‘Pivotal’ study finds benefits of reduced calorie diet for pregnant women with gestational diabetes
Clodie Rolph was diagnosed with gestational diabetes just before her third trimester.
New research from the University of Leicester has found following a reduced calorie diet during the third trimester of pregnancy is safe and beneficial for pregnant women with a body mass index (BMI) of over 25 kg/m2 who have gestational diabetes.
The findings lay the foundation for a new clinical approach that could help thousands of women with gestational diabetes make dietary changes that could help them avoid the challenges of insulin treatment and improve health outcomes.
Published today in Nature Medicine, the study will be presented at the Diabetes UK Professional Conference 2025 in Glasgow. The Dietary Intervention in Gestational Diabetes (DiGest) trial was funded by Diabetes UK and led by researchers at the Universities of Leicester and Cambridge.
Gestational diabetes is a type of diabetes that develops in pregnancy, affecting between 10 to 20% of pregnancies in the UK1. It develops when pregnancy hormones impact the body’s ability to use insulin properly, causing blood sugar to rise to dangerously high levels.
Senior postdoctoral scientist at the University of Leicester, Dr Laura Kusinski, who coordinated the research project said: "While most women with gestational diabetes will have a healthy baby, it can – if left untreated – cause serious health problems for both mother and baby. Babies may grow larger than normal, which can lead to a difficult birth. Women with gestational diabetes are more likely to develop preeclampsia, and around 50% of women will go on to develop type 2 diabetes within five years.”
Risk factors for gestational diabetes include living with overweight or obesity, having a family history of type 2 diabetes, and being from a South Asian, Black or African Caribbean or Middle Eastern background.
It is normal and healthy to gain weight during pregnancy to support the baby’s growth and development, but gaining too much weight can carry risks. Currently, women diagnosed with gestational diabetes receive nutritional advice, but until now, little evidence has existed about appropriate calorie intake for affected women.
In the new study, 425 pregnant women with gestational diabetes and a BMI over 25 kg/m2 tested two different diets from 29 weeks of pregnancy until delivery. One group received a standard healthy, balanced diet including 2,000 kcal per day (control group) and the other group received a nutritionally complete diet including 1,200 kcal per day (reduced calorie group).
Participants received weekly diet boxes containing breakfasts, lunches, dinners and snacks. Each participant’s weight, blood glucose levels and requirement for insulin were monitored closely, as was the health of both mum and baby.
Clodie Rolph, 42, from Suffolk, was diagnosed with gestational diabetes just before her third trimester and was invited to take part in the DiGest trial. She said: “I was really surprised, and a little upset, when I found out I had gestational diabetes. Taking part in the DiGest study has had a really positive impact on my health and I’m so grateful to have been given the opportunity. It was easy to do, I really enjoyed the food and it helped manage my weight over the last trimester of pregnancy. Although challenging at times, all the extra monitoring, eating healthier and being more active was worth it to have a happy, healthy baby girl.”
The trial confirmed that consuming a reduced calorie diet during the third trimester of pregnancy did not pose any health risks and was safe for women with gestational diabetes and their babies.
Across both the control and reduced calorie diet groups, women lost an average of 3kg during the third trimester of pregnancy. While there was no difference in weight loss between the groups during this period, women on the reduced calorie diet were less likely to need insulin treatment to manage their blood sugar levels compared to those in the control group.
Those who lost weight had lower blood sugar levels and improved blood pressure at 36 weeks of pregnancy. Weight loss was also associated with a nearly 50% lower risk of delivering a large baby, which could lead to lifelong benefits for the next generation, reducing babies’ future risk of developing obesity and type 2 diabetes.
The team continued to monitor women for three months after they had given birth. They found those who had lost weight in late pregnancy maintained their weight loss and had improved blood sugar levels, which could help to reduce their heightened risk of type 2 diabetes.
Claire Meek, Professor of Chemical Pathology and Diabetes in Pregnancy at the University of Leicester, who led the study, said: “We know that reduced calorie diets promote weight loss and improve blood sugar levels for people with type 2 diabetes, but this has never before been tested as a way to help women with gestational diabetes minimise weight gain.
“The safety of mothers and babies taking part in our research is my top priority, and most importantly we found that the reduced calorie diet box was perfectly safe for pregnant women with gestational diabetes and overweight or obesity, and their babies. Women on the reduced calorie diet were less likely to need insulin treatment compared to those in the control group, suggesting that their blood sugar levels had been more stable.
“If we used a reduced calorie diet for this group nationally, we predict one in eight women with gestational diabetes could reduce their need for insulin, which we estimate could benefit up to 13,000 women every year.”
Dr Elizabeth Robertson, Director of Research and Clinical at Diabetes UK, said: “Gestational diabetes touches the lives of thousands of women in the UK each year. If left untreated, it increases the risk of poor health for them and their baby not only during pregnancy but over their lifetimes too.
“We’re proud to have funded this pivotal research that addresses a critical missing piece in our understanding of how to safely treat gestational diabetes with dietary changes. With this new understanding, we have the opportunity to help more mothers experience a healthy pregnancy, give birth to healthy babies, and reduce their risk of type 2 diabetes in the future."