Zinc status, dietary zinc intake and metabolic risk in Australian children and adolescents; Nepean Longitudinal Study.

PURPOSE: Zinc is essential for normal growth and metabolism. We aimed to characterise the total and bioavailable dietary zinc intake and plasma zinc concentrations in healthy children, longitudinally, and to examine the association between plasma zinc concentrations, dietary zinc intake and cardiometabolic markers in the same cohort. METHODS: A secondary data analysis of a prospective cohort study, the Nepean Longitudinal Study, which followed an Australian birth cohort at ages 8 (n = 436) and 15 years (n = 290) collecting dietary, anthropometry and biochemistry data (plasma zinc, fasting glucose, insulin and lipid profile). Diet was assessed by a 3-day food record and a food frequency questionnaire at 8 and 15 years, respectively. Zinc bioavailability was determined by the phytate/zinc molar ratio. RESULTS: At 8 years, the median zinc intake was 7.84 mg (interquartile range 6.57-9.35) for boys and 7.06 mg (5.98-8.30) for girls. Three of 345 children reported inadequate absorbable zinc intake, and none reported inadequate total zinc intake. At 15 years, median zinc intake was 11.8 mg (9.41-14.8) for boys and 8.54 mg (6.76-10.7) for girls. The prevalence of inadequate intakes of absorbable zinc and total zinc was 19 and 29 %, respectively. Plasma zinc concentration was not correlated with dietary zinc intake, adiposity nor lipids at either time point, but it was inversely correlated with fasting glucose at 8 year and with insulin at 15 years. CONCLUSIONS: Australian children had an overall adequate zinc status. However, adolescents who reported suboptimal dietary zinc intakes were more likely to have raised insulin concentrations.

Avoidance of meat and poultry decreases intakes of omega-3 fatty acids, vitamin B12 , selenium and zinc in young women.

BACKGROUND: Inadequate nutrient intake and physical inactivity may have adverse health consequences. The present study aimed to describe young female students' dietary intake, food choices and physical activity (PA) patterns, and also to determine the influence of dietary avoidance of meat and poultry on nutrient intake. METHODS: A cross-sectional study of female university students was conducted. Questionnaires were used to measure dietary intakes, food habits and PA. Anthropometric measurements of participants included height, weight and calculated body mass index (BMI). RESULTS: There were 308 participants with a mean (SD) age of 22.9 (3.9) years and a BMI of 21.5 (2.8) kg m(-2) ; 78% were in the BMI range 18.5-24.9 kg m(-2) . Of those who responded to the PA questionnaire (n = 218), 53% reported activity ≥150 min per week, with walking being the largest contributor. Completed food frequency questionnaires were returned by 256 participants. National recommendations for servings of cereals, vegetables, meat, fish and energy-dense 'extra foods' were not met by the majority of participants. Avoidance of animal foods was reported in 23% of women, and resulted in lower intakes of omega-3 fatty acids, vitamin B12 , selenium and zinc (P < 0.05) compared to non-avoidance. Iron intake from animal sources decreased significantly (P < 0.05) with the increase in meat and poultry avoidance. CONCLUSIONS: Female students had a healthy weight and reported adequate physical activity. However, in comparison to meat and poultry consumers, the avoidance of these foods was associated with a lower intake of some micronutrients. A sustained low intake of micronutrients may lead to adverse health effects in the longer-term, such as compromised immune function and iron deficiency anaemia.

Abdominal tuberculosis in a low prevalence country.

