Influence of Carbohydrate Ingestion from Bananas or Sugar Beverage on Natural Killer Cells During Recovery from 75‐km Cycling

Abstract

Natural killer cells are part of the first line of defense against infection. They are also the most responsive of all immune cell types to acute exercise bouts, and their depletion from the bloodstream and potential cytotoxic capabilities loss during the recovery phase open a window for opportunistic infections to develop. Carbohydrate intake has multiple effects for the exercising athlete, including enhanced glucose availability to the working muscle, resulting in reduced post‐exercise cortisol and epinephrine levels, decreased leukocytosis and phagocytosis, and lower inflammatory cytokines. The effect of carbohydrate intake on post‐exercise NK bioactivity has never been directly assessed, and the purpose of this study was to compare ingestion of Cavendish bananas with an equicaloric, sugar‐only beverage or water alone on NK cell release and cytotoxic activity during recovery from an intensive 75‐km cycling bout. Participants included 16 male and female cyclists (age 39.9±2.4 years) who regularly competed in road races and were capable of cycling 75‐km at race pace. This study utilized a randomized crossover approach, and participants engaged in three 75‐km cycling time trials while ingesting water only, bananas and water, and a 6% sugar beverage in an overnight fasted state, with data analyzed using a repeated measures two‐way analysis of variance (ANOVA), or paired two‐tailed student t‐test. Before the exercise bout, participants ingested 5 ml/kg water alone, 6% sugar beverage, Cavendish (with water) adjusted to quantities providing 0.4 g carbohydrate per kilogram of body weight (g carb/kg). During the cycling bout, water was ingested at a rate of 3 ml/kg every 15 minutes, with carbohydrate intake from the 6% sugar beverage and banana adjusted to 0.2 g carb/kg every 15 minutes. Blood samples were collected pre‐ and post‐exercise, and then at 1.5 h and 21 h post‐exercise. Isolation and count of NK cells from whole blood was done using a Magnetic Assisted Cell Sorting technology (Miltenyi, Germany) using a CD56 positive selection. NK cell cytotoxicity was assessed using an Amnis Imagestream flow cytometer (Millipore, MA). NK cell count profile was significantly different in the water group compared to all the other groups (group interaction p=0.0051 by ANOVA), with post‐exercise NK cell counts about 71% higher in the water‐treated group vs all other groups (p<0.05 by Student t‐test). NK cell cytotoxicity was significantly decreased about 70% 1.5 h post‐exercise for all treatments, with no trial differences (time effect, p=0.0057 by ANOVA). In conclusion, these data indicate that carbohydrate ingestion from bananas with water or a 6% sugar beverage compared to water alone attenuates the sharp post‐exercise release of NK cells in the blood compartment, but has little effect on countering the post‐exercise decrement in NK cell cytotoxic potential.Support or Funding InformationSupport provided by Dole Foods, Inc., Westlake Village, CA