Is fasting good for the body?

Intentionally abstaining from food or otherwise reducing caloric intake (known as "fasting") has been growing in popularity, purporting a variety of health benefits. What's the science behind such health claims, and is this practice indeed as beneficial as many believe?

 

First of all, what is Fasting? Generally speaking, there is "Intermittent Fasting", generally lasting 16-48 hours. In contrast, "Periodic Fasting" is generally at least 2 days or longer. Fasting is not uncommon in various cultures and religions; for example, intermittent fasting is a core practice in Ramadan. 

 

There are a multitude of claims floating about online regarding fasting, good or bad. Information regarding Periodic Fasting in particular tends to be less common, in part because fewer people do it regularly. Either way, what does the science say?

 

A study published in PLoS One specifically studied the effect of Periodic Fasting on normal weight or moderately obese subjects to observe safety and tolerability in over 1000 subjects. The protocol included daily clinical monitoring of subjects following the Buchinger fasting program for 5-20 days, which involved drinking 2-3 liters of liquids each day, with average caloric intake of 250 kcal, and also a multi-disciplinary program that included health education and physical activity.

 

Before beginning the fast, all subjects went through a through physical examination to establish a baseline to compare with completion.

 

As expected, weight, BMI, and abdominal circumference showed significant decrease. In addition, systolic blood pressure and diastolic blood pressure also decreased.

 

All of this sounds pretty good so far. But were there any adverse effects from prolonged fasting? Safety of the program was asessed by collecting self-reported and observed mild symptoms every day. Some subjects reported mild symptoms like muscle pain, sleep disturbances, headaches, and hunger in the first days of fasting. (sleep disturbances were most commonly reported, at 14.94%) No fatalities or permanent adverse effects were observed, though two elderly subjects were admitted to the hospital.

 

In addition to adverse events, subjects were asked to self-report if they had major health complaints before beginning this fasting experience, and how this condition was affected by fasting. 404 of 1311 subjects mentioned having a major health commplaint prior to beginning the program - 84.4% reported improvements, 8.7% reported no change, and 6.9% reported the problem getting worse.

 

This study was fairly unique in that other than self-reported effects, comprehensive observation and testing was conducted for subjects throughout the process, including blood lipids and glycaemia, blood count, coagulation, liver function, inflammatory biomarkers, renal function and uric acid, and electrolytes.

 

Overall, results showed that fasting using the Buchinger method in a specialized clinic for 4-21 days was safe and well-tolerated, with a variety of beneficial emotional and physical effects. This is in some contrast to other (water-only) fasting studies where more adverse events were reported. Periodic fasting led to noticeable weight loss and improvements in several cardiovascular risk factors, such as overweight, abdominal circumference, and blood pressure, along with normalization of numerous blood parameters.

 

Now, scientific knowledge is constantly evolving and updating; every person's body is different and it's important to observe how your own body responds rather than rushing headlong into anything. That being said, we can be reasonably certain that fasting, if done correctly, can be quite beneficial!