Effect of a Electrolyte replacement beverage compared with a commercially available Carbohydrate supplement on the rate of fat oxidation during moderate-intensity cycle ergometry exercise

INTRODUCTION

Carbohydrate (CHO) supplementation has long been known to improve endurance

performance, quantified as either an increase in time to fatigue, or an improvement in

performance time for completing a fixed distance/ amount of work (e.g. Coyle et al 1983,

1986; Coggan and Coyle 1988; Hargreaves et al., 1984; Below et al., 1995; Jeukendrup et al.,

1997; Jeukendrup, 2004; Currell and Jeukendrup, 2008). This improvement in endurance

performance is thought to be mediated through the maintenance of euglycaemia and high

intramuscular CHO oxidation rates late in exercise when endogenous CHO stores are

becoming depleted (e.g. Coyle et al., 1986; Coggan and Coyle 1988; Jentjens et al., 2004;

Jeukendrup, 2004).

Despite the significant ergogenic effect of CHO supplementation, CHO Supplementation is

not always appropriate. CHO supplementation is associated with a marked suppression of fat

oxidation, hence reducing the contribution of this substrate to the overall energy expenditure

(e.g. Wagenmakers et al., 1993; Horowitz et al., 1997; Jentjens et al, 2004, 2006; Rowlands

et al., 2005; Jeukendrup et al., 2006; Wallis et al., 2005; Currell and Jeukendrup, 2008).

However, training with low muscle glycogen (which may occur during a prolonged training

session, or when training frequency is high- especially in the absence of CHO

supplementation) has been suggested to increase the rate of fat oxidation, possibly through

enhanced metabolic adaptations in the skeletal muscle (e.g. Yeo et al., 2008; Hulston et al.,

2010), increasing the contribution of fat oxidation and decreasing the requirement of CHO

oxidation to meet the total energy requirement, which may be potentially important for

endurance performance. Furthermore, CHO supplementation may not be appropriate for

those engaged in a weight loss programme who are engaged in exercise to promote the

achievement of a negative energy, and more important, fat balance.

However, sports drinks do not only contain CHO. Many contain electrolytes (e.g. sodium,

potassium etc) to promote fluid uptake and replace electrolytes lost through sweat (to prevent

muscle cramps and hyponnatremia). Therefore, while replacing a sports drink containing

CHO and electrolytes with water will address issues of dehydration and facilitate increases in

the rate of fat oxidation; this is not an appropriate alternative, as electrolyte losses will still

occur. An alternative for those wanting to train/ exercise with no CHO supplementation (i.e.

following a “train low, compete high” strategy or for those wanting to promote fat loss), but still

replace electrolytes lost during the exercise bout, is to supplement with an electrolyte

replacement beverage containing no (or negligible) CHO.

While replacing a CHO based beverage with water has been shown to increase the rate of fat

oxidation, the effect of supplementing with an electrolyte replacement beverage (to improve

fluid uptake and replace essential electrolytes) compared with a CHO based beverage on the

rate of fat oxidation has yet to be demonstrated. Therefore, the aim of this investigation was

to determine the effect of replacing a CHO based sports drink with an electrolyte based sports

drink (containing negligible CHO) on the rate of fat oxidation. It was hypothesised that

supplementing with the electrolyte based sports drink would significantly increase the rate of

fat oxidation compared with the CHO based beverage.

METHODS

Subjects

Twenty-two healthy, recreationally active males (mean ± standard deviation (SD); age 32 ±

8.5 yr; height 178.5 ± 7.3 cm; mass 79.8 ± 8.6 kg) volunteered to take part in the investigation

after providing written informed consent, as approved by the Faculty of Biomedical and Life

Sciences Ethical Review Committee, University of Glasgow (in accordance with the

Declaration of Helsinki). Following familiarisation with the equipment and procedures,

subjects visited the laboratory on at least four occasions, with each visit conducted at a

similar time of day (± 1 hr) on non-consecutive days. Subjects were instructed to consume

their normal diet throughout the testing period, and arrive at the laboratory on the day of the

test rested (no strenuous exercise in the previous 24 hr), and in a fasted state (having

consumed nothing but water in the 12hours prior to the test time).

Protocol 1: Incremental-ramp test

An incremental exercise test (25W.min-1) was performed on a computer-controlled

electromagnetically-braked cycle ergometer (Excalibur Sport, Lode, Groningen, NL) to the

limit of tolerance. Throughout this test inspired and expired volumes (bi-directional turbine,

Jaeger TripleV, Hoechberg, Germany) and gas concentrations (chemical fuel cell (O2) and

infrared (CO2) analyzers; Jaeger Oxycon Pro, Hoechberg, Germany) were sampled at 50Hz,

with the time-aligned volume and gas concentration signals allowing online calculation of

breath-by-breath pulmonary gas exchange and ventilatory variables (e.g. O2 uptake ( 2OV ),

CO2 output ( 2COV ) and ventilation ( EV )). Prior to each test the gas analyzers were

calibrated with one precision-analyzed gas mixture and room air to span the concentration

range observed during exercise, with the turbine volume sensor calibrated using a 3-liter

syringe (Hans Rudolph, Kansas City, MO).

This test allowed estimation of the lactate threshold (LT), using standard pulmonary gas

exchange criteria (Whipp et al, 1986), and determination of peak oxygen uptake ( 2OV peak),

from the average 2OV for an integral number of breaths over the final ~20s of the

incremental phase. Verbal encouragement was given throughout this test.