OBJECTIVE: Abdominal tuberculosis is a rare disease. The clinical and radiological manifestations are non-specific and the diagnosis is difficult. Our objective was to describe the characteristics and treatment of patients presenting with abdominal tuberculosis in a low-incidence country. PATIENTS AND METHODS: We reviewed the clinical, diagnostic, treatment, and outcome features of patients presenting with abdominal tuberculosis diagnosed by bacteriological and/or histological results and managed in five French university hospitals from January 2000 to December 2009. RESULTS: We included 21 patients. The mean diagnostic delay was 13 months. Twelve patients (57%) came from a low-incidence area and only two had a known immunosuppressed condition. Eighteen patients (86%) presented with abdominal symptoms. The main organs involved were the peritoneum (n=14, 66%), the mesenteric lymph nodes (n=13, 62%), and the bowel (n=7, 33%). Sixteen patients (76%) underwent surgery, including two in an emergency setting. Seventeen patients (81%) received six months or more of anti-tuberculosis treatment. Finally, 16 patients (76%) had a positive outcome. CONCLUSION: New diagnostic procedures, and especially molecular biology, may help diagnose unusual clinical presentations of tuberculosis. Invasive procedures are frequently necessary to obtain samples but also for the treatment of digestive involvement.

Turnover of 125I-VLDL and 131I-LDL apolipoprotein B in rabbits fed diets containing casein or soy protein.

Rabbits fed low-fat, cholesterol-free, semi-purified diets containing casein developed a marked hypercholesterolemia compared to rabbits fed a similar diet containing soy protein (plasma cholesterol 281 +/- 31 vs. 86 +/- 9 mg/dl; P less than 0.05). Turnover studies (three per dietary group) were carried out in which homologous 125I-labeled VLDL and 131I-labeled LDL were injected simultaneously into casein- (n = 8) or soy protein- (n = 9) fed rabbits. ApoB-specific activities were determined in VLDL, IDL and LDL isolated from the pooled plasma of two or three rabbits per dietary group. The production rate of VLDL apoB (1.20 +/- 0.3 vs. 1.09 +/- 0.1 mg/h per kg) was similar for the two dietary groups. The fractional catabolic rate of VLDL apoB was lower for the casein group (0.15 +/- 0.03 vs. 0.23 +/- 0.01.h-1; 0.05 less than P less than 0.10). Although the pool size of VLDL apoB was higher in the casein group (8 +/- 2 vs. 5 +/- 0.3 mg/kg), this value did not reach statistical significance. For LDL apoB, the increased pool size in casein-fed rabbits (30 +/- 5 vs. 5 +/- 1 mg/kg; P less than 0.01) was associated with a decreased fractional catabolic rate (0.03 +/- 0.005 vs. 0.08 +/- 0.008.h-1; P less than 0.01) and a 2-fold increase in the production rate of LDL apoB (1 +/- 0.3 vs. 0.4 +/- 0.06 mg/kg per h; 0.05 less than P less than 0.10) compared to rabbits fed soy protein. Analysis of precursor-product relationships between the various lipoprotein fractions showed that casein-fed rabbits synthesized a higher proportion of LDL apoB (95% +/- 2 vs. 67% +/- 2; P less than 0.001) independent of VLDL catabolism. These results support the concept that the hypercholesterolemia in casein-fed rabbits is associated with impaired LDL removal consistent with a down-regulation of LDL receptors. These changes do not occur when the casein is replaced by soy protein.

Urinary isoflavonoid excretion is inversely associated with the ratio of protein to dietary fibre intake in young women.

OBJECTIVE: To examine the prevalence of excretion of urinary isoflavonoids in women and determine any relationships with accustomed macronutrient intake. DESIGN: Volunteers in one of two 4-month studies. Study 1 was a randomised crossover study whereby subjects consumed a placebo or isoflavone supplement for 2 months and crossed over. Study 2 was a parallel design in which subjects consumed a placebo for 1 month and an isoflavone supplement for 3 months. SETTING: All subjects were free-living, healthy volunteers. SUBJECTS: A total of 25 (study 1, n=14; study 2, n=11) premenopausal women were recruited through advertisements. INTERVENTIONS: Volunteers were supplemented for 2 months (study 1) or 3 months (study 2) with purified isoflavones (86 mg/day) derived from red clover. Urinary isoflavonoids were measured during the placebo and the second month of isoflavone treatment. Macronutrient intakes were determined from weighed food records. RESULTS: During isoflavone supplementation, the concentration of urinary total isoflavonoids increased by 15-fold (P<0.0001), with 5.4-fold variation between individuals. Multiple linear regression analysis showed that 24% of this variation could be explained by an interaction between dietary fibre and protein (P=0.047), with a highly significant inverse association between total isoflavonoid concentration and the protein to fibre ratio (r=-0.51, P=0.009). CONCLUSIONS: Supplementation with purified isoflavones results in an increase in urinary isoflavonoid excretion and part of the individual variation in response is associated with an interaction between intakes of protein and dietary fibre. Whether manipulation of these macronutrients could enhance efficacy of isoflavone supplements remains to be determined.

