Long-term variation of dietary fiber intake in subjects with neurological diseases on a classic ketogenic dietary therapy

The classic Ketogenic Dietary Therapy (cKDT), traditionally considered low in fiber, has seen growing interest in improving its nutritional quality. This retrospective cohort study examined long-term changes in dietary fiber intake among paediatric patients with neurological diseases on cKDT, hypothesizing that the introduction of Foods for Special Medical Purposes (FSMPs) would increase fiber consumption without compromising nutritional status or diet efficacy. We included 20 patients on cKDT for at least two years. Changes in fiber intake were assessed by analyzing 3-day food diaries at 1 month post-initiation and at the most recent nutritional evaluation, with data compared to Italian Dietary Reference Values (LARN, 2024). Anthropometric and biochemical parameters were also collected. Over an average observation period of 5.3 ± 2.9 years, data showed a significant increase in fiber intake from 8.7 ± 7.1 to 26.0 ± 14.9 g/day and from 6.8 ± 6.2 to 16.9 ± 11.1 g/1000 kcal ( p = 0.006). This new intake level exceeded the LARN adequate intake (8.4 g/1000 kcal), with adherence percentage increasing from 80.8 ± 74.4% to 202.1 ± 131.5% ( p = 0.006). The contribution of fiber from FSMPs increased from 28.4 ± 26.5% to 58.1 ± 21.3% ( p = 0.002). Meanwhile, subjects’ anthropometric and biochemical parameters, including ketones, remained stable, and biochemical markers indicated maintained ketosis (Capillary Ketones T0: 0.1 ± 0.1 vs. T1: 2.5 ± 1.4 mmol/L; p = 0.001). Our data show that fiber intake in patients on long-term cKDT has more than doubled, primarily due to FSMPs. No substantial changes were observed in measured parameters over follow-up, challenging the outdated perception of cKDT as a low-fiber diet. However, data regarding seizure frequency and specific gastrointestinal tolerability were not systematically collected.