D. A. T. Southgate

Coronary heart disease: seven dietary factors

The dietary factors believed to be linked with the incidence of coronary heart disease are reviewed in the light of evidence with regard to their functional role, either in protection or in promotion. Detailed analysis of the evidence shows that the relations are more complex than the current lipid hypothesis suggests. It is proposed that, in particular, the polyunsaturated/saturated ratio as a measure of the propensity of the diet to influence the incidence of coronary heart disease should be replaced by indices of atherogenicity and thrombogenicity.

First BCR-intercomparison on the determination of folates in food

Abstract The first BCR intercomparison on the determination of folate in food was designed to study the state-of-the-art in folate analysis in a group of experienced vitamin laboratories in Europe. In all 15 participants from 8 countries took part using microbiological and HPLC procedures, enzyme protein-binding assays (EPBA) and commercial radioprotein-binding assay kits (RPBA). The participants were asked to quantify folate levels in a lyophilised Brussels sprout material, which had been specifically prepared as a candidate reference material for vitamin work, using their preferred method of analysis. Three types of deconjugation were also investigated, human plasma (HP), chicken pancreas (CP) and hog kidney (HK). Generally good agreement was obtained by participants using the microbiological procedures. Folate levels determined after CP deconjugate treatment (mean = 984 μ g per 100 g dry matter, SD = 237, n = 6) were 19% higher than those levels found after HP deconjugation (mean = 824 μ g per 100 g dry matter, SD = 147, n = 6). The use of autoclaving followed by deconjugation with either HP or CP enzymes gave lower (10–20%) folate levels (determined by microbiological assay) when compared to refluxing and deconjugation with the same enzymes. Hog kidney deconjugase enzyme and autoclaving/refluxing was not as effective. Although the HPLC results from the 2 participants who were able to complete the study agree reasonably well with the microbiological data, there were differences in the proportion of the individual folate forms measured. One participant found 5-CH 3 THF (55%), THF (25%) and 5-CHOTHF (20%), whereas the other only initially reported 5-CH 3 THF but later confirmed small amounts (10–15%) of THF and 5-CHOTHF forms. Despite the use of HPLC with fluorometric detection, there were some problems in peak identification and calibration. The use of HPLC with UV detection gave unsatisfactory results due to difficulties in resolution of folate compounds and these results were excluded. RPBA results were generally higher (50–60%) than both the microbiological and HPLC results but more variable. EPBA results also varied between the three laboratories using this format but the mean folate content (HP only) agreed favourably with both the HPLC and microbiological results. The major problem identified with these methods was the response of the individual folate forms to the binding-protein used. Careful control of assay pH and calibrant are required if these methods are to be applied to the determination of food folates. Future work will focus on improvements in methodology of each type of assay prior to further intercomparisons.

Dietary Fibre Analysis

Whichever definition is used for dietary fibre the major components are polysaccharides and the classification of these carbohydrates in foods provides the background for the analytical strategies.

Nonstarch polysaccharide consumption in four Scandinavian populations

Nonstarch polysaccharide (NSP) intake was measured in representative samples of 30 men aged 50-59 in 2 urban and 2 rural Scandinavian populations that exhibited a 3-4 fold difference in incidence of large bowel cancer. Intake was measured by chemical analysis of complete duplicate portions of all food eaten over one day by each individual. NSP intakes showed a rural-urban gradient, with 18.4 +/- 7.8 g/day in rural Finland and 18.0 +/- 6.4 g/day in rural Denmark versus 14.5 +/- 5.4 g/day in urban Finland and 13.2 +/- 4.8 g/day in urban Denmark. NSP intakes were also calculated (using food tables) from weighed food records kept over 4 days, one of which was the day on which the duplicate collection was made. Intakes were 2-2.5 g/day higher with this method than with direct chemical analysis, mainly because published tables of values have become outdated and inaccurate as a result of improved methods for measuring NSP in food. Individual variation from day to day in NSP intake was considerable. Average NSP intake and intake of some of its component sugars were inversely related to colon cancer incidence in this geographical comparison. To show a relationship at the individual level between diet and cancer risk in a prospective study would require detailed and accurate methods for the assessment of NSP consumption.

