This post is taken from the Vitamin. Every Thursday, I drop some knowledge bombs on your face to help you reach your goals faster while avoiding all the bullshit.
You know when you’ve been in a deficit for a while, and things start to feel a bit sucky? Hunger is high, you have the energy levels of a sloth on Xanax, you’re irritable, and you start to question whether this dieting stuff is even worth it.
Well, friend, you’re in luck! I’m about to tell you about a top-secret diet strategy that’ll have you back to your perky self in no time while making progress on your goals.
Supposedly, anyway.
What I’m referring to––if the title didn’t give it away––is a diet break.
As you diet and get leaner, a cascade of hormonal changes occurs to prevent you from losing more body mass and ostensibly starving to death. These changes include (but aren’t limited to), an increase in hunger, lethargy, fatigue, and reduced energy expenditure, which can stall fat loss.
As you get leaner, several changes occur in the body that increase hunger and reduce your total daily energy expenditure, all to try and stop you from losing more weight. RMR=resting metabolic rate; TEF=thermic effect of food; PA=physical activity; NEAT=non-exercise activity thermogenesis.
To combat these negative side effects, a common recommendation is to implement a 1-2 week “diet break” where calories are increased to maintenance. The theory goes that this reverses some of the metabolic adaptations, and you can get back to dieting with renewed zeal.
Here’s the kicker, though: Despite how commonly diet breaks are recommended, you might be surprised to learn research on the topic is still sparse and, up until recently, has only been done in sedentary, overweight individuals. 1Davoodi S et al. 20142Byrne et al. 2018
That all changed in 2021 when researchers published the first diet break study on resistance-trained men and women. 3Peos JJ et al. 2021
The researchers found a diet break wasn’t more effective than continuous dieting for increasing fat loss, preserving muscle mass or maintaining resting energy expenditure. However, the diet break did seem to lower the drive to eat due to increased fullness.
Well, we now have a brand new diet break study that revisited the topic in a group of young, resistance-trained females. 4 Siedler RM et al. 2023
What did the researchers do?
38 resistance-trained females were randomised into two groups:
1. Continuous diet group: This group was prescribed a 25% deficit from their predetermined maintenance intake and dieted continuously for six weeks.
2. Diet break group
This group was also prescribed a 25% deficit from their predetermined maintenance intake and dieted for six weeks, but also included two diet breaks where they ate at maintenance.
Both groups followed the same macro targets:
1.8g/kg (0.8g/lb) of protein
40% of calories came from fats
60% of calories came from carbs
Participants resistance trained 3x/week with a volume-matched alternating upper/lower split, and all working sets were taken to 2 reps in reserve (i.e., they stopped 2 reps from failure).
Alongside the resistance training, participants were also instructed to engage in 30 min of low- to moderate-intensity cardio twice per week. Participants in the diet break group were told to refrain from cardio during the diet break weeks.
Results
The main finding of this study was that a diet break didn’t provide any benefits to body composition or resting energy expenditure when compared with continuous dieting.
Across all participants:
There was a mean decrease in body weight from baseline to post-intervention (62.7 kg to 61.5 kg).
fat mass decreased from 15.9 kg to 14.7 kg.
There was no change in muscle mass.
Resting metabolic rate didn’t change over time (1422 kcals to 1434 kcals).
There weren’t any differences in measures of satiety, ease of sticking to the diet, or motivation to diet for the week ahead.
However, the diet break group did experience a decrease in disinhibition (the desire to overeat) over the course of the study. In contrast, the continuous dieting group saw an increase in this parameter.
One likely explanation for this could be that a diet break allows people to eat a bit more food – and often fit in higher calorie foods they wouldn’t be able to during a diet – which reduced the desire to overeat during the dieting period. As the researchers write:
It is possible that by nature of the ability to “practice” restrained, but not excessively restrictive, eating throughout the two week-long diet break periods, participants in the INT group saw fewer deleterious effects of dieting on disinhibition than those dieting continuously, which may bode well for the maintenance of energy balance and weight loss results over the long term.
