Exploring Adherence and Acceptability of an Intermittent Carbohydrate Restriction Regime (ICARB) in Free-Living...

Intermittent carbohydrate restriction (ICARB) presents a promising alternative to intermittent energy restriction for improving metabolic health; however, its practicality in real-world settings remains underexplored. The objective of this study was to evaluate the feasibility, adherence, and acceptability of a 4-week ICARB protocol in free-living adults without prescribed energy restriction.

Healthy adults aged 19-65 years with a BMI of 19-39 kg/m² who were weight-stable, not following a restrictive diet, and free from diagnosed medical conditions were recruited. Exclusion criteria included high physical activity ( > 3 sessions/week), use of weight-altering medications, pregnancy or breastfeeding, and indicators of disordered eating or poor sleep quality. Participants followed a 4-week ICARB protocol, limiting carbohydrate intake to ≤ 50 g on two non-consecutive days per week while maintaining unrestricted intake on the remaining days. Participant perceptions were evaluated through qualitative exit interviews whilst changes in dietary intake, body weight, adiposity, resting energy expenditure (REE), and fasted respiratory quotient (RQ) were also measured.

A total of 37 participants were enrolled, with 34 completing the study (16 male; mean age 22.3 ± 5.4 years; 10 with BMI ≥ 25 kg/m²). On low-carbohydrate days, 24 of 28 participants achieved the ≤ 50 g/day target at both weeks 1 and 4, with mean carbohydrate reduction of 128.7 ± 90.4 g/day in Week 1 and 136.9 ± 101.8 g/day in Week 4 (both p < 0.0001) compared with non-restricted days, reflecting strong adherence to the regimen. Participants who were overweight showed significant reductions in body weight ( - 1.1 ± 1.4 kg; p = 0.04) and fat mass ( - 0.95 ± 1.0 kg; p = 0.02), while no group-level changes were observed. Notably, most participants expressed a willingness to maintain the diet beyond the study period, with suggested durations spanning from an additional 2 weeks to indefinitely. Exit interviews highlighted perceived benefits, including improved dietary awareness, energy, and mood, alongside challenges such as identifying foods that met the carbohydrate criteria, navigating social eating occasions and limited food choices when dining out. Participants also described adaptation strategies, including meal planning and forming consistent routines.

The ICARB protocol was feasible and acceptable over 4 weeks under free-living conditions. These findings support its short-term practicality and adherence potential, warranting longer-term and controlled studies to assess metabolic and behavioural outcomes.

gov. (NCT07056465).