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Dietitian Review: Intermittent Fasting

Updated: May 24

This post was adapted from episode 1 of the Nourished & Free podcast.

Click here to listen to the full episode.

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As a dietitian and anti-diet nutrition coach, one of the #1 questions I get asked is: what do you think of intermittent fasting (IF)? The answer? It’s all laid out here in this intermittent fasting dietitian review.


Because I work with the eating disorder (ED) population, I have a lot of concerns about this fad. I’ll go through those thoughts/concerns as well as what the intermittent fasting research is saying to back up those concerns.


However, I do want to preface this by saying that there is research that could potentially support just about anything as a lifestyle choice, including IF, and you will certainly hear from dietitians who think it’s the best thing ever since sliced bread.


I believe we have to look at the risks vs benefits of intermittent fasting before shouting from the rooftops how great it is, which lucky for you is my job!


So to kick off this intermittent fasting review, let’s first talk through the most common types of intermittent fasting.


Types of Intermittent Fasting


The first is the 5:2: a person eats whatever they want for five days per week and then fasts for the remaining two, eating usually no more than 500 calories.


The second type is when a person eats during a set time throughout the day, then outside of that time period the person fasts. The most popular is the 16:8 (16 fasting hours, 8 feasting).


Intermittent Fasting Dietitian Review: IF Concerns


During my review of intermittent fasting, I came across a number of important concerns about this diet. Let’s look through all of them here.


Concern: Food Guilt

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When we follow strict dietary regimens, guidelines, and rules, we are essentially setting

ourselves up for failure. When we don’t have the self control to follow the rules perfectly, we feel guilty as if we’ve done something naughty or sinful.


For example: it’s not your eating window, but your stomach is eating itself inside out with

hunger. You can’t stop thinking about the potato chips in your cupboard, and find yourself finishing the entire bag. Now you have intensifying feelings of “what have I done? I’ve ruined it. I messed up. I feel bad.”


This is just one example of why intermittent fasting is bad for your relationship with food.


Concern: Binge-Eating


One of the key predictors of binge-eating is restriction, dieting, or fasting… so that’s not very

good news for intermittent fasters. I think it’s important to explain why this is a predictor of binge-eating.


When we restrict our bodies of one of the most basic needs…food… our body fights back. Which makes sense, right? We need food to survive, so when we send the message to our body that we don’t have enough of it, it’s going to beef up the survival instincts it has.


Well, it turns out we have a lot of those. There are many, many mechanisms that activate when our body gets the signal that it’s in a state of food restriction; your biology will drive you towards food.


Because of my education and expertise as a binge eating coach, the connection between intermittent fasting and eating disorders was one of my biggest concerns during this intermittent fasting dietitian review.


Concern: Lack of Interoceptive Awareness


When we engage in restrictive dieting, especially when we have timers set, there’s something that we are completely casting aside, which is interoceptive awareness.


What this means is that we have absolutely no regard for our body feels. Feeling hungry, but it’s not time to eat yet? We ignore the hunger. Feeling full, but your eating window is almost over? We ignore the fullness to push in more food while we can.


When interoceptive awareness is put into practice with intuitive eating, it is shown to create: positive emotional functioning, greater life satisfaction, unconditional self regard and optimism, psychological hardiness, greater motivation to exercise, and greater body appreciation and satisfaction. When we deny interoceptive awareness and engage in dieting, we see the opposite.


Concern: Unnecessary (because we fast overnight, duh)


I think a lot of times when people talk about IF, they act as if we have to force fasting because otherwise it will never occur. This is one of the common ideas I saw while working on this intermittent fasting dietitian review.


We’re told by die-hard fasters that we have to engage in fasting during the day in order to reap the benefits, but the reality is that we fast every night when we’re asleep. We know that during sleeping hours, our body is doing massive amount of restoration and repairing.


There’s a reason we wake up hungry, and it’s because our bodies are ready to have food after fasting overnight.



A cat lies on a bed with white sheets and a woman laying in bed behind


Concern: Intermittent Fasting and Eating Disorders


Can intermittent fasting cause eating disorders? It’s hard to know for sure, but here’s my biggest concern with IF: It can either turn into an eating disorder, or it is a vehicle for an ED to thrive.


In regard to the former statement, we have seen that about 1 in 4 (some reports even state 1 in 3) dieters will develop an ED. For those who are predisposed to developing an ED, engaging in a diet like IF can be the final push over the edge.


