I. A study has been made of the zinc, copper, iron, manganese, protein (nitrogen x 625) and phytic acid contents of nineteen soya-bean-based textured-vegetable-protein (TVP) meat-extenders and meat-substitutes and of three 'ready-prepared' canned meals containing TVP.2. Phytate analysis was performed using a newly-developed method based on Holt's (1955) procedure. This method enabled the phytate content of milligram quantities of TVP to be estimated, with an SD for six

1. The inclusion of phytate (10 g/kg) in a purified diet containing zinc (15 mg/kg) fed to young male rats significantly reduced growth rate and food intake, and promoted a cyclic pattern of food intake characteristic of an uncomplicated Zn deficiency. The decreased growth rate could be accounted for by the reduced food consumption.2. Rats maintained on a Zn-deficient diet (0.5 mg Zn/kg) were found to have a cyclic pattern of food intake and a very slight weight gain. The addition of phytate (10 g/kg) to the Zn-deficient diet promoted a net loss of mean body-weight.3. Rats maintained on the Zn-supplemented diet containing phytate excreted significantly more Zn in their faeces than either pair-fed or ad lib.-fed control rats. Rats given the Zn-deficient diet supplemented with phytate excreted more Zn in their faeces than Zn-deficient control rats.4. Dietary phytate significantly reduced the average daily accumulation (μg/d) and wholebody retention (relative to dietary intake) of iron, copper, manganese and Zn, whether or not the diet was supplemented with Zn.5. The addition of phytate to the lumen fluid of ligated loops of rat duodenum maintained in situ significantly inhibited 65Zn absorption, compared with the control systems without added phytate.6. Other studies using ligated duodenal and ileal loops indicated that Zn is secreted into the gut lumen and approximately one-third of this is normally reabsorbed. Recycling of endogenous Zn may be a significant process in the over-all body economy of this trace element.7. The absorption of 65Zn added to the diet was significantly reduced by dietary phytate. Dietary phytate also reduced the biological half-life of body 65Zn from 91 to 211 h post-administration, possibly by inhibiting reabsorption of endogenous 65Zn and thus promoting a more rapid loss from the body.

The isolation of two forms of hepatic zinc-thioneins after either zinc injection into rats or partial restriction of their food intake is described. The proteins differed slightly in their amino acid composition and electrophoretic mobilities. Increases in liver zinc content after both treatments were synchronous with, and associated almost completely with, increased zinc-binding to these proteins. The time-course for the appearance and disappearance of the zinc proteins is shown. It is suggested that metallothionein is involved in the normal metabolism of zinc, perhaps in some temporary storage or detoxication capacity.

I . Studies were carried out in vitro to examine the effects of phytate on the solubility of the trace elements zinc, copper and manganese. Appropriate volumes of a solution of sodium phytate were added to a mineral solution to achieve phytate :Zn values of from o : I to 45 : I . In a second series the same values for phytate :Zn were achieved by varying the amount of added Zn at a fixed phytate concentration. 2.In both experiments > 85 % of the Zn was rendered insoluble at pH 6.5 even at the lowest value for phytate :Zn (5 : I). The effect of phytate on Zn solubility was greater than effects on Cu or Mn.3. In a dietary study, rats were offered a semi-synthetic egg-albumin-based diet with added phytate. Two series of diets were prepared, the first had a constant Zn content (18.5 mg Zn/kg) and the amount of sodium phytate varied so as to achieve values for phytate :Zn of from o : I to 40 : I (series I). In the second series, the same values for phytate : Zn were achieved by adding a fixed amount of phytate (7.4 g phytic acid/kg) while the amount of Zn was varied (series 2).4. Dietary phytate caused significant reductions in growth rates, plasma Zn concentrations and hair Zn concentrations and greying of the coat a t values for phytate : Zn of I 5 : I, 10 : I , I 5 : I and 15 : I , respectively. 5.While phytate was apparently slightly more effective in reducing Zn status when phytate :Zn values were achieved at the lower absolute levels of phytate and Zn (series I diets), the differences a t equivalent phytate :Zn values were small. It was concluded that phytate :Zn values can be used as an indicator of Zn availability from phytate-rich diets.6. Rats offered three diets containing soya-bean-based textured-vegetable-protein (TVP) exhibited low rates of weight gain compared with rats offered an egg-albumen-based diet of similar Zn content (14.5 mg Zn/kg). Additional Zn supplied in drinking-water (25 mg Zn/l) was without effect on rats consuming the egg-albumin diet but significantly improved the weight gain of rats on the TVP diets.7. It was concluded that phytate naturally present in TVP behaves similarly to phytate added to an otherwise phytate-free diet and that the reduced availability of Zn in TVP diets can be accounted for entirely by their phytate contents.

I. A technique is described for the measurement of the extent of "Zn absorption by different regions of the intestine in the intact rat. Using this technique it was shown that the duodenum contributed 6o%, the ileum 30 % and the jejunum 10 % to the over-all absorption of e6Zn. Negligible absorption of 86Zn occurred from the caecum and colon.2. Using ligated loops of rat duodenum in situ, 85Zn absorption was shown to be rapid, with I % of a 5 pg dose being transferred to the carcase within I rnin of intralurninal dosing.3. When 8sZn was injected into ligated loops in a dose range of 1-200 pg Zn/rnl the rate of absorption was linear with respect to time over the first 15 rnin. The rates of "Zn absorption Y. dose of e6Zn exhibited saturation kinetics indicating absorption by a 'carrier' or enzyme-mediated process.4. The binding of e6Zn to loop tissue showed biphasic kinetics which suggested that at low intraluminal concentrations of Zn (1-50 pg Zn/ml) binding was to specific sites whereas, at higher concentrations (50-200pg Zn/d), non-specific binding occurred. 5.A study of the fate of mucosally bound =Zn showed that over the first 30 min a proportion of the e5Zn was rapidly transfemd to the carcase and this was probably associated with the rapid phase of rsZn absorption described previously. From 30 min up to 6 h after the initial binding, =Zn was also transferred to the carcase albeit at a much slower rate indicating a slow phase of Zn absorption. A study of the kinetics of this slow phase indicated that the loss of bound "Zn to the body was a saturable process indicating an enzyme-or 'carrier'-mediated process. A comparison of the kinetics of the slow and rapid phases of MZn absorption suggests that these processes are distinct.6. Histological examination of mucosal tissue of loops exposed to zoo pg Zn/ml revealed no discernable damage. Similarly, no effect was observed on either arginine or glucose uptake by isolated duodenal loops in siiu, although this concentration of Zn completely abolished fluid uptake. A study of the effect of different doses of Zn showed that jopg Zn/ml inhibited mucosal fluid uptake by more than 50 % and 100 pg Znlml by more than 90 %. It was concluded that these effects were due to a specific action on the fluid-transfer process and not due to a general poisoning of the rnucosa.