We've all heard the adage "You are what you eat." But how often do you think about when you eat? Lately a not-so-new trend called intermittent fasting has been getting lots of buzz as a way to limit caloric intake, stabilize blood sugar and achieve weightloss and other benefits without stringent food restrictions or unrealistic exercise plans. Could fasting be right for you? We checked out what the experts have to say about syncing your food and beverage consumption to the clock.

Intermittent fasting involves alternating between fasting—or times of not eating—and eating. Most traditional diets dictate what you can eat and drink. But this plan tells you when you should eat, and it is typically limited to a specific timeframe. Instead of eating whenever your body signals it’s hungry or you have a craving, you take a break for a certain period each day or limit your eating on certain days each week. Research shows the changes can help your body burn fat and provide additional health benefits.

According to Johns Hopkins neuroscientist Dr. Mark Mattson, humans evolved to be able to go without food for many hours, even several days. In prehistoric times, we were hunters and gatherers who adapted to survive — and thrive — for long periods without eating. It took a lot of time and energy to find food and it often had to be saved for times when food was scarce.

Modern conveniences like fast food and packaged items have made it easier for us to eat any time we want and food is more abundant and available. Combined with an endless supply of 24-7 work and entertainment that keep us up later and sitting idle more, many of us snack over more hours each day than we realize. Johns Hopkins dietitian Christie Williams says extra calories and less activity can mean a higher risk of obesity, type 2 diabetes, heart disease and other illnesses, but intermittent fasting can reverse these conditions.

When do you eat? Intermittent fasting can work a variety of ways, but all involve choosing a time to eat and a time to stop eating. Here are some popular schedules intermittent fasters may try: 

  • Daily time-restricted fasting – Choose one 6, 8, 10 or 12-hour period each day when you eat & fast for the other 12-18 hours
  • The 5:2 approach – Eat only one meal a day 2 days a week (limited to 500–600 calories) & eat regularly the other 5 days
  • Alternate-day fasting – Eat a normal diet one day and either completely fast or have one small meal (around 500-600 calories) the next day
  • A weekly 24-hour fast, also called Eat-Stop-Eat – Fast completely for 24 hours at a time on 1 or 2 days each week
  • The Warrior Diet – Eat very little, usually just a few servings of raw fruit and vegetables, during a 20-hour fasting window, then one large meal at night
  • Meal skipping – A flexible approach that involves occasionally skipping meals according to your hunger level or time constraints

What do you eat? Fasting periods typically permit water and zero-calorie beverages such as black coffee and tea, some allow the addition of items like raw fruit and veggies. Eating periods involve enjoying a variety of good, nutritious food, being mindful not to “make up” for the calories you would have consumed while you were fasting.

How does it work? Mattson says when the body goes without food for several hours, its exhausts sugar stores and starts burning fat. This is known as metabolic switching. “Intermittent fasting contrasts with the normal eating pattern for most Americans, who eat throughout their waking hours,” Mattson says. “If someone is eating three meals a day, plus snacks, and they’re not exercising, then every time they eat, they’re running on those calories and not burning their fat stores.”

Can you stick with it? The following tips from Medical News Today may help people stay on track and maximize the benefits of intermittent fasting:

  • Stay hydrated
  • Avoid obsessing over food with planned distractions
  • Rest, relax and avoid strenuous activity on fasting days
  • Making every calorie count by choosing nutrient-dense foods that are rich in protein, fiber, and healthful fats such as beans, lentils, eggs, fish, nuts, and avocado
  • Select filling yet low-calorie foods like popcorn, raw vegetables, grapes and melon
  • Increase the taste without the calories by seasoning with garlic, herbs, spices, or vinegar
  • Choose foods that are high in fiber, vitamins, minerals, and other nutrients helps to keep blood sugar levels steady and prevent nutrient deficienciesafter fastin

What are the benefits? Research shows that the intermittent fasting periods do more than burn fat. A study published in the New England Journal of Medicine revealed data about a range of health benefits associated with the practice. These include:

  • Weight loss  
  • Boost thinking and memory
  • Improved heart health
  • Lowered blood pressure
  • Enhanced physical performance due to fat loss and muscle mass retention
  • Prevention of diabetes and obesity
  • Improved tissue health
  • Can help with chronic conditions like irritable bowel syndrome, high cholesterol and arthritis

Are there risks? The experts encourage you to check with your doctor before you begin an intermittent fasting regiment. They also warn that going 24 hours or longer periods without food may be dangerous and could encourage your body to store fat in response to starvation.

Side effects? Negative impacts usually subside after a month, but may include:

  • Hunger
  • Fatigue
  • Insomnia
  • Nausea
  • Headaches

Does it work? Researchers and medical experts have mixed opinions about the efficacy of intermittent fasting. Harvard Medical School reports that studies in humans show the practice to be safe and effective, but no more effective than any other diet. They also say it can be hard for many people to fast consistently.

Researchers from the University of Alabama conducted a study with a small group of prediabetic obese men. One group at all their meals between 7 a.m. and 3 p.m. and the other ate the same meals between 7 a.m. and 7 p.m. Both groups maintained their weight, but after five weeks, the 8-hour group had lower insulin levels, improved insulin sensitivity, lower blood pressure and decreased appetite.

“Just changing the timing of meals, by eating earlier in the day and extending the overnight fast, significantly benefited metabolism even in people who didn’t lose a single pound,” said Dr. Monique Tello.

Cedars-Sinai researcher Dr. Suzanne Devkota said one key is choosing foods that help you feel as full as possible when you are limiting calories. Healthier choices and high-fiber foods like salads and raw vegetables will set you up for success.

“If you do it correctly, it's fantastic for your metabolism. With intermittent fasting, one of the reasons it works so well for weight loss is because you introduce this caloric deficit during your week that's pretty profound, but your body never switches into starvation mode because the next day you're eating normally.”

Want to read more about intermittent fasting? Check out:

The Fast Diet by Dr. Michael Mosley
The 5:2 Diet by Kate Harrison
The Obesity Code by Dr. Jason Fung