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Biomedical subjects

Nancy F Krebs

Publications and source records attributed to Nancy F Krebs.

33 records · Page 2Linked to original sources
PubMed2004

Zinc absorption as a function of the dose of zinc sulfate in aqueous solution.

BACKGROUND: Zinc supplements are used extensively in medicine and research and for public health purposes in the prevention and treatment of zinc deficiency. However, little is known about the efficiency of zinc utilization after different doses. OBJECTIVE: The objective was to determine the relation between dose of aqueous zinc and absorbed zinc (AZ) in healthy adults. DESIGN: Eight healthy adults (3 men and 5 women) aged 33.8 +/- 9.8 y (x +/- SD) received 3 pairs of zinc doses (2 and 5, 10 and 15, and 20 and 30 mg) in random order in 3 phases (1 pair per phase). There was a 3-wk washout between phases. Aqueous zinc sulfate labeled with 70Zn or 68Zn was orally administered in the postabsorptive state on days 1 and 6, respectively; intravenous 67Zn was administered 1 h after the first oral zinc dose. Two urine samples were collected daily from days 3 to 15; zinc isotopic ratios were determined by inductively coupled plasma mass spectrometry. Fractional absorption of zinc (FAZ) was determined by dual-isotope-tracer ratio; AZ was calculated by multiplying FAZ by dose. RESULTS: Mean (+/-SD) AZ values at doses of 2.2, 5.2, 10.4, 15.2, 20.3, and 30.1 mg ingested Zn were 1.6 +/- 0.4, 3.5 +/- 1.3, 7.4 +/- 1.0, 9.5 +/- 2.2, 11.0 +/- 4.4, and 11.2 +/- 2.1 mg, respectively. A saturable dose-response model, the Hill equation, was selected to model the relation of AZ to ingested zinc. Parameter estimation by nonlinear regression predicted a maximum zinc absorption of 13 mg for larger doses. CONCLUSIONS: Increases in aqueous zinc doses >20 mg result in relatively small and progressively diminishing increases in AZ postabsorptively in healthy adults.

Absorption↗
PubMed2004

Bariatric surgery for severely overweight adolescents: concerns and recommendations.

As the prevalence of obesity and obesity-related disease among adolescents in the United States continues to increase, physicians are increasingly faced with the dilemma of determining the best treatment strategies for affected patients. This report offers an approach for the evaluation of adolescent patients' candidacy for bariatric surgery. In addition to anthropometric measurements and comorbidity assessments, a number of unique factors must be critically assessed among overweight youths. In an effort to reduce the risk of adverse medical and psychosocial outcomes and increase compliance and follow-up monitoring after bariatric surgery, principles of adolescent growth and development, the decisional capacity of the patient, family structure, and barriers to adherence must be considered. Consideration for bariatric surgery is generally warranted only when adolescents have experienced failure of 6 months of organized weight loss attempts and have met certain anthropometric, medical, and psychologic criteria. Adolescent candidates for bariatric surgery should be very severely obese (defined by the World Health Organization as a body mass index of > or =40), have attained a majority of skeletal maturity (generally > or =13 years of age for girls and > or =15 years of age for boys), and have comorbidities related to obesity that might be remedied with durable weight loss. Potential candidates for bariatric surgery should be referred to centers with multidisciplinary weight management teams that have expertise in meeting the unique needs of overweight adolescents. Surgery should be performed in institutions that are equipped to meet the tertiary care needs of severely obese patients and to collect long-term data on the clinical outcomes of these patients.

Adolescent↗
PubMed2003

Exchangeable zinc pool size in infants is related to key variables of zinc homeostasis.

