Diet Breaks (The MATADOR Study)

It is estimated that 80% to 95% of people who lose weight will regain it post-diet. While this isn’t a solid estimate we can go off of, this percentage is quite staggering regardless since anyone looking to drop weight wants to actually keep it off in the long term, right? One of the biggest issues we face currently is not just getting the initial weight off, but helping individuals maintain that progress after the diet is over.

There are a few factors that can definitely play into why this occurs. “Yo-yo diets” and one’s mindset to dieting are sure to be some of the first to come to mind, but for the purpose of this article and the study to be discussed, this issue can be narrowed down to individuals who have undergone and (adhered to) longer periods of caloric restriction. So, weeks at a time as opposed to short, on-and-off bouts. 

With this said, a huge part of why this weight regain seems to occur can be attributed to the adaptations our bodies undergo while in a caloric deficit. This is known as adaptive thermogenesis and leads to certain adaptations over time, such as dips in our daily expenditure and metabolic rate, for example. We can only diet for so long with these metabolic adaptations at play before we have nothing else to pull from (calories, cardio, etc.), so finding ways to mitigate these adaptations throughout the dieting process can aid in overall weight loss, adherence, and most importantly, weight maintenance post-diet.

The MATADOR study

The MATADOR study (standing for Minimizing Adaptive Thermogenesis and Deactivating Obesity Rebound) aimed to determine whether or not intermittent energy restriction (ER) enhanced weight loss when compared to traditional continuous ER. In addition to this, the researchers wanted to know if intermittent dieting would mitigate metabolic adaptations we often see with caloric restriction. 

“Intermittent energy restriction” is essentially a period of time spent at an energy balance or maintenance (based on the individual and their needs, of course). Continuous ER would mean dieting for weeks sequentially. We can define the intermittent period as a diet break!


51 obese males were split into 2 diet protocols: intermittent (INT) energy restriction or a continuous (CON) energy restriction intervention. Prior to starting the diet period, all subjects underwent a 4-week baseline phase (a weight maintenance phase) in order to gauge their individual caloric needs as well as prepare them for the weeks to come. 

Once baseline needs were assessed, the men participated in 16 total weeks of energy restriction distributed as either: 16 weeks of continuous dieting (CON group), or 16 weeks of ER split up as 8×2-week blocks of dieting, alternating with 7×2-week blocks of weight maintenance (INT group). So overall, the continuous group will be dieting for 16 weeks straight, while the intermittent dieting group will rack up a total of 30 weeks for the dieting portion of the study period.

Post-diet, both groups will complete an 8-week maintenance phase to assess relevant measures. All three of the study’s phases (baseline, diet, post-diet) lasted 28 and 42 weeks for the CON and INT groups, respectively. A strong characteristic to note is that food was provided to the subjects throughout each of these phases as well.

Diet details

Speaking of food, this study was able to strongly control this factor for the participants. All of the subjects were prescribed a 33% reduction in energy intake for their diets; these values were adjusted accordingly to account for expected dips in resting energy expenditure, another adaptation to dieting. 

A ‘base’ diet was provided to the subjects (via delivery to the home) for all main meals as well as morning and afternoon snacks. The plan provided would fit the majority of each participant’s daily energy requirements and the men were also required to report daily food logs for the entirety of the study. 

Key Findings

The intermittent dieting group experienced significantly greater weight loss compared to the continuous dieting group. Alongside this, there was a significantly greater drop in fat mass for the INT group compared to the CON group. As for fat free mass, however, there was only a small, similar change observed for both diet groups. 

Initially, the overall change in REE by week 16 of dieting didn’t seem to differ between the two groups. Although, upon seeing the large difference in weight loss between groups and adjusting for those changes in body composition, it was found that the reduction in REE was significantly smaller for the INT group compared to the CON group. This is despite the larger drop in body weight for the INT group, which is pretty noteworthy.

Post-diet: 8 weeks and 6 months 

While only a portion of the study participants were available for 8-week and 6-month post-diet follow-ups, weight appeared to remain stable for the INT group in the first 8 weeks following the diet intervention. As for the CON group, weight was stable in the first 2 weeks of that 8-week period with small, yet significant increases afterwards.

Coming to 6 months post-diet, weight gain varied between the men, although both groups did regain weight in this period of time. It’s important to remember that weight regain is not an uncommon occurrence when transitioning out of a successful fat loss phase. Depending on many factors, sometimes it may even be necessary (competitive sports, large amount of weight loss, for example). With that said, total weight loss from the end of the baseline phase was still shown to be greater for the INT group compared to the CON group. Additionally, fat mass remained significantly lower than it was at baseline for the INT group, but not significantly different for the CON group. Total weight loss on average between the baseline phase to this 6-month follow-up was 8.1 kilograms (17.8 pounds) greater in the INT group. 

Application for lifestyle and competitive athletes

Diet breaks can be extremely useful! Not only are they great tools for physique competitors who are anticipating long seasons, but for lifestyle clients as well. As popular as the competitive realm may seem, the majority of people undergoing fat loss phases will be people who simply want to improve their lifestyles and form healthy habits. A large part many dieters overlook, however, is the part where these changes need to become a part of your life, rather than just a start and end date. Implementing blocks of dieting and maintenance can be very helpful for keeping focused on short term goals and maintaining diet adherence since these periods at maintenance calories can serve as a “light at the end of the tunnel,” in a way. 

As for competitors, we always recommend taking enough time to diet down. Not only does this ease stress and preserve lean body mass, but it allows us to work in tools like the diet break and refeeds to attenuate metabolic adaptations over time (those of which competitors are all too familiar with). In conjunction with consistency, patience, and a sound plan for nutrition and training, diet breaks can be an amazing tool to use for long term sustainability and balance for dieters.


Byrne, N.M., Sainsbury, A., King, N.A., et al. Intermittent energy restriction improves weight loss efficiency in obese men: the MATADOR study. International Journal of Obesity. 2018; 42: 129-138.

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