Effect of acetate and propionate on calcium absorption from the rectum and distal colon of humans.

To determine the effects of acetate and propionate on calcium absorption from the human distal colon and rectum, six healthy human subjects were given rectal infusions containing 50 mmol CaCl2/L on four separate occasions. Addition of 56.3 mmol acetate/L, 18.7 mmol propionate/L, or acetate and propionate together increased calcium disappearance (expressed as the change in the ratio of calcium to polyethylene glycol) from -5.5 +/- 1.4 to -22.6 +/- 2.8, -23.2 +/- 3.2, and -19.7 +/- 4.6, respectively; P < 0.05. To determine the effects of different acetate and propionate concentrations, six different subjects were studied further. The effects of 18.7 or 56.3 mmol acetate/L on calcium absorption were the same as those of 18.7 mmol propionate/L (-15.7 +/- 1.4), and less than those of 56.3 mmol propionate/L (-20.3 +/- 2.4, P < 0.05). We conclude that both acetate and propionate enhance calcium absorption from the human distal colon, but that propionate has a greater effect at higher concentrations. Further studies are needed to determine the mechanism of calcium absorption from the colon.

Iron absorption in humans as influenced by bovine milk proteins.

The effect of the two major bovine milk protein fractions on the dialyzability of iron in vitro under simulated gastrointestinal conditions and on the absorption of Fe by humans was studied. Liquid-formula meals were prepared from hydrolyzed maize starch, corn oil, and either spray-dried egg white or a milk-protein product. In meals containing egg white, 3.32% of the Fe was dialyzable. The substitution of casein and whey protein products reduced the dialyzable fraction to 0.19-0.56% and 0.86-1.60%, respectively. Percentage Fe absorption was also reduced by the substitution of casein or whey protein for egg white. Mean absorption values fell from 6.67 to 3.65% and 2.53 to 0.98%, respectively. When the intact milk-protein products were replaced by enzyme- or acid-hydrolyzed preparations, the dialyzable fraction increased markedly and in proportion to the extent of hydrolysis. A similar but much smaller effect on absorption was observed. These studies suggest that bovine casein and whey proteins are responsible at least in part for the poor bioavailability of the Fe in some infant formulas.

Iron absorption in humans: bovine serum albumin compared with beef muscle and egg white.

We studied the influence of bovine serum albumin and beef meat on nonheme iron absorption in humans and on dialyzable iron in vitro. The addition of serum albumin to a maize gruel had no significant effect on nonheme Fe absorption whereas the addition of beef meat caused a threefold increase. When added to a bread meal, serum albumin caused a modest 60% increase in nonheme Fe absorption and beef meat had no effect. When added to a protein-free meal, serum albumin reduced Fe absorption by 47% compared with a 72% reduction on addition of egg white. The bioavailability of nonheme Fe from meals containing serum albumin was consistently overestimated by the in vitro technique. We conclude that the facilitation of nonheme Fe absorption by meat is not a general property of all animal protein but is better explained by the action of one or more specific animal tissues.

Effects of calcium concentration, acetate, and propionate on calcium absorption in the human distal colon.

Previous studies have shown that the short-chain fatty acids acetate (Ac) and propionate (Pr) enhance the absorption of calcium (Ca) in the rectum and distal colon of humans, with Pr being more effective than Ac. To investigate the effect of Ac and Pr on the kinetics of Ca absorption from the human rectum and distal colon, six healthy subjects were studied. Solutions containing various concentrations of CaCl2.H2O with 56.3 mmol/L Ac, Pr, or NaCl were rectally infused to each subject. Rectal fluid was sampled at the end of the infusion (0 min), and 30 min later colonic contents were collected. Ca absorption for all treatments increased linearly with Ca concentration. For Ca + NaCl, the slope of regression line was 62 mumol.mmol-1.L Ca. With Ac + Ca, the slope of Ca absorption increased significantly to 113 mumol.mmol-1.L Ca, and with Pr + Ca, the slope increased to 159 mumol.mmol-1.L (P = 0.043 versus Ac + Ca) Ac and Pr absorption were increased by Ca. The data suggest that, over a physiologic range of Ca concentration, in the absence or presence of Ac and Pr, Ca is absorbed in the human rectum and distal colon by a non-saturable diffusion process, and that Ca absorption is enhanced by Ac and Pr. The data also suggest that both Ac and Pr absorption is stimulated by Ca.

Validation of bioelectrical impedance analysis for total body water assessment against the deuterium dilution technique in Asian children.

