Decreased absorption of calcium, magnesium, zinc and phosphorus by humans due to increased fiber and phosphorus consumption as wheat bread

Intestinal fermentation lessens the inhibitory effects of phytic acid on mineral utilization in rats

The specific effects of phytic acid (PA) and resistant starch (RS) on mineral bioavailability, namely, Ca, Mg, Fe, Zn and Cu, were investigated in rats adapted to semipurified diets. The diets provided either 73 g/100 g digestible wheat starch (DS) alone, or 53 g/100 g DS plus 20 g/100 g crude potato starch (RS) and either 0 or 1.1 g/100 g PA. A period of 3 wk was first planned to adapt the rats to their respective diets. Compared with rats fed the DS diets, those fed the RS diets had significant cecal hypertrophy and an accumulation of short-chain fatty acids, together with greater cecal blood flow. RS enhanced the cecal absorption of Ca and Mg (from 0.15 to 0.55 micromol/min for Ca, and from 0.10 to 0.35 micromol/min for Mg). Mineral balance was enhanced significantly by RS (Ca, +46%; Mg +50%; Fe +20%; Zn, + 33% and Cu, +61%). PA had no significant effect on Ca or Mg solubility and absorption in the cecum, and it failed to alter significantly Ca or Mg balance. The apparent absorption of Fe, Zn and Cu was significantly lower in rats fed the DS + PA diet than in rats fed the DS diet (Fe, -35%; Zn, -28%; and Cu, -31%). In rats adapted to the RS diet, the inhibitory effects of PA were practically abolished and the mineral balance was restored to the control values. We conclude that the negative effects of PA on mineral balance are relatively minor compared with the stimulatory effect of RS.

Assessment of the nutritional effects of olestra

Olestra is a mixture of polyesters formed from sucrose and fatty acids derived from edible fats and oils. It is not absorbed or digested and can serve as a zero-calorie replacement for dietary fat. Because olestra is lipophilic and not absorbed, it has the potential to interfere with the absorption of other dietary components, especially lipophilic ones, when it is in the digestive tract with those components. A series of studies were conducted in the domestic pig and in healthy adult humans to define the nature and extent of olestra's effect on fat-soluble vitamins, selected water-soluble micronutrients, and macronutrients, and to demonstrate that the effects of olestra on the absorption of fat-soluble vitamins can be offset by adding extra amounts of the affected vitamins to olestra foods. Before conducting the human and pig studies, the intake of olestra from the consumption of snack foods made with olestra was estimated for various subgroups. The potential for olestra to affect the absorption of nonessential but potentially beneficial dietary phytochemicals was also assessed. In addition, an assessment of how consumption patterns influence the effect of olestra on the absorption of the highly lipophilic carotenoids was made. Finally, the results from the pig and human studies were used to assess the potential for olestra to affect the nutritional status of subgroups of the population who have particularly high nutrient needs or unique dietary patterns that may lead to large olestra-to-nutrient intake ratios.

Comparison of pure inositol hexaphosphate and high-bran diet in the prevention of DMBA-induced rat mammary carcinogenesis

