Adherence and Retention in Early or Late Time-Restricted Eating: A Narrative Review of Randomized Controlled Trials

Time-restricted eating (TRE) is a form of intermittent fasting that involves reducing the time-period in which food is typically consumed daily. While TRE is known to induce health benefits, particularly for adults with obesity, there is currently debate about whether the time of day in which food is consumed also contributes to the health benefits of TRE. Early TRE (eTRE) and late TRE (lTRE) are subtypes of TRE that involve consuming food and caloric beverages either in the early or later part of the day. A growing body of literature indicates that eTRE may offer additional health benefits compared with lTRE. An important and unanswered question, however, is whether most adults can adhere to this type of eating pattern and whether adherence and retention differ between eTRE and lTRE. This narrative review compared adherence and retention in studies that implemented either eTRE or lTRE in adults for 8 weeks or longer. Five databases were searched, and 10 studies met our eligibility criteria. The key finding was that participants had high and comparable levels of adherence and retention in both eTRE and lTRE interventions. Specifically, the mean adherence rate was 81.4% for eTRE and 82.3% for lTRE, while the mean retention rate was 81% for eTRE and 85.8% for lTRE in eligible studies. Thus, the findings support the feasibility of both approaches. The lowest adherence and retention rates occurred in studies in which either eTRE or lTRE regimens were combined with other dietary interventions. Notably, the duration of the eating window did not seem to negatively affect adherence and retention rates for either eTRE or lTRE. More research is warranted to determine the influence of other factors, such as age and study location, on adherence to and retention of both eTRE and lTRE interventions.