Gestational Diabetes, a Common Pregnancy Complication

Gestational Diabetes Mellitus (GDM) is usually defined as glucose intolerance with onset or first recognition in pregnancy. It is a common pregnancy complication that affects between 1–14% of all pregnancies1. The incidence of GDM is increasing worldwide, with the increasing burden of obesity among women of reproductive age. GDM has been related to substantial adverse health outcomes for both mothers and offspring and the impact of GDM goes beyond pregnancy. Women with GDM have an increased risk of perinatal morbidity and a considerably increased risk of impaired glucose tolerance and type 2 diabetes in the years after pregnancy. Children of women with GDM are more likely to be obese and have impaired glucose tolerance and diabetes in childhood and early adulthood. Collectively, this information highlights the importance of identifying modifiable factors for this common pregnancy complication, and of preventing GDM among high-risk populations^1,2.

Fruits: Rich in Antioxidant but also Rich in Sugar!

Fruits are major sources of certain nutrients such as vitamin C, flavonoids, magnesium, and fibre. Fruits have high antioxidant and fibre content as well as relatively low energy density and low glycemic load. In addition, fruits contain numerous bioactive components, such as vitamins, minerals, carotenoids, folates, flavonoids, and polyphenol, which have been suggested to be beneficial in insulin sensitivity and/or pancreatic β-cell function by relieving oxidative stress³.

On the other hand, fruits have relatively high sugar (i.e. fructose) content and thus there is some concern that high consumption of fruits may increase the risk of diabetes. Epidemiological data on habitual fruit intake and diabetes risk among pregnant women are scant. Fruit juices (100% juice) are conventionally considered as healthy and nutritious beverages. However, the relatively high sugar content and low fibre in fruit juices have raised concerns about high consumption during pregnancy. Studies on the association of fruit juices with GDM risk are lacking. In addition, nutrient components and antioxidant profiles of fruit varies by type. Therefore, different fruits and fruit juices may have different health effects. Thus studies on the associations of specific types of fruit with health outcomes are also needed.

Apple Consumption Reduces Risk of GDM

In a recent study based on a large prospective cohort of U.S. women², the Nurses’ Health Study II, we assessed the association of pre-pregnancy habitual consumption of fruit, fruit juices and their subgroups with GDM risk. In general, we observed that habitual high consumption of fruits in total before pregnancy was not associated with increased GDM risk. Among specific fruits, higher apple consumption (>1/day) was associated with a modestly reduced risk of GDM. The finding of an inverse association between apple intake and GDM risk is consistent with two studies on apples and type 2 diabetes risk^4,5. Apples provide a low glycemic index source of carbohydrate, and are a major source of flavonoids. However, in the current study, the association of apple intake with GDM remained significant after the adjustment of flavonoid intakes. We speculate that other polyphenolic compounds (i.e., catechins), antioxidants (i.e., vitamin C and β-carotene), or unidentified dietary factors in apples, individually or in combination, may contribute to the potentially protective effects of apples on GDM risk².

For Fruit Juices, We Cannot Conclude

The association of total fruit juices with GDM risk was nonlinear, with the lowest risk being among women in the 3^rd quintile of consumption (~half serving/day). The interpretation of this nonlinear association needs to be cautious. On one hand, vitamins, minerals, and phytochemicals in fruit juices may have beneficial effects for diabetes. On the other hand, fruit juices have lower fibre contents and higher glycemic load than whole fruit. At a moderate level of consumption, the beneficial effects from some components (i.e., vitamins and minerals) may counterbalance the potential adverse effects of the rapidly absorbed sugars. In this study, however, we were unable to completely rule out residual confounding from some unmeasured health behaviors associated with moderate fruit juice consumption².

Our data suggest that pre-pregnancy higher consumption of whole fruits in total is not associated with increased GDM risk. There is some evidence that suggested a lower risk of GDM associated with higher apple consumption (>1/day). The association of fruit juices with GDM risk appears to be nonlinear, with the lowest risk being among women with modest consumption. Further studies are warranted to confirm our observation.