Dietary intakes of phytate and its meal distribution pattern amongst staff and students in an institution of higher education

Low-phytate wholegrain bread instead of high-phytate wholegrain bread in a total diet context did not improve iron status of healthy Swedish females: a 12-week, randomized, parallel-design intervention study

PURPOSE

To investigate the effects of eating wholegrain rye bread with high or low amounts of phytate on iron status in women under free-living conditions.

METHODS

In this 12-week, randomized, parallel-design intervention study, 102 females were allocated into two groups, a high-phytate-bread group or a low-phytate-bread group. These two groups were administered: 200 g of blanched wholegrain rye bread/day, or 200 g dephytinized wholegrain rye bread/day. The bread was administered in addition to their habitual daily diet. Iron status biomarkers and plasma alkylresorcinols were analyzed at baseline and post-intervention.

RESULTS

Fifty-five females completed the study. There was a significant difference in change over time in total body iron stores between the two groups (p < 0.035). In the low-phytate bread group (n = 24) there were significant within-group decreases in both ferritin (mean 12%; from 32 ± 7 to 27 ± 6 μg/L, geometric mean ± SEM, p < 0.018) and total body iron (mean 12%; from 6.9 ± 1.4 to 5.4 ± 1.1 mg/kg, p < 0.035). Plasma alkylresorcinols indicated that most subjects complied with the intervention

CONCLUSIONS

In Swedish females of reproductive age, no statistically significant difference in iron status was detected after 12 weeks of high-phytate wholegrain bread consumption. However, consumption of low-phytate wholegrain bread for 12 weeks resulted in a reduction of markers of iron status. Although single-meal studies clearly show an increase in iron bioavailability from dephytinization of cereals, medium-term consumption of reduced phytate bread under free-living conditions suggests that this strategy does not work to improve iron status in healthy women of reproductive age.

An estimate of phytate intake and molar ratio of phytate to zinc in the diet of the people in the United Kingdom

Objective

To estimate the phytate intake and molar ratio of phytate to zinc in the diet of the people in the United Kingdom.

Design

Tables of the phytate content of foods were developed from twenty-eight published and unpublished studies. They were then applied to the nutrient databank of the National Diet and Nutrition Survey (NDNS). The study is a retrospective analysis of data on daily consumption of foods and drinks from the NDNS of children, adolescents, adults and the elderly based on 4–7 d weighed intakes.

Subjects

A total of 6786 British participants aged 1·5 years and above, who participated in the NDNS, 1992–2001.

Setting

England, Scotland and Wales.

Results

The median daily intakes of phytate for children, adolescents, adults and the elderly population were 496, 615, 809 and 629 mg/d, respectively. Although there were differences in phytate intakes between men and women, and for children, adolescents and elderly populations, after adjusting for differences in energy intake, there was no significant variation. The median phytate-to-zinc molar ratios for children, adolescents, adults and the elderly population were 11·8, 10·4, 9·7 and 8·7, respectively. Overall, the main sources of phytate were cereal and cereal products (e.g. breakfast cereals and breads), vegetables, potatoes and savoury snacks (e.g. chips and crisps), hot drinks and miscellaneous foods (e.g. commercial toddler foods and drinks, chocolate and soups), fruits and nuts.

Conclusions

The present study estimated the dietary intake of phytate and the phytate-to-zinc molar ratio of the diet of the UK population, which can be used for estimating the average requirement of zinc. Further research should focus on the completion and validation of the tables of phytate content of UK foods, to assess (and if necessary improve) the accuracy and precision of these findings.

Effects of Mediterranean diets with low and high proportions of phytate-rich foods on the urinary phytate excretion

BACKGROUND

Important health benefits have been reported recently to phytate intake. This includes the prevention of pathological calcifications such as renal calculi, dental calculi and cardiovascular calcification, due its action as crystallization inhibitor of calcium salts, and as preventive of cancer.

AIM OF STUDY

The aim of this study was to establish a relation between the intake of phytate, through consumption of typical components of the Mediterranean diet (including nuts), and its excretion in urine.

METHODS

This study recruited participants from subjects included in a larger trial (PREDIMED) of food habits, that were assigned to one of two diet groups: (1) the Mediterranean diet with low proportion of phytate-rich food group, where participants were asked to maintain their usual diet; and (2) the Mediterranean diet with high proportion of phytate-rich food group, where participants were asked to increase phytate-rich foods in their diet. Phytate intake was assessed on the basis of a food frequency questionnaire. Urinary phytate excretion was determined in 2-h urine samples.

RESULTS

The overall phytate consumption of the Mediterranean diet with high proportion of phytate-rich food group (672 +/- 50 mg) was significantly higher than the Mediterranean diet with low proportion of phytate-rich food group (422 +/- 34 mg), representing a 59% difference. Urinary phytate excretion was also significantly higher (54%) in the Mediterranean diet with high proportion of phytate-rich food group (1,016 +/- 70 microg/L) than the Mediterranean diet with low proportion of phytate-rich food group (659 +/- 45 microg/L).

