Effect of a High Fiber Diet Compared to a Moderate Fiber Diet on Calcium and Other Mineral Balance in Subjects with Type 2 Diabetes Mellitus

Abstract

Objective: High levels of dietary fiber, especially soluble fiber, are recommended to lower serum cholesterol levels and improve glycemic control in patients with type 2 diabetes mellitus (T2DM). It is not clear, however, how high levels of fiber affect mineral balance.

Research Design and Methods: In a randomized, cross-over study, 13 patients with T2DM, were fed a high fiber (HF) (50 g total and 25 g soluble fiber) and a moderate fiber (MF) (24 g total and 8 g soluble fiber) diet of the same energy, macronutrient, calcium, magnesium, and phosphorus content for 6 weeks each. Intestinal calcium absorption was determined by fecal recovery of ⁴⁷Ca. Stool weight and mineral content were assessed during 3 days and 24 h urinary mineral content and serum chemistry were assessed over 5 days at the end of each phase. The results were compared by repeated measures ANOVA.

Results: Compared to the MF diet, the HF diet increased stool weight (165±53 vs. 216±63 g/d, p=0.02), and reduced 24 h urinary calcium (3.3±1.7 vs. 2.4±1.2 mmol/d, p=0.003) and phosphorus (29.2±5.5 vs. 26.0±3.2 mmol/d, p=0.003) excretion, and serum calcium concentration (2.33±0.06 vs. 2.29±0.07 mmol/L, p=0.04). Calcium absorption, stool calcium, magnesium, and phosphorus content, and serum phosphorus concentration were not significantly different on the two diets.

Conclusions: A high fiber diet rich in soluble fiber has a small impact on calcium and phosphorus balance in subjects with T2DM. It may be prudent to ensure adequate intake of calcium and other minerals on the HF diet.