The exchangeable zinc pool (EZP) is the sum of the combined pools that exchange with zinc in the plasma within 48-72 h and is thought to be critical for zinc-dependent biological processes. The size of the EZP in adults has been found to be positively related to dietary zinc intake, daily absorbed zinc and fecal excretion of endogenous zinc. In this study, we examine data on EZP size in relation to variables of zinc homeostasis in normal infants on different feeding regimens. Data from 45 male infants who participated in one of four different studies contribute to the analysis. The feeding regimens include exclusive breastfeeding (n = 9; age, 2-5 mo); breastfeeding plus modest supplementation with cow's milk-based formula (n = 16; age, 3-4 mo); exclusive formula feeding (n = 4; age, 3-4 mo) and exclusive breastfeeding plus complementary foods (n =16; age, 7 mo). Fractional absorption was determined by fecal monitoring after oral administration of zinc-stable isotopes. Urine enrichment 4-8 d posttracer was used to determine endogenous fecal zinc (7-mo-old infants excepted) and EZP size. Univariate correlations and multivariate regression analyses were performed between EZP and age, weight, dietary zinc intake, fractional absorption, total absorbed zinc and endogenous fecal zinc. Results include no significant relationship between EZP size and age, body weight or fractional absorption but a positive relationship with daily absorbed zinc and endogenous fecal zinc excretion. We conclude that the amount of absorbed zinc is not tightly regulated, and that endogenous fecal zinc is dependent on and responsive to the zinc status of the organism.

Homeostasis↗
PubMed2003

Validation of a food frequency questionnaire in preschool children.

BACKGROUND: Support for the validity of food frequency questionnaires (FFQ) in preschool children using parental report is limited. METHODS: We obtained dietary information for 68 children age 1-3 years using three or four 24-hour recalls and a FFQ regarding the child's diet covering one year from families in Denver, CO from 1997 to 1999. FFQs were completed by the parents, and recalls were collected via interviews with the parents and alternate caregivers, where applicable. Nutrient biomarkers were measured in the plasma of 38 of the children. All nutrients were adjusted for energy intake using residuals, and log-transformed where necessary. RESULTS: Correlations (Pearson r) between the FFQ and the average of the recalls were 0.33 for protein, 0.41 for carbohydrate, 0.39 for fat, 0.42 for vitamin C, 0.27 for alpha-tocopherol, and 0.08 for total energy intake. We found no substantial changes in these correlations after stratification by whether or not meals and snacks were provided by caregivers other than the parents. The highest correlations (Spearman r) with biological measures were 0.51 between plasma ascorbic acid and FFQ vitamin C, and 0.48 between plasma and FFQ alpha-tocopherol. CONCLUSIONS: The FFQ shows mostly good agreements with multiple 24-hour recalls and biomarkers in preschool children. In addition, the validity of the FFQ using parental report does not appear to be compromised when there are meal providers in addition to the parents.

Biomarkers↗
PubMed2003

Prevention of pediatric overweight and obesity.

The dramatic increase in the prevalence of childhood overweight and its resultant comorbidities are associated with significant health and financial burdens, warranting strong and comprehensive prevention efforts. This statement proposes strategies for early identification of excessive weight gain by using body mass index, for dietary and physical activity interventions during health supervision encounters, and for advocacy and research.

Adolescent↗
PubMed2002

Zinc and breastfed infants: if and when is there a risk of deficiency?

Infancy is a time of relatively high zinc requirements. Human milk provides an excellent source of highly bioavailable zinc and generally meets the needs of the healthy young exclusively breastfed infants for the first several months of life. Investigations of exclusively breastfed infants less than 6 mo of age have generally found zinc homeostasis and status to be adequate, although there are indications that zinc intake from human milk alone may become limiting by around 6 mo of age. Exceptions may be small for gestational age and low birth weight infants, who may well benefit from increased zinc intake before 6 mo of age. The older infant clearly becomes dependent on non-human milk sources of zinc, i.e., from complementary foods. Traditional early complementary foods, such as cereals, fruits, and vegetables provide very modest amounts of zinc, and for those high in phytic acid, bioavailability may be low. Introduction of animal products or zinc supplementation may be important to meet the older infant's zinc requirements This is likely to be particularly important in less protected environments with a high infectious burden and limited dietary options.

Age Factors↗
PubMed2002

Disease severity at time of referral for pediatric failure to thrive and obesity: time for a paradigm shift?

The percent of ideal body weight at first visit to pediatric referral clinics was compared by chart review between patients with failure to thrive and obese patients. Results indicated that underweight children were mildly underweight, whereas the overweight children were severely so. In primary care settings, underweight children may be referred more aggressively than overweight children.

Adolescent↗
PubMed2002

Lower calcium absorption in infants fed casein hydrolysate- and soy protein-based infant formulas containing palm olein versus formulas without palm olein.