CONCLUSIONS

Mediterranean diets high in whole cereals, legumes and nuts compared to Mediterranean diets low in these phytate-rich foods increase the urinary phytate excretion in humans.

Dietary fibre and phytate--a balancing act: results from three time points in a British birth cohort

An investigation was carried out to determine whether there were significant changes in the intake of dietary fibre (NSP) and phytate of adult men and women in the UK from 1982 (aged 36 years) to 1999 (aged 53 years). The 1253 subjects studied were members of the Medical Research Council National Survey of Health and Development; a longitudinal study of a nationally representative cohort of births in 1946. Food intake was recorded in a 5 d diary at age 36 years in 1982, 43 years in 1989 and 53 years in 1999. The food composition database was amended with revised values for phytate. Outcome measures were mean intakes of total NSP and phytate by year, sex and food source. There were significant changes in total NSP and phytate intake over the three time points. Intakes of NSP rose significantly between 1982 and 1999 for men and women but phytate intakes rose significantly only between 1989 and 1999. Cereal foods were the most important source of both NSP and phytate. Between 1989 and 1999 there was a significant increase in the contribution from pasta, rice and other grains. The present study shows that an increase in dietary fibre that is in accordance with dietary guidelines would almost inevitably be accompanied by a rise in phytate. The increased dietary phytate is discussed in relation to its recognised inhibition of mineral absorption and its merits with regard to protection against some cancers and other diseases of an ageing population.

Estimativa da disponibilidade de zinco em refeições com preparações padronizadas da alimentação escolar do município de Campinas

OBJETIVO: Este estudo se propôs a avaliar razões molares fitato:Zn e fitatoxCa:Zn/MJ de preparações para escolares entre 7 e 14 anos. MÉTODOS: A padronização das receitas foi realizada em uma escola e submetida a teste de aceitação, por meio da avaliação do rejeito. As refeições habitualmente usadas foram submetidas à estimativa de disponibilidade de zinco por meio do cálculo das razões molares fitato:Zn e fitatoxCa:Zn/MJ. Os cálculos dietéticos foram realizados pelo programa Nut Win (versão 1.5) e foram usados os valores de 15 e 22 para as razões molares fitato: zinco e fitatoxCa:Zn/MJ, respectivamente, como pontos de corte para o risco à absorção de zinco. RESULTADOS: Os resultados mostram que 50,0% das preparações apresentam risco à absorção de zinco segundo fitato: Zn, e 40,0% segundo fitatoxCa:Zn/MJ; 82,0% dos cardápios fornecem menos do que 15,0% das recomendações de cálcio e 63,6% apresentam grande probabilidade de inadequação de lipídeos. CONCLUSÃO: A aplicação das razões molares para avaliação dos cardápios na alimentação escolar indica que a disponibilidade do zinco pode estar comprometida, o que pode ser revertido com o aumento da freqüência de alimentos fonte, como as carnes.

Phytate intake and molar ratios of phytate to zinc, iron and calcium in the diets of people in China

OBJECTIVE

To assess the phytate intake and molar ratios of phytate to calcium, iron and zinc in the diets of people in China.

DESIGN

2002 China Nationwide Nutrition and Health Survey is a cross-sectional nationwide representative survey on nutrition and health. The information on dietary intakes was collected using consecutive 3 days 24 h recall by trained interviewers.

SUBJECTS

The data of 68 962 residents aged 2-101 years old from 132 counties were analyzed.

RESULTS

The median daily dietary intake of phytate, calcium, iron and zinc were 1186, 338.1, 21.2 and 10.6 mg, respectively. Urban residents consumed less phytate (781 vs 1342 mg/day), more calcium (374.5 vs 324.1 mg/day) and comparable amounts of iron (21.1 vs 21.2 mg/day) and zinc (10.6 vs 10.6 mg/day) than their rural counterparts. A wide variation in phytate intake among residents from six areas was found, ranging from 648 to 1433 mg/day. The median molar ratios of phytate to calcium, iron, zinc and phytate x calcium/zinc were 0.22, 4.88, 11.1 and 89.0, respectively, with a large variation between urban and rural areas. The phytate:zinc molar ratios ranged from 6.2 to 14.2, whereas the phytate x calcium/zinc molar ratios were from 63.7 to 107.2. The proportion of subjects with ratios above the critical values of phytate to iron, phytate to calcium, phytate to zinc and phytate x calcium/zinc were 95.4, 43.7, 23.1 and 8.7%, respectively. All the phytate/mineral ratios of rural residents were higher than that of their urban counterparts.

CONCLUSIONS

The dietary phytate intake of people in China was higher than those in Western developed countries and lower than those in developing countries. Phytate may impair the bioavailability of iron, calcium and zinc in the diets of people in China.

