Intermittent fasting from a dietician's perspective

Intermittent fasting can be hard to define as it encompasses everything from eating literally nothing for a day or more to eating within an eight hour daily window.

Andy De Santis, RD 5 minute read January 25, 2022
Alarm clock and plate with cutlery . Concept of intermittent fasting, lunchtime, diet and weight loss

If you enjoy intermittent fasting and it adds to your life, then you may gain a few extra health points. GETTY

Intermittent fasting (IF), according to a survey of my fellow dieticians, is expected to continue to be the number one “diet trend” of 2022 — even ahead of the keto diet, which IF has kicked out of first place for the second consecutive year.

Certainly, given that IF does not require one to omit the majority of foods available to them, it makes sense to consider it a more “sustainable” trend. However, you do not need to do intermittent fasting to be healthier, no matter what your friends, family or some internet guru says.

And while IF may seem intriguing — and can be beneficial for some — that doesn’t mean it’s the best thing since sliced bread (although thankfully, unlike a keto diet, you can indeed eat bread with IF ).

What is intermittent fasting?

Intermittent fasting can be hard to define as it encompasses everything from eating literally nothing for a day or more — which is rare and less frequently practiced— to eating within an eight hour daily window. This is known as 16:8 — a more common practice that involves fasting for 16 hours and restricting the time you eat to eight hours. This often amounts to little more than skipping breakfast.

Is it worth a try?

First of all, intermittent fasting will never be more important than enjoying your daily life, your mental health, a good relationship with food and your overall dietary pattern. So if you have to sacrifice any of the above in order to fit in a fasting regimen, that’s a big red flag. This is also true of individuals with very high calorie needs like growing adolescents, pregnant/breastfeeding women, and those who take medication where the absorption or functionality is contingent on food intake at specific times.

If, on the other hand, you can confidently say that fasting intermittently has improved your quality of life, then for you, IF is worth exploring.

There are two areas of consideration when it comes to intermittent fasting: the practical aspect and the scientific/theoretical aspect.

The practical aspects of IF

If you find that consistently maintaining a 16 hour gap between your last bite one day and first bite the next genuinely improves your life and dietary pattern, that’s cool. But my primary concern is whether or not the foods you are omitting to facilitate this “fasting period” are being replaced elsewhere.

There are a wide number of foods that may be considered more likely to be consumed at breakfast which include things like yogurt, nuts, seeds and fruit — among others — that are at risk of omission if someone takes the IF path and starts skipping breakfast.


The scientific aspects of IF

This is where it gets more interesting.

There are certainly a number of influential and intelligent individuals who champion intermittent fasting from the scientific perspective in ways that could be fairly equated to “over-selling.” And while the human scientific evidence around intermittent fasting is growing, it’s not at the level yet where we can say you should try fasting if it isn’t for you.

There are certainly a number of studies, including recently published 2021 papers from JAMA , the Journal Of Endocrinology & Metabolism and Frontiers In Nutrition, which have demonstrated that various forms of intermittent fasting may help with weight loss and certain important metabolic markers like insulin resistance. But my sense is that it’s the less studied and more theoretical aspects of fasting that get people intrigued.

What do I mean by that? I am talking about those “bio-hacking” type findings in studies that have appeared in the Journal Of Proteomics which demonstrated that a month of ~14 hour daily fasts increased the production of a certain “anti-Alzheimer’s” proteins or the Scandinavian Journal Of Medicine And Science In Sports which found that training while fasted (not advisable when exercise is longer than 60 minutes), may lead to beneficial metabolic changes in muscles.

There was also a report in the New England Journal Of Medicine which linked the benefits of fasting to metabolic switching and cellular stress resistance. Metabolic switching is used to describe your body’s ability to switch between using carbohydrates and fat as energy sources (this is considered a good thing) which is facilitated by fasting. Cellular stress resistance, to put it simply, is the concept that intermittent fasting places a low level of stress on the body (a metabolic workout of sorts) which ultimately makes it stronger.

Findings and claims like these are largely preliminary and, scientifically, we don’t yet truly understand the long-term health effects of intermittent fasting. IF certainly represents an intriguing paradigm, but it will never be more important than the totality of a person’s dietary pattern, and should be treated as such.

The bottom line? If you enjoy intermittent fasting and it adds to your life, then you may gain a few extra health points. But if it detracts from your life, compromises your intake patterns and/or relationship with food, it simply isn’t worth it.

While intermittent fasting is definitely scientifically interesting, it isn’t a necessity or a magic bullet for good health.


Andy is a registered dietitian and author who has operated a private practice in Toronto since 2015. He spends his free time eating, writing and talking about kale @AndyTheRD. He can be reached at

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