The strength calculation is based on a former study of fat oxidation in patients with CPT II deficiency. Ørngreen et al 2005 In this study we described fat oxidation of patients and carriers with respectively two and one CPT2 gene mutations compared with the fat oxidation in healthy controls. The expected effect of bezafibrate on the fat oxidation in the CPT II patients is expected to be the difference between the mean value of fat oxidation in patients with CPT II deficiency and the mean value of the fat oxidation in heterozygous carriers of one CPT2 gene mutations. The strength calculation indicates that a number of 11 subjects need to be included. The aim is to include 11 patients from respectively the groups of patients with CPT II deficiency and the groups of patients with VLCAD deficiency. If somehow it turns out that we cannot include that many patients. The two groups will be pooled into one group. This can be done because of the similarity of the two groups both in symptoms and in fat oxidation, which is one of the primary outcomes, during exercise.Ørngreen et al 2005, Ørngreen et al 2004 Missing data: As long as a patient has completed at least one treatment period, results will be included in the data. Differences between treatments in the individual will be assessed by a paired Student's t-test. A p value < 0.05 (two-tailed testing) will be considered significant.