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Competing Interests: Competing interests: We have read and understood BMJ policy on declaration of interests and declare the following interests: DSL received research grants (to Boston Children’s Hospital) from the National Institutes of Health, Nutrition Science Initiative, the Laura and John Arnold Foundation and other philanthropic organisations unaffiliated with the food industry; and received royalties for books on obesity and nutrition that recommend a low glycaemic load diet. FBH received research support from California Walnut Commission and lecture fees from Metagenics. LT received grants (to University of Lausanne) from the Swiss National Science Foundation from the Swiss Federal Bureau for Sport, and research support from Sorematec Italy (to Hôpital Intercantonal de la Broye) for a clinical trial related to physical activity in the treatment of patients with the metabolic syndrome; and received speakers fees from the Gatorade Sport Science Institute, Soremartec Italy, and Nestlé SA. JBM received research grants from the Australian National Health and Medical Research Council, the European Union, the Glycemic Index Foundation; and received royalties for books on nutrition that recommend a low glycaemic index diet. She oversees a glycaemic index testing service at the University of Sydney and is president and non-executive director of the Glycemic Index Foundation. Provenance and peer review: Commissioned; externally peer reviewed.

Objective: To determine whether higher intake of baked or boiled potatoes, French fries, or potato chips is associated with incidence of hypertension., Design: Prospective longitudinal cohort studies., Setting: Healthcare providers in the United States., Participants: 62 175 women in Nurses' Health Study, 88 475 women in Nurses' Health Study II, and 36 803 men in Health Professionals Follow-up Study who were non-hypertensive at baseline., Main Outcome Measure: Incident cases of hypertension (self reported diagnosis by healthcare provider)., Results: Compared with consumption of less than one serving a month, the random effects pooled hazard ratios for four or more servings a week were 1.11 (95% confidence interval 0.96 to 1.28; P for trend=0.05) for baked, boiled, or mashed potatoes, 1.17 (1.07 to 1.27; P for trend=0.001) for French fries, and 0.97 (0.87 to 1.08; P for trend=0.98) for potato chips. In substitution analyses, replacing one serving a day of baked, boiled, or mashed potatoes with one serving a day of non-starchy vegetables was associated with decreased risk of hypertension (hazard ratio 0.93, 0.89 to 0.96)., Conclusion: Higher intake of baked, boiled, or mashed potatoes and French fries was independently and prospectively associated with an increased risk of developing hypertension in three large cohorts of adult men and women., (Published by the BMJ Publishing Group Limited. For permission to use (where not already granted under a licence) please go to http://group.bmj.com/group/rights-licensing/permissions.)

Objective: To determine if a low glycaemic index diet in pregnancy could reduce the incidence of macrosomia in an at risk group., Design: Randomised controlled trial., Setting: Maternity hospital in Dublin, Ireland., Participants: 800 women without diabetes, all in their second pregnancy between January 2007 to January 2011, having previously delivered an infant weighing greater than 4 kg., Intervention: Women were randomised to receive no dietary intervention or start on a low glycaemic index diet from early pregnancy., Main Outcomes: The primary outcome measure was difference in birth weight. The secondary outcome measure was difference in gestational weight gain., Results: No significant difference was seen between the two groups in absolute birth weight, birthweight centile, or ponderal index. Significantly less gestational weight gain occurred in women in the intervention arm (12.2 v 13.7 kg; mean difference -1.3, 95% confidence interval -2.4 to -0.2; P=0.01). The rate of glucose intolerance was also lower in the intervention arm: 21% (67/320) compared with 28% (100/352) of controls had a fasting glucose of 5.1 mmol/L or greater or a 1 hour glucose challenge test result of greater than 7.8 mmol/L (P=0.02)., Conclusion: A low glycaemic index diet in pregnancy did not reduce the incidence of large for gestational age infants in a group at risk of fetal macrosomia. It did, however, have a significant positive effect on gestational weight gain and maternal glucose intolerance., Trial Registration: Current Controlled Trials ISRCTN54392969.

Objective: To study different nutrients and food additives as risk factors for insulin dependent diabetes mellitus in childhood., Design: Prospective case-control study. Parents of the children being studied were asked to fill in a questionnaire regarding the children's frequency of consumption of various foods. Parents of children with diabetes were asked about the period before onset of the disease., Setting: Population based study throughout Sweden., Subjects: 339 Children aged 0-14 who had recently developed insulin dependent diabetes mellitus and 528 control children matched for age, sex, and county of residence who were traced through the official Swedish population register., Main Outcome Measures: Foods were classified according to their content of protein, fat, carbohydrates, monosaccharides or disaccharides, nitrosamines, nitrates or nitrites, vitamin C, and fibres. The frequency of intake was categorised as high, medium, and low and the relative risk for developing insulin dependent diabetes was estimated for the three frequencies of intake and calculated as odds ratios., Results: Significant linear trends for dose response in odds ratios by frequency of intake were shown for solid foods containing high amounts of protein (odds ratio for low frequency of intake 1.0; medium 2.3; and high 5.5), and nitrosamines (1.0; 1.7; 2.6) and significant but non-linear trends were found for carbohydrates (1.0; 1.3; 4.4) and nitrates or nitrites (1.0; 0.8; 2.4). The significant trends were not affected when the results were standardised for possible confounders. No significant increases in odds ratios were found for protein, monosaccharides and disaccharides, vitamin C, and fibres., Conclusion: Nutrients and food additives such as protein, carbohydrate, and nitrosamine compounds may influence the risk of developing insulin dependent diabetes in childhood and significant trends in odds ratios indicate a causal relation.