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Here’s what experts say about the benefits—and risks—of intermittent fasting

Here’s what experts say about the benefits—and risks—of intermittent fasting

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“So what are you doing with the food?”

My annual physical was going well and my doctor was asking me about my diet. “A little of everything in moderation?” I said, shrugging; then I countered, “What should I do you what shall we do with the food?”

“Well,” replied the doctor, “I practice intermittently starvation.”

I had heard the hype over the years about how fasting could help maintain a healthy weight and potentially prevent everything from Alzheimer’s disease to sleep apnea to crab. But it was the sight of my energetic, razor-sharp doctor – who is my age but doesn’t look anywhere near it – that was the most convincing case I’ve ever seen for starvation.


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As someone who has never uttered the phrase “I forgot to eat,” who carries granola around specifically to stave off hunger pangs, I thought I was about as unlikely a candidate for skipping a meal as you’d find. And the information about intermittent fasting seemed so confusing, so contradictory, that I wasn’t even sure where to start. Do you restrict certain foods? Do you only eat at certain times of the day? Do you not eat at all some days? Most importantly, though, I wanted to know: What’s really in it for me?

As it turns out, quite… maybe.

“Intermittent fasting isn’t about what you eat, it’s about when,” he says Elizabeth Ward, a registered dietitian and nutrition consultant in the Boston area. “With no calorie restrictions or special foods to prepare or buy, IF (intermittent fasting) is more of a lifestyle than a prescribed diet.”

However, the way this is done can be flexible.

“There are several types of IF, including time-restricted feeding and no or very little food for days at a time,” Ward continues. “On the 16:8 plan, only calorie-free drinks are allowed for 16 hours, and you eat during an eight-hour period of your choosing. The 5:2 plan consists of eating as usual on five days of the week and consuming 25% of your daily calories (about 500 for women and 600 for men) on the other days. Alternative fasting (ADF) allows for calorie-free drinks every other day of the week and eating on other days.”

Most people discover IF because they are interested in losing or maintaining weight because it seems to promise dramatic and fast results. This is definitely an easy way to limit calories and avoid less nutrient dense foods.

“Breakfast in America is usually a high-carb, high-sugar, high-calorie meal,” says New York City doctor James Stullman, a doctor in my local practice. “And after 7 p.m., it’s a really challenging time. Many of my patients, myself included, are hungry at 9:30 p.m. We eat cookies or something sweet. So if you’re disciplined enough not to eat after seven hours, you’ll probably get rid of all the nasty carbs that are the real problem.”

But unlike other diets, intermittent fasting appears to offer real potential health benefits because it triggers various processes that can make the body more efficient. A 2021 paper in the journal Nutrients explains: “As a result of periods of restricted food intake, the human body initiates a metabolic transition from glucose to stored lipids, resulting in a cascade of metabolic, cellular and circadian changes which have been associated with multiple health benefits in animal models and humans. Periods of IF are associated not only with weight and metabolic diseases, but also with a reduction in the risk/prevalence of neurological diseases.

And a wide-ranging 2019 New England Journal of Medicine review of “Effects of Intermittent Fasting on Health, Aging, and Disease” reports that “The metabolic shift from glucose-based to ketone-based energy” may lead to “increased resistance to stress, increased life expectancy and reduced incidence of diseases including cancer and obesity.”

Intermittent fasting is associated with a reduction in inflammation, which is believed to contribute to several chronic diseases.”

There is science to back up why intermittent fasting can be healthy for your cells. Christine Kingsley, Director of Health and Wellness at the lung institute and advanced practice registered nurse, explains that “during intermittent fasting, the body achieves lower glucose levels more efficiently by catalyzing the activation of brain synapses and resistance to stress. This allows the brain to function at its fullest capacity as humanly possible, which is why verbal memory is greatly improved during and after practice.”

There are other potential benefits.

Intermittent fasting also usually means that your body isn’t busy digesting while resting. This can lead to better sleep, experts say.

One of the main effects is a reduction in insulin levels,” he says John Landry, Registered Respiratory Therapist and Founder and CEO of Respiratory therapy area. “Hhigh insulin levels are associated with an increased risk of chronic diseases such as diabetes and heart disease. By lowering insulin levels through intermittent fasting, people can reduce their risk of these conditions. Intermittent fasting has also been linked to a reduction in inflammation, which is thought to contribute to several chronic diseases.” He adds, “Currently, there is limited research on the effects of intermittent fasting on lung health. However, some studies suggest that intermittent fasting may have potential benefits for respiratory function, such as reducing inflammation and improving oxidative stress.

Intermittent fasting also usually means that your body isn’t busy digesting while resting. This can lead to better sleep, experts say.

“An IF schedule where your last meal is at least two to three hours before bedtime (disclaimer: for the general population, not night shift workers) can support healthy sleep and optimal daytime energy in many ways,” says Chester WuBoard Certified Doctor of Psychiatry and Sleep Medicine with the Sleep and Energy App RISE. “It allows for better digestion, reducing the risk of heartburn and acid reflux that keep you up at night.” Plus, he says, “when we sleep, our brains clear out waste products. But if your body is busy digesting food, the blood is diverted to the digestive system, leaving the brain with fewer resources to do the job.”

Regardless of the perceived benefits of IF, some people absolutely shouldn’t try it. As Elizabeth Ward explains, this includes “people under 18 and over 75; pregnant and lactating women; people on medications that must be taken with food at certain times of the day; people with a chronic illness, such as kidney disease; people with a history of an eating disorder.” She adds, “IF can be triggered. Preoccupation with mealtimes can encourage obsessive behaviors around food. In addition, exercise reduces glucose and insulin levels, and people relying on IF, they may need to alter the intensity and timing of exercise to prevent fatigue.”

I may be intrigued by intermittent fasting, but my current lifestyle is not realistically compatible with it. I could get by with just black coffee for breakfast, but I’m not ready for always early dinners yet. People who have families who travel or socialize, or maintain irregular working hours, are also likely to struggle to stay on intermittent fasting. And any meal plan is only as good as your ability to stick to it. So for now, I’ll continue to pay more attention to what I eat than when. “First and foremost,” says Dr. Stullman, “is your food choices.”

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