Dietary zinc intake of a group of long-stay mentally handicapped women: some bioavailability considerations

Dietary factors affecting zinc bioavailability were evaluated according to their relative distribution in the individual daily meals making up the basic diet of 17 institutionalized, mentally handicapped adult women. Mean intake values of zinc, phytate, nonstarch polysaccharides (NSP), calcium, protein, and energy were calculated from a dietary survey of 7 consecutive days, which also served to obtain values for the two zinc bioavailability predictor formulas, phytate/Zn millimolar ratio and [Ca][phytate]/[Zn][energy] ratio. Mean daily zinc intake was 8.5 +/- 1.8 mg, with noon and evening meals accounting for the highest contribution to this value (45% and 35%, respectively), whereas breakfast meals' contribution was 16%. The mean protein intake was 55 +/- 13 g, with noon and evening meals being the major contributors to total daily intake (42% and 38%, respectively). Breakfast meals accounted for 77% of daily phytate intake, giving a respective phytate/Zn millimolar ratio of 20.4 +/- 7.6 and a [Ca][phytate]/[Zn][energy] ratio of 336 +/- 127 mmol/Mcal. Values for both ratios based on noon and evening meals were negligible in comparison. The mean daily NSP intake was 9.8 +/- 4.2 g, with 53% of total daily intake supplied from breakfast meals, whereas noon and evening meals accounted for 30% and 14%, respectively. The results, while suggesting that zinc bioavailability is unlikely to be adversely affected, indicated that dietary fiber intake levels are probably inadequate, particularly in view of the nonambulant condition and low physical activity prevalent in such individuals, who may, as a consequence, be susceptible to health disorders associated with impaired bowel function and constipation.

Iron and zinc status of young women aged 14 to 19 years consuming vegetarian and omnivorous diets

OBJECTIVE

To assess the iron and zinc status of young females, aged 14 to 19 years, consuming vegetarian and omnivorous diets.

METHODS

Dietary intakes (via 3-day weighed food records), BMI, and laboratory indices of iron and zinc status were compared in a convenience sample of 79 lacto-ovo-vegetarians (LOV), 16 semi-vegetarians (SV), and 29 omnivorous (OM) females.

RESULTS

Twenty-nine percent LOV, 44% SV, and 17% OM had low iron stores (i.e., plasma ferritin < 12 micrograms/L); only 3% had anemia. As well, 24% LOV, 33% SV, and 18% OM had serum zinc < 10.71 mumol/L and 14% LOV, 14% SV, and 17% OM had hair zinc < 1.68 mumol/g. Intakes of iron and ascorbic acid from the weighed food records were associated with serum iron (p < 0.04) and total iron binding capacity (negatively; p < 0.02), respectively, whereas Phy:Zn molar ratios were associated with serum zinc (negatively; p < 0.04). Z-scores for BMI were associated with serum zinc (p < 0.02) and diet type (p < 0.001); serum AP activity was associated with age (p < 0.0001) and oral contraceptive use (p < 0.04).

CONCLUSIONS

Suboptimal iron and zinc status was attributed to low intakes of poorly available iron and zinc in all dietary groups.

Phytate and zinc bioavailability

This review discusses evidence from human studies on the effects of dietary phytate on zinc bioavailability. In vitro and animal experiments have implicated calcium as a potentiating factor because it reacts with phytate, and zinc binds to the precipitate. Magnesium also reacts similarly to calcium, but most studies have not considered this factor. Protein provides amino acids, some of which are able to desorb zinc from the precipitate and improve bioavailability. Some predictive ratios, derived from animal studies, have been directly applied to human studies. The studies reviewed included those on: zinc status of groups, apparent absorption of zinc in normal subjects and ileostomists, true absorption using a stable isotope, plasma tolerance, and the accumulation in the body of a radioisotope. It was concluded that detrimental effects of phytate could be demonstrated on zinc bioavailability, but that the studies had not been designed specifically to demonstrate whether the interactions found in animal studies also apply to humans. It is suggested that more targeted research is required before predictive ratios are used for humans.

Binding of zinc and calcium to inositol phosphates (phytate) in vitro

Inositol compounds with three to five phosphate groups (IP3-IP5) were produced by hydrolysis of phytate (inositol hexaphosphate, IP6) and their binding affinities for calcium and zinc investigated at neutral pH with relative concentrations that had been found in a range of students' meals. Zn solubility was negligible at many of these concentrations, with less Zn bound to precipitates of Ca-IP6 than Ca-IP5. The capacity to precipitate Zn at these ratios fell between IP5 and IP3. Zn was partially desorbed by soluble chelators (histidine and picolinate), especially when it had been adsorbed to preformed Ca-IP precipitates. A lower proportion of Zn was accessible to soluble chelators from Ca-IP4 than the other compounds. IP3-IP4 were hydrolysed by phytase more readily than IP5-IP6.