In regard to the latter statement, there’s reason to believe that IF has turned into a convenient explanation to justify disordered eating behaviors. Providers could be missing a hugely dangerous threat to their patients' health if they view IF as a normal (or even positive) lifestyle choice.


When an individual is suffering from an ED, the ED will fight hard to stick around, so any vehicle that can be used to normalize their behaviors will be used.

A woman wears black underwear and holds a yellow measuring tape around her hips before reading an intermittent fasting dietitian review

Concern: Using Intermittent Fasting for Weight Loss


One of the biggest reasons we see IF utilized is as a weight loss tactic. Will intermittent fasting work for weight loss? It depends. SOME PEOPLE may find that this is helpful for long term weight loss (like, a tiny fraction).


However, I don’t agree with utilizing a diet for weight loss at all. Why? Well because of everything else I’ve said up to this point. It’s not worth the risks that we know by now are almost guaranteed.


Additionally, chasing weight loss oftentimes doesn’t resolve the underlying issues of poor choices in behaviors and/or body dissatisfaction. If image and number is our chief concern and motivation, then our choices to manipulate those things are typically unsustainable.


As a culture, we want results and we want them fast. So we turn to cheap tactics like pills, diets like IF, shakes, intense programs, and even surgery. In the process of chasing fast results, we never actually rehabilitate the reasons for why we make the choices we do and how we feel in our skin. As a result, these tactics simply don’t last.


This is one of the reasons why this intermittent fasting dietitian review is so critical: so we can strip away any health claims related to the diet and look at it for its health impacts.



Concern: Food Choices During Eating Window


Last concern I’ll bring up is the concern of what food is being consumed during this eating window. As intuitive eaters, balancing food groups and nutrients comes naturally as our bodies guide us to the nutrients we are in need of. However, when interoceptive awareness is out the window and we’re in a scarcity mindset, we often choose foods that don’t serve us as well as others.


For example, in dieting it’s common to see the “I deserve this” mindset. After being ‘good’, the individual will eat foods that aren’t the most nutritious. I don’t often see someone rewarding their fast with a really nourishing bowl of veggies, whole grains, lean meats, etc.


a woman wearing a lab coat uses a dropper to put blue liquid into test tubes

What the Intermittent Fasting Research Says


It’s always important to evaluate what the literature says, especially when we’re looking at something that relates to the human body.


One intermittent fasting research study that was published in 2020 looked at the 16:8 schedule of IF on 116 participants, including a control group who ate 3 consistent meals throughout the day. The study lasted for 12 weeks, included both men and women with ages ranging from 18 to 64 years old, and all participants had a BMI between 27 and 43 (categorically overweight or obese).


The researchers concluded that between the groups, IF was not more effective in weight loss than eating throughout the day.


Source


Another intermittent fasting study also published in 2020 which lasted a year long. This study looked at 3 different groups: out of 332 participants, there was a group following continuous daily energy restriction, week-on, week-off energy restriction, and a 5:2 IF pattern.


The first thing I want to highlight about this study is that only 146 participants completed it. That means less than ½ of the people could finish the study, regardless of their group.


The second thing to note about this study is that the continuous daily energy restriction group instructed women to consume only 1,000 calories daily for a year, and men to consume 1,200 calories daily for a year, i.e. to starve themselves for a year. The reason I bring this up in relation to IF is that this group actually had a lower dropout rate than the IF group!


Comparing the two, the group asked to consume 1,200 cals or less/day had a 49% drop out rate, while the IF group had a 58% dropout rate.


Source


Moral of the story?


Intermittent Fasting was even more torturous than a miserably restrictive 1,000 calorie/day diet.


Intermittent Fasting Dietitian Review: The Bottom Line


If it’s not sustainable and there’s a risk of disordered eating, I don’t see why we’re encouraging intermittent fasting at all. And that’s why this intermittent fasting review article is by no means giving IF a gold star.


If anything, we should be tuning in to our body rather than tuning out and punishing it with desperate attempts at weight loss.


As with any diet, there will always be supporters and small handful of studies that seem promising. However, we must look at the bigger picture.


IF can lead to binge eating, food guilt, lack of interoceptive awareness, and can lead to or disguise an eating disorder.


To find a sustainable solution for you, I recommend giving intuitive eating a try!


If you’re ready to see how intuitive eating can help you create a healthy relationship with food, visit yatesnutrition.com/services to find out more about how I can help!



Listen to the full podcast episode below!













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