The effects of lentils on calcium balance in healthy males
Dahl, Wendy Joanne
Nutritional recommendations encourage the Canadian population to increase its intake of complex carbohydrates with a resulting increase in dietary fibre. Diets high in insoluble fibre are thought to compromise calcium status by increasing faecal calcium excretion. Calcium status is of particular concern due to the risk of osteoporosis. A six week study was conducted to determine the effect of Laird lentil fibre and starch on calcium balance. In a randomized experimental design, ten males (19-37 years) consumed a control diet for three weeks and the control diet plus 130 g lentils providing 13 g NSP; 80% insoluble, for three weeks. Seven-day food records were used to adjust the study diet to the subjects' usual calcium and energy intakes. Ultra-pure water was consumed throughout the study. Duplicate diets of food consumed were prepared. Radio-opaque markers were given and complete faecal collections were made. Twenty-four hour urine collections were made in weeks three and six. Tablets containing PABA were given to validate the completeness of urine collections. Lentils increased faecal weight (control 130.6 Â± 11.8 g/d (Mean Â± SEM); lentil 189.6 Â± 21.2 g/d (P = 0.027). Calcium balance was maintained during both the control (0.4 Â± 0.8 mmol/d) and lentil periods (- 0.6 Â± 0.9 mmol/d) (P = 0.503). Faecal calcium remained unchanged (28.5 Â± 1.7 mmol/d; 29.7 Â± 1.5 mmol/d) (P = 0.434). Urine calcium decreased from 5.43 Â± 0.44 mmol/d to 4.53 Â± 0.41 mmol/d (P = 0.0001). Possible mechanisms which may explain the change in renal calcium excretion are changes in dietary calcium, urinary sodium excretion, net acid excretion or renal potassium excretion. Dietary calcium did not significantly change (34.4 Â± 1.8 mmol/d; 33.6 Â± 1.9 mmol/d) (P = 0.095). Renal sodium excretion decreased (149 Â± 4 mmol/d; 133 Â± 3 mmol/d;) (P = 0.0003). Renal net acid excretion remained unchanged (49.2 Â± 4.2 mmol/d; 52.3 Â± 3.1 mmol/d) (P = 0.24). Renal potassium excretion increased (90.8 Â± 4.7 mmol/d; 102.5 Â± 3.1 mmol/d) (P = 0.015). This study shows that adding Laird lentils to the diet does not adversely affect calcium status. The significant decrease in renal calcium excretion may be due to a combination effect from the changes in dietary phosphorus, renal sodium and potassium with the change in renal potassium excretion demonstrating the greatest effect. Also, the resistant starch present in Laird lentils may have had an effect on renal calcium excretion.