The effect of zinc supplementation on plasma lipids and low-density lipoprotein oxidation in males.

Recent studies in animals and in vitro support the hypothesis that zinc, an essential micronutrient, possesses antioxidant properties. The aims of this study were to determine whether zinc provides antioxidant protection in humans by decreasing low-density lipoprotein (LDL) oxidizability and to determine the effect of zinc supplementation on plasma lipid and its distribution among lipoproteins. Ten healthy male volunteers were recruited to participate in a randomized crossover trial. Subjects were asked to consume 50 mg zinc as 220 mg zinc sulphate (equivalent to 4 x recommended dietary intake, or RDI) daily for 4 weeks, followed by placebo, and vice versa. Venous blood samples were collected at 2-week intervals for the determination of plasma lipids and the in vitro oxidizability of LDL in the presence of copper ions. No changes in the oxidizability of LDL or the plasma concentrations of total cholesterol, high-density lipoprotein (HDL) cholesterol and its subfractions, LDL cholesterol, or triacylglycerol were observed following zinc supplementation compared to placebo. Plasma zinc concentrations were increased significantly, indicating that the lack of effect was not due to poor compliance. The antioxidant effect of zinc in relation to LDL was not demonstrated in humans at this dose, and higher doses are unlikely to be effective given the adverse interaction with copper metabolism and the potential decrease in the activity of superoxide dismutase, a free radical quenching enzyme. The findings of this study suggest that zinc provides little, if any, antioxidant protection against LDL oxidation in humans.

Green tea or rosemary extract added to foods reduces nonheme-iron absorption.

BACKGROUND: Phenolic compounds act as food antioxidants. One of the postulated mechanisms of action is chelation of prooxidant metals, such as iron. Although the antioxidative effect is desirable, this mechanism may impair the utilization of dietary iron. OBJECTIVE: We sought to determine the effect of phenolic-rich extracts obtained from green tea or rosemary on nonheme-iron absorption. DESIGN: Young women aged 19-39 y consumed test meals on 4 separate occasions. The meals were identical except for the absence (meal A) or presence (meal B) of a phenolic-rich extract from green tea (study 1; n = 10) or rosemary (study 2; n = 14). The extracts (0.1 mmol) were added to the meat component of the test meals. The meals were extrinsically labeled with either 55Fe or 59Fe and were consumed on 4 consecutive days in the order ABBA or BAAB. Iron absorption was determined by measuring whole-body retention of 59Fe and the ratio of 55Fe to 59Fe activity in blood samples. RESULTS: The presence of the phenolic-rich extracts resulted in decreased nonheme-iron absorption. Mean (+/-SD) iron absorption decreased from 12.1 +/- 4.5% to 8.9 +/- 5.2% (P < 0.01) in the presence of green tea extract and from 7.5 +/- 4.0% to 6.4 +/- 4.7% (P < 0.05) in the presence of rosemary extract. CONCLUSION: Phenolic-rich extracts used as antioxidants in foods reduce the utilization of dietary iron.

Folic acid enrichment of bread does not appear to affect zinc absorption in young women.

