MTNR1B Genotype and Breakfast Glucose Response – EMJ

POSTPRANDIAL glucose response was significantly influenced by both MTNR1B genotype and breakfast composition, according to findings from a randomised crossover trial.

The findings suggest that a protein enriched breakfast reducing genotype-related differences observed after a carbohydrate rich meal.

Breakfast Composition Modified Glucose Response by Genotype

Researchers investigated whether variation in the melatonin receptor 1B gene (MTNR1B) altered glucose responses to different breakfast types in a real-world setting.

The risk allele G has previously been associated with impaired glucose tolerance, elevated fasting glucose, and increased risk of Type 2 diabetes.

The study included 54 healthy adults aged 18 to 48 years who completed two breakfast interventions separated by one week.

Following an overnight fast, participants consumed either a carbohydrate-rich porridge breakfast, or a protein enriched equivalent breakfast.

Continuous glucose monitoring was used to assess postprandial glucose levels over 120 minutes, after which participants crossed over to the alternate breakfast condition.

Carbohydrate Rich Breakfast Revealed Genotype Differences

Investigators found that fasting glucose differed significantly between genotype groups.

Participants with the GG genotype had higher fasting glucose compared with those carrying CC or CG genotypes.

The strongest genotype effect emerged following the carbohydrate rich breakfast.

Participants with the GG genotype demonstrated significantly greater glucose exposure than those with CC genotype and CG genotype, with no significant differences observed between CC and CG groups.

Protein Enrichment Mitigated Genetic Effect

Notably, genotype-related differences disappeared when participants consumed the protein enriched breakfast.

The researchers suggested that increasing protein content may help offset the impaired glucose handling associated with the GG genotype during periods when endogenous melatonin levels remain elevated in the early morning.

They also noted that individuals with the GG genotype exhibited higher chronotype scores and fasting glucose concentrations, both factors that may have implications for future metabolic risk.

Overall, the findings indicate that MTNR1B genotype influences postprandial glucose response to breakfast composition and support the potential value of personalised dietary advice based on genetic profile.

The researchers concluded that adjusting meal composition during periods of elevated melatonin may help improve glucose control and potentially reduce future Type 2 diabetes risk.

Reference

King A et al. Interaction of melatonin receptor 1B (MTNR1B) genotype and type of breakfast (protein-enriched v carbohydrate-rich) on postprandial glucose response: a randomised crossover trial. Eur J Clin Nutr. 2026;DOI:10.1038/s41430-026-01794-3

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