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There is an increasingly large body of published evidence from observational studies that demonstrates an association between increased consumption of wholegrain foods and reduced risk of a number of non-communicable diseases such as cardiovascular diseases (CVD), Type 2 diabetes and some cancers. The strength of evidence is strongest for CVD, and this has resulted in a number of health claims in the UK and elsewhere based on the assertion that ‘whole grains are good for your heart’. In the US and Canada this has been further interpreted as a positive need for whole grains in the diet and for these countries there are explicit recommendations for consuming (at least) 3 servings of whole grain per day; equivalent to 48g of whole grain dry matter per day. Other countries including Australia and Denmark are considering setting similar guidelines. In the UK there is no such recommendation, although there is a recommendation to eat more whole grains and to consume whole grains whenever possible. Currently the European Food Safety Authority is examining proposals from a number of EU member countries to establish a European consensus on whole grains and health for use on foods. Whilst the evidence for the health benefits of whole grain is considered ‘convincing’, including now a number of meta-analyses, the largest majority of data are derived from cross-sectional and cohort studies. The data from intervention studies is limited. There is a need, therefore, for high quality randomised controlled intervention studies investigating the impact of increased whole grain-intake on markers of disease risk. To date, no studies have investigated consumer perceptions of wholegrain foods, including reasons for and barriers to their consumption. Understanding this area is necessary to develop targeted dietary guidelines and strategies.
The WHOLEheart study was designed to address this issue and specifically to measure the impact of increased whole grain-intake on known markers of CVD risk. The specific aims of the study were to:
1. To test the impact of the inclusion of 60g/day and 120g/day of whole grains into the diets of non-whole grain consuming adults who were overweight, but otherwise healthy in a randomised, controlled dietary intervention on a number of previously documented cardiovascular disease risk factors. The primary outcome measure was change in fasting plasma LDL-cholesterol concentration.
2. To compare self-reported intake of wholegrain foods with the measured concentrations of mammalian lignans in blood and plasma samples, and thereby assess the potential use of lignans as a biomarker of whole-grain intake.
3. To elucidate participant attitudes, priorities, language and framework of understanding of wholegrain foods in order to better understand barriers to whole-grain consumption.
Approximately 300 overweight, low whole grain-consuming adults, average age 45 years, 49% male, were randomly allocated to 3 intervention groups; Control Group (CG, no change in diet), Intervention Group 1 (IG1, 3 x 20g servings of whole grain per day for 16 weeks), and Intervention Group 2 (IG2, 3 x 20g servings of whole grain per day for 8 weeks followed by 6 x 20g servings of whole grain for a further 8 weeks). Duplicate samples of fasting blood were collected within 7 days at baseline, at 8 weeks and 16 weeks of intervention for measurement of a range of markers of CVD risk which included: concentration of lipids (total, LDL and HDL cholesterol and triglycerides), markers of insulinaemic response (insulin, glucose, NEFA, QUICKI), markers of inflammatory status (sialic acid, CRP, IL-6, fibrinogen and PAI-1) and markers of endothelial function (ICAM-1, VCAM-1 and E-selectin). Anthropometric measurements (weight, BMI, waist measurement, body fat percentage), 24-hour urine collections, blood pressure and dietary intake (by FFQ and food diary) were recorded at the same time points. Spot urine collections were also recorded at 4 and 12 weeks. One month post-intervention participants completed further diet records by FFQ and attended focus group discussions, the purpose of which was to explore acceptance of the dietary intervention and barriers to whole grain-consumption.
Intervention foods were provided in pre-weighed packages individually apportioned for males and females. These included a selection of wholegrain breakfast cereals, wholewheat pasta and brown rice. Wholewheat bread was also provided. Participants were instructed on how to achieve their target level of intake and were provided with calendars to aid compliance.
