Plasma potassium concentration and content changes after banana ingestion in exercised men

Context: Individuals prone to exercise-associated muscle cramps (EAMCs) are instructed to eat bananas because of their high potassium (K⁺) concentration and carbohydrate content and the perception that K⁺ imbalances and fatigue contribute to the genesis of EAMCs. No data exist about the effect of bananas on plasma K⁺ concentration ([K ⁺]_p) or plasma glucose concentration ([glucose] _p) after exercise in the heat. Objective: To determine whether ingesting 0, 1, or 2 servings of bananas after 60 minutes of moderate to vigorous exercise in the heat alters [K⁺]_p or [glucose]_p and whether changes in [K⁺]_p result from hypotonic fluid effluxes or K⁺ ion changes. Design: Crossover study. Setting: Laboratory. Patients or Other Participants: Nine euhydrated men (age= 27 ± 4 years, height=180.3 ± 8.4 cm, mass=84.9 ± 26.1 kg, urine specific gravity ≤ 1.006) without EAMCs volunteered. Intervention(s): On 3 separate days, participants completed 60 minutes of moderate to vigorous cycling (temperature = 36.4°C ± 1.1°C, relative humidity=19.4% ± 2.5%) and then ate 0 g (0 servings), 150 g (1 serving), or 300 g (2 servings) of bananas. Blood samples were collected at -3, 5, 15, 30, and 60 minutes postingestion. Main Outcome Measure(s): The [K ⁺]_p, changes in plasma K⁺ content, plasma volume changes, and [glucose]_p. Results: The [K⁺] _p differed between conditions at 60 minutes; 2 servings (4.6 ± 0.3 mmol/L [conventional unit = 4.6 ± 0.3 mEq/L]) was greater than 1 serving (4.5 ± 0.2 mmol/L [conventional unit = 4.5 ± 0.2 mEq/L]) and 0 servings (4.4 ± 0.3 mmol/L [conventional unit = 4.4 ± 0.3 mEq/L]) (P < .05). The [K⁺]_p was greater at 60 minutes than at -3 and 5 minutes in the 1-serving condition and was greater at 30 and 60 minutes than at -3 and 5 minutes in the 2-servings condition (P < .05). Percentage change in K⁺ content was greater only at 30 and 60 minutes postingestion than at baseline in the 2-servings condition (4.4% ± 3.7% and 5.8% ± 2.3% increase, respectively) (P < .05). The plasma volume changes among conditions were unremarkable. The [glucose]_p was greater in the 2-servings condition than in all other conditions at 15, 30, and 60 minutes (P < .05). Conclusions: The effect of banana ingestion on EAMCs is unknown; however, these data suggested bananas are unlikely to relieve EAMCs by increasing extracellular [K⁺] or [glucose]_p. The increases in [K⁺]_p were marginal and within normal clinical values. The changes in [K⁺]_p, plasma K ⁺ content, and [glucose]_p do not occur quickly enough to treat acute EAMCs, especially if they develop near the end of competition.