More recently, another group of researchers conducted a systematic review (study of studies) and meta-analysis (statistical analysis of the included studies) on the impact of diet breaks and refeeds. 5Poon et al. 2024
Specifically, the researchers wanted to see whether diet breaks and refeeds (collectively referred to as ‘intermittent dieting’) would better attenuate metabolic adaptation (based on resting metabolic rate) and lead to better body composition outcomes than continuous energy restriction (i.e. dieting without intermittent breaks).
Both intermittent dieting and continuous energy restriction reduced total body mass, body fat, body fat percentage, BMI, waist circumference, and lean mass but there was no significant difference between the groups.
However, intermittent dieting won out against continuous energy restriction when it came to resting metabolic rate. Intermittent dieting led to an RMR reduction of ~39 kcals/day. Meanwhile, continuous energy restriction led to an RMR reduction of ~92 kcals/day.
INT = intermittent dieting; CER = continuous energy restriction
The weighted between-group difference in RMR was ~47 kcals, which was ‘statistically significant’ (I intentionally put this in quote marks and I’ll explain why later).
In other words, people following an intermittent dieting approach had, on average, a ~47-calorie smaller drop in their metabolism each day compared to those on a continuous diet.
The researchers also conducted sub-group analyses to determine whether the type of intermittent dieting (i.e. diet breaks or refeeds), duration of the intervention (≤8 weeks and >8 weeks), and population characteristics (i.e. overweight/obese vs resistance-trained individuals) influenced RMR changes.
Participant characteristics were the only factor that influenced RMR changes in the subgroup analyses, with people who were overweight or obese seeing a larger decrease in their metabolic rate (~73 kcals/day) compared with resistance-trained individuals (~11 kcals/day).
But this makes sense since the magnitude of weight loss was higher in the overweight/obese groups (about 7 kg) versus the resistance-trained groups (about 2 kg), and we know metabolic adaptation increases with the magnitude of weight loss.
Take a break or nah?
All in all, there’s nothing sexy or groundbreaking here––whether you decide to diet continuously, implement an occasional diet break, or take a weekly refeed, neither will impact your metabolic rate to any meaningful degree nor provide any superior benefits in body composition.
If you just read the abstract of this study, it would be tempting to think intermittent dieting has a special advantage, but this raises an important point about how something can be statistically significant in a study but practically insignificant in the real world. I don’t think anyone’s getting excited about a 50-kcal ‘advantage’ in metabolism.
That said, I still think there are advantages to using intermittent dieting strategies that extend beyond metabolism or body composition.
As far as weekly refeeds go, you might simply enjoy eating a bit more on the weekend (in a controlled fashion – notcheat days) because it helps increase adherence. I don’t think there’s anything wrong with that.
Taking a complete week or two off from a diet (i.e., a diet break) might not do much for your metabolism or improve fat loss/muscle retention, but it might benefit mood, appetite, and adherence.
As noted in the study by Siedler and colleagues discussed earlier, the diet break group experienced a decrease in disinhibition (the desire to overeat). In contrast, the continuous dieting group saw an increase in this parameter.
Peos and colleagues found the diet break group experienced a significant increase in fullness compared to the continuous dieting group. [3] This same research group conducted a secondary analysis of their main study and found a one-week diet break increased mental alertness and reduced hunger and irritability while increasing fullness and food satisfaction. 6Peos JJ et al. 2021
These aren’t trivial things.
If a diet break can help improve mood, energy, focus, and dietary adherence, you’re more likely to stick to the diet over the long term versus grinding your way through a deficit despite feeling like shit. You certainly don’t need to force a diet break every few weeks, but writing them off completely when they can be a useful tool in the dieting toolbox for reasons beyond metabolism is a bit shortsighted.
In any case, if you’re looking to implement diet breaks or refeeds as a strategy to help preserve your metabolism, increase fat loss, and improve muscle retention, the current research seems to paint a fairly neutral picture–it can be another way to set up your diet, but it’s not going to impact any of these parameters to any meaningful degree.
Thanks for reading. If you enjoyed this, you’d love the Vitamin
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