Pathophysiology/Complications ORIGINAL ARTICLE Dietary Glycemic Index, Glycemic Load, Fiber, Simple Sugars, and Insulin Resistance The Inter99 study 1,2 1,4 CATHRINE LAU, MSC OLUF PEDERSEN, MD, DMSC he rising prevalence of disorders as- 1,2 1 KRISTINE FÆRCH, MSC BENDIX CARSTENSEN, MSC sociated with insulin resistance, 1,3 3 CHARLOTTE GLUMER¨ , MD, PHD TORBEN JØRGENSEN, MD, DMSC 2 1 including type 2 diabetes, cardio- NGE ETENS MSC, PHD NUT ORCH OHNSEN MD, DMSC T I T , K B -J , vascular disease, and the metabolic syn- drome, is commonly attributed to changes over time in dietary patterns and physical activity levels (1–4). Preventive strategies against these disorders, therefore, often in- OBJECTIVE — To examine the relationship between daily glycemic index, daily glycemic corporate dietary recommendations. How- load, simple sugars, dietary fiber, and the prevalence of a measure of insulin resistance in 30- to 60-year-old nondiabetic Danish men and women. ever, only few observational studies have investigated the independent effects of car- RESEARCH DESIGN AND METHODS — The Inter99 study is a nonpharmacological bohydrate-related dietary factors and obe- intervention study. We used baseline data and examined cross-sectional associations between sity on the degree of insulin resistance. The carbohydrate-related dietary factors and an estimate of insulin resistance in 5,675 subjects at official carbohydrate-related recommen- 30–60 years. The dietary intake was estimated from a self-administered food frequency ques- dations are high intake of fiber-rich car- tionnaire, and insulin resistance was estimated using the homeostasis model assessment of bohydrates (Ͼ55 E% [energy percent] insulin resistance (HOMA-IR). Multiple regressions were performed with HOMA-IR as the carbohydrate, 25–35 g fiber), low con- dependent variable and carbohydrate-related factors as explanatory variables. All models were sumption of sugar (Ͻ10 E% sugar), and adjusted for age, sex, smoking, physical activity, total energy intake, BMI, and waist circumfer- ence. five to six servings of fruit and vegetables per day (5–7). No official recommenda- RESULTS — Intake of lactose was positively associated with HOMA-IR (P Ͻ 0.0001), tions exist regarding the glycemic index whereas daily glycemic load and intake of glucose, fructose, dietary fiber, total carbohydrate, and glycemic load of the diet. fruit, and vegetables were inversely associated with HOMA-IR (P Ͻ 0.05). Intake of dietary fiber One observational study involving explained the associations with daily glycemic load and total carbohydrate and attenuated the 2,834 subjects has examined the glycemic association with fruit and vegetables. No significant associations were observed for daily glyce- index and glycemic load of the diet in re- mic index or sucrose. lation to a measure of insulin resistance (8). This study suggests that diets with a CONCLUSIONS — Habitual intake of diets with a high glycemic index and high glycemic load or diets with a high content of total carbohydrate including simple sugars was not associated high glycemic index and glycemic load with the probability of having insulin resistance. Furthermore, intake of dietary fiber was in- are positively associated with the preva- versely associated with the probability of having insulin resistance. lence of insulin resistance. Few observa- tional studies have examined the intake of Diabetes Care 28:1397–1403, 2005 simple sugars in relation to insulin resis- tance, and in general no associations have been observed (9,10). Most observational studies have not found significant associ- ●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●● ations between intake of total carbohy- From the 1Steno Diabetes Center, Gentofte, Denmark; the 2Department of Human Nutrition, LMC Centre for drate and estimates of insulin resistance Advanced Food Studies, the Royal Veterinary and Agricultural University, Frederiksberg, Denmark; the (8,10–12). Observational studies have 3Research Centre for Prevention and Health, Glostrup, Denmark; and the 4Faculty of Health, University of Aarhus, Aarhus, Denmark. consistently suggested that foods rich in Address correspondence and reprint requests to Cathrine Lau, MSC, Steno Diabetes Center, Niels different types of dietary fiber are associ- Steensens Vej 2, DK-2820 Gentofte, Denmark. E-mail: [email protected]. ated with a reduced probability of devel- Received for publication 2 February 2005 and accepted in revised form 11 March 2005. oping insulin resistance (8,11,13–15). C.L. has received research support from the Danish Research Agency, Ministry of Science Technology and Whereas observational studies sug- Innovation. C.G., B.C., and K.B.