Intercomparison of methods for the determination of vitamins in foods. Part 1. Fat-soluble vitamins

An intercomparison of methods involving 18 European laboratories was organized to assess the state-of-the-art of vitamin determination in foods. Each laboratory received identical samples of dry food reference material (homogeneous powders, milk powder, pork muscle and haricot vert beans), which were recently certified for major dietary components and elements. Each laboratory was requested to perform the analyses by its own methods. Results for fat-soluble vitamins are reported. All participants isolated the fat-soluble vitamins by alkaline saponification. For retinol, only high-performance liquid chromatography (HPLC), reversed- or normal-phase, was applied, with both ultraviolet (UV) and fluorescence detection. Results in milk powder showed a relative standard deviation of reproducibility (RSDReprod) of only 10%. Carotene was determined by HPLC (reversed- and normal-phase) and with open-column chromatography at atmospheric pressure. For beta-carotene results in milk powder agreed very well; the RSDReprod was 14%. The values reported for haricot vert beans showed poor agreement; the RSDReprod was 52%. A major part of this variability was due to differences in methodological principles. The results for alpha-tocopherol in milk powder and haricot vert beans agreed very well, with RSDSReprod of 16 and 15%, respectively. Only HPLC (reversed- and normal-phase) with UV and fluorescence detection was applied.

Dietary fibre and related substances.

An Introduction to the Dietary Fibre Hypothesis.- Sources, Chemical Composition and Analysis of Dietary Fibre.- Effects of Fibre and Resistant Starch on Intestinal Motility and Function.- The Antinutritional Effects of Cell Wall Polysaccharides.- Effects of Dietary Fibre on Mucosal Cell Proliferation.- Adverse Effects of Substances Associated with Fibre.- Toxicological and Regulatory Aspects of Dietary Fibre.

Dietary fibre in the British diet

PREVIOUS calculations1 have shown little change in the total intake of fibre in the United Kingdom from 1880 to 1970. There has been, however, a substantial decline in the consumption of fibre from cereals, except during the Second World War. The hypothesis that relates a low intake of fibre to various diseases2 refers to dietary fibre3,4 which includes lignin and all the polysaccharides in the diet which are not hydrolysed by the endogenous secretions of the human digestive tract5. However, the values for fibre used in previous calculations were for ‘crude fibre’6, and that underestimates dietary fibre to an uncertain extent4. Now that values for dietary fibre in a range of foodstuffs are available7,8 we have repeated the earlier calculations to provide an assessment of the changes in the intakes of dietary fibre during the past century.

Assuring the Quality of Analytical Data

The current uses of food composition data depend on the reliability of these data yet achieving reliability and demonstrating that it has been achieved is by no means easy. Little of the extensive literature on analytical quality control refers specifically to food composition studies, except where these studies are carried out for regulatory purposes. In addition, there is little that addresses the other aspects of quality that concern those producing food composition data bases.

Trace elements: databases and food composition compilations

Abstract While it is nutritionally desirable to include values for trace elements in compilations of food compositional data such as nutritional databases, their inclusion does create special problems for the compilers. These relate to the availability of data for many of the trace elements that conform to the criteria for data quality that many users of the databases require. The natural variability in all concentrations of many trace elements in foods effectively imposes limits on the predictive accuracy of any database and it is ideally desirable to have sound measures of statistical variability in order to maximise the benefits of including values for trace elements.

The contribution of different groups of foodstuffs to the intake of dietary fibre

The intake of Dietary Fibre (which is defined as the sum of lignin and the polysaccharides not hydrolysed by the endogenous secretions of the human digestive tract) is derived from the plant cell walls in the diet and other non-structural polysaccharides either present naturally in foods, or derived from polysaccharide food additives such as gums or algal polysaccharides.