Inositol hexaphosphate (IP6), abundant in cereals and legumes, has been demonstrated to be a promising anticancer agent in different in vivo and in vitro models. Because IP6 is particularly abundant in the bran part of certain mature seeds such as wheat, we investigated whether a high-fiber bran diet containing high IP6 shows a dose-response inhibition of 7,12-dimethylbenz[a]anthracene (DMBA)-induced rat mammary carcinogenesis. Starting at two weeks before DMBA intubation, rats were divided into five groups and fed AIN-76A diet only or AIN-76A diet containing 5%, 10%, or 20% Kelloggs' All Bran; the fifth group received 0.4% IP6 given in drinking water, an amount equivalent to the IP6 content in 20% bran. After carcinogen administration, the rats remained on these regimens for 29 weeks. Compared with the carcinogen control, at 29th week, tumor incidence was reduced by 16.7%, 14.6%, and 11.4% in rats fed 5%, 10%, and 20% bran, respectively (not statistically significant). However, rats given 0.4% IP6 in drinking water, equivalent to that in 20% bran, had a 33.5% reduction in tumor incidence (p < 0.02) and 48.8% fewer tumors (p < 0.03). These data show that supplemental dietary fiber in the form of bran exhibited a very modest, statistically nonsignificant inhibitory effect, which was also not dose dependent. In contrast, animals given IP6 showed significant reduction in tumor number, incidence, and multiplicity. Thus IP6 an active substance responsible for cereal's beneficial anticancer effect, is clearly more effective than 20% bran in the diet. In practical terms, intake of IP6 may be a more pragmatic approach than gorging enormous quantities of fiber for cancer prophylaxis.

In vitro mineral binding capacity of three fiber sources for Ca, Mg, Cu and Zn by two different methods

Acid-washing centrifugation (AWC) and cold-hot-water-enzyme incubation (WEI) methods were used to study the binding capacity (BC) of wheat bran, rice bran, and oat fiber for calcium, magnesium, copper, and zinc. Treated fibers were analyzed for protein, phytic acid (PA), total dietary fiber (TDF), and minerals. Protein content was significantly (P < 0.05) lower in WEI fibers than AWC fibers. WEI fibers had low protein concentration and no PA but higher TDF values (P < 0.05). Levels of Mg were the highest among the minerals studied. AWC treatment was significantly (P < 0.05) more efficient in stripping minerals than the WEI treatment. AWC fibers bound more minerals. Results indicate that the BC values of the fibers for minerals by the two methods were not comparable.

[Zinc--update of an essential trace element]

Since the recognition of zinc as an essential trace element in man and animals there has been a remarkable progress in our knowledge of the role of zinc in nutritional physiology, biology and medicine during the last few decades. Highlights in zinc research, mechanisms and homeostatic regulation of zinc absorption, sources of zinc intake, dietary factors and mineral interactions affecting zinc bioavailability are reviewed in the present paper. This is followed by an overview of the biochemical functions of zinc in enzymes, gene expression, endocrinology, immunology and oxidative stress. General signs and metabolic consequences of zinc deficiency as well as excessive intake and toxicity of zinc are summarized. Furthermore, national and international dietary zinc recommendations and different methods to determine the zinc status are discussed.

Phytic acid in health and disease

Phytic acid (PA), a major phosphorus storage compound of most seeds and cereal grains, contributes about 1 to 7% of their dry weight. It may account for more than 70% of the total kernel phosphorus. PA has the strong ability to chelate multivalent metal ions, especially zinc, calcium, and iron. The binding can result in very insoluble salts that are poorly absorbed from the gastrointestinal tract, which results in poor bioavailability (BV) of minerals. Alternatively, the ability of PA to chelate minerals has been reported to have some protective effects, such as decreasing iron-mediated colon cancer risk and lowering serum cholesterol and triglycerides in experimental animals. Data from human studies are still lacking. PA is also considered to be a natural antioxidant and is suggested to have potential functions of reducing lipid peroxidation and as a preservative in foods. Finally, certain inositol phosphates, which may be derived from PA, have been noted to have a function in second messenger transduction systems. The potential nutritional significance of PA is discussed in this review.