-J. hold stock in and have received research support from Novo Nordisk. Abbreviations: 2-h PG, 2-h postchallenge plasma glucose; FFQ, food frequency questionnaire; FPG, gest that intake of dietary fiber has an fasting plasma glucose; HOMA-IR, homeostasis model assessment of insulin resistance. important role in determining insulin re- A table elsewhere in this issue shows conventional and Syste`me International (SI) units and conversion sistance, the precise nature of the relation- factors for many substances. ships between glycemic index, glycemic © 2005 by the American Diabetes Association. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby load, simple sugars, total carbohydrate, marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact. and insulin resistance is uncertain. The DIABETES CARE, VOLUME 28, NUMBER 6, JUNE 2005 1397 Carbohydrates and insulin resistance dietary recommendations given may All participants gave a written con- pleted in advance of the first visit. Based therefore not be in favor of the prevention sent before taking part in the Inter99 on answers about physical activity level of insulin resistance in particular. The in- study. The protocol was in accordance during work and leisure time (27), all in- fluence of carbohydrate-related dietary with the Helsinki Declaration and ap- dividuals were categorized as either being factors on insulin resistance thus needs proved by the local ethical committee. “physically active” or “physically inac- further attention. tive.” The group of “physically inactive” The purpose of the present study was Dietary data was either not physically active at work to examine the relationship between daily The participants completed a self- and during leisure time, only minor phys- glycemic index, daily glycemic load, sim- administered FFQ during their first visit ically active at work (sitting/walking) ple sugars, dietary fiber, and the preva- to the Research Centre. They were asked combined with no activity during leisure lence of insulin resistance estimated by to report their dietary intake during the time, or physically inactive at work com- the homeostasis model assessment of in- month before examination. The FFQ in- bined with minor activity during leisure sulin resistance (HOMA-IR) in 30- to 60- cluded 198 questions on food items and time (sitting/walking/cycling). Those cat- year-old nondiabetic Danish men and beverages with additional questions re- egorized as “physically active” did at least women participating in the Inter99 study. garding portion sizes of some selected minor physical activity both at work and food items. Where no portion size was during leisure or did moderate amounts RESEARCH DESIGN AND specified, a standard portion size for of physical activity at work (walking stair- METHODS — This study used base- women and men, respectively, was used ways/heavy work) or during leisure time line data from the Danish population– (19). The consumed quantity of food was (sport/competitive sport). based Inter99 study, which is an obtained by multiplying the portion size Smoking status was categorized as intervention study on diet, physical activ- with the corresponding consumption fre- “daily and occasional smokers,” “ex- ity, and smoking with the aim to decrease quency. All food items in the FFQ were smokers,” and “never-smokers.” Missing the incidence of cardiovascular diseases. linked to a food item in the Danish Food values of physical activity (n ϭ 65) and The overall aim, data collection methods, Composition Databank (20). The amount smoking status (n ϭ 41) were classified in and nondietary baseline results of the In- of macronutrients and simple sugars was separate categories and included in the ter99 study have been reported elsewhere calculated as energy percentages (E%). In analyses as such. (16,17). addition, the intake of total carbohydrate In 1999, the study population com- and simple sugars was calculated as grams Anthropometric data prised 61,301 individuals born in 1939– per day (g/day). The reported intake from Waist circumference was measured once 1940, 1944–1945, 1949–1950, 1954– dietary fiber, fruit, and vegetables was with a tape measure under the clothes and 1955, 1959–1960, 1964–1965, and also estimated in grams per day (g/day). A midway between the lowest point of the 1969–1970, resident in 11 municipalities detailed description of the questionnaire costal margin and highest point of the il- in the southwestern part of Copenhagen and estimation of the dietary intake of the iac crest with the participant in the stand- County. All individuals were drawn from population is published elsewhere (21). ing position. Weight was measured to the the Civil Registration System. An age- and The glycemic index for carbohydrate-