Utilization of nutrients in milk- and wheat-based diets by men with adequate and reduced abilities to absorb lactose. I. Energy and nitrogen

Abstract

Four healthy men with proved reduced ability to absorb lactose (LM) and two control subjects were fed diets based exclusively on milk or wheat proteins for four successive 12-day periods. Milk protein diets contained 48 g lactose from milk, approximately one-half that amount from lactose-reduced milk, or no lactose (simulated milk). The fourth diet was comprised of milk-free wheaten foods and contained no lactose. Protein and energy intakes were held to minimally adequate levels to test the hypothesis that ingestion of lactose leads to nutritionally significant fecal losses of nutrients in cases of diminished lactose absorption. Two LM subjects showed no evidence of malabsorption when the diet contained 48 g of lactose in four divided doses, given with meals. The other two LM subjects had elevated levels of hydrogen in the breath and increased fecal losses of moisture, dry solids, and energy that were lactose dose dependent. These parameters and fecal fat and nitrogen excretion were markedly increased with the wheat diet in all cases, irrespective of lactose absorption status. In LM subjects, fecal losses with wheat were greater than or equal to losses sustained with 48 g lactose in the diet. Five men maintained body weight equally well or poorly throughout a range of metabolizable energy intakes given in each case; energy intake and body weight change were significantly related only in one subject. Nitrogen (N) balance with milk diets was significantly related to metabolizable energy intake in four subjects. After this was taken into account, there were no significant differences in N balance among the milk treatments. At milk N intakes of 94 mg/kg, energy intake determined the sign and magnitude of the N balance irrespective of the ability to absorb lactose except as this resulted in decreased energy availability. The maximum difference in fecal energy loss among milk treatments, for the two poorest absorbers at the highest lactose dosage, was equal to 1.6 to 1.7 kcal/kg or 4% of intake. N balance was distinctly poorer with the wheat diet; true N equilibrium was not achieved in any subject with 98 mg/kg wheat N in the diet.