The effect of bedtime snacks on morning fasting blood glucose in gestational diabetes mellitus: a randomized controlled trial.

TL;DR

A randomized controlled trial found that eating 25g of nuts before bed did not reduce fasting blood glucose or morning hyperglycemia in women with gestational diabetes, and may have worsened post-meal glucose spikes and lipid levels .

What the study found

Current clinical guidelines often recommend bedtime snacks for pregnant women with gestational diabetes mellitus (GDM) to prevent overnight glucose drops and morning hyperglycemia. The reasoning is intuitive: a snack should stabilize blood sugar overnight. But supporting evidence has been thin. This new study from Ma'anshan Maternal and Child Health Care Center in China directly tested this assumption in 62 women diagnosed with GDM.

Researchers randomly assigned women to either eat 25 grams of nuts at bedtime for 8 weeks or eat nothing. Throughout the intervention, women tested their fasting blood glucose three times per week using home glucose meters. They also measured post-meal glucose levels twice weekly and had labs drawn around week 34 of pregnancy to assess glycated hemoglobin, cholesterol, and triglycerides. The primary question was simple: does the bedtime snack reduce fasting blood glucose levels or the incidence of high morning glucose?

The answer was no. After adjusting for factors like pre-pregnancy weight, mid-pregnancy glucose, and diet, the snack group had essentially identical fasting glucose levels compared to the control group (4.96 mmol/L versus 4.90 mmol/L; the difference was not statistically significant). The proportion of women experiencing elevated fasting glucose was also similar between groups (26% versus 19%, p=0.335). This finding directly contradicts the presumed benefit behind current recommendations.

But there were additional concerns. Women in the snack group had significantly higher low-density lipoprotein (LDL) cholesterol in late pregnancy (3.21 mmol/L versus 2.52 mmol/L), suggesting the nuts worsened lipid profiles. Post-hoc analysis also revealed that elevated 1-hour postprandial glucose, the glucose spike that occurs after eating, was more common in the snack group (42% versus 28%). Birth outcomes, including birth weight and delivery timing, showed no differences between groups. The researchers concluded that bedtime snacking should not be recommended as a glycemic control strategy in GDM.

What this means for you

If you have gestational diabetes, this study suggests that following the conventional advice to eat a bedtime snack may not help and could potentially backfire. The snack did not prevent morning high blood sugar, which was the original justification for the recommendation. Worse, it appeared to amplify glucose spikes after meals and increase LDL cholesterol, both unfavorable for metabolic health during pregnancy.

That said, this is a single trial with a modest sample size testing one specific intervention (25g of nuts). Different snack compositions, different calorie amounts, or different macronutrient ratios might behave differently. Nut-based snacks are relatively high in fat and protein but low in carbohydrates, which might not be ideal for preventing nocturnal glucose dips. The finding does, however, challenge the blanket recommendation and suggests individualized approaches may be needed.

If you have GDM, the evidence-based strategies with stronger support include regular post-meal walks to blunt glucose spikes, consistent meal timing, and monitoring your glucose response to your specific foods. Your clinician can help determine whether a bedtime snack is useful for your particular glucose patterns rather than assuming it helps everyone.

Study details

Sources

Study: Xu et al. (2025). "The effect of bedtime snacks on morning fasting blood glucose in gestational diabetes mellitus: a randomized controlled trial." *Acta Diabetologica*. PubMed: 39888449

Clinical trial registration: ChiCTR2300078399