The effect of fiber source in enteral products on fecal weight, mineral balance, and growth rate in rats

The effect of two fiber systems in enteral formulas on fecal output, mineral balance, weight gain, and cecal short-chain fatty acid production was studied in rats. Enteral products tested had either no fiber; soy fiber (3.4 g of total dietary fiber/8 fluid oz); a fiber blend containing 75% oat fiber, 17.5% gum arabic, and 7.5% carboxymethylcellulose (3.4 g of total dietary fiber/8 fluid oz); or the same blend at 4 g of total dietary fiber/8 fluid oz. Food, feces, and urine were analyzed for nitrogen, calcium, magnesium, iron, and zinc. Cecal contents were analyzed for short-chain fatty acids. Weight gain, intake, food efficiency, and nitrogen balance were unaffected by fiber source. Fecal weight was increased by the fiber blend (p < .05). Calcium and magnesium balances were similar for all groups fed fiber-containing products but were lower for the fiber-free group (p < .05). Iron balance was significantly lower for rats fed the fiber blend at 4 g/8 fluid oz as compared with the other treatment groups (p < .05). Cecal acetate, propionate, and total short-chain fatty acid concentrations for rats fed the soy-fiber diet were significantly higher than for the other three diets (p < .05). Rats fed the fiber blend at the higher level had a significantly higher percentage of butyrate production than rats fed the other three diets (p < .05).(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of type of diet and incubation time on in sacco release of Cu, Fe, Mn and Zn from Italian ryegrass, untreated and ammonia treated wheat straw

Artificially dried ryegrass, untreated and ammonia-treated wheat straw were ground and incubated in nylon bags in the rumen of three sheep each fed with diets based on roughage or concentrate. Dry matter degradability, the concentration and the release of the trace elements Cu, Fe, Mn and Zn from the incubated feeds were measured after 0 (washing loss), 6, 12, 24, 48 and 72 h rumen incubation time. Dry matter degradability, trace element concentration and their release were significantly influenced by the kind of incubated feeds, incubation time and feeding of sheep. Cu- (1.8-6.9 mg kg-1 DM) and Zn concentrations (36-103 mg kg-1 DM) of straw residues in the bags were much higher than those of original straw (1.2-1.6 and 8.1-9.9 mg kg-1 DM resp.). The inflow of Cu and Zn in the bags containing straw residues was higher than their release. The Cu-, Fe- and Mn-release from ryegrass was similar to the dry matter degradability, but the Zn-release was much lower.

Reduction of phytic acid in soybean products improves zinc bioavailability in rats

The inhibitory effect of phytic acid in soybean products on zinc bioavailability was evaluated in two experiments in rats. In Experiment 1, soybean flours containing different natural phytic acid levels produced by sand culture techniques that limited phosphorus during growth of the soybean plants were formulated into diets. The rats fed a higher phytic acid level diet had lower food intake, depressed weight gain, and lower tibia zinc gain (P < 0.05). A negative, linear relationship between tibia zinc gain and dietary phytic acid level was found. In Experiment 2, two commercially produced soybean isolates containing either normal phytic acid level or a reduced level were formulated into diets. Slope ratio analysis revealed that relative zinc bioavailability from phytic acid-containing soybean isolate-based diets was significantly reduced (P < 0.05) compared with control diets. Reduced phytic acid soybean isolate-containing diets resulted in a significant increase of zinc bioavailability compared with normal phytic acid diets (P < 0.01). These results coupled with other reports indicate that phytic acid is the primary inhibitory factor in soybean products that results in reduced zinc bioavailability and that phytate reduction in soybean protein increases zinc bioavailability.

Mineral excretion of rats fed on diets containing faba beans (Vicia faba L.) or faba bean fractions

