Meat protein excretion

Such acid and calcium excretion may be important in development of osteoporosis. To test diets of meat and vegetable protein upon urinary acid and calcium, nine human adults, aged 22 to 69 years, were fed isonitrogenous diets of chicken or soy beans in seven-day feeding periods. Diets provided daily ... 

The meat diet resulted in markedly greater titratable acid and calcium excretion compared with the soy diet (P<0.02). This occurred despite the fact that each diet contained the same amounts of protein, calcium, phosphorus, and sulfur. Increased urinary calcium excretion in subjects accompanied this increased output of TTA (P<0.02) ... 

Dietary phosphorus exerts variable influence on calcium loss depending on the nature of the dietary protein. Humans fed food containing abundant phosphorus to calcium excreted little more calcium unless the meat content of the diet changed markedly. 

Carnitine, L-3-hydroxy-4-(trimethylammonium)butyrate, is a water-soluble, tri-methylammonium derivative of y-amino-jS-hydroxybutyric acid, which is formed from trimethyllysine via y-butyrobetaine [40]. About 75% of carnitine is obtained from dietary intake of meat, fish, and dairy products containing proteins with trimethyllysine residues. Under normal conditions, endogenous synthesis from lysine and methionine plays a minor role, but can be stimulated by a diet low in carnitine. Carnitine is not further metabolized and is excreted in urine and bile as free carnitine or as conjugated carnitine esters [1, 41, 42]. Adequate intracellular levels of carnitine are therefore maintained by mechanisms that modulate dietary intake, endogenous synthesis, reabsorption, and cellular uptake. 

Limited data are available about the effects of individual dietary components on absorption, and consequently the requirement, of Mn. Dietary protein and phosphorus levels (33), calcium level (34) and the effect of a partial substitution of soy protein for meat (28) have been tested in balance studies without any obvious effect of Mn absorption or retention. However, since the main route of excretion is via the bile, the conventional balance technique is probably not sensitive enough to identify dietary factors that influence Mn absorption. 

Several mechanisms may contribute to the association of meat with colon cancer. The heterocyclic amines and polycyclic aromatic hydrocarbons present in cooked meat are metabolized, in the body, to mutagens that may condense with DNA to form adducts. If the adduct occurs at a vital base, and if the adduct is not promptly repaired, cancer may result. Another possible mechanism is related to the enhanced excretion of bile salts into the intestines that occurs with a high-fat diet. In brief, the increased amount of bile salts (with a high-fat diet) that reaches the large intestines is metabolized by the gut microflora to an increased amount of modified bile salts. Specifically, lithocholic acid and deoxycholic acid are formed. These modified bile salts are thought to contribute to the conversion of a normal gut cell to a cancer cell. Recent studies suggest that chronic exposure of gut cells to these modified bile salts may result in chronic activation of protein kinase C and chronic... 

Ascorbic acid (as-KOR-bik AS-id), or vitamin C, is one of the most important dietary vitamins for humans because it plays a crucial role in building collagen, the protein that serves as a support structure for the body. It is a water-soluble vitamin, which means that the body excretes any excess vitamin C in the urine and cannot store a surplus. For that reason, humans must consume vitamin C in their daily diets. Vitamin C is found in many fruits and vegetables and most kinds of fresh meat. Citrus fruits, such as oranges and lemons, are especially rich in the compound. 

Pyrrolidine is the simple five-membered cyclic amine and pyrrolidine alkaloids such as nicotine contain this ring. All are made in nature from ornithine. Ornithine is an amino acid not usually found in proteins (it s one carbon atom shorter than lysine) but most organisms use it, often in the excretion of toxic substances. If birds are fed benzoic acid (PhC02H) they excrete dibenzoyl ornithine. When dead animals decay, the decarboxylation of ornithine leads to putrescine, the smell of rotten meat. 

The amount of calcium excreted in the urine is related to skeletal size, the acid-base regulation of the body, and the dietary protein intake. Urinary excretion of calcium rises when dietary protein is increased and falls when dietary protein is decreased, it appears that calcium losses can be substantial when protein intake is high hence, if this type of diet is continued for a prolonged period, it could result in a considerable loss of body calcium and even osteoporosis. FHow-ever, studies show that a high protein intake from a high meat diet has little effect on calcium excretion, possibly because of the high phosphate intake with the meat diet. A recent study suggests that increased phosphorus intakes reduce urinary excretion of calcium and lower serum calcium levels. 

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