A diet break is a planned pause, usually 1 to 2 weeks long, in the middle of a long diet, during which you eat at maintenance calories. Afterwards the cut continues with the same deficit as before.
It differs from a refeed, which lasts only 1 to 2 days, and from a reverse diet, where you raise calories step by step after a diet has ended.
What studies show
In the MATADOR study (Byrne et al. 2018) with men with obesity, two weeks of dieting alternated with two weeks at maintenance. This group lost more fat than the group dieting continuously, but took almost twice as long. Closer to recreational lifters is the ICECAP trial (Peos et al. 2021) with resistance-trained adults: no difference in fat loss, fat-free mass, strength or resting metabolic rate, but less hunger in the group with breaks.
Based on current evidence, a diet break does not make your diet more effective if you train, but it does make it easier to live with. You buy staying power and pay for it with time.
What the scale does
With more carbs your glycogen stores refill, and glycogen is stored with about three to four parts water. In an ICECAP analysis, body weight rose by 0.6 kg on average during the one-week break, without a significant change in fat mass. Back in a deficit, that part drops off again within a few days.
Example: At 80 kg trend weight and a corridor of plus or minus 1.5 percent, your trend should stay between 78.8 and 81.2 kg during the break. This is a worked example. If it climbs steadily out of the band over two weeks, you are eating above maintenance.