Dietary intake of whole grains was increased slightly above targets for IG1 and IG2 at 8 weeks (average intake 80g/day) and was marginally below target in IG2 at 16 weeks (115g/day). This change in pattern of food intake was associated with a significant increase in the proportion of daily energy derived from carbohydrates and a reduction in the proportion of daily energy derived from fat. The intake of dietary fibre was, on average, increased from baseline by approximately 5g per day at 8 weeks for IG1 and IG2, and by 11g per day in IG2 at 16 weeks (p<0.001). Intake of a range of B-vitamins and several minerals was higher in those consuming whole grains (B vitamin (P<0.001 for folate, niacin riboflavin and thiamine), iron (P<0.001), magnesium (P<0.001), manganese (P<0.001) and zinc (P<0.001)). Sodium intake was higher in IG1 and IG2 compared with the CG, but the differences were not consistent between IG1 and IG2 at 8 and 16 weeks. Total energy intake increased slightly in the intervention groups, and fruit was displaced from the diet at the highest level of wholegrain intake (P = 0.045).
Body weight, BMI, waist and hip circumference, blood pressure and percentage of body fat were unaffected by dietary intervention and remained constant across all three intervention groups throughout the 16 weeks of follow-up. The chosen markers of CVD risk, including total and LDL-cholesterol concentrations, measures of insulin sensitivity, haemostatic markers and inflammatory markers were all unaffected by the dietary intervention.
The mammalian lignan, enterolactone, was detected in the majority of plasma samples tested, but enterodiol was only found in a small number of subjects. The relationship between whole grain-intake and plasma enterolactone concentrations was poor, although some subjects showed a dose-response relationship with increasing whole grain-intake.
The focus group data showed that the personal acceptance of wholegrain foods was influenced by taste acceptability and dietary acceptability, mediated by the health beliefs, food experiences and motivation to improve health or weight management. Barriers to consumption were associated with personal issues such as likes and dislikes, product-related issues such as cooking requirements and situational issues such as availability while eating away from the home. In the context of the intervention, incorporation of an average of 3 servings of whole grains per day was considered sustainable by most participants, however, 6 servings of whole grains per day was not considered sustainable.
Summary and conclusions: Positive changes towards a more healthful diet were observed in participants who ate more whole grains; in particular increased intake of dietary fibre, an increase in the proportion of daily energy derived from carbohydrates and a reduction in the proportion of daily energy from fat. Intake of some vitamins and minerals was also improved. Increased consumption of whole grain foods in this study did not affect body weight or composition, or alter (positively or negatively) plasma markers of CVD risk. Within the participants there were, however, individuals who demonstrated a positive response to the dietary change, and the reasons why some, but not all participants responded warrants further investigation. There were positive attitudes towards consuming the wholegrain foods mainly at the lower level of intake, although barriers to consumption still existed. These factors should be taken into consideration when promoting whole grain-consumption in the future.
Whole-grain foods used in this study were kindly provided by Cereal Partners UK, Weetabix, Allied Bakeries and PepsiCo.
Overall project lead: Professor Chris Seal, Senior Lecturer in Food Studies, School of Agriculture, Food & Rural Development. Expertise: experimental research studies, including dietary interventions and wholegrain food consumption.
Project expert in qualitative methodologies: Dr Sharon Kuznesof, Research Associate, School of Agriculture, Food & Rural Development. Expertise: development, application and analysis of focus group based research
MRC Human Nutrition Research
Project lead (Cambridge): Dr Susan Jebb, Head of Nutrition and Health Group/Dr Carmel Moore, Research Associate, Nutrition and Health Group. Expertise: controlled experimental research studies, including dietary interventions. Obesity and related metabolic disease.
Ross AB, Bourgeois A, Macharia HN, Kochhar S, Jebb SA, Brownlee IA, Seal CJ. Plasma alkylresorcinols as a biomarker of whole-grain food consumption in a large population: results from the WHOLEheart Intervention Study. Am J Clin Nutr. 2012 Jan;95(1):204-11.
Brownlee IA, Moore C, Chatfield M, Richardson DP, Ashby P, Kuznesof SA, Jebb SA, Seal CJ. Markers of cardiovascular risk are not changed by increased whole-grain intake: the WHOLEheart study, a randomised, controlled dietary intervention. Br J Nutr. 2010 Jul;104(1):125-34.
Brownlee IA, Moore CS, Chan K, Chatfield M, Ashby P, Richardson DP, Kuznesof S, Jebb SA, Seal CJ. Impact of whole grain inclusion on dietary intake and risk factors for cardiovascular disease in a large-scale randomised, controlled dietary intervention (the WHOLEheart) study. Cereal Foods World 2008;53(4 Suppl):A22.