BACKGROUND: In several countries cereals are now enriched with folic acid to reduce the risk of neural tube defects. Human studies suggest that folic acid interferes with zinc absorption. This raises concerns about the zinc status of high-risk groups such as infants, pregnant women, and older persons. OBJECTIVE: We sought to determine the effect of added folic acid on zinc absorption from white bread with high and low zinc contents. DESIGN: Zinc absorption was measured in 15 healthy women (22-33 y), each of whom consumed 4 single meals spaced 2 wk apart in a randomized crossover design. The servings of bread (100 g) differed in zinc and folic acid contents as follows: A, 1.2 mg Zn and 17 microg folic acid; B, 1.2 mg Zn and 144 microg folic acid; C, 3.0 mg Zn and 17 microg folic acid; and D, 2.9 mg Zn and 144 microg folic acid. Meals were extrinsically labeled with 65Zn and absorption was estimated from whole-body retention measurements. Folate status was assessed by measuring plasma and erythrocyte folate and plasma homocysteine concentrations. RESULTS: Mean (+/-SD) zinc absorption did not differ significantly in relation to the folate content of the breads at either the low zinc content (38.8 +/- 13.5% and 40.6 +/- 16.5% for A and B, respectively; P = 0.74) or the high zinc content (26.7 +/- 9.3% and 22.7 +/- 6.6% for C and D, respectively; P = 0.16). There was no significant correlation between folate status and zinc absorption (r < 0.3, P > 0.1). CONCLUSION: Fortification of white bread with a commonly used amount of folic acid did not appear to influence zinc absorption at either a high or a low zinc content.

The effect of zinc supplements on lipoproteins and copper status.

As part of a study to determine the effect of 150 mg zinc/day on plasma lipoproteins, healthy young female (n = 26; mean age 27 years) and male (n = 21; mean age 28 years) volunteers took part in a double-blind cross-over trial lasting 12 weeks. During 6 weeks of supplementation, plasma Zn rose significantly in both groups, indicating compliance. Plasma total cholesterol remained unchanged in both males and females. However, mean LDL-cholesterol decreased from 2.38 to 2.17 mmol/l in females and there was a trend for total HDL-cholesterol to be redistributed in that HDL2 rose and HDL3 fell slightly. In parallel with these changes in females, Zn supplements reduced the ferroxidase activity of serum caeruloplasmin (from 13.0 to 11.3 U/ml) and the antioxidant activity of erythrocyte superoxide dismutase (E-SOD) (from 4557 to 3638 U/g Hb) and CuZn E-SOD (from 2184 to 1672 U/g Hb). Plasma Cu and haematocrit were unaffected. No such changes were seen in males in either lipoproteins or these indicators of Cu status. Since the females were lighter than the males but received the same dose, a dose-response effect rather than a sex difference cannot be ruled out. Overall, Zn supplements significantly decrease a major risk factor for CHD in females but reduced their Cu status.

Influence of dietary minerals on apolipoprotein B metabolism in rabbits fed semipurified diets containing casein.

Rabbits were fed semipurified casein diets containing either 4% or 2.5% mineral mix for 8 weeks. Both groups maintained weight throughout the experimental period. The plasma total cholesterol concentration was significantly higher after 4 weeks on diet and slightly higher after 8 weeks in animals fed the lower level of minerals. Plasma IDL- and LDL-cholesterol concentrations after 4 weeks and HDL-cholesterol concentrations after 8 weeks were significantly higher in animals fed the 2.5% compared to those fed the 4% mineral mix. Kinetic experiments showed that in rabbits fed the lower level, the fractional catabolic and production rates of VLDL-apo B were lower and a greater proportion of IDL-apo B was derived from sources other than VLDL compared to the animals fed the higher level. LDL-apo B kinetics were not significantly different between the 2 groups. These data suggest that a reduction in dietary minerals enhances casein-induced hypercholesterolemia.

The effect of supplementation with isoflavones on plasma lipids and oxidisability of low density lipoprotein in premenopausal women.