Protocol 2: Sub-LT constant-load tests

Each subject then completed two constant-Power tests (on separate days) at the power

output equivalent to 90% LT (moderate-intensity) on a standard road bike mounted to a

computer-controlled indoor trainer (Computrainer, Racermate, WA, USA). Following

calibration of the trainer in accordance with manufacturers guidelines (warm-up at 100Watts

for 10min to ensure the temperature of the system has stabilised, allowing the rolling

resistance to be appropriately set), subjects completed 60min cycling at a constant speed

while in the same gear on the road bike (determined during the familiarisation session and

standardised for each subsequent session).

15min prior to the start of the test 250ml of the appropriate beverage was ingested, while

during the 60min moderate-intensity ride 1 litre of the appropriate drink was consumed (CHO:

66.6g CHO, 0.64g Na+, 34mg Mg2+; all l.-1 or ELEC 4g CHO, 0.5g Na+, 120mg Mg2+; all l.-1),

with this split into 250ml doses at time 0, 15, 30 and 45min. In addition, following a 2min run-

in, 2min expired air samples were collected in Douglas bags every 10min (i.e. between 8-10,

18-20 etc) for estimation of 2OV and 2COV , allowing estimation - via indirect calorimetry – of

the rate of energy expenditure (EE) and fat and CHO oxidation using the equations described

by Frayn (1983), i.e.:

Rate of fat oxidation (g.min-1) = ( 2OV - 2COV )/ 0.57

Rate of CHO oxidation (g.min-1) = (1.40 * 2COV - 2OV )/ 0.30

Rate of EE (kJ.min-1) = (Rate of CHO oxidation * 15.6)/ (Rate of fat oxidation * 39)

Statistics

Paired Student’s t-tests were used to examine any difference in the rate of EE and fat and

CHO oxidation between CHO and ELEC conditions. Data are presented as mean ± SE,

unless otherwise stated. Statistical significance was accepted when P > 0.05.

RESULTS

Incremental-ramp test: From the incremental-ramp exercise 2OV peak was 4.14 ± 0.14 l·min-1

(52.3 ± 1.8 mL·kg-1·min-1) and was reached at an average work rate of 341 ± 13 W. LT

occurred at 2.19 ± 0.10 l·min-1, which was equivalent to 52.7 ± 1.4 % of 2OV peak, giving an

average work rate for the moderate-intensity constant-load tests (90% LT) of 113 ± 8 W.

Sub-LT constant-load tests: There was no significant difference in total EE for each

constant-load test (CHO: 2283.7 ± 115.8 vs. ELEC: 2269.4 ± 121.8 kJ; Figure 1), with this

also reflected in the rate of EE (CHO: 38.1 ± 1.9 vs. ELEC: 37.8 ± 2.0 kJ.min-1;P = 0.727)

Figure 1: Mean (± SE) Total Energy expenditure for the moderate-intensity constant-load tests when consuming a carbohydrate based supplement (CHO) or an electrolyte replacement beverage (ELEC)

However, although there was no difference in EE, ingestion of ELEC significantly increased

the rate (ELEC: 0.47 ± 0.04g·min-1; P = 0.001; Figure 2A), and consequently the total amount

of fat oxidised (ELEC: 28.4 ± 2.3g) during exercise, compared with the ingestion of CHO

(Rate: 0.35 ± 0.03g·min-1; Amount: 21.2 ± 2.0g). Hence, with the ingestion of ELEC the total

amount of fat oxidised during the 60min exercise bout was increased by 41.4 ± 10.4%.

Consequently, due to the unchanged EE and significant increase in the rate of fat oxidation

when consuming ELEC, CHO oxidation rates were significantly decreased when consuming

ELEC compared with CHO (CHO: 1.56 ± 0.09 g·min-1 vs. ELEC: 1.24 ± 0.10 g·min-1; P >

0.001; Figure 2B), with the total amount of CHO oxidised also significantly reduced during the

exercise bout (CHO: 93.5 ± 5.2 g vs. ELEC: 74.4 ± 6.2 g), reflecting a 20.5 ± 4.7% decrease

in the total amount of CHO oxidised when consuming ELEC.

Figure 2: The mean (± SE) of (2A) Rate of fat oxidation and (2B) Rate of CHO oxidation during moderate-intensity constant-load exercise when consuming a carbohydrate based supplement (CHO) or an electrolyte replacement beverage (ELEC).

Hence, as a consequence of the increase in the rate of fat oxidation when ingesting ELEC,

the proportion of fat contributing to the total EE was significantly greater (CHO: 35.5 ± 2.2 %

vs. ELEC: 48.6 ± 3.2 %; P < 0.001) and the proportion of CHO was significantly less (CHO:

64.5 ± 2.2 % vs. ELEC: 51.4 ± 3.2 %; P < 0.001; Figure 3), reflecting a 42.0 ± 9.6 % increase

in the contribution of fat oxidation to the energy expenditure during the exercise bout.

Figure 3: Contribution of carbohydrate (CHO; Hashed box)) and Fat oxidation (Grey box) to the total energy expenditure when consuming the CHO or Electrolyte replacement drink during the exercise bout. The mean rates (± SE) of substrate utilisation, in addition to the overall difference in the rate of fat oxidation between conditions, are displayed.

CONCLUSION

The results of this study suggest that replacing a carbohydrate based sports drink with an

electrolyte based beverage containing negligible CHO significantly increased the rate of fat

oxidation, and consequently the amount of fat oxidised during the exercise bout, with subjects

oxidising, on average, ~41% more fat in this study. This result is consistent with previous

research showing an increase in the rate of fat oxidation when water is consumed instead of a

CHO based supplement (Wagenmakers et al., 1993; Horowitz et al., 1997; Jentjens et al,

2004, 2006; Rowlands et al., 2005; Jeukendrup et al., 2006; Wallis et al., 2005; Currell and

Jeukendrup, 2008). However, supplementing with electrolytes, rather than water, during

exercise is important to promote rehydration and replace the electrolytes lost through sweat.

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