Oxidation of independent and combined ingested galactose and glucose during exercise

Abstract

Coingestion of glucose and galactose has been shown to enhance splanchnic extraction and metabolism of ingested galactose at rest; effects during exercise are unknown. This study examined whether combined ingestion of galactose and glucose during exercise enhances exogenous galactose oxidation. Fourteen endurance-trained male and female participants [age, 27 (5) yr; V̇o_2peak, 58.1 (7.0) mL·kg^-1·min^-1] performed cycle ergometry for 150 min at 50% peak power on four occasions, in a randomized counterbalanced manner. During exercise, they ingested beverages providing carbohydrates at rates of 0.4 g.min^-1 galactose (GAL), 0.8 g.min^-1 glucose (GLU), and on two occasions 0.8 g.min^-1 total galactose-glucose (GAL + GLU; 1:1 ratio). Single-monosaccharide ¹³C-labeling (*) was used to calculate independent (GAL, GLU, GAL* + GLU, and GAL + GLU*) and combined (GAL* + GLU*, COMBINE) exogenous-monosaccharide oxidation between exercise. Plasma galactose concentrations with GAL + GLU [0.4 mmol.L; 95% confidence limits (CL): 0.1, 0.6] were lower (contrast: 0.5 mmol.L; 95% CL: 0.2, 0.8; P < 0.0001) than when GAL alone (0.9 mmol.L; 95% CL: 0.7, 1.2) was ingested. Exogenous carbohydrate oxidation with GAL alone (0.31 g·min^-1; 95% CL: 0.28, 0.35) was marginally reduced (contrast: 0.05 g·min^-1; 95% CL: -0.09, 0.00007; P = 0.01) when combined with glucose (GAL* + GLU 0.27 g·min^-1; 0.24, 0.30). Total combined exogenous-carbohydrate oxidation (COMBINE: 0.57 g·min^-1; 95% CL: 0.49, 0.64) was similar (contrast: 0.02 g·min^-1; 95% CL: -0.05, 0.09; P = 0.63) when compared with isoenergetic GLU (0.55 g·min^-1; 95% CL: 0.52, 0.58). In conclusion, coingestion of glucose and galactose did not enhance exogenous galactose oxidation during exercise. When combined, isoenergetic galactose-glucose ingestion elicited similar exogenous-carbohydrate oxidation to glucose suggesting galactose-glucose blends are a valid alternative for glucose as an exogenous-carbohydrate source during exercise.NEW & NOTEWORTHY Glucose and galactose coingestion blunted the galactosemia seen with galactose-only ingestion during exercise. Glucose and galactose coingestion did not enhance the oxidation of ingested galactose during exercise. Combined galactose-glucose (1:1 ratio) ingestion was oxidized to a similar extent as isoenergetic glucose-only ingestion during exercise. Galactose-glucose blends are a viable exogenous carbohydrate energy source for ingestion during exercise.

Keywords: metabolism; nutrition; physical activity; substrate oxidation; sugars.

Graphical abstract

Figure 1.

Breath ¹³CO₂ enrichment during 150 min exercise at 50%W_max. n = 14 (11 male participants, 3 female participants).

Figure 2.

Substrate oxidation during exercise. Exogenous carbohydrate oxidation (A), endogenous carbohydrate oxidation (B), total carbohydrate oxidation (C), and fat oxidation (D), during 150 min exercise at 50%W_max. n = 14 (11 male participants, 3 female participants).

Figure 3.

Plasma glucose (A), lactate (B), insulin (C), NEFA (D), glycerol (E), and galactose (F) concentrations during 150 min exercise at 50%W_max. n = 14 (11 male participants, 3 female participants). NEFA, nonesterified fatty acid.