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You've heard a lot about the benefits of eating fruits and vegetables, but did you know that a diet rich in these natural foods can be key to having a healthy pregnancy?
In a study published in July 2019 in the peer-reviewed International Journal for Vitamin and Nutrition Research, a multi-disciplinary team of scientists in Tehran, Iran, investigated the association of consuming fruits, vegetables and dairy products with instances of gestational diabetes mellitus (GDM) in pregnant women.
Gestational diabetes is a condition that afflicts women during pregnancy who did not have diabetes before becoming pregnant. GDM typically onsets around the middle of the pregnancy term, between 24 and 28 weeks, and can recur during subsequent pregnancies.[i] Doctors will often recommend eating a balanced diet and getting regular exercise to control GDM, although some women also require insulin to manage the condition.
This prospective study was conducted over a period of 17 months on a random sample of pregnant women between 18 and 45 years of age who were in the first half of their pregnancies and who had agreed to attend prenatal clinics in any of five hospitals affiliated with universities of medical sciences in different districts of Tehran, Iran.
Participants' dietary intakes were assessed during the 6th week of pregnancy using a 168-item, validated, semi-quantitative food frequency questionnaire. Between 24 and 28 weeks of gestation, all participants underwent a scheduled oral glucose tolerance test to determine whether or not they had gestational diabetes mellitus. Diagnosis of GDM was based on criteria set by the American Diabetes Association.
Eating More Fruits and Veggies Lowers Gestational Diabetes Risk
Of 1,026 study participants, 71 tested positive for gestational diabetes mellitus. Based on results of BMI (body-mass index) tests and the results of the food questionnaires, researchers determined that a diet high in fruit and vegetable intake was "significantly and inversely associated with GDM risk."
Women who consumed 2.1 servings per day or less had significantly higher odds ratio for GDM than those who consumed at least 4.9 servings per day, after adjustment for confounding factors. No association was found between dairy products and GDM. Researchers concluded that fruit and vegetable consumption in women of reproductive age has beneficial effects in the prevention of GDM.[ii]
Other studies have produced similar findings. A prospective cohort study published in November 2018 followed 1,337 pregnant women in Western China, assessing dietary intakes at 15 to 20 weeks of gestation with a validated food frequency questionnaire and determining GDM with oral glucose tolerance tests at 24 to28 weeks of gestation.
A total of 199 women, 14.9% of participants, developed GDM. Exploratory factor analysis was performed to derive dietary patterns, three of which were identified: a plant-based pattern, a meat-based pattern and a high protein-low starch pattern. At the end of the study, researchers determined that there was no significant association between early pregnancy dietary patterns and GDM risk later in pregnancy, but a high protein-low starch diet was associated with lower risk for GDM among women who were overweight pre-pregnancy.[iii]
In addition to the increased risk of recurring GDM in subsequent pregnancies, women with prior gestational diabetes mellitus are at higher risk of developing Type 2 diabetes. A March 2019 study published in the European Journal of Nutrition explored associations between dietary intake of fruits and vegetables and abnormal glucose tolerance among women with prior gestational diabetes mellitus.
In this Canadian cohort study, a total of 281 women with prior GDM were recruited around six years after their pregnancy. Dietary intake was obtained with a validated food frequency questionnaire, and anthropometric measurements such as height, weight and BMI were measured along with glycemic components, during a clinical visit. These readings allowed researchers to stratify the women according to normal glucose tolerance or abnormal glucose tolerance, a significant factor in the development of Type 2 diabetes.
Results of the study were determined via a cross-sectional analysis, showing that of the 281 participants, a total of 155 women had normal glucose tolerance and 126 had abnormal glucose tolerance. Women with abnormal glucose tolerance had significantly less fruits and vegetables in their diets and tended to have lower fruit servings than women with normal glucose tolerance.