OBJECTIVE: Quantitative balance studies were performed to compare fat and calcium absorption in healthy, full term infants fed casein hydrolysate-based (CHF) and soy protein-based (SPF) infant formulas with or without palm olein (PO). Previous studies have reported that PO significantly reduced absorption of both fat and calcium in cow's milk-based formulas in which most of the calcium is inherent in the milk protein. In both SPF and CHF virtually all calcium is added as calcium salts. METHODS: Two randomized, blinded, crossover balance studies were conducted in normal term infants using a three-day home balance method. One study evaluated 10 infants fed commercially available CHF with or without PO, and the other study evaluated 12 infants fed commercially available SPF with or without PO. Fat and calcium absorption were determined based on the weight of formula intake, weight of stools, and measured calcium and fat in formula and stools. RESULTS: Fat and calcium intake did not differ between the groups fed CHF. However, infant's calcium and fat absorption was less, 41 +/- 6% (Mean +/- SEM) and 92.0 +/- 0.8%, respectively, when fed CHF with PO compared to 66 +/- 5% and 96.6 +/- 1.1%, respectively, when fed CHF without PO, (p < 0.01). For infants fed SPF, fat and calcium intake did not differ between the feeding groups. Mean calcium absorption was also significantly less when infants were fed SPF with PO, 22 +/- 3%, than when fed SPF with no PO, 37 +/- 4% (p < 0.05). Fat absorption did not differ between the two SPFs. CONCLUSION: This study demonstrates that PO, as the predominant fat, is associated with significantly lower absorption of calcium from infant formulas in which calcium salts are the source of calcium. These findings corroborate previous reports of this negative effect of PO in cow milk-based infant formulas in which most of the calcium is a component of the cow milk protein source.

Calcium↗
PubMed2002

Zinc homeostasis during lactation in a population with a low zinc intake.

BACKGROUND: There is a major increase in endogenous zinc excretion, specifically via the mammary gland, in early human lactation. Whereas fractional absorption of dietary zinc has been reported to increase in early human lactation, it is not known to what extent adaptive mechanisms may maintain zinc homeostasis, especially when dietary zinc intake is relatively low. OBJECTIVE: The objective of this study was to quantitate major variables of zinc homeostasis during early lactation in subjects from a population whose habitual dietary zinc intake is low. DESIGN: We studied 18 free-living lactating women from a rural community of northeast China whose infants were exclusively breast-fed. The subjects were studied at approximately 2 mo of lactation with use of stable isotopes of zinc and metabolic collection techniques. Milk volume was measured with use of a deuterium enrichment method. RESULTS: The mean (+/-SD) secretion of zinc in milk was 2.01 +/- 0.97 mg/d, the intake of zinc was 7.64 +/- 1.61 mg/d, and the fractional absorption of zinc was 0.53 +/- 0.09, for a total daily zinc absorption of 4.00 +/- 0.71 mg/d. Endogenous zinc excretion in urine and feces was 0.30 +/- 0.10 and 1.66 +/- 0.97 mg/d, respectively. CONCLUSIONS: Zinc balance, including zinc secreted in breast milk, was maintained at approximately 2 mo of lactation in women whose habitual diet was low in zinc. Homeostasis was achieved by high fractional absorption of zinc and intestinal conservation of endogenous fecal zinc.

Adult↗
PubMed2002

Zinc homeostasis in Malawian children consuming a high-phytate, maize-based diet.

BACKGROUND: Zinc deficiency in children is an important public health concern in the developing world, and the consumption of predominantly cereal-based diets with a high phytate content may contribute to the risk. The gastrointestinal tract plays a central role in absorbing and conserving zinc, yet it has not been carefully studied in such children. OBJECTIVE: This study investigated zinc homeostasis in healthy, free-living Malawian children with habitually high-phytate diets to better understand the role of the gastrointestinal tract. DESIGN: We evaluated zinc homeostasis in 10 children aged 2-5 y who were consuming a maize-based diet (phytate:zinc molar ratio of 23:1). Zinc stable isotopes were administered orally and intravenously. The tracer and tracee were measured in urine and feces. RESULTS: Endogenous fecal zinc was high in comparison with results for this measure in previous studies. Typical correlations seen in subjects consuming a low-phytate diet between total absorbed zinc, the size of the exchangeable zinc pool, and endogenous fecal zinc were not observed. Fractional absorption of zinc was 0.24. CONCLUSIONS: Zinc homeostasis was perturbed, particularly by large, endogenous fecal zinc losses, in this vulnerable population. The effects of interventions to improve zinc status, including dietary phytate reduction, on zinc homeostasis merit further study.

