All About Fasting

By Jessie Funchion, MS, RD, LDN

 

What is fasting?

A partial or total abstention from all foods or a select abstention from prohibited foods.

 

 What are the different types of fasting?

1)    Intermittent fasting – cycle between periods of eating and fasting. A common way to do this is to alternate days, for example fast for 2 days a week (only eat one meal, 600-800 calories) and eat as usual for 5 days a week.

2)    Gentle Fast – Examples include avoiding food between meals (~4 hour ‘fast’) or overnight (~12-16 hours).

3)    Caloric restriction – This involves eating a reduced calorie diet, as low as 600-800 calories a day for an extended period of time.

 

How long as fasting been around?

Fasting has been used in various ways for thousands of years! There’s documentation of various spiritual and philosophical writers from centuries ago using fasting as a means of gaining mental clarity or spiritual enlightenment. Various religious also incorporate fasting, such as Islam during Ramadan.

 

Why would someone fast today?

In addition to fasting or avoiding certain foods for religious or personal beliefs, there is a growing body of research to support the use of fasting for various medical conditions. One key finding is that calorie restriction can actually change the way genes are expressed in normal cells. It appears that during fasts, cells can better repair themselves! This is due to an upregulation of antioxidants and DNA repair pathways. Subtext: Fasting may actually slow the aging process of cells.

There is also some research to support the use of fasts for weight loss and weight management, blood sugar regulation and type 2 diabetes, cognitive health and cancer. What’s unclear is if the benefits are simply from the reduction in calories, or the actual fast, meaning going several hours without eating.

 

What should I eat during non-fasting days/hours?

A normal, balanced diet. In the studies that showed health benefits from fasting, participants ate a maximum of 125% of their calorie needs during non-fasting days or hours. So while they may have overeaten slightly, participants were not gorging themselves when they broke the fast! If anything, overeating in excess will likely negate the positive benefits of the fast, and eliminate any potential calorie deficit for the day or week.

 

Who should NOT try fasting?

Anyone who falls into the following categories should NOT try fasting:

·      Pregnant or nursing

·      History of eating disorder

·      Underweight

·      Pediatric population

·      Type 1 diabetes

·      Medically unstable

·      Cognitive decline

·      Cancer cachexia

 

Should I try it?

Like any diet change, adherence is key. The benefits of fasting are likely to disappear once a person stops fasting. It may be helpful to accomplish a short-term goal, but long-term maintenance and the changes you make after fasting are likely to be more important.

 

Sources:

Dietitian Central Webinar: A Primer on Fasting by Lindsay Malone, RD

Today’s Dietitian: Fasting Regimens for Weight Loss