Results of recent clinical studies have lead to the hypothesis that isoflavones are cardioprotective. The aims of this trial were to determine the effect of supplementation with isoflavonoid phytoestrogens on plasma cholesterol concentrations and its distribution among lipoproteins and whether supplementation with isoflavones influences oxidisability of low density lipoprotein (LDL) ex vivo. Fourteen healthy premenopausal women participated in a randomised cross-over trial lasting four menstrual cycles (approximately 4 months). The subjects were asked to consume 86 mg of isoflavones daily for the duration of two menstrual cycles followed by placebo for an equivalent period, or vice versa. Venous blood samples were collected initially and at the end of the second and fourth menstrual cycles for the determination of plasma lipid concentrations and the resistance of LDL to copper-induced oxidation ex vivo. Accustomed dietary intake of isoflavones and lignans during the placebo period were 6.87+/-3.0 and 1.80+/-0.22 mg/day (mean+/-S.E.M.), respectively, and these did not change during the supplementation period. The intake of other dietary components remained constant during the trial. Supplementation resulted in a 5-fold increase in urinary isoflavone excretion (12.2+/-14.2 versus 70.1+/-10.3 micromol/24 h, placebo and isoflavone periods, respectively, P=0.0001). No changes in the oxidisability of LDL (lag time of 32.9+/-3.1 versus 30.4+/-2.9 min) or the plasma concentrations of total cholesterol (4.03+/-0.21 versus 4.11+/-0.18 mmol/l) or triacylglycerol (0.67+/-0.04 versus 0.73+/-0.06 mmol/l) were observed following supplementation. However a significant period effect (P=0.024) was observed and a trend towards a carryover effect (P=0.086) was noted for the concentration of HDL(3) cholesterol. Further studies are required to clarify the potential effect of isoflavones on HDL metabolism and the interaction with plasma steroid hormones during the menstrual cycle.

The effect of Max Epa on low density lipoprotein metabolism: perspectives from an animal model.

Rabbits were fed low fat cholesterol-free diets containing casein as the source of protein (27% w/w). One group of 6 animals was supplemented with fish oil (Max Epa; 0.5 ml oil/kg body weight) and compared with 6 animals which were supplemented with a mixture of corn, palm and soybean oils (1:1:1 v/v). VLDL triacylglycerol concentrations were lower in those supplemented with Max Epa. LDL cholesterol and the kinetics of LDL-apo B were unaffected. The results indicate that in endogenously hypercholesterolaemic animals with low triacyglycerol concentrations, casein and possibly other animal proteins, override any effect of this dose of fish oil on LDL metabolism.

The effect of a lipid-lowering diet on plasma lipids and lipoproteins in mildly hypercholesterolaemic subjects: a potential role for occasional treats.

The aim of the study was to compare the effect of a lipid-lowering diet containing chocolate confectionery with an equivalent diet that is chocolate-free. In a parallel design trial, 42 free-living subjects (19 men and 23 women), aged 46.9 yr, mildly hypercholesterolemic (6.9 mmol/L) were allocated to an American Heart Association/National Cholesterol Education Program Step 1 diet that included chocolate confectionery or an identical regimen containing no chocolate. Blood samples for the analysis of plasma lipids were obtained initially, then at 6 and 12 weeks after dietary therapy. Both groups of subjects showed a trend toward a reduction in saturated fat, with those allowed chocolate reaching borderline significance (P < 0.057). Plasma cholesterol and low density lipoprotein cholesterol concentrations were significantly lower (P < 0.03) whereas plasma triacylglycerol was significantly higher (P < 0.02) in the control group compared with the chocolate group. High density lipoprotein cholesterol was reduced in both groups. Subgroup analysis on patients with the apo E3/E3 phenotype showed that the response was identical between the control and chocolate groups. The inclusion of a modest amount of chocolate confectionery did not detract from the response of a lipid-lowering diet.

Nutritional considerations in the variability of plasma cholesterol measurements.

