Postprandial effect of breakfast glycaemic index on vascular function, glycaemic control and cognitive performance (BGI study): study protocol for a randomised crossover trial

Sanchez-Aguadero et al. Trials (2016) 17:516 DOI 10.1186/s13063-016-1649-x STUDY PROTOCOL Open Access Postprandial effect of breakfast glycaemic index on vascular function, glycaemic control and cognitive performance (BGI study): study protocol for a randomised crossover trial Natalia Sanchez-Aguadero1,8*, Luis Garcia-Ortiz1,2, Maria C. Patino-Alonso3,4, Sara Mora-Simon4,5, Manuel A. Gomez-Marcos1,6, Rosario Alonso-Dominguez1, Benigna Sanchez-Salgado1 and Jose I. Recio-Rodriguez1,7 Abstract Background: Postprandial glycaemic response affects cognitive and vascular function. The acute effect of breakfast glycaemic index on vascular parameters is not sufficiently known. Also, the influence of breakfasts with different glycaemic index on cognitive performance has been mostly studied in children and adolescents with varying results. Therefore, the purpose of this study is to analyse the postprandial effect of high and low glycaemic index breakfasts on vascular function and cognitive performance and their relationship with postprandial glycaemic response in healthy young adults. Methods/design: This is a crossover clinical trial targeting adults (aged 20–40 years, free from cardiovascular disease) selected by consecutive sampling at urban primary care health clinics in Salamanca (Spain). Each subject will complete three interventions with a washout period of one week: a control condition (consisting of water); a low glycaemic index breakfast (consisting of dark chocolate, walnuts, yogurt and an apple, with an overall glycaemic index of 29.4 and an energy contribution of 1489 kJ); and a high glycaemic index breakfast (consisting of bread, grape juice and strawberry jam, with an overall glycaemic index of 64.0 and an energy contribution of 1318 kJ). The postprandial effect will be assessed at 60 and 120 minutes from each breakfast including blood sampling and cognitive performance evaluations. Measurements of arterial stiffness and central haemodynamic parameters will be taken at –10, 0, 15, 30, 45, 60, 75, 90, 105 and 120 minutes. Discussion: The differences in postprandial glycaemic response due to breakfast glycaemic index could affect vascular parameters and cognitive performance with important applications and implications for the general population. This could provide necessary information for the establishment of new strategies in terms of nutritional education and work performance improvement. Trial registration: ClinicalTrials.gov: NCT02616276. Registered on 19 November 2015. Keywords: Glycaemic index, Postprandial period, Vascular stiffness, Blood glucose, Cognition * Correspondence: 1 Primary Care Research Unit, The Alamedilla Health Centre, Castilla and León Health Service (SACYL), Institute of Biomedical Research of Salamanca (IBSAL), Salamanca, Spain 8 Primary Care Research Unit, The Alamedilla Health Centre, Av. Comuneros N° 27, 37003 Salamanca, Spain Full list of author information is available at the end of the article © The Author(s). 2016 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated. Sanchez-Aguadero et al. Trials (2016) 17:516 Background The glycaemic index (GI) is a measure of the speed with which a carbohydrate is absorbed compared to a reference product (pure glucose) [1, 2]. Diets with a high GI increase the risk of diseases related to lifestyles such as type 2 diabetes mellitus [3, 4]. A recent meta-analysis of 14 prospective studies found that high GI diets are associated with an increased risk of cardiovascular disease (CVD) [5], while a reduction in dietary GI can favourably affect the incidence of coronary disease in women [6]. Low GI diets might reduce the risk of CVD because they decrease postprandial glycaemia with different metabolic effects including differences in insulin sensitivity, circulating lipid concentrations and vascular function [3]. Regarding this latter aspect, the currently accepted gold standard to assess arterial stiffness is the carotidfemoral pulse wave velocity (PWV) [7], which has been related to increased morbidity and mortality in both patients with CVD and healthy individuals [8, 9]. Likewise, the augmentation index (AIx) is a measure of wave reflection and arterial stiffness that has been shown to be a predictor of both future cardiovascular events and all-cause mortality [10]. In this way, the Lifestyles and Vascular Aging (EVIDENT) study [11] analysed the relationship between lifestyle and arterial aging in a sample of 1553 subjects who were free from CVD. We concluded that low GI diets were associated with lower AIx values. In this regard, a reduction in central haemodynamic parameters, AIx and PWV, at 60 minutes from food intake has been reported in healthy adults, perhaps because of an increase in insulin and/or visceral vasodilatation [12]. Another possible explanation for these findings might be the postprandial hypotension that occurs after a meal due to decreased cortisol secretion and activation of the parasympathetic system [13]. For these reasons, although the effects of various macronutrients on vascular function have been explored in a number of studies [14–17], Taylor et al. [12] underlined the importance of analysing the impact of different types of meals on parasympathetic activity, central blood pressure (CBP) and vascular function parameters. Of particular interest is the carbohydrate (CHO) content of a meal, which changes postprandial glucose and insulin levels and results in varying AIx reductions in postmenopausal women [18]. Thus, breakfast would play a fundamental role, because traditional breakfast foods tend to be high in CHOs, and there can be variability in the GI of these CHOs. It appears that consuming food early in the day can have a beneficial metabolic impact regardless of GI and that low GI meals can be of more value for glycaemic control in the morning than the evening [19]. However, despite the fact that breakfast patterns are associated with metabolic profiles [20], few Page 2 of 8 authors have studied their effect on cardiovascular responses. Ahuja et al. [21] found that a light breakfast (1301 kJ energy) reduced AIx, CBP and blood pressure (BP), and increased heart rate (HR) in adults versus fasting (water). In contrast, a trial aimed to compare the dietary effects of a high GI with a low GI breakfast replacement in obese and overweight individuals reported no differences in BP or insulin concentration between breakfasts together with ben (...truncated)