Depending on who you ask in the fitness industry, people might tell you that a diet break is the best thing since sliced bread for breaking weight loss plateaus, or they may say that diet breaks are a total waste of time.
If you’ve followed my content for any period of time you’ll know that the real answer about the importance and benefits of diet breaks probably falls somewhere in the middle, and any approach should be dependent on the nature of the client who you are working with.
Any weight loss journey involves some degree of dietary restrictions and disciplined eating habits. While staying committed to your goals is essential, it’s equally important to listen to your body’s cues and prioritize your overall well-being. This brings us to the concept of a diet break.
But what exactly is a diet break, and should you consider incorporating it into your weight loss plan?
In this blog post, we will delve into the topic of diet breaks and explore the potential benefits and considerations associated with taking a break from your structured dieting routine. We’ll shed light on the science behind diet breaks, examine their potential effects on metabolism, hormones, and psychological well-being, and provide practical tips on how to implement them effectively.
Table of Contents
What Are Diet Breaks?
Before we go into whether or not you should recommend a diet break to your client, let’s first talk a little bit about the history of the diet break to see why they came about in the first place.
The concept of the diet break was beginning to gain steam probably around 6 or 7 years ago as a tactic to include in a fat loss phase in order to mitigate some of the metabolic adaptations that inevitably occur when eating in a calorie deficit.
For those unfamiliar, there are many adaptations your body goes through as you’re in a fat-loss phase, and one of those adaptations is the downregulation in energy expenditure beyond what would be expected from having a lower body mass — in other words, reduced metabolic rate.
Knowing that there is a metabolic adaptation after being in a caloric deficit for a while, the thought was, “Hey, maybe if we take things slower, include time periods where we take dieting stress off the body and include more food, there won’t be as many negative adaptations.”
If this sounds to you like mini reverse dieting, you’re right. Reverse dieting is an essential part of your client’s fitness journey because you do not want them to diet forever.
The idea of taking a diet break has been tested in scientific literature numerous times in the past 6–7 years; for example, we have the famous MATADOR study that showed both more fat loss and less of a decrease in resting energy expenditure in the group that took diet breaks.
However, we also have conflicting data, and the study we’ll be talking about today is one of those pieces of conflicting data that didn’t necessarily show any positive effects of taking diet breaks.
This particular study had some names you might recognize, as many of these study authors are also in the fitness space as science communicators, including Bill Campbell, Eric Trexler, and Menno Henselmans.
The Study on Taking a Diet Break
I’m going to break down some specifics about the study, which include some of its limitations. The reason for that is there are many studies that people love to cherry-pick, and many times the results of a certain study cant be extrapolated to the general population as a whole because of certain limitations. These limitations are important to know to understand why we might be seeing conflicting data in the literature.
Who Went on a Diet Break
First, let’s look at the study population.
Paying attention to the population of a study is an essential factor for figuring out whether the findings of the study can be applied to other populations or for identifying a reason why previous studies found different results.
For example, a study that finds efficacy for L-carnitine supplementation for weight loss in an obese cohort with type 2 diabetes absolutely cannot be applied to people who are just looking to lose 20–30 lbs.
The study population used here were already decently lean, young, resistance-trained females.
What does resistance trained mean? To be included in the study, they had to have had at least 6 months of continuous, productive resistance training experience.
These individuals also have built-in resilience due to age, as well, which we have to take into account. The average age of the participants was 21 years old in the control group and 23 years old in the intervention group. The average body fat percentage for these women was around 24% as well, which would roughly translate to 14–15% body fat for a male.
All of these aspects are very different from 90% of the diet break or intermittent energy restriction literature we have so far. Most studies on diet breaks are done in 40–60-year-old obese men or mixed-gender cohorts that most likely don’t exercise; or at least that wasn’t a requirement.
How the Study Approached a Diet Break
Before the intervention, the researchers used a technique that we’re probably all familiar with to get a good idea of their energy expenditure; they asked the participants to track their regular food habits and body weight over a period of 14 days.
The average maintenance calories were around 1,700–1,800, which put the average weight loss calorie intake around 1,250-1,400, depending on the participant. The participants also underwent resting metabolic rate testing through indirect calorimetry before the start of the study, as well as each week that the study went on to assess any drops in their resting metabolic rate.
The participants were randomized to the intervention group or the control group. Both groups were going to be in a 25% calorie deficit for 6 weeks total; however, the intervention group took 1-week diet breaks back to their maintenance calories after the 2nd and 4th weeks of eating in a caloric deficit. The control group was at a 25% calorie deficit for 6 weeks, and the diet break group’s entire period was 8 weeks, but they were only in a calorie deficit for 6 weeks.
