PracticeUpdate Diabetes March 2019

EDITOR’S PICKS 14

Carbohydrate Quality and Human Health: A Series of Systematic Reviews and Meta-Analyses The Lancet

COMMENT By Mark A. Pereira PhD T his research makes a timely con- tribution to the literature on dietary carbohydrates and risk for non- communicable diseases and mortality. The investigators scoured the literature and conducted scientifically rigorous systematic reviews and meta-analyses, including 243 cohort studies and clinical trials spanning decades. This particular research is timely because the need for ample carbohydrate in the human diet is being called into question and hotly debated among contemporary nutri- tion scientists and preventive medicine practitioners. The findings provide con- firmation of current dietary guidelines in developed countries, with clear answers about the role of dietary carbohydrate quality and food groups. Plant-based, whole foods with mini- mal processing, including whole grains, whole fruits, vegetables, legumes, nuts, and seeds, form the foundation of a prudent dietary pattern based on the body of scientific evidence as reflected in this research study by Reynolds and colleagues. Dietary fiber is the key measurable and defining feature of a high-quality, plant-based diet. Indeed, as described by Reynolds and colleagues, the evidence on dietary fiber is stronger than any other dietary characteristic, with graded inverse dose–response associations with all-cause mortality, cardiovascular disease, diabetes, colon cancer, and body weight. Recommenda- tions to eat a plant-based, prudent diet, to replace refined grains with whole grains, and to accumulate 25+ grams of dietary fiber per day are appropriate, important, and strongly supported by the totality of scientific literature on diet and chronic diseases.

Take-home message • This is a series of systematic reviews and meta-analyses that evaluated the interplay between dietary carbohydrate quality and health outcomes and the predictive potential of certain markers. In all, 185 prospective studies and 58 clinical trials are presented here, including 4635 participants and 135 million person-years of data. Increased intake of dietary fiber was associated with lower bodyweight, systolic blood pressure, and total cholesterol, with maximal benefit observed in association with 25 to 29 g of fiber intake daily. The authors report that whole grain intake provided similar benefits. Diets focusing on reducing glycemic load had a less pronounced impact on reducing the risk of adverse health outcomes. • The results indicate that dietary fiber and whole grain intake is associated with reduced risk of adverse health outcomes. Abstract

BACKGROUND Previous systematic reviews and meta-analyses explaining the relationship between carbohydrate quality and health have usually examined a single marker and a limited number of clinical outcomes. We aimed to more precisely quantify the predictive potential of sev- eral markers, to determine which markers are most useful, and to establish an evidence base for quantitative recommendations for intakes of dietary fibre. METHODS We did a series of systematic reviews and meta-analyses of prospective studies pub- lished from database inception to April 30, 2017, and randomised controlled trials published from database inception to Feb 28, 2018, which reported on indicators of carbohydrate qual- ity and non-communicable disease incidence, mortality, and risk factors. Studies were iden- tified by searches in PubMed, Ovid MEDLINE, Embase, and the Cochrane Central Register of Controlled Trials, and by hand searching of previous publications. We excluded prospec- tive studies and trials reporting on participants with a chronic disease, and weight loss trials or trials involving supplements. Searches, data extraction, and bias assessment were dupli- cated independently. Robustness of pooled estimates from random-effects models was considered with sensitivity analyses, meta-re- gression, dose-response testing, and subgroup analyses. The GRADE approach was used to assess quality of evidence. FINDINGS Just under 135 million person-years of data from 185 prospective studies and 58 clinical trials with 4635 adult participants were included in the analyses. Observational data suggest a 15–30% decrease in all-cause and cardiovascular related mortality, and incidence of coronary heart disease, stroke incidence and mortality, type 2 diabetes, and colorectal cancer when compar- ing the highest dietary fibre consumers with the lowest consumers. Clinical trials show signifi- cantly lower bodyweight, systolic blood pressure,

and total cholesterol when comparing higher with lower intakes of dietary fibre. Risk reduc- tion associated with a range of critical outcomes was greatest when daily intake of dietary fibre was between 25 g and 29 g. Dose-response curves suggested that higher intakes of dietary fibre could confer even greater benefit to protect against cardiovascular diseases, type 2 diabetes, and colorectal and breast cancer. Similar findings for whole grain intake were observed. Smaller or no risk reductions were found with the observa- tional data when comparing the effects of diets characterised by low rather than higher glycae- mic index or load. The certainty of evidence for relationships between carbohydrate quality and critical outcomes was graded as moderate for dietary fibre, low to moderate for whole grains, and low to very low for dietary glycaemic index and glycaemic load. Data relating to other dietary exposures are scarce. INTERPRETATION FINDINGS from prospective stud- ies and clinical trials associated with relatively high intakes of dietary fibre and whole grains were complementary, and striking dose-re- sponse evidence indicates that the relationships to several non-communicable diseases could be causal. Implementation of recommendations to increase dietary fibre intake and to replace refined grains with whole grains is expected to benefit human health. A major strength of the study was the ability to examine key indicators of carbohydrate quality in relation to a range of non-communicable disease outcomes from cohort studies and randomised trials in a single study. Our findings are limited to risk reduction in the population at large rather than those with chronic disease. Carbohydrate Quality and Human Health: A Series of Systematic Reviews and Meta-Anal- yses. Lancet 2019 Jan 10;[EPub Ahead of Print], A Reynolds, J Mann, J Cummings, et al. www.practiceupdate.com/c/78481

Dr. Pereira is Professor, Division of Epidemiology & Community Health at the School of Public Health, University of Minnesota in Minneapolis, Minnesota.

PRACTICEUPDATE DIABETES