The effect of food preparation on the bioavailability of carotenoids from carrots using intrinsic labelling.

A strategy to reduce the incidence of vitamin A deficiency is to improve precursor bioavailability from meals. Since vitamin A precursors are fat-soluble, we noted that carotenoids are more easily absorbed from food if prepared in such a way that the food matrix containing provitamin A (β-carotene) is sufficiently fat rich. To quantify this effect, we have developed a stable isotope methodology.

The effect of different meals on the absorption of stable isotope-labelled phylloquinone.

Few studies have investigated the absorption of phylloquinone (vitamin K1). We recruited twelve healthy, non-obese adults. On each study day, fasted subjects took a capsule containing 20 microg of 13C-labelled phylloquinone with one of three meals, defined as convenience, cosmopolitan and animal-oriented, in a three-way crossover design.

Effects of dietary supplementation with the green tea polyphenol epigallocatechin-3-gallate on insulin resistance and associated metabolic risk factors: randomized controlled trial.

Animal evidence indicates that green tea may modulate insulin sensitivity, with epigallocatechin-3-gallate (EGCG) proposed as a likely health-promoting component. The purpose of this study was to investigate the effect of dietary supplementation with EGCG on insulin resistance and associated metabolic risk factors in man. Overweight or obese male subjects, aged 40-65 years, were randomly assigned to take 400 mg capsules of EGCG (n 46) or the placebo lactose (n 42), twice daily for 8 weeks.

Energy density of the diet and change in body fatness from childhood to adolescence; is there a relation?

Background: The contribution of energy density (ED) of the total diet to increased risk of obesity from childhood into adolescence is unclear.

Objective: We assessed the relation between the ED of the diet in childhood, calculated in a number of ways, and change in adiposity from childhood to adolescence.

Design: In a prospective study, 48 children (30 boys, 18 girls) were initially studied at age 6-8 y (baseline) and followed up at age 13-17 y.

An investigation of a novel three-dimensional activity monitor to predict free-living energy expenditure.

The aim of this study was to assess the capability of the 3dNX accelerometer to predict energy expenditure in two separate, free-living cohorts. Twenty-three adolescents and 14 young adults took a single dose of doubly labelled water and wore a 3dNX activity monitor during waking hours for a 10-day period while carrying out their normal routines. Multiple linear regression with backward elimination was used to establish the strength of the associations between various indices of energy expenditure, physical activity counts, and anthropometric variables.

Efficiency of autoregulatory homeostatic responses to imposed caloric excess in lean men.

Obesity implies a failure of autoregulatory homeostatic responses to caloric excess. We studied the mechanisms, effectiveness, and limits of such responses in six lean (21.9 +/- 1.

Prevalence of Helicobacter pylori infection among Egyptian children: impact of social background and effect on growth.

Objective: The study aim was to assess the prevalence of Helicobacter pylori infection in Egyptian schoolchildren and its effect on growth parameters.

Design: A cross-sectional population-based study was conducted among 286 schoolchildren (168 boys and 118 girls), with a mean age of 11.04 +/- 0.

Estimating under-reporting of energy intake in dietary surveys using an individualised method.

Under-reporting (UR) of energy intake (EI) by self-reported dietary methods is well-documented but the methods used to estimate UR in population-based studies commonly assume a sedentary lifestyle. We compared estimated UR using individualised estimates of energy requirements with a population cut-off based on minimum energy needs. UR was estimated for 1551 adults aged 19-64 years enrolled in the National Diet and Nutrition Survey.

Use of stable-isotope techniques to validate infant feeding practices reported by Bangladeshi women receiving breastfeeding counseling.

Background: The World Health Organization recommends exclusive breastfeeding until age 6 mo. Studies relying on mothers' self-reported behaviors have shown that lactation counseling increases both the rate and duration of exclusive breastfeeding.

Objective: We aimed to validate reported infant feeding practices in rural Bangladesh; intakes of breast milk and nonbreast-milk water were measured by the dose-given-to-the mother deuterium dilution technique.

Plasma phylloquinone (vitamin K1) concentration and its relationship to intake in British adults aged 19-64 years.

Plasma phylloquinone (vitamin K1) concentration from non-fasted blood samples was examined by season, smoking status, socio-demographic factors and phylloquinone intake in a nationally representative sample of 1154 British individuals aged 19-64 years from the 2000-1 National Diet and Nutrition Survey. Geometric mean plasma phylloquinone concentration was 0.94 (95% CI 0.

Comparative dietary intake and sources of phylloquinone (vitamin K1) among British adults in 1986-7 and 2000-1.