Biological Availability↗
PubMed2002

Zinc absorption from a low-phytic acid maize.

BACKGROUND: Phytic acid reduction in cereal grains has been accomplished with plant genetic techniques. These low-phytic acid grains provide a strategy for improving the mineral (eg, zinc) status in populations that are dependent on grains, including maize (Zea mays L.), as major dietary staples. OBJECTIVE: The objective was to compare the fractional absorption of zinc from polenta prepared from maize low in phytic acid with that prepared from a wild-type isohybrid maize (control) after short-term consumption by adults whose habitual diet is low in phytic acid. DESIGN: Healthy adults served as their own control subjects in a crossover design. All meals on 1 d consisted of polenta prepared from a low-phytic acid maize homozygous for the recessive low phytic acid 1-1 (lpa1-1). On the preceding or following day, all meals consisted of polenta prepared from a sibling isohybrid homozygous wild-type maize with a "normal" phytic acid content. The low-phytic acid maize contained approximately 60% less phytic acid than did the wild-type maize. All test meals were extrinsically labeled with zinc stable-isotope tracers. The fractional absorption of zinc was determined on the basis of fecal enrichment. RESULTS: The molar ratios of phytic acid to zinc in the polenta prepared from lpa1-1 maize and the wild-type maize were 17:1 and 36:1, respectively. The corresponding fractional absorptions of zinc were 0.30 +/- 0.13 and 0.17 +/- 0.11, respectively (P < 0.005). CONCLUSION: Substitution of a low-phytic acid grain in a maize-based diet is associated with a substantial increase in zinc absorption.

Absorption↗
PubMed2002

Zinc absorption and exchangeable zinc pool sizes in breast-fed infants fed meat or cereal as first complementary food.

BACKGROUND: The aims of this study were to compare the absorption efficiency of zinc from rice cereal and meat, with and without human milk, in 7-month-old breast-fed infants and to compare the size of exchangeable zinc pools in the infants according to the assigned complementary food. METHODS: Fractional absorption of zinc was measured in male infants using extrinsic labeling with a stable isotope of zinc in a test meal of either pureed beef (n = 9) or iron-fortified infant rice cereal (n = 9). The effect on fractional absorption of the addition of human milk to each complementary food was measured in each infant with a second oral zinc isotope. Fractional absorption was measured using fecal monitoring of isotope excretion, and exchangeable zinc pool size was calculated from isotopic enrichment in urine. RESULTS: Fractional absorption of zinc did not statistically differ between the beef (0.41 +/- 0.11) and cereal (0.36 +/- 0.05) test meals, although the trend showed that beef had higher fractional absorption than cereal. The higher intake of zinc from the beef versus cereal test meal resulted in a 16-fold greater amount of absorbed zinc ( P = 0.0002). The addition of human milk caused significant decreases in fractional absorption of zinc (0.07 +/- 0.02, P = 0.01) and absorbed zinc (0.04 +/- 0.01 mg, P < 0.0001). The size of the exchangeable zinc pool did not differ according to group but was strongly correlated with mean daily zinc intake ( r = 0.72, P = 0.003). CONCLUSIONS: These results confirm that meat as a complementary food for breast-fed infants can provide a rich source of dietary zinc that is well absorbed. The significant positive correlation between zinc intake and exchangeable zinc pool size suggests that increasing zinc intake positively affects metabolically available zinc.

Animals↗
PubMed2002

Community-based dietary phytate reduction and its effect on iron status in Malawian children.

This study describes a community-based method used in rural Malawi to remove dietary phytate, an inhibitor of iron absorption, and notes an improvement in the iron status of ten children who participated in the trial. Phytate was removed by soaking maize flour in excess water with phytase and decanting the water before cooking the flour. Iron status, as measured by soluble transferrin receptor and zinc protoporphyrin, was improved but not normal.

Biological Availability↗