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

Abstract

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.

Figure 1.

A, Plasma potassium concentration ([K⁺]_p) over 60 minutes postingestion of 0, 1, or 2 servings of bananas (mean ± SD). ^a Indicates 1 serving < 1 serving at 60 minutes. ^b Indicates 2 servings < 2 servings at 30 minutes. ^c Indicates 2 servings < 2 servings at 60 minutes. ^d Indicates 0 servings and 1 serving < 2 servings. B, Percentage change in plasma potassium (K⁺) content from baseline over 60 minutes postingestion of 0, 1, or 2 servings of bananas (mean ± SD). ^a Indicates 2 servings < 2 servings at 30 minutes. ^b Indicates 2 servings < 2 servings at 60 minutes. ^c Indicates 2 servings > 0 servings. C, Plasma volume changes over 60 minutes postingestion of 0, 1, or 2 servings of bananas (mean ± SD). ^a Indicates greater than 60 minutes. One and 2 servings of bananas are equivalent to 150 and 300 g of bananas, respectively.

Figure 2.

Plasma glucose concentration over 60 minutes postingestion of 0, 1, or 2 servings of bananas (mean ± SD). ^a Indicates < 15, 30, and 60 minutes within 1 and 2 servings. ^b Indicates 1 serving < 1 serving at 30 minutes. ^c Indicates 2 servings < 2 servings at 30 and 60 minutes. ^d Indicates 0 servings < 1 serving < 2 servings. One and 2 servings of bananas are equivalent to 150 g and 300 g of bananas, respectively.