Using data from 7 d weighed dietary records, dietary intake and sources of phylloquinone (vitamin K1) were examined by socio-demographic and lifestyle factors in 1916 participants aged 16-64 years from the 1986-7 Dietary and Nutritional Survey of British Adults, and 1423 participants aged 19-64 years from the 2000-1 National Diet and Nutrition Survey. Using UK-specific food content data, geometric mean phylloquinone intakes were estimated as 72 (95% CI 70, 74) and 67 (95% CI 65, 69) microg/d in 1986-7 and 2000-1 respectively (P<0.001).

Analysis of isotope ratios in vitamin K1 (phylloquinone) from human plasma by gas chromatography/mass spectrometry.

Vitamin K(1) is a fat-soluble vitamin required for the gamma-carboxylation of vitamin K-dependent proteins. Recent work has suggested an important role for vitamin K(1) in bone health beyond its more established function in the control and regulation of blood coagulation. However, current UK recommended intakes do not reflect this recent evidence.

Measurement of gastric emptying by the 13C-octanoate breath test--rationalization with scintigraphy.

The (13)C-octanoate breath test has not achieved universal acceptance for the measurement of solid phase gastric emptying, largely because the results are not comparable with those from direct methods such as scintigraphy. To convert breath-test data to their scintigraphic equivalent scale corrections are applied which have been obtained from population studies, but there is no guarantee that these are applicable in all cases. We propose an alternative method applicable on an individual basis based upon a simple physiological model which does not require any change to the breath-test protocol.

A stable isotope minimal model protocol with oral glucose administration.

A protocol for investigating glucose metabolism whereby stable isotope tracer is given intravenously after an oral glucose challenge is described. Frequent sampling of plasma glucose and insulin allows the tracer disappearance to be interpreted on the basis of established minimal models. We have investigated the glucose effectiveness and insulin sensitivity parameters and their reproducibility in a group of six healthy adults, each studied twice.

13C- and 2H-labelled glucose compared for minimal model estimates of glucose metabolism in man.

In the present study, we have investigated the use of 1-[(13)C]glucose and GC/combustion/isotope-ratio MS as an alternative to 6,6-[(2)H(2)]glucose and GC/MS in the determination of parameters of glucose metabolism using the IVGTT (intravenous glucose tolerance test) interpreted by labelled (hot) minimal models. The study has been done in four populations, normoglycaemics (subdivided into lean and obese individuals), subjects with impaired glucose tolerance and those with diabetes mellitus. Although the use of carbon label may in some circumstances be compromised by substrate recycling, our hypothesis was that this would not be an issue under the condition of suppression of hepatic glucose production during the short timescale of an IVGTT.

The 'anomalous' absorption of labelled and unlabelled vitamin C in man.

Previous studies of vitamin C absorption in man using stable isotope probes have given results which cannot easily be reconciled with those obtained using non-isotope measurement. In order to investigate some of the apparent paradoxes we have conducted a study using two consecutive doses of vitamin C, one labelled and one unlabelled, given 90 min apart. Compatibility of the experimental results with two feasible models was investigated.

Glycogenesis and glucose oxidation during an intravenous glucose tolerance test in man.

The quantity of deuterated glucose customarily given in labelled IVGTTs (intravenous glucose tolerance tests) changes the isotopic composition of the subject's body water enough to be detected by mass spectrometric techniques. Glucose undergoing direct glycogenesis does not contribute label to the body water pool, and isotope incorporated into it must have come from glucose that has either been oxidized or undergone indirect glycogenesis. By subtracting the amount of label found in body water from the total amount of glucose utilized, as calculated from the minimal model of glucose disappearance, it should be possible to study the partitioning of the dose given between direct glycogenesis in skeletal muscle and other metabolic pathways.

Stable isotope techniques in human nutrition research: concerted action is needed.

Use of stable isotopes in applied nutrition has been a developing field for over 60 years. The past 20 years has seen improvements in computer and mass-spectrometer technology that has opened up even greater possibilities in the understanding of human metabolism. While improvements in technology can bring great opportunities, it can also cause problems if there is no consensus among the stable isotope user-community on standardization of new techniques and methods.

Measurement of deuterium oxide by infrared spectroscopy and isotope ratio mass spectrometry for quantifying daily milk intake in breastfed infants and maternal body fat.

Measurements of deuterium oxide concentrations (DOC) in saliva by infrared spectroscopy (IRS) and isotope ratio mass spectrometry (IRMS) were compared for the calculation of infants' milk intake and maternal body fat. Deuterium oxide (30 g) was given to the mother. DOC by IRS and IRMS were 340 +/- 209 and 345 +/- 202 ppm.