What Is Intermittent Fasting, and Is it Right for You?

You’ve seen celebrities and maybe even friends, family or coworkers touting the benefits of intermittent fasting.

While it’s gained popularity, there are plenty of questions. Foremost: Is it a weight-loss fad or a safe and effective way to drop the pounds?

Intermittent fasting explained

Fasting, or voluntarily abstaining from eating, is nothing new. It’s been around for thousands of years and was used more for religious purposes than for health reasons until recently. 

There are two types of fasting:

Absolute fasting is when no food or water is consumed. It’s not recommended for health purposes and is usually done for religious reasons.  

Intermittent fasting is incorporating periods of fasting into a healthy diet. This approach allows the intake of noncaloric fluids such as water, tea, coffee and broth during the fast. It can be done for varying lengths of time:

• A short-duration fast is  less than 24 hours
• A long-duration fast is  longer than 24 hours but less than three days
• An extended-duration fast is longer than three days

Common methods

A common fasting schedule includes three meals in a 12-hour window; for example, three normal meals between 7 a.m. and 7 p.m. This was the common eating pattern in the U.S. before the 1970s, when obesity was less common. Today this pattern is still seen as a way to preserve health, and weight loss may result from it.

Another fasting schedule is to consume two meals in eight hours and fast for 16 hours. For example, this could be a lunch at 11 a.m. and dinner at 6 p.m. Most of the publicized fasts use a pattern like this in conjunction with a lower carbohydrate diet to have the best effect for weight loss. Note that extremely low-carbohydrate diets are not advisable for people with diseases such as diabetes.

Fasting for 20 hours and eating one larger meal (between noon and 3 p.m., for example) is also common. 

Research and results

The short- and long-duration intermittent fasting methods are currently the most researched for help with weight loss, fatty liver disease, diabetes and metabolic diseases, and during cancer treatment. 

Despite the research, the jury is still out on how effective they are. For instance, the theory that fasting can help with diabetes due to decreased insulin resistance hasn’t been proven. 

On the other hand, small studies of people fasting have shown decreased levels of the “hunger hormone” ghrelin, decreased appetite and increased fat burning. But the population sizes of these studies has been too small to consider the results conclusive.

It’s also important to note that there are no long-term study results with humans to indicate that intermittent fasting is an effective way to lose weight or manage disease. Most conclusions have been made in animal studies.

So the question remains: Is it the fasting itself that’s beneficial, or the reduction in calories that often accompanies it? Experts say further research is needed.

Risks of intermittent fasting

While we’re not entirely sure if intermittent fasting is effective, we know it can have risks. They include:

• Electrolyte imbalances
• Hypoglycemia (low blood sugar)
• Malnutrition

The following people should not fast:

• Children
• Those who are malnourished or underweight
• Those who are pregnant or breastfeeding
• Those who’ve previously been diagnosed with anorexia

The following people should use extreme caution when fasting:

• Those with diabetes, gout and GERD
• Those taking medications such as aspirin, metformin, SGLT2 diabetes drugs or insulin; or iron or magnesium supplements
• Those who’ve had recent surgeries, infections or illnesses that may have compromised their nutritional status

Make a smart decision

All that said, intermittent fasting schedules can offer attractive lifestyle options for many people. And fasting can certainly be done in a healthy way when you’re mindful about what and how much you eat. 

As with any diet or lifestyle change, make an informed decision. Consult professional resources, such as the Academy of Nutrition and Dietetics, for more information, and be sure to involve your primary care provider or a dietitian.