician before beginning any diet or nutritional plan, and to begin slowly.

Additionally, fasting may not be appropriate for everyone and it is not recommended for children, those with Type 1 diabetes, or women who may be pregnant or breastfeeding.

Toni began slowly, adding more time each day building up to an 8- and 16-hour model.

It may not be for everyone, but she says she not only lost weight but has increased energy and feels better overall.

"It's a lifestyle not a diet. I don't think I'll ever go back to eating like I did; this is great."