The high-fiber vegetable diet provided almost 1 g of plant
sterols daily. Studies have shown that plant sterols, b-sitosterol
and b-sitostanol, reduce serum cholesterol and the LDL cholesterol
to HDL cholesterol ratio,54,55 possibly through reducing
cholesterol absorption.56 The high-fiber vegetable diet resulted
in greater fecal cholesterol and bile acid outputs than the
other 2 diets. Urinary mevalonate excretion was also greater on
the high-fiber vegetable diet compared with the control indicating
increased cholesterol biosynthesis to replenish the increased
sterol loss.57 There was no evidence of high-fecal
propionate levels or reduced insulin secretion as indicated by
reduced urinary C-peptide output to explain the lower cholesterol
levels on the high-fiber vegetable diet.