Can the consumption of colorful fruits and vegetables improve the management of gestational diabetes?

By Dr. Liji Thomas, MDReviewed by Lily Ramsey, LLMSep 1 2023

Gestational diabetes mellitus (GDM) is becoming a common pregnancy complication worldwide. Its management has been the focus of much research.

A new paper from the University of Nevada, published in the Nutrients Journal, explores the dietary effects of consuming colorful fruits and vegetables (CFV).

Study: Effects of an Eating Pattern Including Colorful Fruits and Vegetables on Management of Gestational Diabetes: A Randomized Controlled Trial. Image Credit: monticello/Shutterstock.com

Introduction

GDM typically begins in the second or third trimester of pregnancy and affects up to a tenth of pregnancies in the USA. The consequences are due to the abnormal metabolic pathways triggered by hyperglycemia.

They include maternal hypertension and pre-eclampsia, with accompanying fetal growth restriction in many cases.

The insulin resistance in the mother can also affect the pancreatic development and function in the fetus, causing neonatal hypoglycemia. Macrosomia, or large babies, may occur in poorly controlled GDM, with an increased risk of birth complications such as shoulder dystocia or Cesarean section.

Long-term complications are also known to occur, such as type 2 diabetes mellitus in the adult offspring. Thus, good glucose control is essential in GDM.

Most efforts to control the blood glucose center on insulin and metformin, with lifestyle counseling based on dietary modifications and physical activity. These increase insulin sensitivity, thus improving glucose uptake by the peripheral tissues, especially skeletal muscle, following exercise.

The importance of lifestyle counseling extends to reducing the need for strict dietary control, besides promoting cheaper and easier changes without side effects. Moreover, they can be continued indefinitely to promote long-term health.

Prior research has indicated a link between dietary changes that lower carbohydrate intake and increase vegetable protein consumption and the risk of GDM.

Fresh fruit intake is also associated with a lower GDM risk. Whole berries and raw vegetables have specifically been linked to better glycemic control in non-pregnant diabetic individuals.

This may be traced to the presence of high amounts of plant polyphenols that positively affect the insulin-mediated metabolic pathways, enhancing glucose uptake and reducing hyperglycemia.

This effect is expected to be observed in pregnant diabetics as well. Moreover, their potential efficacy in treating and preventing GDM is an important research focus.

The current study, therefore, took the form of a randomized controlled trial (RCT) based on both exercise and the incorporation of berries and leafy vegetables into the diet of women with GDM. The outcome was a better cardiometabolic profile.

What did the study show?

The trial was conducted at the UNLV School of Medicine Maternal Fetal Medicine Clinic at Sunrise Hospital in Las Vegas, Nevada.

All 38 women in the trial were 18-45 years old, Hispanic, and at 24-28 weeks of gestation, with a history of hyperglycemia and a diagnosis of type 2 or gestational diabetes mellitus before the current pregnancy. All had singleton pregnancies.

None were smokers or used alcohol, and no lactating mothers were included.

The study used two approaches, one based on dietary education and the other on dietary intervention. The first group was counseled about healthy food choices per the USDA (US Dietary Allowances) guidelines.

The second group was asked to ingest one cup of whole berries and one cup of leafy vegetables daily and to walk for 15-30 minutes after each meal. The berries and vegetables were to be eaten in whole form rather than blended or juiced.

Both were asked to keep a food diary for three days a week. The study continued until the second visit at 38-40 weeks.

The results showed that the second group consumed more vegetables and fruits but did not become significantly more physically active.

Vegetable and fruit intake met 57% of their recommended dietary allowance (RDA) vs. 44% in the first group. Breaking this down, the nutritional intervention group met 68% and 57% of their fruit and vegetable intake, respectively, compared to the control group's performance of 50% and 44% RDA, respectively.

They also consumed more fiber (23 vs. 15 g/day on average. Higher fiber intake in the second trimester is linked to a markedly better control of blood glucose, and this is also the point at which GDM is typically diagnosed.

In addition, it reduces blood lipids and glycosylated hemoglobin levels, thus improving the prognosis of this condition.

They achieved better control of blood glucose levels, with the random (postprandial) blood glucose concentration being, on average, 112 vs. 128 mg/dL at 38-40 weeks in the second vs. the first group, respectively.

This is of clinical relevance as it has been shown in other research to be linked to a lower risk of future type 2 diabetes and the risk of future cardiovascular disease (CVD) in diabetes.

Oxidative stress is linked to the development of GDM. The intervention group had a higher antioxidant intake and greater total serum antioxidant capacity.

The flavonoid intake was increased in the second group due to the rich concentration of these compounds in berries and leafy vegetables (62 vs. 45 g/day in the intervention vs. control group, respectively). Flavonoids are associated with antioxidant and anti-inflammatory effects in large concentrations.

The intervention group showed lower inflammation levels, as signaled by their serum interleukin-6 (IL-6) levels (26 vs. 35 in the intervention vs. control group, respectively).

IL-6 is involved in the GDM disease process as it promotes inflammation, leading to endothelial dysfunction and insulin resistance. The reduction in IL-6 may thus reflect better insulin sensitivity in these GDM patients associated with higher flavonoid consumption.

In the control group, their 'good cholesterol' (HDL, high-density lipoprotein) levels also improved to 51 mg/dL, vs 43 mg/dL.

Earlier research linked flavonoids to improvements in other cardiometabolic markers in diabetes, including HDL, insulin, and postprandial glucose levels.

What are the implications?

There is little evidence to support nutritional guidelines in GDM treatment, as most research focuses on its prevention. The current study is thus unique in its scope, and the positive findings assume greater significance in the light of its population.

This consisted wholly of Hispanic women, among the groups at highest risk for GDM and its complications, suggesting that the study findings could benefit women at greatest risk.

The findings of this RCT strongly indicate an improvement in dietary composition and cardiometabolic risk in pregnant diabetics with the single addition of whole berries and green leafy vegetables in specified quantities to the diet.

This was despite the lack of significantly more exercise in the intervention group, even though they had been instructed to walk for 15-30 minutes after each meal.

This indicates that the differences in metabolic and dietary profiles in this trial are due to dietary intervention alone. This finding may be firmly established as a causative association due to the RCT design.

The results also suggest that whole berries and leafy vegetables might directly alter metabolic pathways fundamental to GDM.

The control group received the standard counseling provided as part of prenatal care but with significantly less success, showing that nutritional intervention is far more effective when it provides evidence-based specific guidance.

"Given the significance of these findings and the relative ease of [the intervention], whole berry and leafy vegetable supplementation must be incorporated in the clinical management of newly diagnosed gestational diabetes patients."