To illustrate the big difference a small dietary improvement can make, a single serving increase of fruits and vegetables was associated with a reduced likelihood of having abnormal glucose tolerance. Researchers concluded that higher intake of fruits and vegetables in the diet may be associated with a lower likelihood of abnormal glucose tolerance and decreased risk of developing Type 2 diabetes among women with prior gestational diabetes mellitus.[iv]
Leafy Greens and Dark Yellow Vegetables Lower Diabetes Risk
Researchers from Harvard and the U.S. Centers for Disease Control and Prevention partnered to explore the dietary connection between fruit and vegetable intake and women at risk of Type 2 diabetes, once referred to as adult-onset diabetes but now occurring more frequently in children as well.
In the 2004 study chaired by Brigham and Women's Hospital at Harvard Medical School in Boston, Massachusetts, researchers analyzed prospective data from the Women's Health Study (WHS) taken from 1993 to 2003, to evaluate the hypothesis that a high intake of fruits and vegetables protects against onset of Type 2 diabetes and to explore whether specific subgroups of fruits and vegetables differentially affect diabetes risk.
The WHS comprised 39,876 female health professionals who were at least 45 years of age and who were free of heart disease, stroke or cancer at the time of the study and who had not been previously diagnosed with diabetes. Detailed diet information was provided by 38,018 (95%) of participants who completed a 131-item semiquantitative food frequency questionnaire, which included 28 vegetables and 16 fruit types.
Participants were asked to accurately reflect their long-term dietary intake as a way of establishing good validity to the data. Average daily intakes of individual fruits and vegetables were calculated by multiplying intake frequency by portion size, with total intake computed by summing the intake of individual items.
Vegetables were divided into groups, including cruciferous (broccoli, cabbage, cauliflower, Brussels sprouts), dark yellow (carrots, yellow squash, yams, sweet potatoes), green leafy (spinach, kale, lettuce), and other (corn, mixed vegetables, celery, eggplant, mushrooms, and beets). Diagnosis of Type 2 diabetes was based on self-reports, the validity of which was confirmed according to the American Diabetes Association diagnostic criteria. Analytical models were adjusted for age, total calories and smoking, and follow-up was conducted for an average of 8.8 years.
Results showed a "significant inverse relationship with diabetes risk and total fruit and vegetable intake," further supporting the findings of similar studies. It is important to note that not all fruits and vegetables were equal in terms of positive health impact. Of the specific foods studied, intake of green leafy and dark yellow vegetables was significantly associated with reduced risk of Type 2 diabetes, while starchy vegetables such as potatoes showed a significant positive association with Type 2 diabetes risk.[v]
[i] CDC.gov, Pregnancy, During pregnancy, Diabetes, Gestational, https://www.cdc.gov/pregnancy/diabetes-gestational.html
[ii] Inverse relation between fruit and vegetable intake and the risk of gestational diabetes mellitus. Mirmiran P, Hosseinpour-Niazi S, Moghaddam-Banaem L, Lamyian M, Goshtasebi A, Azizi F. Int J Vitam Nutr Res. 2019 Jul;89(1-2):37-44. PMID: 31188080
[iii] Dietary patterns during pregnancy and risk of gestational diabetes: a prospective cohort study in Western China. Mak, J.K.L., Pham, N.M., Lee, A.H. et al. Nutr J 17, 107 (2018) doi: 10.1186/s12937-018-0413-3
[iv] Associations between fruit and vegetables intake and abnormal glucose tolerance among women with prior gestational diabetes mellitus. Mercier R, Perron J, Weisnagel SJ, Robitaille J. Eur J Nutr. 2019 Mar;58(2):689-696. PMID: 29569007
[v] A Prospective Study of Fruit and Vegetable Intake and the Risk of Type 2 Diabetes in Women. Simin Liu, Mary Serdula, Sok-Ja Janket, Nancy R. Cook, Howard D. Sesso, Walter C. Willett, JoAnn E. Manson, Julie E. Buring. Diabetes Care Dec 2004, 27 (12) 2993-2996; DOI: 10.2337/diacare.27.12.2993