In 2020, a scoping review by K. Ahern and team found that low protein intake and unstable blood sugar from high-carb diets worsened anxiety by 20-30%, as they disrupt serotonin production and spike stress hormones like cortisol. A 2016 study by K. M. Whitaker showed skipping breakfast raised cortisol levels in women by 15-25%, increasing morning stress and anxiety.

In 2025, J. Tan and a team reviewed 12 observational studies from databases like PubMed and Embase up to September 2024. They analyzed how skipping breakfast affects depression risk, using data from various groups and checking study quality with a standard tool.