In terms of diet composition, protein was set to 1.8 g/kg or 0.8 g/lb, and then the rest of the calories were split 60% from carbohydrates and 40% from fat.
The researchers also wrote and supervised their resistance training programs, which was a basic 3-day per week alternating upper-lower split. This is also very different from most diet break research out there, which doesn’t include resistance training at all.
What was Measured?
The participants were required to upload their myfitnesspal data to a spreadsheet for the researchers to view throughout the study to check on compliance.
The participants filled out a 5-point questionnaire at the beginning of, and each week throughout the study to assess a few psychological aspects. These questions included:
- Hunger over the past seven days;
- fullness over the past seven days;
- desire to eat over the past seven days;
- ease of sticking to the diet for the past seven days; and
- motivation to diet for the week ahead.
The researchers did a good thing here since many of the studies done so far just assess the physiological aspects and not necessarily any psychological aspects, and we know psychological aspects can really affect compliance in the real world.
Along with that, researchers measured resting metabolic rate weekly, body weight daily, and body fat percentage and fat-free mass before and after the intervention.
The Results of the Diet Break Study
Both groups lost about 1.5% body fat. However, the diet break group did end up losing more body weight in general; 1.7 kg compared to 0.7 kg.
Now, if they both had the same amount of fat loss but the diet break group lost more weight, then you might think this came from fat-free mass, and that’s correct. The diet break group lost, on average, 0.4 kg of fat-free mass, while the continuous diet group gained 0.4 kg of fat-free mass. However, the weight difference wasn’t statistically significant, meaning it could have been due to chance. I’ll comment more on that in a bit, however.
In terms of resting metabolic rate, it didn’t change at all for either group throughout the study; it was around 1,440 on average at the start and remained at 1,440 after the study was completed. This does make sense since we know most of the reduction in energy expenditure comes from downregulation in non-exercise activity thermogenesis (NEAT) whenever someone is in a calorie deficit. There certainly can be reductions in resting metabolic rate, as seen in studies like the biggest loser study, but it’s mostly NEAT.
Most of the psychological aspects weren’t too different between groups. Hunger and desire to eat increased about the same between both groups, but scores for ease of sticking to the diet or motivation to diet for the week ahead weren’t terribly different between groups.
However, impulsivity decreased over time for the diet break group and increased for the control group. This is basically a measure of impulse control and the ability to inhibit yourself from eating, which was better in the diet break group, indicating a potential psychological benefit there.
Should I Take Diet Breaks?
Why might we see no real effects from this diet break study when others have shown results?
The Length of the Study
First off, there’s a large variety in these studies, meaning that not every study uses the same type of diet break, nor study length, nor percent energy restriction (calorie deficit). Some use alternate day fasting, the MATADOR study used 2-week diet breaks, etc.
As another example, this study had participants eating in a calorie deficit for 6 weeks total with 2 weeks of diet breaks at maintenance calories in the intervention group, while the MATADOR study was 16 weeks of eating in a calorie deficit with a total of 14 weeks of diet breaks.
Basically, in this study, the whole weight loss phase for the trained females taking diet breaks was 8 weeks, and in the MATADOR study, it was 30 weeks; significantly more drawn out. There was also a greater calorie deficit (33%) during the periods of restriction in the MATADOR. A larger degree of restriction has been associated with more BMR downregulation.
Not to mention the study population. The MATADOR was done on obese, sedentary men, whereas this study was done on lean, resistance-trained women. What we can conclude, then, is that in obese and sedentary men in a 33% deficit, taking longer diet breaks may stem some of the adaptations, whereas it doesn’t seem to have a terribly large effect on what I would deem a mini cut of 6 weeks in leaner, resistance-trained females.
There is really only one other study on the effectiveness of a diet break that was done in a resistance-trained population, which was done by Jackson Peos et al. in 2021. In that particular study, the calorie deficit during the restriction periods was significantly larger (34%) and the study was longer (12 weeks).
At the end of the study, both groups saw resting metabolic rate decreases that were around the same, so again, this showed no benefits to body composition or resting metabolic rate between either the diet break group or the non-diet break group.
It’s important to note, though, that there were actual decreases in resting metabolic rate in that study, whereas this one didn’t show any. It’s possible if the current study we’re addressing was carried out significantly longer, we might have seen a decrease in resting metabolic rate, but it still probably wouldn’t be different between groups. Then again, we might not since this study was a 25% deficit vs. a 34% deficit in the Peos study.