The concentration of plasma cholesterol is influenced by biological factors as well as clinical and analytical ones. Day-to-day variation can provide a misleading estimate of plasma cholesterol as it can differ by up to 12%. Seasonal variations occur with elevated concentrations in (northern hemisphere) winter relative to summer, possibly due to diet and life-style influences. Clinical and analytical factors also contribute to the variation. These include the manner with which blood is collected, the nutritional state of the subject and subsequent specimen handling. Analytical factors such as the effectiveness of the reagents and controls chosen, as well as the extent of interference by agents of metabolic or dietary origin, can introduce a bias into the analysis. More control can be exerted over the clinical and analytical factors compared with biological variation.

The effect of calcium carbonate and calcium citrate on the absorption of zinc in healthy female subjects.

OBJECTIVES: The aim of this study was to determine the effect of calcium carbonate and calcium citrate on zinc absorption. DESIGN: The zinc tolerance test (ZTT), which is the plasma zinc response to an oral zinc challenge, was used to quantitate zinc absorption. A physiological test dose of zinc (4.5 mg elemental zinc as 20 mg zinc sulphate) was used. Subjects underwent ZTTs on three separate occasions, each time consuming in random order, either 4.5 mg elemental zinc, zinc with 600 mg elemental calcium as calcium carbonate or zinc with 600 mg elemental calcium as calcium citrate. SETTING: Metabolic ward conditions. SUBJECTS: Nine, free-living, healthy female subjects recruited from the University population. INTERVENTIONS: Blood samples were obtained at 30 min intervals for 4 h postdose. RESULTS: The area under the plasma zinc curve (AUC) (mean +/- SEM) following the coingestion of zinc with calcium carbonate (438.4 +/- 129.0 mumol Zn.min/100 g albumin) and calcium citrate (308.0 +/- 110.5) was significantly lower (P < 0.017) than when zinc was ingested alone (1561.7 +/- 240). Urinary excretion of calcium was significantly higher (P < 0.017) at 4 h after supplementation with calcium citrate (0.83 +/- 0.12 mumol Ca/mumol creatinine) compared with calcium carbonate (0.40 +/- 0.11). CONCLUSIONS: The decrease in zinc absorption following the ingestion of zinc with different forms of calcium suggests that an antagonistic competition occurred between the minerals and that elemental calcium is the inhibiting factor.

The effect of increasing dietary zinc on the activity of superoxide dismutase and zinc concentration in erythrocytes of healthy female subjects.

Zinc has many diverse functions and is essential for growth and development. Although a number of dietary constituents inhibit its absorption, a reliable index of zinc intake and/or bioavailability remains to be identified. The aim of this study was to test the hypothesis that recent changes in zinc intake and/or bioavailability are reflected in a subfraction of erythrocytes. Six healthy female volunteers were asked to supplement their diet with 50 mg of elemental zinc per day for 12 days. Venous blood samples were obtained before and during supplementation at 4-day intervals. A subfraction of erythrocytes was isolated from each sample and zinc concentration was measured in this subfraction, in the unfractionated erythrocytes and in the plasma. These showed no significant temporal change. Erythrocyte superoxide dismutase (E-SOD), a marker of copper status, showed a significant 20% decrease (P < 0.02) in its activity in both the subfraction and the unfractionated erythrocytes following supplementation. Hence, a detrimental effect on copper metabolism (as measured by the marker enzyme E-SOD) can be detected within 12 days of supplementation with a moderate amount of zinc.

Urinary zinc as a marker of zinc intake: results of a supplementation trial in free-living men.

Twenty-four adult male volunteers were asked to ingest 50 or 100 mg elemental zinc (as zinc sulphate) for 7 days. The design was a randomized cross-over trial with a 3 week wash-out period. A significant increase in 24 h urinary zinc excretion occurred after supplementation with 100 mg with a change from 48.0 +/- 4.6 (mg Zn/mmol creatinine, mean +/- SE) at day 0 to 82.6 +/- 15.9 at day 7 (P < 0.05). No significant change was observed following supplementation with 50 mg zinc. Taken together with published data, this suggests urinary zinc excretion is sensitive only to extreme changes in dietary zinc intake.