The effects on faecal mineral excretion of two commercial varieties (local cultivar and Troy cultivar) of raw faba beans (Vicia faba L., minor) meal (VFM) and its fractions have been studied in growing rats. Diets contained local-VFM (dark seed coat) and Troy-VFM (light seed coat) at 474-500 g/kg diet, hull (VFH) from both varieties at 65 g/kg diet, and the insoluble cotyledon residue (VFCR) obtained from the Troy variety at 237 g/kg diet. Rats were pair-fed on diets which had been supplemented with amino acids to target requirements and contained similar amounts of zinc, manganese, iron and copper. With VFM diets the apparent absorption of Zn and Mn was significantly reduced. On the other hand, with hulls the apparent absorption of Fe was reduced while that of Cu slightly increased. As the amounts of calcium, phosphorus and magnesium in VFM and VFH diets were higher than in the controls, the increased intake resulted in a significant increase in both the apparent absorption and the faecal excretion of these minerals. The inclusion of VFCR in the diet had no significant effect on the mineral content of faeces. The relatively low concentrations of phytate in the bean seeds of 7.8 and 6.7 g/kg for the local and Troy cultivars respectively, could not adequately account for the increased mineral excretion. The results suggest that other seed constituents, possibly the soluble non-starch polysaccharides, may be involved in the elevated loss of Zn and Mn in rats fed on diets containing faba bean for extended periods, while some insoluble structural hull components may interfere with the absorption of Fe from the gut.

Wheat bran in the selective therapy of absorptive hypercalciuria: a study performed on 18 lithiasic patients

The binding properties of raw vegetable fiber towards bivalent cations suggested the prescription of brain as a dietary supplement to limit intestinal calcium absorption in hypercalciuric patients. A group of 18 patients with a specific diagnosis of absorptive hypercalciuria received a dietary supplement of 14 gm. wheat bran at the 2 principal meals for 90 days. A complete assessment of mineral metabolism was performed after 45 and 90 days. Mean basal calciuria was 357 mg. per 24 hours and a significant decrease was noted after 45 days (245 mg. per 24 hours) and 90 days (240 mg. per 24 hours), with a p value of less than 0.01. Urinary oxalate did not vary significantly (0.34 to 0.38 to 0.31 mMol. per 24 hours) and neither did phosphate levels (1,020 to 900 to 893 mg. per 24 hours). A slight and pathologically insignificant decrease was noted in serum iron and urinary magnesium; this fact could be considered a side effect owing to the nonselective binding properties of fiber. Therefore, the positive results achieved confirm the effective action of wheat bran in the treatment of correctly diagnosed absorptive hypercalciuria.

Calcium in the diet: food sources, recommended intakes, and nutritional bioavailability

Calcium nutritional status among some groups in the United States is suboptimal when judged by calcium intakes and the high prevalence of osteoporosis. Unfortunately, however, it is not clear that increases in calcium intake will have a significant impact on osteoporosis or other chronic diseases that have been linked to calcium nutriture. There is still considerable controversy surrounding the issue of calcium RDAs. The body's ability to adapt to varying levels of calcium intakes, the lack of sensitive indicators of calcium status, and the complexity and slow progression of chronic diseases such as osteoporosis make it very difficult to establish the role of diet in this regard. Great progress has been made in the study of calcium absorption. Much is known about the mechanisms involved in calcium absorption and its regulation. Thus, a rapidly advancing field and further developments will be invaluable to our understanding of the role of diet in calcium nutrition. Calcium bioavailability is affected by diet composition and the chemical form of calcium in foods. The calcium in dairy products is readily absorbed in the intestine. Lactose enhances calcium absorption efficiency under some conditions. Components of plants such as fiber, phytate, and oxalic acid may depress calcium absorption. High intakes of protein increase urinary losses of calcium but this effect may be partially offset by the phosphate association with most high-protein foods. Calcium absorption from salts used in supplement tablets is generally good. Absorption from salts such as calcium carbonate which require acid for dissolution may be poor in persons with achlorhydria unless the tablets are consumed with a meal. The practical significance of factors that may alter calcium bioavailability in normal mixed diets is difficult to assess. It may be a significant factor when calcium intakes are marginal or when absorption by the active transport, vitamin D-dependent process is impaired or not fully developed, i.e., it may be significant when vitamin D status is poor, in the elderly, and in young infants.