We have several more points to consider, though.
The Calorie Deficit
This group was just in a 25% deficit at around 1,250 calories, which, yes, seems low, but that’s what it came out to be with more sophisticated measurement tools than we have access to as coaches.
There are about 4 or 5 previous studies, including the Peos study, that clearly show when energy restriction goes to 35-40% or more, or protein intake isn’t kept at least at 0.8 g/lb, there are significant reductions in fat-free mass and resting metabolic rate.
In this study, the intervention group lost about 3.8 lb in 6 weeks, so less than 1 lb a week. A very modest rate of fat loss and much slower than many of our clients expect to go. The fat-free mass loss in the diet break group may have had something to do with how the resistance training was programmed, which I’ll touch on in a bit.
How Much Fat Mass Did Participants Have?
Next up, we have to consider starting body fat levels. While these women were lean, they weren’t competitive physique athletes dieting down to absurdly low body fat. To this date, there isn’t a diet break study on competitive physique athletes who have to get down to unhealthy body fat levels, where we’d expect to see severe metabolic adaptation.
Women competing in physique sports typically have to go above a 40% calorie deficit to reach their desired physique and do way more activity than the participants in this study did. There are a lot of anecdotes in the fitness space from folks saying they believe diet breaks preserved lean mass in these situations, so I’d be very curious to see an actual study done on physique athletes.
Why would the diet break group have lost more fat-free mass?
Well, first, it could have been due to chance, but it could have also been due to how the resistance training program was designed.
The researchers equated volume between groups throughout the entire study period, meaning the groups did the same volume, however, the diet break group did it over 8 weeks, whereas the control group did it over 6 weeks, resulting in a higher weekly resistance training volume for the control group.
As an example, the average weekly volume for the intervention group on hamstrings, quads, and biceps was 9 sets per week, whereas, in the control group, it was 12 sets per week.
The researchers also did not control extra activity, meaning any one of the participants in the groups could have been doing extra cardio or had higher step counts.
A Diet Break Has Psychological Benefits
I think one of the main benefits we see here, that we see consistently across literature on the topic, is the psychological benefits.
Sure, 7 out of 8 of the metrics around psychology weren’t different between groups, but disinhibition was, and the more inhibition you have, the better you can stick to a diet, and previous studies have shown lower disinhibition to be much better for weight maintenance phases after a dieting phase in previous studies.
If you combine this and past research with multiple hundreds of anecdotes in the health and fitness space, we can see that diet breaks can be a huge benefit for the psychological portion of dieting and allow people a lot more freedom, which has huge implications for successful weight maintenance and lifestyle change in lifestyle populations.
If you suggest to your client that they take a diet break, they may have better control of their food intake, which will allow them to continue losing fat without a significant amount of discomfort or a mental challenge.
Diet Breaks Should be Used on a Case-by-Case Basis
What can we really conclude about the study about whether you or your client should take a diet break?
We can conclude exactly what the study showed. In fairly lean, resistance-trained females seeking to lose fat, the use of diet breaks within the context of six weeks of a prescribed 25% reduction in energy intake does not improve the efficiency of fat loss and has no beneficial effect on fat-free mass and resting metabolic rate.
What this means is that we have to consider our client’s population, the length of their calorie deficit, and deficit severity. In relatively lean men and women who are resistance training with a modest deficit of 25%, it’s probably not going to impart physiological benefits, but if you know your client is going to need a mental break for better adherence, a diet break can be a huge benefit.
If the deficit is larger, the individual is sedentary, and the weight loss phase is significantly longer, we might start to see physiological benefits in addition to psychological benefits.
In any case, I’m looking forward to when the body of literature grows significantly more and we have studies on physique competitors and other populations who have been left out so far in order to really see where and what type of diet breaks can be most effective.
Madelin Siedler et al. The Effects of Intermittent Diet Breaks during 25% Energy Restriction on Body Composition and Resting Metabolic Rate in Resistance-Trained Females: A Randomized Controlled Trial. Exercise Physiology and Sports Medicine. Journal of Human Kinetics volume 86, 2023, 117–132 DOI: 10.5114/jhk/159960
Peos JJ, Helms ER, Fournier PA, Ong J, Hall C, Krieger J, Sainsbury A. Continuous versus Intermittent Dieting for Fat Loss and Fat-Free Mass Retention in Resistance-trained Adults: The ICECAP Trial. Med Sci Sports Exerc. 2021 Aug 1;53(8):1685-1698. doi: 10.1249/MSS.0000000000002636. PMID: 33587549.