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, Andrew Blannin and a team from the University of Birmingham in the UK studied 55 endurance-trained amateur men. They gave groups 3 g/day of EPA-rich fish oil (2.3 g EPA, 0.3 g DHA), DHA-rich algae oil (0.3 g EPA, 2.3 g DHA), or a placebo for 6 weeks. They tested heart rate, perceived effort, breathing ratio, and a 24 km bike time trial before and after.

A 2025 meta-analysis published in Physiological Measurement evaluated 56 studies assessing the Apple Watch’s accuracy in monitoring health metrics. The findings indicate that while the device reliably measures heart rate and step counts, its accuracy in estimating energy expenditure (calories burned) is limited.