Folate intake is strongly influenced by various methods of cooking that can degrade the natural forms of the vitamin in foods. The aim of the present study was to determine the effect of different cooking methods on folate retention in various foods that contribute to folate intake in the UK diet. Typical purchasing and cooking practices of representative food folate sources were determined from a questionnaire survey of local shoppers (n 100). Total folate was determined by microbiological assay (Lactobacillus casei NCIMB 10463) following thermal extraction and tri-enzyme (a-amylase, protease and conjugase) treatment in raw foods and after typical methods of cooking. Boiling for typical time periods resulted in only 49 % retention of folate in spinach (191·8 and 94·4 mg/100 g for raw and boiled spinach respectively; P, 0·005), and only 44 % in broccoli (177·1 and 77·0 mg/100 g for raw and boiled broccoli respectively, P, 0·0001). Steaming of spinach or broccoli, in contrast, resulted in no significant decrease in folate content, even for the maximum steaming periods of 4·5 min (spinach) and 15·0 min (broccoli). Prolonged grilling of beef for the maximum period of 16·0 min did not result in a significant decrease in folate content (54·3 and 51·5 mg/100 g for raw and grilled beef respectively). Compared with raw values, boiling of whole potatoes (skin and flesh) for 60·0 min did not result in a significant change in folate content (125·1 and 102·8 mg/100 g for raw and boiled potato respectively), nor was there any effect on folate retention whether or not skin was retained during boiling. These current results show that the retention of folate in various foods is highly dependent both on the food in question and the method of cooking. Thus, public health efforts to increase folate intake in order to improve folate status should incorporate practical advice on cooking.

Background-Meta-analyses predict that a 25% lowering of plasma homocysteine would reduce the risk of coronary heart disease by 11% to 16% and stroke by 19% to 24%. Individuals homozygous for the methylenetetrahydrofolate reductase (MTHFR) 677C3 T polymorphism have reduced MTHFR enzyme activity resulting from the inappropriate loss of the riboflavin cofactor, but it is unknown whether their typically high homocysteine levels are responsive to improved riboflavin status. Methods and Results-From a register of 680 healthy adults 18 to 65 years of age of known MTHFR 677C3 T genotype, we identified 35 with the homozygous (TT) genotype and age-matched individuals with heterozygous (CT, nϭ26) or wild-type (CC, nϭ28) genotypes to participate in an intervention in which participants were randomized by genotype group to receive 1.6 mg/d riboflavin or placebo for a 12-week period. Supplementation increased riboflavin status to the same extent in all genotype groups (8% to 12% response in erythrocyte glutathione reductase activation coefficient; PϽ0.01 in each case). However, homocysteine responded only in the TT group, with levels decreasing by as much as 22% overall (from 16.1Ϯ1.5 to 12.5Ϯ0.8 mol/L; Pϭ0.003; nϭ32) and markedly so (by 40%) in those with lower riboflavin status at baseline (from 22.0Ϯ2.9 and 13.2Ϯ1.0 mol/L; Pϭ0.010; nϭ16). No homocysteine response was observed in the CC or CT groups despite being preselected for suboptimal riboflavin status. Conclusions-Although previously overlooked, homocysteine is highly responsive to riboflavin, specifically in individuals with the MTHFR 677 TT genotype. Our findings might explain why this common polymorphism carries an increased risk of coronary heart disease in Europe but not in North America, where riboflavin fortification has existed for Ͼ50 years.

We thank Powers et al for their positive comments on our article. 1 Their criticism is that our sample is not representative of the United Kingdom or European populations, and that our interpretation of the results in relation to food policy is therefore inappropriate.The statement that statistical inference is compromised is misleading because it is very clear in our article that the inference is not being made about the general population, but rather a subpopulation, ie, people homozygous for the MTHFR 677C3 T polymorphism (ie, TT genotype). To specifically investigate this subpopulation, we screened 680 healthy adults and identified just over 10% with the TT genotype; this is typical of populations worldwide. Powers et al have inappropriately compared homocysteine levels in our TT subpopulation with those found in the general UK population. The correct comparison is with other studies that report homocysteine levels in TT genotype subpopulations. Homocysteine values in one such meta-analysis 2 were comparable with our data and were 25% higher in people with TT compared with CC (wild-type) genotypes; however, the extent of elevation varied considerably between studies, 2 presumably because of differences in the prevailing status of folate and/or riboflavin. The elevated homocysteine in TT supopulations is generally far less marked within US compared with European populations where (unlike the United States) there is no exposure to mandatory fortification with folate or riboflavin. Correspondingly, this polymorphism carries an increased risk of cardiovascular disease in European populations but not in those in North America. 3 We feel that our findings can contribute to the debate regarding food fortification with folate and related B-vitamins currently being considered by many governments. In our study, 1 the marked homocysteine-lowering effect of riboflavin in people with the TT genotype was achieved with very low doses (1.6 mg/d, ie, recommended dietary level). If a sufficiently powered clinical trial proves that homocysteine is linked in a causative way to heart disease or stroke, then exposure of the general population to low-dose riboflavin through fortification (as in the United States) may offer a cheap, safe, and effective means of reducing disease risk among substantial subpopulations who carry the TT genotype and are unaware of it. DisclosuresNone. Helene

To provide a tool to study folate bioavailability under controlled conditions, a methodology was developed to produce extracts representative of natural food folates but removed from their matrix and sufficiently concentrated so as to elicit a response in biomarkers of folate status without distorting usual dietary intake patterns. Egg, spinach, and yeast were selected to represent the wide range in extent of folate conjugation found in foods (0, 60, and 100% polyglutamyl folate, respectively). The protocol, which was based on extracting food folates using only reagents safe for human consumption, was optimized in the laboratory (thermal extraction for 10 min in a 2% ascorbate solution at pH 5) and then adapted for industrial scale production in a food-processing facility. Results showed that the extracts were 2.3-12 times more concentrated in folate compared with their corresponding food sources. Neither the mono- to polyglutamate ratio nor the distribution of the main folate derivatives was altered during processing, making these extracts suitable for use in human bioavailability studies.