Mechanisms of Dietary Protein-Induced Changes in Calcium Absorption Efficiency

We undertook a randomized, double-blind, crossover study in 14 healthy women who were required to ingest a 6-day low protein diet supplemented with CaSR-AAA (calcium-sensing receptor-activating amino acids), DAA (dibasic amino acids) or methylcellulose capsules (control). All subjects ingested all three diets in random order. Prior to each experimental diet subjects consumed an 11 day adjustment diet. Calcium absorption was measured on day 5 of each dietary intervention using dual-stable calcium isotopes. The clinical trial tested the hypothesis that dietary protein affects the efficiency of intestinal calcium absorption by activating the calcium sensing receptor (CaSR). Supplementation with CaSR-AAA did not significantly increase Ca absorption. However, a trend towards improved Ca absorption was observed with DAA (25.2±1.4% vs. 22.3±1.4%, P=0.094). To further elucidate the mechanisms by which dietary protein improves Ca absorption, we established and validated a 45Ca in vitro transport model. Differentiated Caco-2 cells were exposed to different concentrations of amino acids for 6 and 72 hours. Prolonged amino acid treatment significantly enhanced total transepithelial Ca transport (P=0.0048). Subsequent in vitro studies utilized our recently validated transport model and focused on the functional role of Cldn-2 in total transepithelial Ca transport. Cldn-2 is a tight junction protein that was previously shown to be upregulated by dietary protein in rats. Total transepithelial Ca transport was significantly reduced when Cldn-2 was stably knocked down in Caco-2 cells (P\u3c 0.0001). The contribution of Cldn-2 to amino acid-induced increases in Ca transport will be explored in future studies

Development of a Technology-Assisted Food Frequency Questionnaire for Elementary and Middle School Children: Findings from a Pilot Study

Background: This pilot study collected preliminary data for the modification of the VioScreen Food Frequency Questionnaire (FFQ), an adult-validated, self-administered, web-based dietary assessment tool for use in older children. Methods: A convenience sample of 55 children, aged 6−14 years, completed the VioScreen FFQ and 3-day diet record (reference standard). Caregivers completed a short sociodemographic questionnaire. Reported dietary intakes from the VioScreen FFQ and 3-day diet record were calculated using standard nutrient databases, and descriptive statistics were used to examine differences in food/beverage items and portion sizes between the two methods. Informal focus groups obtained user feedback and identified components of the VioScreen FFQ that required modifications. Results: The highest de-attenuated Pearson correlation coefficients between the VioScreen FFQ and 3-day diet record were observed for iron (r = 0.69), saturated fat (r = 0.59), and vegetables (r = 0.56), and the lowest were for whole grains (r = 0.11) and vitamin C (r = 0.16). Qualitative feedback was overall positive, and six technological modifications were identified. Conclusion: Findings from this pilot study provided valuable information on the process of evaluating the use of the VioScreen FFQ among older children, and will inform the future development of a modified version for this population

The Effect of Dietary Glycemic Properties on Markers of Inflammation, Insulin Resistance, and Body Composition in Postmenopausal American Women: An Ancillary Study from a Multicenter Protein Supplementation Trial.

Controversy exists as to whether high glycemic index/glycemic load (GI/GL) diets increase the risk of chronic inflammation, which has been postulated as a pathogenic intermediary between such diets and age-related alterations in body composition and insulin resistance. We conducted an ancillary study to a randomized, double-blind trial comparing the effects of a whey protein supplement (PRO, n = 38) and a maltodextrin supplement (CHO, n = 46) on bone density to evaluate the impact of a calibrated increase in GI/GL on inflammation, insulin resistance, and body composition in a healthy aging population. Markers of inflammation, HOMA, body composition, and GI/GL (estimated from 3-day food records) were assessed at baseline and 18 months. By 18 months, the GL in the CHO group increased by 34%, 88.4 +/- 5.2 --> 118.5 +/- 4.9 and did not change in the PRO group, 86.5 +/- 4.1 --> 82.0 +/- 3.6 (p < 0.0001). Despite this change there were no differences in serum CRP, IL-6, or HOMA at 18 months between the two groups, nor were there significant associations between GL and inflammatory markers. However, trunk lean mass (p = 0.0375) and total lean mass (p = 0.038) were higher in the PRO group compared to the CHO group at 18 months There were also significant associations for GL and change in total fat mass (r = 0.3, p = 0.01), change in BMI (r = 0.3, p = 0.005), and change in the lean-to-fat mass ratio (r = -0.3, p = 0.002). Our data suggest that as dietary GL increases within the moderate range, there is no detectable change in markers of inflammation or insulin resistance, despite which there is a negative effect on body composition