Trace mineral balance during acute diarrhea in infants

To evaluate the magnitude of copper and zinc losses during acute diarrhea requiring hospitalization, we studied 14 infants, 3 to 14 months of age, and compared them with a control group of 15 infants of similar age, birth weight, and nutritional status. Metabolic balance studies were conducted in the study group during an initial 48 hours (period 1) and on days 6 and 7 after admission (period 2). The control group was studied after recovery from respiratory disease. Copper and zinc content of feces, urine, and food samples was measured by atomic absorption spectrophotometry. Mean (+/- SD) fecal losses were higher for period 1 in the diarrhea group than in control subjects: Cu 55.7 +/- 21.2 versus 28.8 +/- 6.7 micrograms/kg/body weight/day (p less than 0.01); Zn 159.4 +/- 59.9 versus 47.4 +/- 6.4 micrograms/kg/day (p less than 0.0001). For period 2, Zn losses were similar in both groups, but Cu balance remained negative only in the study group. Retention of Zn for the study group went from -21.2 +/- 46.7 in period 1 to 204.5 +/- 103.0 micrograms/kg/day in period 2 (p less than 0.0001), and fecal weight decreased from 70.5 +/- 20.6 in period 1 to 36.8 +/- 20.0 gm/kg/day in period 2. Fecal weight and fecal losses were correlated: r = 0.71 (p less than 0.01) for Cu and r = 0.81 (p less than 0.001) for Zn. Plasma mean Cu and Zn levels were low in period 1 but rose in period 2, especially for Zn. A negative correlation was found between fecal Zn losses and plasma Zn: r = 0.74 (p less than 0.001). We conclude that acute diarrhea leads to Cu and Zn depletion and that plasma levels and Cu balance remain abnormal a week after admission.

Mineral retention in young men consuming soy-fiber-augmented liquid-formula diets

The effect of a nutritionally complete liquid-formula diet without soy polysaccharide or with the fiber source at 20, 30, or 40 g/d on mineral retention in young men was examined. Addition of 20 g soy polysaccharide to the liquid formula significantly (p less than 0.05) improved the retentions of copper, iron, zinc, and magnesium over the diet without added fiber. The highest level of soy polysaccharide (40 g/d) resulted in significantly (p less than 0.05) lower Cu, Zn, Fe, and Mg retentions than did the 20-g diet and the 30-g diet had an intermediate effect. Except for slightly negative Cu (-0.1 +/- 0.4 mg) and Fe (-0.6 +/- 3.7 mg) retentions on the 40-g diet, retentions of all minerals remained positive throughout this study. The liquid-formula diet supplemented with 40 g soy polysaccharide could have a deleterious effect on mineral retentions in persons consuming the diet as their sole nutritional source.

Energy, protein, zinc and copper status of twenty-one elderly inpatients: analysed dietary intake and biochemical indices

1. Duplicate diet analysis for energy, protein, zinc and copper with estimates of biochemical status for Zn and Cu were undertaken in twenty-one elderly long-stay inpatients (mean age 82 (range 63-89) years) consuming their customary hospital diet and in a stable medical condition. Fourteen patients had a long-standing and significant healing problem, either a leg ulcer or pressure sore. 2. Mean daily intakes of energy (5.2 MJ), protein (45 g), Zn (85 mumol) and Cu (14 mumol) were low in comparison with both official recommendations and levels of intake at which metabolic equilibrium was observed in healthy elderly people studied by the same methods (Bunker et al. 1984a). 3. Mean leucocyte Zn (9 pmol/10(6) cells) and Cu (7.5 pmol/10(6) cells) were low in comparison with results from healthy elderly people (Bunker et al. 1984a), implying suboptimal status for these elements. Those patients with healing problems tended to have the lower values within the range. 4. Recommendations are made with respect to improving nutritional status in this disadvantaged group of people.

