The diet-body offset in human nitrogen isotopic values: a controlled dietary study

The "trophic level enrichment" between diet and body results in an overall increase in nitrogen isotopic values as the food chain is ascended. Quantifying the diet-body Δ(15) N spacing has proved difficult, particularly for humans. The value is usually assumed to be +3-5‰ in the archaeological literature. We report here the first (to our knowledge) data from humans on isotopically known diets, comparing dietary intake and a body tissue sample, that of red blood cells. Samples were taken from 11 subjects on controlled diets for a 30-day period, where the controlled diets were designed to match each individual's habitual diet, thus reducing problems with short-term changes in diet causing isotopic changes in the body pool. The Δ(15) N(diet-RBC) was measured as +3.5‰. Using measured offsets from other studies, we estimate the human Δ(15) N(diet-keratin) as +5.0-5.3‰, which is in good agreement with values derived from the two other studies using individual diet records. We also estimate a value for Δ(15) N(diet-collagen) of ≈6‰, again in combination with measured offsets from other studies. This value is larger than usually assumed in palaeodietary studies, which suggests that the proportion of animal protein in prehistoric human diet may have often been overestimated in isotopic studies of palaeodiet.

Dietary intakes and food sources of phytoestrogens in the European Prospective Investigation into Cancer and Nutrition (EPIC) 24-hour dietary recall cohort

BACKGROUND/OBJECTIVES

Phytoestrogens are estradiol-like natural compounds found in plants that have been associated with protective effects against chronic diseases, including some cancers, cardiovascular diseases and osteoporosis. The purpose of this study was to estimate the dietary intake of phytoestrogens, identify their food sources and their association with lifestyle factors in the European Prospective Investigation into Cancer and Nutrition (EPIC) cohort.

SUBJECTS/METHODS

Single 24-hour dietary recalls were collected from 36,037 individuals from 10 European countries, aged 35-74 years using a standardized computerized interview programe (EPIC-Soft). An ad hoc food composition database on phytoestrogens (isoflavones, lignans, coumestans, enterolignans and equol) was compiled using data from available databases, in order to obtain and describe phytoestrogen intakes and their food sources across 27 redefined EPIC centres.

RESULTS

Mean total phytoestrogen intake was the highest in the UK health-conscious group (24.9 mg/day in men and 21.1 mg/day in women) whereas lowest in Greece (1.3 mg/day) in men and Spain-Granada (1.0 mg/day) in women. Northern European countries had higher intakes than southern countries. The main phytoestrogen contributors were isoflavones in both UK centres and lignans in the other EPIC cohorts. Age, body mass index, educational level, smoking status and physical activity were related to increased intakes of lignans, enterolignans and equol, but not to total phytoestrogen, isoflavone or coumestan intakes. In the UK cohorts, the major food sources of phytoestrogens were soy products. In the other EPIC cohorts the dietary sources were more distributed, among fruits, vegetables, soy products, cereal products, non-alcoholic and alcoholic beverages.

CONCLUSIONS

There was a high variability in the dietary intake of total and phytoestrogen subclasses and their food sources across European regions.

An approach based on ultra-high pressure liquid chromatography-tandem mass spectrometry to quantify O6-methyl and O6-carboxymethylguanine DNA adducts in intestinal cell lines

O⁶-methylguanine (O⁶-MeG) and O⁶-carboxymethylguanine (O⁶-CMG) are characteristic promutagenic and toxic DNA adducts formed by nitrosated glycine derivates and N-nitrosopeptides. Since endogenous nitrosation has been hypothesised as a plausible origin for the association between red and processed meat intake and colorectal cancer, a highly sensitive, fast and specific quantitative assay is needed to correlate the dose of individual DNA adducts with the effects of food consumption and individual digestive and metabolic processes. An ultra-high pressure liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) assay for quantitation of O⁶-MeG and O⁶-CMG, using the deuterated analogues as internal standards (ISTD), was developed. Samples of calf thymus DNA containing O⁶-MeG and O⁶-CMG were purified by acid hydrolysis and solid phase extraction prior to quantification by UHPLC-MS/MS in the selected reaction monitoring mode. The method was successfully validated in terms of repeatability (RSD<10%), reproducibility (RSD<15%) and linearity (99.9%) by incubating 0.1mg calf thymus DNA with the known N-nitroso compound potassium diazoacetate (KDA). The limit of quantitation was 30 fmol mg⁻¹ DNA for O⁶-MeG or 1 adduct per 10⁸ nucleotides and 50 fmol mg⁻¹ DNA for O⁶-CMG or 1.7 adducts per 10⁸ nucleotides. Subsequently, the method was applied to human colon carcinoma cell lines, Caco-2 and HT-29, treated with KDA to illustrate its capability to quantify O⁶-MeG and O⁶-CMG DNA adducts using biological relevant models in vitro. This method will support further research to unravel the mechanistic basis of endogenous nitrosation processes upon consumption of red and processed meat products.

Urinary sucrose and fructose as biomarkers of sugar consumption: comparison of normal weight and obese volunteers

Using urinary sugars as a biomarker of consumption, we have previously shown that obese people consume significantly more sugars than individuals of normal weight. However, there is concern that recovery of this biomarker may differ between normal weight and obese individuals. A total of 19 subjects, divided into two groups according to their body mass index (BMI) (normal weight BMI < or = 25 kg/m(2), n=10; obese BMI > or = 30 kg/m(2), n=9), participated in a randomized crossover dietary intervention study of three diets providing 13, 30 and 50% of energy from sugars for 4 days each while living in a volunteer suite. The mean urinary sucrose and fructose excretions in 24-h urine increased with increasing sugar consumption over the three dietary periods in both BMI groups and were significantly different between the diets (P < 0.01). There was no significant interaction effect of BMI class on the mean urinary excretions of these sugars with different sugar intakes, either as absolute values or expressed as a percentage of total sugar intake. In conclusion, BMI does not affect the validity of sucrose and fructose excretions in 24-h urine collections used as biomarkers to estimate total sugar consumption.