Dietary iron requirements are dependent on the amount and availability of food iron ingested. On the basis of recent studies of food iron absorption employing extrinsic tag techniques, the availability of heme iron has been defined and estimates of the availability of nonheme iron based on the amounts of enhancing substances appear possible. A model has been developed whereby the availability of iron in a given meal may be estimated. Calculations are made on a meal basis of 1) the amount of heme iron and its availability, and 2) the amount of nonheme iron and its availability as influenced by the meal's content of enhancing factors. Examples of these calculations are provided.

The ability of various animal proteins to enhance the absorption of dietary nonheme iron was evaluated by performing multiple radioiron absorption measurements in 70 volunteer subjects. Protein equivalent substitutions of nine animal foods were made in two basic test meals. The first was a standard meal of high iron availability (mean absorption, 8.3%) containing beef muscle as the animal protein. The second was a semisynthetic meal of low iron availability (mean absorption, 1.4%) containing ovalbumin as the protein source. Two categories of animal protein were defined. Substitution of beef, lamb, pork, liver, fish, and chicken for the egg ovalbumin in the sannisynthetic meal resulted in a significant, 2-fold to 4-fold increase in iron absorption whereas no increase was observed with milk, cheese, or egg. Reciprocal findings were obtained when these foods were substituted for the beef contained in the standard meal. All sources of animal proteins are not equivalent in their effect on nonheme iron absorption.

A sizable segment of the population was found to be taking large quantities of vitamin C to reduce the number or severity of upper respiratory infections. To determine the affect of this supplementation on iron balance, multiple radioiron absorption tests were performed in 63 male subjects. The increase in iron absorption from a semisynthetic meal was directly proportional to the amount of ascorbic acid added over a range of 25 to 1,000 mg. The ratio of iron absorption with/without ascorbic acid at these two extremes was 1.65 and 9.57, respectively. The relative increase was substantially less when the test meal contained meat. A large dose of vitamin C taken with breakfast did not effect iron absorption from the noon or evening meal. A telephone survey of 100 individuals revealed that 67 were taking supplemental ascorbic acid in doses ranging as high as 2 g daily. The average intake of supplemental ascrobic acid in this population was 280 mg daily. If taken only with breakfast, this level of supplementation would produce a nearly 2-fold increase in the amount of iron absorbed daily. If taken in divided doses with each mean, the increase in iron absorption would be more than 3-fold.

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Patients with chronic renal failure exhibit plasma fatty acid patterns indicative of essential fatty acid deficiency. The plasma fatty acid profile of 25 hemodialysis patients with a history of pruritus symptoms indicated lower 20:3n-9 (eicosatrienoic acid), 20:4n-6 (arachidonic acid), and 20:5n-3 (eicosapentaenoic acid) concentrations; a higher 18:1n-9 (oleic acid) concentration; and above-normal ranges of prostaglandin E2 (PGE2) compared with 22 subjects chosen from a normal population. No significant difference in 22:6n-3 (docosahexaenoic acid) was shown between the hemodialysis patients and the normal subjects. The dietary intake of 20:5n-3 was higher and that of 18:1n-9 lower in the patients compared with the normal population group. In this 8-wk double-blind study the hemodialysis patients were randomly assigned to receive daily supplements of 6 g ethyl ester of either fish oil, olive oil, or safflower oil. At the end of 8 wk of treatment the fish oil group (FO group) had a greater decrease in 18:1n-9 (P < 0.05), greater increases in 20:5n-3 and 22:6n-3 (P < 0.01), and trends toward a greater decrease in 20:4n-6, a greater increase in PGE2 concentrations, and greater improvement in pruritus scores (0.10 > P > 0.05) compared with the other two groups. The increases in 20:5n-3 and 22:6n-3 in the FO group indicate compliance with fish oil supplementation. Results indicate that hemodialysis patients have abnormal fatty acid profiles and increased PGE2 values. Fish oil intervention changes the fatty acid profile and may improve the symptoms of pruritus.

Dietary intake and iron status was evaluated in 52 nonpregnant premenopausal women who were not using Fe supplements. Subjects were separated into three groups based on their habitual consumption of red meat (RM), fish and/or poultry (FP), or lacto-ovovegetarian (LV) sources of protein. No differences were observed among the groups in demographic characteristics (eg, age, height, weight, reported number of menstrual days per year) or total Fe intake. However, those women consuming red meat as their predominant source of protein demonstrated superior Fe status, especially reflected by higher serum ferritin concentrations (RM = 30.5 micrograms/L; FP = 15.6 micrograms/L; and LV = 19.1 micrograms/L). Thus, form rather than amount of dietary Fe appears to be most influential on Fe status; the basis for the distinctly lower Fe stores among heavy users of fish and/or poultry remains to be determined.