Effects of cecal oxytetracycline infusion, and dietary avidin and biotin supplementation on the biotin status of nongravid gilts

Systematic review of the effects of the intestinal microbiota on selected nutrients and non-nutrients

PURPOSE

There is considerable interest in the effects of the intestinal microbiota (IM) composition, its activities in relation with the metabolism of dietary substrates and the impact these effects may have in the development and prevention of certain non-communicable diseases. It is acknowledged that a complex interdependence exists between the IM and the mammalian host and that the IM possesses a far greater diversity of genes and repertoire of metabolic and enzymatic capabilities than their hosts. However, full knowledge of the metabolic activities and interactions of the IM and the functional redundancy that may exist are lacking. Thus, the current review aims to assess recent literature relating to the role played by the IM in the absorption and metabolism of key nutrients and non-nutrients.

METHODS

A systematic review (PROSPERO registration: CRD42015019087) was carried out focussing on energy and the following candidate dietary substrates: protein, carbohydrate, fat, fibre, resistant starch (RS), and polyphenols to further understand the effect of the IM on the dietary substrates and the resulting by-products and host impacts. Particular attention was paid to the characterisation of the IM which are predominantly implicated in each case, changes in metabolites, and indirect markers and any potential impacts on the host.

RESULTS

Studies show that the IM plays a key role in the metabolism of the substrates studied. However, with the exception of studies focusing on fibre and polyphenols, there have been relatively few recent human studies specifically evaluating microbial metabolism. In addition, comparison of the effects of the IM across studies was difficult due to lack of specific analysis/description of the bacteria involved. Considerable animal-derived data exist, but experience suggests that care must be taken when extrapolating these results to humans. Nevertheless, it appears that the IM plays a role in energy homeostasis and that protein microbial breakdown and fermentation produced ammonia, amines, phenols and branch chain fatty acids, and a greater diversity in the microbes present. Few recent studies appear to have evaluated the effect of the IM composition and metabolism per se in relation with digestible dietary carbohydrate or fat in humans. Intakes of RS and prebiotics altered levels of specific taxa that selectively metabolised specific prebiotic/carbohydrate-type substances and levels of bifidobacteria and lactobacilli were observed to increase. In controlled human studies, consistent data exist that show a correlation between the intake of fibre and an increase in bifidobacteria and short-chain fatty acids, in particular butyrate, which leads to lower intestinal pH. Dietary polyphenols rely on modification either by host digestive enzymes or those derived from the IM for absorption to occur. In the polyphenol-related studies, a large amount of inter-individual variation was observed in the microbial metabolism and absorption of certain polyphenols.

CONCLUSIONS

The systematic review demonstrates that the IM plays a major role in the breakdown and transformation of the dietary substrates examined. However, recent human data are limited with the exception of data from studies examining fibres and polyphenols. Results observed in relation with dietary substrates were not always consistent or coherent across studies and methodological limitations and differences in IM analyses made comparisons difficult. Moreover, non-digestible components likely to reach the colon are often not well defined or characterised in studies making comparisons between studies difficult if not impossible. Going forward, further rigorously controlled randomised human trials with well-defined dietary substrates and utilizing omic-based technologies to characterise and measure the IM and their functional activities will advance the field. Current evidence suggests that more detailed knowledge of the metabolic activities and interactions of the IM hold considerable promise in relation with host health.

Relative availability of zinc in ground beef and soybean protein for young swine compared with zinc carbonate as the standard

The experimental objective was to determine the relative availability of endogenous Zn in soybean protein (SP) and cooked ground beef (GB) compared with the availability of Zn from ZnCO(3) for young swine. Crossbred pigs (4 trials with total n = 104) were weaned at an average age of 11 d, placed in metabolism cages, and allotted to 13 treatments. The basal semipurified negative control (NC) diet contained 2 mg of Zn/kg and wet-autoclaved spray-dried egg albumen (AEA) as the protein source. Reference diets were made by adding 3, 6, or 9 mg of Zn/kg from ZnCO(3) to the NC diet. The AEA in the NC diet was replaced with SP or GB to make diets with 3, 6, and 9 mg of Zn/kg from SP and GB. Positive control (PC) diets were made by adding 101 mg of Zn/kg from ZnCO(3) to the diets with 9 mg of Zn/kg from ZnCO(3), SP, or GB. Diets were mixed with deionized water and fed to appetite in gruel form every 3 h from 0800 to 2300 h. Pigs were weighed and blood samples were taken on d 7, 14, 21, and 28. Plasma concentrations of Cu, Fe, Zn, glucose, and urea N were determined. Total urine and fecal grab samples (Cr(2)O(3) in diets) were collected from d 7 to 14 and d 21 to 28 to determine Cu, Fe, Zn, and N apparent balance and energy utilization. On d 29, pigs were scored visually for parakeratosis and dosed orally with (65)Zn from ZnCl(2). Pigs were counted for whole body gamma radioactivity on d 29 and d 34 to 36, with Zn retention estimated by extrapolation to zero time. Pigs were killed on d 36 (NC on d 29). Samples of skin, tongue, and esophagus were taken for histological evaluation, and a tibia bone was excised for measurements and breaking strength. Pigs fed the diets with 9 mg Zn/kg from GB or ZnCO(3) were not different in Zn availability and retained about 70% Zn (apparent balance and (65)Zn) compared with 30% (P ≤ 0.05) for pigs fed the diet with 9 mg Zn/kg from SP. Also, pigs fed the diets with 9 mg Zn/kg from GB or ZnCO(3) had greater (P ≤ 0.05) growth performance, bone weight and breaking strength, % N retention, and % ME utilization, and smaller plasma urea N concentrations and parakeratosis scores (visual and histological) than pigs fed the diet with 9 mg Zn/kg from SP. Pigs fed the PC diets were not different in any response criteria. In conclusion, apparent Zn availability was not different from cooked GB and ZnCO(3), and Zn availability from cooked GB and ZnCO(3) was markedly greater than Zn availability from SP for young swine.