The effect of ascorbic acid on plasma lipids and oxidisability of LDL in male smokers.

OBJECTIVE: The aims of this study were to investigate the effect of ascorbic acid (AA) supplementation on the oxidisability of low density lipoprotein (LDL) in vitro and on plasma lipoproteins under controlled dietary conditions. DESIGN: Randomised single-blind cross-over trial. SETTING: Free living subjects. SUBJECTS: Eight male smokers (age: 25 +/- 2.4 y, BMI: 20.7 +/- 0.5, cigarettes per day: 19.1 +/- 2.4; means +/- s.e.). INTERVENTIONS: Dietary intake was determined in all subjects were advised to achieve an intake as close as possible to the recommended dietary intake of AA (40 mg). After two weeks on the baseline diet, subjects were asked to consume 1 g AA per day for two weeks followed by two weeks of placebo supplementation, or vice versa. In view of the carry-over effects of plasma AA, a wash-out period was incorporated between treatments. Duplicate venous blood samples were collected before and after supplementation and the plasma concentrations of AA, lipids and lipoproteins were determined. The in vitro copper-induced oxidisability of LDL was assessed by monitoring of the absorbance of 234 nm. RESULTS: No changes in the plasma lipids or the oxidisability of LDL were found after AA supplementation compared to placebo. Plasma AA concentrations doubled on average after supplementation indicating that the lack of effect was not a result of poor compliance. CONCLUSIONS: AA supplementation at this dose did not alter plasma lipids of LDL oxidisability in male smokers.

Effects of dietary casein and soy protein on metabolism of radiolabelled low density apolipoprotein B in rabbits.

Rabbits fed semipurified diets containing casein have elevated plasma cholesterol levels compared to those fed soy protein. As part of continuing studies on the mechanism of casein-induced hypercholesterolemia, two groups of six rabbits were fed these diets for 14 to 16 weeks. Animals fed the casein diet were found to have significantly higher plasma concentrations of protein, cholesterol, triacylglycerol, phospholipid and apolipoprotein B (apo B) associated with low density lipoprotein (LDL) than those fed the soy protein diet. Kinetic studies showed that the fractional catabolic rate of LDL-apo B was significantly lower in animals fed casein than in those fed soy protein regardless of whether the tracer LDL was obtained from donors fed casein or soy protein. The production rate of LDL-apo B was higher in casein-fed animals but this was not statistically significant. These results show that the efficiency of removal of LDL is significantly reduced in animals fed casein compared to those fed soy protein, and that the source of LDL did not affect the efficiency of its subsequent removal. The accumulation of LDL in casein-fed animals is consistent with down-regulation of the LDL receptor.

Dietary protein and cholesterol metabolism--interaction of minerals.

Increased dietary zinc has been shown to reduce plasma total cholesterol in rabbits fed casein. However, the mechanism is not clear. The minerals associated with casein and soya protein are different and present in amounts which can alter the overall mineral composition of the diet. In particular, casein has a much higher ratio of zinc/copper than soy protein. Utilising a range of copper concentrations (2-80 micrograms/g diet) in 14 experiments with casein diets showed a linear relationship between the cholesterolaemic response and copper concentration (when both log transformed) in groups (n = 6) of rabbits fed for 12 weeks (r = -0.70, p less than 0.05). The lower the copper, the greater the response. In no case was the copper content deficient, indicating some interaction must be reducing its availability. Similar analysis utilising the range of zinc (10-125 micrograms/g) in the diets also showed an enhanced response at low intakes (r = -0.85, p less than 0.05). To elucidate the mechanism, 2 groups of rabbits were fed casein diets containing 21 and 68 mg zinc/kg diet for 12 weeks. Low density apolipoprotein B (LDL-apoB) turnover was carried out using 125I labelled LDL-apoB and data was fitted to the 2 pool model. The production of LDL-apoB was reduced in animals fed the higher dietary zinc. Zinc appears to act by enhancing the production of LDL-apoB in casein fed animals, perhaps by reducing the availability of copper.