Evidence-based practice within nutrition: what are the barriers for improving the evidence and how can they be dealt with?

BACKGROUND: Evidence-based clinical research poses special barriers in the field of nutrition. The present review summarises the main barriers to research in the field of nutrition that are not common to all randomised clinical trials or trials on rare diseases and highlights opportunities for improvements. METHODS: Systematic academic literature searches and internal European Clinical Research Infrastructure Network (ECRIN) communications during face-to-face meetings and telephone conferences from 2013 to 2017 within the context of the ECRIN Integrating Activity (ECRIN-IA) project. RESULTS: Many nutrients occur in multiple forms that differ in biological activity, and several factors can alter their bioavailability which raises barriers to their assessment. These include specific difficulties with blinding procedures, with assessments of dietary intake, and with selecting appropriate outcomes as patient-centred outcomes may occur decennia into the future. The methodologies and regulations for drug trials are, however, applicable to nutrition trials. CONCLUSIONS: Research on clinical nutrition should start by collecting clinical data systematically in databases and registries. Measurable patient-centred outcomes and appropriate study designs are needed. International cooperation and multistakeholder engagement are key for success.

Influence of a Mediterranean Dietary Pattern on Body Fat Distribution: Results of the PREDIMED-Canarias Intervention Randomized Trial.

OBJECTIVE: To assess the influence of a Mediterranean dietary pattern (MeDiet) on anthropometric and body composition parameters in one of the centers of the PREDIMED randomized dietary trial. SUBJECTS/SETTINGS: 351 Canarian free-living subjects aged 55 to 80 years, with type 2 diabetes or ≥3 cardiovascular risk factors. INTERVENTION: Participants were randomly assigned to one of 3 different dietary interventions: MeDiet + extra-virgin olive oil (EVOO), MeDiet + nuts (walnuts, almonds, and hazelnuts), or a control low-fat diet. Total energy intake was ad libitum. OUTCOME MEASURES: Measures included changes in anthropometric measures (weight, body mass index [BMI] and waist circumference [WC]), body fat distribution, energy, and nutrient intake after 1 year. Body composition (percentage of total body fat [%TBF], total fat mass [TFM], free fat mass [FFM], percentage of truncal fat [%TrF], truncal fat mass [TrFM]) and total body water (TBW) were estimated by octapolar electrical impedance analysis. STATISTICAL ANALYSES: Paired t tests were conducted to assess within-group changes. Analyses of variance (ANOVAs) were used to assess the effect of the dietary intervention on the percentage change in anthropometric variables, body composition, and dietary intake profile. All pairwise comparisons that were statistically significant in ANOVA were subsequently adjusted using the Benjamini-Hochberg test, which penalizes for multiple comparisons. RESULTS: After 1 year of intervention, significant within-group reductions in all anthropometric variables were observed for the MeDiet + EVOO and the control group. The MeDiet + nuts group exhibited a significant reduction in WC and TBW. The control group showed a significant increase in %TBF and a reduction in TBW. The control group showed a significant increase in the percentage of total body fat and a reduction in TBW. However, we did not find any between-group significant difference in anthropometric or body composition changes. CONCLUSIONS: Mediterranean diets enriched with EVOO or specific mixed nuts (walnuts, almonds, hazelnuts) that contain approximately 40% total fat can be alternative options to low-fat diets for weight maintenance regimes in older overweight or obese adults.

Assessing the impact of dietary habits on health-related quality of life requires contextual measurement tools.

The increase of non-communicable diseases at all ages has fostered the general concern for sustaining population health worldwide. Unhealthy lifestyles and dietary habits impacting physical and psycho-social health are well known risk factors for developing life threatening diseases. Identifying the determinants of quality of life is an important task from a Public Health perspective. Consumer-Reported Outcome measures of health-related quality of life (HRQoL) are becoming increasingly necessary and relevant in the field of nutrition. However, quality of life questionnaires are seldom used in the nutrition field. We conducted a scientific literature search to find out the questionnaires used to determine the association between dietary habits and quality of life. A total of 13 studies were eligible for inclusion. Across these studies the short form-36, a generic (non-disease specific) HRQoL measurement instrument was the most widely used. However, generic measures may have limited content validity in the context of dietary habits interventions. We recommend additional contextual diet-specific HRQoL measures are also needed for evaluating the impact of diet habits on daily life functioning and well-being.

Misreporting in nutritional surveys: methodological implications.

The reliability of the information collected in dietary assessment can be affected by different factors. One of the main sources of error in dietary assessment is misreporting which encompass under- and overreporting. Underreporting of food intake is one of the major problems in the assessment of habitual dietary intake. Physical and psychosocial characteristics that are related to energy underreporting include sex, age, weight, BMI, fear of negative evaluation and dieting among others. At present, diverse reference methods are employed to verify the results of dietary assessment and double labelled water is used as the gold standard method. Underreporting affects the estimation of nutrient intake and also alters associations between diet and disease assessed in epidemiological studies. Therefore, underreporting has to be considered and addressed by researchers through development and improvement of dietary intake adjustment methods, and taking advantage of the new technologies for assessing dietary intake in order to minimize underreporting bias.

La fiabilidad de la información recogida en la evaluación dietética puede verse afectada por diferentes factores. Una de las principales fuentes de error en la evaluación de la dieta es la declaración errónea de consumo de alimentos, que abarca la infradeclaración y sobredeclaración de la dieta. La infradeclaración de la ingesta de alimentos es uno de los principales problemas en la evaluación de la ingesta dietética habitual. Las características físicas y psicosociales que están relacionadas con la infradeclaración de energía incluyen el sexo, edad, peso, índice de masa corporal, el miedo a la evaluación negativa y estar bajo un régimen de dieta, entre otros. En la actualidad, se emplean diversos métodos de referencia para verificar los resultados de la evaluación dietética, no obstante, el método estándar es el agua doblemente marcada. La infradeclaración afecta a la estimación de la ingesta de nutrientes y también altera las asociaciones entre dieta y enfermedades en estudios epidemiológicos. Por lo tanto, la infradeclaración tiene que ser considerada y abordada por los investigadores a través del desarrollo y la mejora de los métodos de ajuste de la dieta y el aprovechamiento de las nuevas tecnologías para la evaluación de la ingesta dietética con el fin de minimizar el sesgo ocasionado por la infradeclaración.

Effect of a Mediterranean Diet Intervention on Dietary Glycemic Load and Dietary Glycemic Index: The PREDIMED Study.

Objective. To compare the one year effect of two dietary interventions with MeDiet on GL and GI in the PREDIMED trial. Methods. Participants were older subjects at high risk for cardiovascular disease. This analysis included 2866 nondiabetic subjects. Diet was assessed with a validated 137-item food frequency questionnaire (FFQ). The GI of each FFQ item was assigned by a 5-step methodology using the International Tables of GI and GL Values. Generalized linear models were fitted to assess the relationship between the intervention group and dietary GL and GI at one year of follow-up, using control group as reference. Results. Multivariate-adjusted models showed an inverse association between GL and MeDiet + extra virgin olive oil (EVOO) group: ß = -8.52 (95% CI: -10.83 to -6.20) and MeDiet + Nuts group: ß = -10.34 (95% CI: -12.69 to -8.00), when comparing with control group. Regarding GI, ß = -0.93 (95% CI: -1.38 to -0.49) for MeDiet + EVOO, ß = -1.06 (95% CI: -1.51 to -0.62) for MeDiet + Nuts when comparing with control group. Conclusion. Dietary intervention with MeDiet supplemented with EVOO or nuts lowers dietary GL and GI.