Maldigestion and colonic fermentation of wheat bread in humans and the influence of dietary fat.

A fraction of wheat bread is malabsorbed in healthy humans. The malabsorbed fraction is bigger than what can be accounted for by in vitro measurements of dietary fibers and resistant starch. To determine whether it is a specific fraction defined by the structure of the starch molecule or a variable amount--which depends on the individual, the amount ingested, and other components of the meal--we performed a dose-response study on wheat bread in healthy human volunteers. Malabsorption was evaluated by using the breath-hydrogen test. Test meals were as follows: 20 g wheat bran mixed in 100 mL water; bread made from 25, 75, 100, 150, and 200 g white wheat flour (WWF); bread made from 0 g WWF and 20 g wheat bran; and bread made from 100 g WWF served with 11 or 26 g butter, corresponding to 20% or 35% of energy from fat in the meals. Three of seven volunteers malabsorbed a fraction of the bread made from 25 g WWF and five of seven a fraction of the bread made from 75 g WWF. All volunteers malabsorbed a fraction of the 100-g WWF bread, Bread made from 180 g WWF and 20 g wheat bran resulted in a breath-hydrogen response of the same magnitude as that from bread made from 200 g WWF alone. The 100-g WWF bread + 11 g butter resulted in a significantly higher breath-hydrogen response than did the bread alone, whereas the 100-g WWF bread + 26 g butter resulted in an average response of the same magnitude as that from bread alone. We conclude that the malabsorbed fraction of wheat bread was dependent on the amount ingested, the composition of the meal, and individual gastrointestinal handling. Fermentation of wheat bran resulted in a very low breath-hydrogen response compared with lactulose or wheat bread. Addition of 11 g butter to the bread seemed to increase the malabsorbed fraction of the starch, an effect that was abolished when the amount of butter was increased to 26 g.