The Role of Carbohydrate Restriction in Intermittent Energy Restriction: Exploring Independent Health Effects

<strong>Background: </strong>The increasing prevalence of cardiometabolic diseases underscores the need for dietary interventions that enhance metabolic health beyond the effects of weight loss and conventional energy restriction. Intermittent energy restriction (IER) and low-carbohydrate diets (LCDs) enhance fat oxidation and metabolic flexibility, but the interplay between caloric and carbohydrate restriction complicates the identification of their distinct metabolic effects. This PhD project aims to isolate the independent effects of carbohydrate restriction from energy restriction in IER and to investigate the feasibility of a novel intermittent carbohydrate restriction (ICR) diet as a strategy that may provide metabolic improvement while maintaining weight. <strong>Methods: </strong>A short-term cross-over study investigated the independent effects of carbohydrate restriction at varying energy levels on fasting and postprandial cardiometabolic risk markers and energy metabolism. A survey assessed perceptions, facilitators and barriers of ICR diet. And a four week feasibility study evaluated ICR’s impact on body composition, energy metabolism, and adherence in free-living healthy individuals, complemented by thematic analysis. Finally, an RCT protocol was developed to examine cardiometabolic effects of ICR against conventional IER. <strong>Results: </strong>The cross-over study demonstrated that carbohydrate restriction elicits comparable reduction in triacylglycerol and respiratory quotient and increases in non-esterified fatty acids and ketone levels, independent of energy intake. These changes were significantly different from non-restricted diet. The survey estimated potential challenges with ICR, including hunger, cravings, social constraints, and limited food choices, though less so than IER and LCDs. The 4-week ICR study demonstrated high retention (91.9%), good compliance (77.4%), and strong acceptability with minimal lifestyle disruption. Despite these anticipated barriers, 84% of participants expressed willingness to continue the diet. <strong>Conclusion: </strong>Carbohydrate restriction, independent of energy reduction, has been shown to elicit effects similar to those observed in short-term severe energy restriction, akin to a restrictive day in IER, providing a basis for the ICR regimen. Subsequent studies confirmed that ICR is both well-perceived and feasible among free-living healthy individuals, suggesting that ICR could be a sustainable strategy. A long-term study is planned to assess its impact on cardiometabolic risk markers, with further research needed to explore ICR as a public health intervention, especially for those not seeking weight loss.