Carbohydrate ingestion but not mouth rinse maintains sustained attention when fasted

• We compared ingestion versus mouth rinse of isocaloric carbohydrate on attention.
• Ingesting only 1.5 g carbohydrate provided cognitive benefits in a fasted state
• Mouth rinsing isocaloric carbohydrate did not provide similar benefits as ingestion
• Prevention of mental fatigue with low carbohydrate was not related to blood glucose

Carbohydrate (CHO) receptors in the mouth signal brain areas involved in cognitive tasks relying upon motivation and task persistence; however, the minimal CHO dose that improves mental activity is unclear.PurposeTo determine if CHO (via ingestion or oral rinse) influences sustained attention without eliciting glycemic responses when in a fasted state.MethodsStudy A: Six healthy adults completed five treatment trials, ingesting 0–6% CHO solutions to evaluate glycemic response. Peak blood glucose for 6% and 1.5% CHO was greater (p < 0.05) than 0% and 0.4% CHO; thus, the low 0.4% CHO was evaluated further. Study B: Following an overnight fast, ten healthy adults completed three trials in a crossover design: 1) 400 ml 0.4% CHO ingested serially via 25 ml boluses, 2) 375 ml 0% CHO control (CON) ingested followed by one 25 ml 6% CHO isocaloric (1.5 g CHO) mouth rinse, and 3) CON ingest followed by CON rinse. Following treatments, a 20 min Continuous Performance Task (CPT) was performed to assess accuracy and precision.ResultsAccuracy and precision were not different during the first 5 min of CPT. However, accuracy was maintained with CHO ingest (p = 1.0) but decreased over 20 min (p < 0.05) with both CHO and CON rinse treatments. Precision tended to decline over 20 min CPT with CON (p = 0.06) and CHO rinse (p = 0.05) but were maintained with CHO ingest (p = 1.0). No differences in glycemic responses were observed between treatments.ConclusionsCompared to mouth rinsing CON or CHO (1.5 g in 6% CHO), ingestion of an isocaloric low-CHO drink maintained sustained attention over a mentally fatiguing task and appears effective after fasting without eliciting a glycemic response.