Evidence-Based Guideline of the German Nutrition Society: Carbohydrate Intake and Prevention of Nutrition-Related Diseases

The relative contribution of nutrition-related chronic diseases to the total disease burden of the society and the health care costs has risen continuously over the last decades. Thus, there is an urgent necessity to better exploit the potential of dietary prevention of diseases. Carbohydrates play a major role in human nutrition – next to fat, carbohydrates are the second biggest group of energy-yielding nutrients. Obesity, type 2 diabetes mellitus, dyslipoproteinaemia, hypertension, metabolic syndrome, coronary heart disease and cancer are wide-spread diseases, in which carbohydrates could have a pathophysiologic relevance. Correspondingly, modification of carbohydrate intake could have a preventive potential. In the present evidence-based guideline of the German Nutrition Society, the potential role of carbohydrates in the primary prevention of the named diseases was judged systematically. The major findings were: a high carbohydrate intake at the expense of total fat and saturated fatty acids reduces the concentrations of total, LDL and HDL cholesterPublished online: January 23, 2012 Dr. Daniela Strohm Department of Science, German Nutrition Society Godesberger Allee 18 DE–53175 Bonn (Germany) Tel. +49 228 3776 623, E-Mail strohm @ dge.de © 2012 S. Karger AG, Basel 0250–6807/12/0605–0001$38.00/0 Accessible online at: www.karger.com/anm Hauner et al. Ann Nutr Metab 2012;60(suppl 1):1–58 2 indicate that there is a very high potential to prevent these diseases, and this has not yet been fully exploited [WHO, 2003, 2009]. According to its constitution, the German Nutrition Society (DGE) aims to improve the health of the general public by developing and communicating scientifically based nutritional recommendations which contribute to the primary prevention of nutrition-related diseases. Already in 2006, with this intention a Guideline Commission published an evidence-based guideline regarding fat intake and prevention of nutrition-related diseases, which is publicly available (www.dge.de/leitlinie). Next to fat, carbohydrates are the second big group of energy-yielding nutrients, providing an important part of human nutrition. Correspondingly, they could have a substantial influence on the prevention of nutrition-related diseases. In the context of systematically investigating macronutrients regarding their preventive potential, a Guideline Commission of the DGE has addressed the question of the role of carbohydrate intake on the occurrence of nutrition-related diseases in healthy individuals [DGE, 2011a]. For this purpose, the current knowledge based on human studies was critically reviewed, and scientifically validated information was extracted. The results of this evidence-based guideline should contribute to reduce consumer’s uncertainty which is caused by contradictory statements regarding the influence of nutritional carbohydrate intake. Especially in recent years, there has been intensive and controversial discussion about this [Mack and Hauner, 2007]. The aim of this evidence-based guideline regarding carbohydrate intake and the prevention of certain nutrition-related diseases is: • to perform a systematic review of the scientific literature on the effects of carbohydrate intake on the development and prevention of diseases; • to separately assess single qualitative parameters of carbohydrate intake in this context; • to provide scientifically based information on the effects of carbohydrate quantity and quality for nutrition experts and the media. Because of the clinical significance of nutrition-related diseases and their relevance in preventive medicine, this systematic review focussed on obesity, type 2 diabetes mellitus, dyslipoproteinaemia, hypertension, metabolic syndrome, coronary heart disease (CHD) and cancer. Due to limited rescources, it was not possible to include all diseases for which an impact of carbohydrate intake has been suggested, like gastrointestinal diseases and dental caries. 2 Methodological Approach 2.1 Key Questions The key questions were: does the quantity and quality of carbohydrate intake have an impact on the development of nutritionrelated diseases like obesity, type 2 diabetes mellitus, dyslipoproteinaemia, hypertension, metabolic syndrome, CHD and cancer? If so, of which directions are the observed effects and how strong is the impact of carbohydrate intake? Last but not least, what are the resulting practical recommendations for primary prevention? First, the aspects of carbohydrate intake to be investigated were identified. The Guideline Commission agreed on the following to be considered in the present guideline: • total carbohydrates (percentage of energy intake or absolute amount) • monoand disaccharides (sugar), sugar-sweetened beverages • polysaccharides • dietary fibre/whole-grain products • glycaemic index (GI) and glycaemic load (GL) The Guideline Commission has chosen this selection due to the relevance of these aspects and in order to cover important prevention potentials of carbohydrate intake. In addition, sufficient study data are available for these aspects. 2.2 Search Strategy A systematic literature search was performed regarding the key questions. The focus was on meta-analyses, systematic reviews and original papers published between 1975 and December 2009. Meta-analyses from 2010 published before December 15, 2010, were also included. The search was conducted explicitly for human studies in English or German language. The literature search was performed using the PubMed database (www.ncbi.nlm.nih.gov/pubmed) and reviewing the reference lists of guidelines, reviews and original papers. 2.3 Classification of the Literature into Levels of Evidence The classification of the levels of evidence which evaluate the study design and results with regard to their potential relevance was conducted according to the judgement scheme of the World Health Organization (WHO) [WHO, 2003]. The judgement of the selected literature was performed on the basis of the levels of evidence shown in table 1 . The focus of the judgement was put on randomised controlled intervention studies 1 with the best evidence (level of evidence I) and prospective cohort studies with the second best evidence (level of evidence II). Case-control studies (level of evidence III) and non-analytic studies (level of evidence IV) were not included. In case-control studies, it is principally possible to use detailed assessment instruments; however, this advantage does not outweigh the methodological weakness of the ‘wrong’ chronology of exposure and disease occurrence and the associated sources of bias. Cross-sectional studies were not considered for this guideline either, because they do not allow statements regarding chronology (risk of reverse causation), and because existing diseases possibly lead to bias in the nutritional assessment. 1 The present DGE guideline includes mainly intervention studies with a duration of at least 12 weeks.