A 34-year-old woman with a history of recurrent hypoglycaemia and hepatomegaly is found to have a deficiency in carnitine palmitoyltransferase I (CPT I). Her brother, diagnosed at age 28, has a deficiency in long-chain 3-hydroxyacyl-CoA dehydrogenase (LCHAD). Which clinical feature best distinguishes CPT I deficiency from LCHAD deficiency?