Page 67 - Journal of Special Operations Medicine - Winter 2016

Several researchers have compared the use of vari- factor among comparisons of differing CHO substrates
ous types of CHOs in sports drinks for support of is the differing rates of ingestion. Higher rates of con-
athletic performance (e.g., comparisons of galactose sumption of drinks with higher concentrations of CHO
[from lactose], fructose, maltose, and/or sucrose). Glu- appear to increase CHO oxidation rates, regardless
cose monomers are absorbed via a sodium-dependent of CHO source. However, in the field, higher con-
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transporter (SGLT1), which can transport both glucose centrations of CHO in the drink may adversely affect
and galactose, whereas fructose is transported via a consumption.
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sodium-independent transporter, GLUT5. The differ-
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ing transporters for glucose and fructose prevent com- Key Mechanisms of Action
petitive inhibition at the brush border, which means that Gastric emptying rates are frequently identified as a fac-
the presence of one does not slow the transport of the tor in athletic performance. Slower emptying rates have
other, permitting higher concentrations of absorption of been associated with increased gastric discomfort, de-
the monomers. However, this apparent advantage of the creasing athletic performance. Gastric emptying rates
presence of fructose in a sports drink may be offset by as well as total oxidation of exogenous CHO are faster
the necessary conversions of fructose to glucose before for glucose polymers than for glucose alone. When solu-
oxidation for energy support. 16 tions of glucose, sucrose, and glucose polymers (GPs;
e.g., MD) at varying concentrations (7.5%, 10%, or
Previous studies have provided evidence that the CHOs’ 15% weight per volume) and molecular weight (GP 11
structure and concentration play important roles in and GP ) were compared, results indicated that glucose
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absorption rates from the GIT as well as oxidation had the slowest gastric emptying rate. Overall, total
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for energy production within the body. For example, exogenous CHO oxidation rates were greater for GPs
in vivo perfusion of human duodenal tissues perfused than for glucose and may indicate a decided advantage
with glucose or maltose provides evidence that glucose to the use of GPs in a sports drink compared with those
monomers hydrolyzed from the maltose disaccharide consisting primarily of glucose. The longer the chain
are absorbed more quickly than when glucose is pro- length, the greater the oxidation rate, which may indi-
vided as the monomer itself. 10,12 Although increasing the cate that the digestion and absorption rates are greater
CHO concentrations may compensate for the faster rate for the GPs as compared with single molecules or di-
of absorption of glucose from maltose, the concentra- saccharides. Higher oxidation rates of GPs would also
9
tions of CHO containing various glucose molecules of translate to greater energy available to the athlete.
varying chain lengths may allow greater absorption and
use of glucose compared with drinks containing glucose Maintenance of body-water homeostasis is crucial
from mono- and disaccharides alone. Although Anasta- to health of the host and is referred to specifically as
siou et al reported no differences when MD was added normohydration, or euhydration. Osmolality is de-
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to a sports drinks (provided to cyclists and tested after fined as the concentrations of solutes, or dissolved
fasting) in comparison with glucose and maltose, the ex- substances, in various bodily fluids and affects water
perimental design added MD in the same amount (4.9g) transport and retention between the inside of the gut
to all drinks, making it impossible to clearly delineate its and the inside of the host. The lower osmolality of
4
effect. Additionally, although higher levels of CHO in- CeraSport compared with other sports drinks may al-
take, such as a combination of glucose and sucrose, in- low better absorption of water from the GIT into the
creased oxidation rates of exogenous CHO, these were blood stream, maintaining positive hydration status
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provided in a higher concentration than is preferred for and decreasing the risk of EHI, thereby mitigating EHI
palatability (i.e., 270g of CHO over 2.5 hours). Using during prolonged battlefield and training operations.
MDs, which are less sweet, as a source of glucose in a Measurement of pre- and postexercise body weight (a
sports drink may increase palatability, which, in turn, reliable indicator of hydration status) of Soldiers who
may result in increased consumption, especially in hot consumed either water or CeraSport during prolonged
environments, whereas, an overly sweet taste (e.g., in exercise in hot weather revealed significantly greater
drinks containing combinations of fructose, sucrose, body weight maintenance when CeraSport was con-
and glucose) may decrease intake. sumed, indicating a more positive hydration state,
2
thus decreasing the risk of EHI.
Various rates of exogenous CHO oxidation tested in
athletes have been reported previously. Although MD Additionally, it is imperative that consumption of CHOs
combined with fructose has been reported to increase during prolonged military missions is sufficient to sustain
CHO oxidation rates, other studies have not reported energy levels and maintain cognitive function of person-
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any significant increase in athletic performance when nel. Cognitive function is influenced by hydration sta-
fructose is combined with MD. One confounding tus and maintenance as well as glucose concentrations,
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Rice-Based Rehydration Drink 51