UK Trial Tests Low-Calorie Diets for Gestational Diabetes in Pregnancy

A study from the United Kingdom, led by researchers at the Institute of Metabolic Science, University of Cambridge, is investigating whether a carefully controlled reduced-calorie diet can improve health outcomes for pregnant women diagnosed with gestational diabetes mellitus (GDM). The DiGest trial — short for Dietary Intervention in Gestational diabetes — represents one of the most rigorous attempts yet to answer a question that affects hundreds of thousands of American pregnancies every year: what should a pregnant woman with GDM actually eat?

What the Study Is Testing

The trial enrolled 500 women in the UK who had been diagnosed with GDM and had a body mass index (BMI) of 25 kg/m² or higher — meaning they were overweight or obese. Starting at 28 weeks of pregnancy, participants were randomly assigned to one of two fully prepared meal-delivery plans: a standard diet of 2,000 calories per day, or a reduced-energy diet of 1,200 calories per day. Crucially, neither the women nor their caregivers knew which plan they were receiving — a design that helps eliminate bias.

Researchers tracked dietary compliance using food diaries, monitored blood sugar levels continuously, and measured weight changes throughout the remainder of each pregnancy. The primary goals were to assess whether the lower-calorie diet reduced infant birth weight and limited excessive maternal weight gain. Secondary outcomes included rates of cesarean section, large-for-gestational-age (LGA) babies, and the mother's blood glucose levels after delivery.

The Science Behind Modest Weight Loss in Pregnancy

Prior observational research has suggested that modest weight loss of approximately 1.3–4.4 lbs (0.6–2 kg) after 28 weeks of pregnancy may reduce the risk of cesarean delivery, LGA infants, and elevated postpartum blood sugar. However, intentional caloric restriction during pregnancy has historically been approached with caution. This trial, using a fully controlled food-delivery method, is designed to test whether a structured reduction is both safe and effective.

Why This Matters for US Patients

Gestational diabetes affects approximately 6–9% of pregnancies in the United States — roughly 240,000 to 300,000 cases annually — making it one of the most common pregnancy complications American women face. Despite this prevalence, clear dietary guidelines specifically tailored to GDM patients who are also overweight or obese remain limited in the US. The American College of Obstetricians and Gynecologists (ACOG) provides general nutritional guidance, but stops short of prescribing specific caloric targets for this population.

The UK uses NICE (National Institute for Health and Care Excellence) diagnostic criteria for GDM, which differ slightly from the two most common US diagnostic thresholds (Carpenter-Coustan and IADPSG criteria). This means some women diagnosed in the UK might not be flagged in certain US clinical settings — an important nuance for American patients to discuss with their providers.

Results from the DiGest trial could directly inform future US dietary protocols for GDM management, potentially giving American ob-gyns a stronger evidence base for recommending structured meal plans during pregnancy.

What to Ask Your Doctor

If you have been diagnosed with GDM and are overweight or obese, ask your healthcare provider whether a structured, calorie-monitored meal plan might be appropriate for your pregnancy. Do not attempt to restrict calories during pregnancy without medical supervision.

Source: Kusinski, Murphy, De Lucia Rolfe. "Dietary Intervention in Pregnant Women with Gestational Diabetes; Protocol for the DiGest Randomised Controlled Trial." Nutrients, 2020. PMID: 32331244. DOI: 10.3390/nu12041165