Carbohydrate restriction in midlife is associated with higher risk of type 2 diabetes among Australian women: A cohort study
Authors: Ellie D&#x27;Arcy
Allison Hodge
Jessica Rayner
Lynda J Ross
Danielle A J M Schoenaker
Journal: Nutrition Metabolism and Cardiovascular Diseases (2020)
Discipline: CLINICAL MEDICINE
Keywords: Carbohydrates; Cohort study; Gestational diabetes; Nutrition; Type 2 diabetes.
Affiliations: Nutrition and Dietetics, School of Allied Health, Griffith University, Queensland, Australia., Nutrition and Dietetics, School of Allied Health, Griffith University, Queensland, Australia; Integrated Primary Care and Partnerships, Western New South Wales Local Health District, NSW, Australia., Cancer Epidemiology Division, Cancer Council Victoria, Melbourne, Victoria, Australia; Centre for Epidemiology and Biostatistics, Melbourne School of Population and Global Health, University of Melbourne, Parkville, Victoria, Australia., School of Medicine, Faculty of Science, Medicine and Health, and Illawarra Health and Medical Research Institute, University of Wollongong, Wollongong, NSW, Australia; The Robinson Research Institute and Discipline of Obstetrics and Gynaecology, University of Adelaide, Adelaide, South Australia, Australia; Centre for Behavioural Research in Cancer, Cancer Council Victoria, Melbourne, Victoria, Australia. Electronic address: .

Abstract:  Background and aims: Low-carbohydrate diets (LCDs) are increasingly popular but may be nutritionally inadequate. We aimed to examine if carbohydrate restriction in midlife is associated with risk of developing type 2 diabetes (T2DM), and if this association differs by previous gestational diabetes (GDM) diagnosis. Methods and results: Dietary intake was assessed for 9689 women from the Australian Longitudinal Study on Women's Health in 2001 (aged 50-55) and 2013 (aged 62-67) via validated food frequency questionnaires. Average long-term carbohydrate restriction was assessed using a low-carbohydrate diet score (highest quartile (Q4) indicating lowest proportion of energy from carbohydrates). Incidence of T2DM between 2001 and 2016 was self-reported at 3-yearly surveys. Log-binomial regression was used to estimate relative risks (RR) and 95% CIs. During 15 years of follow-up, 959 women (9.9%) developed T2DM. Carbohydrate restriction was associated with T2DM after adjustment for sociodemographic factors, history of GDM diagnosis and physical activity (Q4 vs Q1: RR 1.27 [95% CI 1.10, 1.48]), and this was attenuated when additionally adjusted for BMI (1.10 [0.95, 1.27]). Carbohydrate restriction was associated with lower consumption of fruit, cereals and high-fibre bread, and lower intakes of these food groups were associated with higher T2DM risk. Associations did not differ by history of GDM (P for interaction &gt;0.15). Conclusion: Carbohydrate restriction was associated with higher T2DM incidence in middle-aged women, regardless of GDM history. Health professionals should advise women to avoid LCDs that are low in fruit and grains, and to consume a diet in line with current dietary recommendations. 

Retracted: No

PubPeer comments:
 This paper raises some questions. Firstly, the strong conclusion: Carbohydrate restriction was associated with higher T2DM incidence in middle-aged women, regardless of GDM history. In fact, the carbohydrate intake in the high -LCD score quartile, 36.5% of energy, with 60 grams of that from sugar, does not describe any low carbohydrate diet recommended in medicine or popular culture, and this discrepancy is not noted by the authors. Low carbohydrate diets were not popular in Australia prior to 2013, and very few if any women following this dietary pattern would have been included in the study. Under such conditions, there is a risk of the LCD score indicating a preference for deep-fried food instead. Secondly, the LCD score is not associated with T2DM once adjusted for BMI - 1.10 (0.95, 1.27). The p-value is 0.03, but this needs be interpreted cautiously in light of the wide 95% confidence interval and the known unreliability of food frequency questionnaires, for which no validation coefficients have been supplied. Because there is a much higher % of obese subjects in the high LCD score category, which would argue for bias by indication if any were actually following a low-carbohydrate diet, this step of the adjustment is critical. The title of this paper should not have claimed an association. Thirdly, not one of the citations is an RCT of low-carbohydrate diet for glycemic control or of carbohydrate restriction (low GI diet, can be as low as 140g carbohydrate day in RCTs) for gestational diabetes. Yet such gold standard evidence has not shown that any of the harms from carbohydrate restriction which the less robust LCD score epidemiology has claimed will result. So why did the authors not include this evidence of benefit and discuss a  paradox , which would have been a more intellectually honest way of proceeding on the question? There is not one sentence in the paper which I can quote as evidence that the authors are aware of the medical indications for carbohydrate restriction in diabetes, gestational diabetes, or pre-diabetes. This is a striking omission and imbalance Fourthly, and most importantly, there are indeed significant correlations between foods and the risk of T2DM in this paper. White bread, consumers vs non-consumers - 1.37 (1.22, 1.53). As the strongest association in the paper, this should have been in the abstract. Instead the conclusion states  Women should be advised to avoid carbohydrate restricted diets low in fruit and grains yet white bread is a grain, and low carbohydrate fruits are available (tomato, zucchini, bean pod, olive, avocado, berries) - would eating these increase diabetes risk? As usual, the LCD score is not transparent, but we know from other papers of this type that fat and protein are given the same value, yet alcohol, a non-carbohydrate food that tends to displace carbohydrate in the diet, and one which is even harder to recall accurately than food, is not included. Fat is not a physiological facsimile of protein, and the LCD score thus lacks a physiological basis. ,