The effects of dietary manipulations on excretion of the
porphyrin precursors,
delta-aminolevulinic acid (ALA), and
porphobilinogen (PBG) were studied in eight patients with
acute intermittent porphyria. Three diet periods of 9-17 days comprised each study. In each patient, a "baseline"
protein, fat, and
carbohydrate intake was kept constant throughout. In addition, during the first diet period each patient received 150 g
dextrose; during the second, this was replaced by an isocaloric amount of neutral fat; and during the third, the fat was replaced by 150 g
glycerol. In each of the patients, three comparisons of the effect of diet on both ALA and PBG excretion were made: (1) 300 g
carbohydrate versus 150 g
carbohydrate (
dextrose versus fat), (2) 150 g
carbohydrate + 150 g
glycerol versus 150 g
carbohydrate (
glycerol versus fat), and (3) 300 g
carbohydrate versus 150 g
carbohydrate + 150 g
glycerol (
dextrose versus
glycerol). For each of these three diet comparisons, there are sixteen individual comparisons possible for the effect of diet on
porphyrin precursor excretion, eight for ALA and eight for PBG. Thus, the mean values for ALA and PBG excretions during each of the diet periods are statistically compared internally within each individual patient. Increasing
carbohydrate intake from 150 g to 300 g by isocaloric substitution of
dextrose for fat produced a significant (p less than 0.05) decline in eight of the sixteen comparisons of ALA and PBG excretion. Addition of 150 g
glycerol by isocaloric substitution for fat caused a significant (p less than 0.05) decline in nine of the sixteen possible comparisons. In the sixteen comparisons of isocaloric
dextrose and isocaloric
glycerol-substituted diets,
dextrose produced significantly (p less than 0.05) lower
porphyrin precursor excretion in four cases and
glycerol produced significantly (p less than 0.05) lower values in five. One patient showed no significant change on any of the diets. Of the four patients having symptoms believed referrable to
porphyria during the study, three reported an improvement in symptoms during the high
glycerol intake. The effects of dietary perturbations on
porphyrin precursor excretion in
acute intermittent porphyria are variable, but
glycerol appears to be capable of decreasing the excretions and may prove useful in treating some of these patients.