[Biological availability of zinc in whole grain products with different phytate contents]

Due to its high phytate content, the bioavailability of zinc in whole meal cereal products is distinctly lower as compared to foods of animal origin. The effect of reducing the phytate content of cereal products made from rye and wheat on growth, zinc content of femur and blood serum, as well as on the activity of serum alkaline phosphatase was investigated during a 3-week feeding trial in growing rats. The reduction of phytate was achieved by controlling the phytase activity originally present in cereals. By these treatments, the molar phytic acid/zinc ratio in the cereal products was reduced from 27-37 to 3-18. The four parameters under investigation showed a significant improvement in zinc bioavailability with decreasing phytic acid/zinc ratios. The relevance of these results for man and the value of the molar phytic acid/zinc ratio as an indicator of the bioavailability of zinc in foods are discussed.

The effect of vegetables and beet fibre on the absorption of zinc in humans from composite meals

1. The absorption of zinc in humans from composite meals, was determined by extrinsic labelling of the meals with 65Zn and measurement of the whole-body retention of the radioisotope. 2. Low-Zn (mean 25 mumol) chicken meals with 150 g white bread or 225 g potatoes, carrots, turnips, cabbage or green peas were studied. The effect of a beet-pulp-fibre preparation used as a breakfast cereal, in bread and as a meat extender on Zn absorption was also studied. 3. The mean percentage absorption from the chicken meals with white bread, carrots and cabbage was significantly different from the meals with potatoes, turnips and green peas. When the amount of Zn in the meals was taken into account a slightly higher absorption was observed from the white-bread meal compared with the meals with potatoes and cabbage, while no differences were seen between the vegetable meals. 4. The beet-pulp-fibre preparation did not affect the extent of Zn absorption when used as a meat extender. The absorption of Zn was higher when the beet fibre was included in bread than when used as müesli. 5. The results obtained suggest that, besides the low-Zn content in vegetables, a large intake of vegetables or a pure-vegetable-fibre preparation has no significant effect on Zn availability from animal-protein-based meals.

Effect of wheat bran on bowel function and fecal calcium in older adults

Seven healthy older volunteers participated in a 33-day study consisting of three sample collection periods, a 10-day control, and two 10-day experimental periods. Subjects consumed their usual self-selected diets throughout and a daily wheat bran supplement (30 g) during the two experimental periods. Food intake was recorded daily by subjects and accuracy and completeness checked daily by personal interview. Apparent calcium absorption decreased significantly from 22.1 +/- 5.6% (mean +/- SD) during the control to 8.6 +/- 5.2% during the second bran period. The wheat bran supplement significantly increased wet and dry stool weights but had no effect on stool moisture or defecation frequency. Gastrointestinal transit time of a dose of chromium decreased significantly, from 75 +/- 33 to 54 +/- 19 hr; of a dose of polyethylene glycol insignificantly, from 98 +/- 59 to 69 +/- 46 hr. Mean recovery of 21 doses of chromium of 98.7 +/- 5.0% verified that stool collection was complete. The results suggest that the ability of wheat bran to regulate bowel function in the apparently healthy older adult may be accompanied by increased fecal calcium losses similar to what has been reported for younger adults.

Relationship of cytotoxic activity of natural killer cells to growth rates and serum zinc levels of female RIII mice fed zinc

This study examined a) the dietary zinc (Zn) requirement of RIII female weanling mice and b) the cytotoxicity of murine natural killer (NK) cells obtained from spleens of these mice fed varying levels of Zn. Zn was fed in a biotin-enriched egg albumen diet in amounts ranging from 0.9 to 40.4 micrograms/g diet. During a 28-day growth assay, maximum carcass growth was obtained with a diet containing 5.4 micrograms Zn/g diet. Maximal serum levels of Zn, however, were observed in mice fed diets containing 3.4 micrograms Zn/g diet. The cytotoxic activity of NK cells obtained from spleens of selected treatment groups was maximal at 40.4 micrograms Zn/g diet and was significantly higher (p less than or equal to 0.05) than that observed in spleens from mice fed diets that maximized carcass growth rates and serum Zn concentrations. It is concluded that female RIII mice have a dietary Zn requirement for growth similar to that observed for other murine strains but considerably lower than that reported for the rat. Our findings also suggest that RIII NK cells are particularly sensitive to dietary Zn intake: the optimal functional activity of these cells may result from intake of Zn higher than that necessary to maximize carcass growth and serum Zn concentrations.

