Intermittent Fasting: Does It Work? Two Registered Dietitians Weigh In

Intermittent Fasting Does It Work 2 Registered Dietitians Weigh In
Portrait of Meg Hirshberg Meg Cadoux

Intermittent fasting (or IF) is one of the most popular health trends right now. There is no shortage of claims about the benefits of IF in the media. The list ranges from weight loss to improved mental clarity to decreased inflammation to reduced cancer risk. But what is IF, and is it as beneficial as people claim? And more importantly, is intermittent fasting safe for you?

We asked Crystal Pace, our nutrition expert, and Taylor Scialo, an oncology registered dietitian, whether the buzz around IF was all hype, or whether it was an effective dietary pattern. They dug deep into the scientific literature and put together an enlightening webinar and eBook on this topic. We strongly recommend checking out one of these resources for a full understanding of the risks and benefits of IF.

Here is a quick summary of their findings.

First, a definition: Intermittent fasting (or IF) is an eating pattern that cycles between periods of not eating – or eating very few calories – and periods of normal eating. IF entails having periods (of the day, or days of the week) when individuals have little to no calorie consumption. Unlike calorie restriction diets, intermittent fasting does not prescribe WHAT or HOW MUCH to eat, but rather, WHEN to eat. 

There are many different styles of IF. Examples include a “16:8” or a “14:10” cycle, in which you fast for 16 hours and eat over an 8-hour period; or, fast for 14 hours and eat over a 10-hour period. 

Does Intermittent Fasting work? 

The answer is, it depends on why you are doing it. Most people fast to lose weight. While cutting the number of hours you eat does tend to result in lower calorie consumption–and therefore some short-term weight loss–in the long run, fasting does not work better than a calorie-restricted diet. 

However, intermittent fasting has been shown to be beneficial for a range of health markers, including reduced blood sugar, blood pressure, cholesterol, and inflammatory markers, in addition to improved insulin sensitivity and gut microbiome, and more.

Based on these reported benefits, many studies do support that fasting may help to prevent and treat chronic diseases, including cardiovascular disease (such as stroke, coronary heart disease, and heart failure), pre-diabetes, and diabetes. IF can help to restore the natural cycle of daytime eating and nighttime fasting. While high-powered studies are lacking, fasting for overall health is reasonable to consider. However, depending on your situation, there are certain risks. (Please see the webinar or eBook for more on this.)

Can fasting reduce cancer risk? There is promising data showing that fasting decreases inflammation in the body. This is important because chronic inflammation can damage cells and increase the likelihood of cancer. Given that fasting may help reduce overall inflammation, it’s reasonable to think that fasting may have a role in reducing cancer risk in some way. However this has yet to be confidently established in research. 

Is fasting beneficial for cancer treatment? Unfortunately, the research on fasting and cancer does not use IF in the more traditional forms (such as “16:8” or “14:10”), but rather measures the effectiveness of fasts that last 24, 48, 72, and sometimes even 96 hours around a person’s chemotherapy treatment (i.e. 48 hours before and 24 hours after treatment). 

The studies also looked at fasting in addition to chemotherapy, not as a sole means of cancer treatment. In this treatment setting — combining chemotherapy with IF — many patients experienced reduced side effects from chemotherapy (such as less nausea, vomiting, and fatigue). This may have been due to reduced damage to healthy cells while fasting. 

So, does this mean everyone should fast during and around chemotherapy treatments? Unfortunately, the studies themselves have limitations that keep clinicians from being able to make this recommendation for everyone. 

We strongly recommend that anyone undergoing cancer treatment involve their cancer care team before engaging in a fasting regimen.

To learn more about the risks and benefits IF, and some considerations before getting started, please see the eBook or webinar! The eBook and our Toolkit includes a useful questionnaire you can use to see if IF is right for you.

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