Background/Objectives: Low-carbohydrate (LCD) and ketogenic diets (KD) are increasingly adopted by athletes due to their ability to enhance fat oxidation and induce metabolic adaptations. While their effects on aerobic power and capacity have been widely investigated, their influence on anaerobic performance remains unclear. Given the strong dependence of high-intensity exercise on glycolytic metabolism and muscle glycogen availability, carbohydrate restriction may have significant implications for short-duration maximal efforts and repeated high-intensity exercise. Therefore, this systematic review and meta-analysis aimed to evaluate the effects of LCD and KD on anaerobic performance outcomes in trained athletes. Methods: A comprehensive search of five electronic databases (PubMed, SCOPUS, Web of Science, SPORTDiscus, and Cochrane Central Register of Controlled Trials) identified 13 unique studies (yielding 15 study-level entries across three anaerobic performance domains) meeting comprehensive inclusion criteria. Individual study sample sizes ranged from n = 5 to n = 65 participants, reflecting substantial inter-study variability that should be considered when interpreting pooled estimates. Outcomes included peak and mean power output, repeated sprint performance, blood lactate responses, and markers of substrate utilization. Study quality was assessed using the Newcastle–Ottawa Scale, and meta-analyses were performed using random-effects models where appropriate. Results: Overall, the effects of carbohydrate-restricted diets on anaerobic performance were domain-specific. Some studies reported maintained or slightly improved peak power during single maximal efforts, while others showed no effect. Impairments were more consistently observed in repeated high-intensity exercise. Repeated sprint performance was impaired in several studies, likely reflecting reduced muscle glycogen availability and limited glycolytic ATP production. Carbohydrate restriction consistently increased fat oxidation and was associated with lower blood lactate concentrations during high-intensity exercise. Random-effects meta-analyses yielded domain-specific pooled effect sizes: maintained-to-slightly-improved anaerobic power output (Cohen’s d = +0.29; 95% CI: −0.08 to +0.66), modestly impaired repeated sprint ability (d = −0.33; 95% CI: −0.80 to +0.14), and a large, consistent reduction in blood lactate concentration (d = −0.89; 95% CI: −1.20 to −0.58). Given substantial between-study heterogeneity in intervention durations (2 days to 12 weeks), dietary composition, athlete populations, and outcome measures (1RM, Wingate, CMJ within the power domain; varied protocols within the RSA and lactate domains), these pooled estimates should be interpreted as exploratory rather than confirmatory. Conclusions: LCD and KD appear to have domain-specific effects on anaerobic performance in trained athletes. Although single, short-duration efforts may be preserved in some contexts, repeated, high-intensity performance appears to be more susceptible to impairment. These findings highlight the importance of aligning dietary strategies with the metabolic demands of training and competition.
Gawelczyk et al. (Sat,) studied this question.