Extrusion cooking of a high-fibre cereal product. 2. Effects on apparent absorption of zinc, iron, calcium, magnesium and phosphorus in humans

1. The effect of extrusion cooking, using mild conditions, of a high-fibre cereal product on apparent small bowel absorption of zinc, iron, calcium, magnesium and phosphorus was studied. 2. Seven ileostomy subjects were studied during two periods (each of 4 d), on a constant low-fibre diet supplemented with either 54 g/d of a bran-gluten-starch mixture or the corresponding extruded product. 3. The apparent absorption of Zn, Mg and P was significantly decreased (P less than 0.05) during the period with extruded product compared with the period with bran-gluten-starch. No difference was found for Fe and Ca. 4. The negative effect of extrusion cooking of a product containing phytic acid on availability of Zn, Mg and P was small but could be of nutritional relevance in foodstuffs that are consumed frequently and in infant formulas.

Comparison of the effect of cell wall and hull fiber from canola and soybean on the bioavailability for rats of minerals, protein and lipid

Hull or cell wall material, isolated from canola (Brassica napus cv. Regent) or soybean (Glycine max) or cellulose was added to a basal, semipurified diet at a level of 12% and fed to growing male Wistar rats. The apparent availability of Cu, Fe, Ca, P and protein were lower when the fiber-containing diets were fed compared to the control diet. The availability of Mg was lower when the canola hull (CH) and cellulose (CE) diets were fed, whereas Zn availability was lower when the canola cell wall (CCW) and CE diets were fed, compared to the control diet. Determination of the feed transit time, by using the unabsorbable marker Cr2O3, demonstrated that the CE and soybean cell wall (SCW) diets had the fastest transit rates, followed by the CH, soybean hull (SH), CCW and control diets. Determination of the in vitro binding of the various fibers to metal ions demonstrated that CH was the strongest chelator, whereas CE had the lowest binding affinity for any of the minerals tested. At the termination of the trial, intestinal segments were removed and the in vitro mucosal transport of Cu, Fe, Mn and Zn were compared. The CCW diet consistently demonstrated lower transport for the four minerals, especially in the ileal segment.

Comparative metabolism of L-methionine, DL-methionine and DL-2-hydroxy 4-methylthiobutanoic acid by broiler chicks

1. Metabolism, in broiler chicks, of DL-2-hydroxy 4-methylthiobutanoic acid (DL-HMB), DL-methionine and L-methionine was compared in vivo using 14C-labelled tracers. 2. The distribution of L-[1-14C]methionine and DL-[1-14C]HMB in the major body tissues was examined for a period of 120 min after administration. 3. The relative oxidation (14CO2 exhaled), excretion and incorporation into tissue protein of L-[1-14C]methionine, DL-[1-14C]methionine and DL-[1-14C]HMB were measured in fed birds. 4. Tissue distribution of L-[1-14C]methionine and DL-[1-14C]HMB differed during 60-90 min following administration. 5. The production of 14CO2 from each of the tracers was similar but excretion of 14C-labelled material was very different with the greatest excretion from DL-[1-14C]HMB and the least from L-[1-14C]methionine. 6. The incorporation of 14C into tissue proteins varied with the tracer given and the tissue examined. Liver and kidney had equivalent incorporation from each of the tracers while other tissues examined showed lower incorporation from DL-[1-14C]methionine and DL-[1-14C]HMB. 7. The results show that DL-HMB, D-methionine and L-methionine are metabolized differently in vivo and that they are excreted in differing proportions. There is also a difference in the ability of each to act as a precursor for protein synthesis in tissues other than liver.