Prepregnancy Time-Restricted Eating and Exercise Training Do Not Improve Glycaemic Control in High-Risk Gestational Diabetes: Insights from the BEFORE THE BEGINNING Trial

Highlight

– A combined intervention of exercise training and time-restricted eating initiated before pregnancy and continued during pregnancy showed no significant effect on glucose tolerance at 28 weeks gestation in individuals at elevated risk of gestational diabetes mellitus (GDM).
– Adherence to the prescribed intervention decreased during pregnancy, with only around 37%-44% meeting adherence criteria before and during pregnancy.
– The exercise intervention targeted a weekly Personal Activity Intelligence (PAI) score ≥100, while time-restricted eating limited the daily energy intake window to ≤10 hours for at least five days per week.
– This study provides robust evidence from a well-conducted randomized controlled trial (RCT) that these specific lifestyle modifications may not sufficiently improve late-pregnancy glycaemic control in this high-risk population.

Study Background and Disease Burden

Gestational diabetes mellitus affects approximately 7–14% of pregnancies worldwide and is associated with increased risks of adverse maternal and fetal outcomes including preeclampsia, cesarean delivery, macrosomia, and long-term risks of type 2 diabetes in both mother and offspring. Despite standardized screening and diagnostic protocols, effective strategies to prevent or mitigate GDM remain limited. Lifestyle interventions focusing on diet and physical activity are recommended, yet evidence supporting specific modalities preceding and during pregnancy is sparse. Time-restricted eating (TRE), a form of intermittent fasting that limits caloric intake to specific time windows, has garnered interest for improving metabolic health. Exercise interventions quantified by personalized metrics such as Personal Activity Intelligence (PAI) optimize cardiovascular benefits. Investigating these combined interventions starting before conception may provide opportunities for primary prevention of GDM in individuals with recognized risk factors.

Study Design

The BEFORE THE BEGINNING trial was a single-center, randomized controlled trial conducted at a university hospital in Trondheim, Norway. It enrolled 167 individuals contemplating pregnancy and possessing at least one established risk factor for GDM. Participants were randomly assigned in a 1:1 ratio to receive either the lifestyle intervention or standard care.

The intervention group engaged in:
– Exercise training aiming to achieve a weekly Personal Activity Intelligence (PAI) score of ≥100. PAI translates heart rate data into a personalized activity score reflecting cardiovascular benefit.
– Time-restricted eating with all caloric intake confined to a ≤10-hour window on at least five days per week.

These interventions were initiated before pregnancy and sustained through gestation.

The primary outcome was the two-hour plasma glucose level during a standard oral glucose tolerance test (OGTT) at 28 weeks of gestation. Intention-to-treat principles guided all analyses.

Key Findings

Of the 167 randomized participants (84 intervention; 83 control), 111 became pregnant during the follow-up period (56 intervention; 55 control). After exclusions (prepregnancy diabetes in one intervention participant and twin pregnancy in one control participant), glycaemic data from 109 participants were analyzed.

– The primary endpoint, two-hour plasma glucose at 28 weeks, showed no statistically significant improvement in the intervention group versus controls. The mean difference was 0.48 mmol/L (95% CI, -0.05 to 1.01; P=0.08), favoring the control group by a non-significant margin.

– Adherence to the intervention was moderate before pregnancy, with 31/83 (37%) participants meeting predefined adherence criteria. Among those who became pregnant, 24/55 (44%) adhered pre-pregnancy.

– Average daily eating windows during the prepregnancy period were close to the target (mean 9.9 hours/day; SD 1.2), and average weekly PAI scores achieved 111 points (SD 54), slightly above the goal.

– Adherence to both time-restricted eating and exercise diminished during pregnancy, reflecting challenges in maintaining lifestyle modifications during gestation.

– No significant adverse events related to the intervention were reported.

Expert Commentary

This rigorous trial provides valuable insights into the challenges and potential limitations of lifestyle interventions targeting GDM prevention in a high-risk population. The findings align with previous trials demonstrating mixed or limited effects of similar interventions on maternal glycaemic outcomes.

Several factors may explain the null results. Declining adherence during pregnancy attenuates expected metabolic benefits. Also, heterogeneity in participants’ baseline risk profiles and metabolic phenotypes may blunt intervention efficacy. The relatively modest sample size and power might have limited detection of smaller but clinically relevant effects.

Moreover, the use of a combined lifestyle intervention complicates disentangling the independent effects of time-restricted eating versus exercise. Future studies could assess these modalities separately and explore longer-term metabolic endpoints.

Importantly, time-restricted eating, while promising in nonpregnant populations, lacks extensive safety data in pregnancy; this trial supports its relative safety but underscores feasibility challenges.

Current clinical guidelines recommend individualized lifestyle counseling emphasizing balanced nutrition and physical activity during pregnancy. This study suggests that time-restricted eating combined with PAI-targeted exercise, as applied here, may not enhance glucose tolerance but does not preclude benefits from alternative or more intensive approaches.

Conclusion

The BEFORE THE BEGINNING trial demonstrates that initiating a combined lifestyle intervention of time-restricted eating and exercise training prior to and through pregnancy does not significantly improve glucose tolerance at 28 weeks gestation in people at increased risk of gestational diabetes. Moderate adherence and diminished engagement during pregnancy likely contribute to these findings. While safe, these specific interventions may need to be supplemented or modified to achieve meaningful metabolic benefits in this population. Further large-scale, well-powered trials are warranted to refine preventive strategies and optimize maternal and fetal outcomes in high-risk pregnancies.

References

1. Sujan MJ, Skarstad HM, Rosvold G, et al. Time restricted eating and exercise training before and during pregnancy for people with increased risk of gestational diabetes: single centre randomised controlled trial (BEFORE THE BEGINNING). BMJ. 2025 Sep 9;390:e083398. doi:10.1136/bmj-2024-083398.
2. American Diabetes Association. 2. Classification and Diagnosis of Diabetes: Standards of Medical Care in Diabetes—2024. Diabetes Care. 2024;47(Suppl 1):S17-S29.
3. Gipson DS, Shapiro AL, Newton KI, et al. Lifestyle intervention for prevention of gestational diabetes in high-risk populations: a systematic review and meta-analysis. Diabetes Res Clin Pract. 2023;193:110024.
4. Wilmot EG, Edwardson CL, Davies MJ, Yates T. Behavioral approaches to type 2 diabetes prevention: efficacy and application. Diabetologia. 2022;65(2):188-199.
5. Manoogian ENC, Panda S. Circadian rhythms, time-restricted feeding, and healthy aging. Ageing Res Rev. 2017;39:59-67.