Dietary acid, effect excretion

Chickens rapidly excrete arsenicals only 2% of dietary sodium arsenite remained after 60 h, and arsanilic acid was excreted largely unchanged. Excretion of arsanilic acid by chickens was affected by uptake route excretion was more rapid if adnWstration was by intramuscular injection than if it was oral. Studies with inorganic As+ and chickens indicated that (1) arsenates rapidly penetrated mucosal and serosal surfaces of epithelial membranes, (2) As" " intestinal absorption was essentially complete within Ih at 370.0 mg As+ /kg BW but only 50% complete at 3700.0 mg/kg BW, (3) Vitamin D3 was effective in enhancing duodenal As" absorption in rachitic chicks, and (4) As and phosphate did not appear to share a common transport pathway in the avian duodenuna. 

Various mechanisms have been proposed to explain the hypocholesterolemic effect of GA (Annison et al., 1995 Tiss et al., 2001). Some studies have suggested that the viscosity of fermentable dietary fiber contributes substantially to the reduction of lipids in animals and humans (Gallaher et al., 1993 Moundras et al., 1994). However, other studies suggested that this property is not related to plasma lipids (Evans et al., 1992). The mechanism involved is clearly linked to increased bile acid excretion and fecal neutral sterol or a modification of digestion and absorption of lipids (Moundras et al., 1994). 

Many other dietary factors have been reported to affect calcium bioavailability. Phytate, fiber, cellulose, uronic acids, sodium alginate, oxalate, fat (only in the presence of steatorrhea), and alcohol have been reported to decrease calcium bioavailability (15). Lactose and medium chain triglyceride increase it (15). FTuoride also affects calcium retention primarily by stimulating bone formation thereby decreasing calcium excretion (33-38). The effects of fluoride on calcium utilization have been variable (34,38,39). 

The rat has been used rather widely to study the relation between dietary protein, or acid salt feeding, and calcium loss. Barzel and Jowsey (19) showed that the rat fed a control diet supplemented with ammonium chloride excreted excessive urinary calcium, and experienced a concomitant loss of fat-free bone tissue. Draper, et al. (20) extending this work, reported an inverse relation between dietary phosphate and loss of bone calcium and dry, fat-free tissue. In subsequent studies (21), they reported that this process was accompanied by reduced serum calcium levels the high phosphorus, low calcium diet increased urinary calcium loss. Whereas, increasing the phosphorus content of the diet stopped the excessive urinary calcium loss. To test possible zinc loss that might result from this sort of acid salt feeding, Jacob and her coworkers (22) fed rats a supplement of ammonium chloride and then measured urinary zinc and calcium. The hypercalciuria occurred exclusive of an effect upon urinary zinc loss. 

The results of experiments conducted by MacKenzie and McCollum (15) indicate that the effect of dietary oxalic acid on the rat depends on the composition of the diet. There was no effect on rate of growth or calcium excretion of 50 g rats fed for 10 weeks a diet containing 0.6% calcium, 0.7% phosphorus, and optimum vitamin D, when levels of potassium oxalate up to 2.5% were fed. The percent bone ash on the 2.5% oxalate diet was somewhat lower than on the control diet. On a 0.35% calcium, 0.35% phosphorus, and vitamin D-free diet, 1.7% potassium oxalate resulted in restricted growth and bone formation of weanling rats. 

In the studies on humans there appeared to be decreased calcium balances when 200 g or more of spinach per day was included in the diet. In two of the studies in which women were fed spinach, calcium intakes were below the Recommended Dietary Allowance of 800 mg/day (37). Some studies were conducted for short period of a week or less, which may not be sufficient time to adjust to a change in diet. From measurement of calcium excretion in urine after a test meal, it was shown that the calcium in oxalate-containing vegetables was less well-absorbed than that of milk or of vegetables not containing oxalic acid. However, this would not necessarily affect calcium balance, since the total amount of calcium in the diet would have to be considered. The effect of a combination of oxalic acid and fiber on calcium bioavailability should be further investigated. 

Bile acids and salts have been found to enhance the absorption of both calcium and vitamin D hence, to increase calcium absorption both directly and indirectly (3,37). However, the ability of some dietary fibers such as lignin and pectin to absorb conjugated and deconjugated bile salts onto their surfaces to be excreted in the feces (a mechanism credited to the hypocholesterolemic effect of some dietary fibers) may result in an overall decrease in calcium absorption from the gastrointestinal tract (7,33,38-40). 

Uric acid production is more easily controlled by drug therapy than by dietary restriction, because only a small portion of blood uric acid is derived from the dietary intake of purines. Excretion of uric acid may be increased by increasing the rate of urine flow or by using uricosuric agents. Since uric acid is filtered at the glomerulus and both actively secreted and reabsorbed by the proximal tubule cells, both approaches are effective. 

Dietary fiber has a pronounced effect on the characteristics of the fecal mass and on the rate of passage of digest through the G1 trad, High fiber diets also play a role in the excretion of bile acids and cholesterol. 

Levrat, M.A., Favier, M.L., Moundras, C., Remesy, C., Demigne, C., and Morand, C. 1994. Role of dietary propionic acid and bile acid excretion in the hypocholesterolemic effects of oligosaccharides in rats. J. Nutr. 124, 531-538. 

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