BACKGROUND/OBJECTIVES: To develop and cross-validate bioelectrical impedance analysis (BIA) prediction equations of total body water (TBW) and fat-free mass (FFM) for Asian pre-pubertal children from China, Lebanon, Malaysia, Philippines and Thailand. SUBJECTS/METHODS: Height, weight, age, gender, resistance and reactance measured by BIA were collected from 948 Asian children (492 boys and 456 girls) aged 8-10 years from the five countries. The deuterium dilution technique was used as the criterion method for the estimation of TBW and FFM. The BIA equations were developed using stepwise multiple regression analysis and cross-validated using the Bland-Altman approach. RESULTS: The BIA prediction equation for the estimation of TBW was as follows: TBW=0.231 × height(2)/resistance+0.066 × height+0.188 × weight+0.128 × age+0.500 × sex-0.316 × Thais-4.574 (R (2)=88.0%, root mean square error (RMSE)=1.3 kg), and for the estimation of FFM was as follows: FFM=0.299 × height(2)/resistance+0.086 × height+0.245 × weight+0.260 × age+0.901 × sex-0.415 × ethnicity (Thai ethnicity =1, others = 0)-6.952 (R (2)=88.3%, RMSE=1.7 kg). No significant difference between measured and predicted values for the whole cross-validation sample was found. However, the prediction equation for estimation of TBW/FFM tended to overestimate TBW/FFM at lower levels whereas underestimate at higher levels of TBW/FFM. Accuracy of the general equation for TBW and FFM was also valid at each body mass index category. CONCLUSIONS: Ethnicity influences the relationship between BIA and body composition in Asian pre-pubertal children. The newly developed BIA prediction equations are valid for use in Asian pre-pubertal children.

Short chain fatty acid absorption from the human distal colon: interactions between acetate, propionate and calcium.

OBJECTIVE: Our purpose was to conduct a preliminary study to see if propionate and calcium affected acetate absorption, and acetate and calcium affected propionate absorption from the human distal colon. METHODOLOGY: We studied six healthy subjects on eight occasions in randomized order after overnight fasts. Test solutions (300 ml) were infused into the rectum, retained for 30 minutes, and then the infusion fluid was collected for analysis. The infusion solutions contained combinations of sodium acetate (56.25 mmol/L), sodium propionate (18.75 mmol/L) and calcium chloride (50 mmol/L) plus polyethylene glycol (PEG) as an unabsorbable marker. RESULTS: The reduction in the acetate:PEG concentration ratio over 30 minutes after acetate alone, 4.1 +/- 4.2, was significantly less than after acetate plus propionate, 40.2 +/- 11.9, and acetate plus calcium, 34.0 +/- 8.9 (p < 0.05). However, the change in acetate:PEG ratio when acetate, propionate and calcium were all infused together, 13.2 +/- 4.6, was no different from acetate alone. The reduction in the propionate:PEG concentration ratio after propionate alone was 15.7 +/- 3.3, and this was not significantly affected by adding acetate and calcium either alone or together. CONCLUSIONS: We conclude that the absorption of acetate in the rectum and distal colon of humans may be influenced by the presence of calcium and propionate. More detailed kinetic studies are required to confirm these results and characterize the transport mechanisms involved.

Availability of calcium for absorption in the small intestine and colon from diets containing available and unavailable carbohydrates: an in vitro assessment.

An in vitro method simulating conditions in the small intestine and colon was used to study the effects of various carbohydrates on Ca release from basal diet (BD) containing dairy products. During enzymatic digestion of BD, 28.5 +/- 0.3% of the Ca was released. This was reduced by 3, 22 and 27% by adding bread, psyllium or pectin to BD, respectively (P < 0.05). After enzymatic digestion, the residue from BD was fermented releasing 11.9 +/- 1.2% of the Ca, a value which was significantly less than with pectin (13.7 +/- 0.9%) and greater than with psyllium (4.4 +/- 0.2%) addition. The total Ca release ranged from 26.5 +/- 0.8 to 42.2 +/- 1.0% with bread>BD>pectin>psyllium. Lactulose did not differ significantly from BD. These results suggest that carbohydrates may bind Ca and reduce its availability for absorption in the small intestine. However, if the carbohydrate is fermented, bound Ca may be released for potential absorption in the colon, whereas less fermented carbohydrates may continue to bind Ca in the colon. The in vitro method described may be useful for estimating total Ca availability. However, studies in humans are required to validate these results.