Manganese dietary phytates

Manganese is a nutritionally important trace element for chicks. Dietary energy and protein sources contain very little bioavailable Mn, and these feed ingredients reduce the biopotency of inorganic Mn supplements. This adverse effect is exerted primarily in the intestine as a result of reduced Mn absorption and is mediated by the fiber and/or ash components of the feedstuffs. Gut absorption efficiencies are higher when a phytate-and fiber-free casein-dextrose diet is fed than when a corn-soybean meal diet is fed. Dietary interrelationships exist between Mn and Co and between Mn and Fe. Cobalt increases Mn absorption and may precipitate Mn toxicosis. Excess dietary Mn reduces Fe utilization, but excess Fe does not affect Mn utilization. Eimeria acervulina infection increases Mn absorption. 

In our first study described above (2), a negative balance of -0.02 mg Mn was found on a dietary level of 0.11 mg/day. This figure is small considering levels reported from past studies. However, the diet fed to the subjects was semi-purified, not whole foods. It is believed that retention of the mineral was enhanced by increased physiological needs caused by a manganese depletion from consumption of such a low dietary level. Furthermore, the diet did not contain any phytates and limited amounts of fiber. 

A number of factors that may influence human requirements of manganese have been investigated in the literature. These factors include the iron status and age of the individual and dietary factors such as iron, calcium, phosphorus, phytates and fiber. 

The influence of three dietary factors - pectin, cellulose and phytates - on plasma uptake of manganese (Mn) was studied in adults administered Mn tolerance tests. Plasma samples were collected at hourly intervals following administration of various doses of several Mn salts. It was found that a 40 to 50 mg dose of elemental Mn was necessary to produce consistent plasma responses and that manganese chloride (MnCl ) was better absorbed than the sulfate or acetate form. In fasting subjects, plasma Mn was 0.64, 1.29, 1.12, 0.95, and 0.75 ug/L at hours 0, 1,... 

Since almost nothing is known about the effect of isolated fibers on the absorption of manganese and constituents of dietary fiber vary both in chemical and physical properties, the effects of two major types of fiber — cellulose and pectin — were examined using our protocol. The effect of phytate was also measured since it is associated with high fiber foods and has been reported to increase requirements for manganese (40). 

Experiments In this laboratory examined the effects of small (100 and 300 mg) doses of sodium phytate administered In capsule form on plasma uptake of 50 mg of MnCl. As shown In Figure 5, the 300 mg dose of phytate produced a moderate reduction In manganese response, which was manifested chiefly at hours three and four of the test. The relatively modest effect of phytate on manganese uptake Is somewhat unexpected, since It has been shown that phytic acid may be a more potent Inhibitor of trace element absorption than dietary fibers (35). However, the doses of sodium phytate administered to our subjects were much smaller than the typical daily Intake of 600 to 800 mg (54). Thus we are now Investigating the effects of larger doses of phytate on manganese uptake. 

In a series of manganese tolerance tests, three dietary components —cellulose, pectin, and phytate—were found to reduce plasma uptake of manganese. Although the amount of manganese administered (40-50 mg) in these tolerance tests was much larger than that typically consumed (0.9 to 7.0 mg per day) (55,56), the results were similar to those obtained in bioavailability studies with other trace elements. Thus it appears that diets high In fiber and phytates also reduce the bloavailabllity of manganese. 

Wheat bran and whole wheat cereals quantitatively contain high amounts of manganese and are often listed as particularly valuable sources of manganese. However, zinc also is contained in appreciable amounts in wheat bran and whole wheat products but is poorly absorbed by the human from these sources. This has been attributed to either the phytate or the fiber contents of these products or a combination of these two dietary factors. These same factors may also affect the absorption of manganese. 

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