Cognitive Effects of Taurine and Related Sulphur-Containing Amino Acids: A Systematic Review of Human Trials and Considerations for Plant-Based Dietary Transitions

As diets shift towards more plant-based patterns, nutrients mainly supplied by animal-sourced foods are receiving greater attention. Among these are sulphur-containing amino acids (SCAAs) such as taurine, methionine, and cysteine. These compounds play important roles in neuroprotection, antioxidant defence, and cellular signalling; functions that are closely linked to cognitive health. This systematic review examined the effects of SCAA supplementation on cognitive performance in randomised controlled trials (RCTs). Eight RCTs involving 244 healthy participants met the inclusion criteria. All trials focused exclusively on taurine; no studies were found that tested methionine or cysteine. Each used an acute, single-dose design, assessing key cognitive domains and mood outcomes. Overall, acute doses of taurine (typically 1-3 g, up to ~50 mg/kg) produced, at best, small and inconsistent improvements in cognitive function. Most cognitive outcomes showed no effect. Trials that combined taurine with caffeine showed more reliable performance benefits, but they did not isolate taurine's independent effects. Similarly, any positive effects on mood or well-being were minor, inconsistent, and typically observed only under specific conditions, such as when taurine was combined with caffeine, exercise, or sleep deprivation. Importantly, none of the studies measured participants' habitual diets, baseline SCAA status, or specifically recruited individuals with low intake of animal-source foods. This means the cognitive effects of reduced SCAA intake in plant-based diets remain unknown. Current evidence from acute taurine trials provides limited support for short-term benefits to cognition or mood. Longer-term, well-designed studies are urgently needed. These should assess habitual diet and baseline SCAA status and focus on populations with lower animal-derived food intake. Only then can we determine whether lower SCAA availability in plant-based diets represents a nutritional 'green gap' with implications for brain health.