Nutritional and Health Aspects of Sweeteners - Sweeteners: Nutritional Aspects, Applications, and Production Technology - page 354

been made to reduce the unfavorable metabolic perturbations caused when carbohydrates that have
a high GI are ingested before exercise. These attempts have focused on the use of low-GI foods,
which produce a lower postprandial hyperglycemia and hyperinsulinemia compared to high-GI car-
bohydrates. Such a response may elevate free fatty acid oxidation during exercise, leading to a better
maintenance of carbohydrate availability (O'Reilly et al. 2010). However, although there is a poten-
tial beneit regarding exercise performance and substrate utilization when low-GI carbohydrates are
ingested, variations in research methodology on the GI of meals consumed before exercise have led
to inconclusive indings (American College of Sports Medicine 2009).
Regardless of controversies in the literature and because prolonged fasting is harmful to health
and performance (Maughan 2010), athletes are advised to ingest a preexercise meal or snack that
will provide suficient luid to maintain hydration, be it high in carbohydrates and low in fat and
iber to facilitate gastric emptying and minimize gastrointestinal distress and composed of familiar
foods. In terms of timing and quantity for preexercise euhydration, the exercising individual should
drink about 5-7 mL per kg body mass of a sports beverage at least 4 h before exercise. This would
allow enough time to optimize hydration levels and for the excretion of any excess luid as urine
(American College of Sports Medicine 2009). In addition, consuming sports drinks with sodium
and/or salted snacks instead of plain water alone can help stimulate thirst and retain needed luids
(American College of Sports Medicine 2007).
11.6.2 Ingestion of Carbohydrate Beverages during exercise
The effects of carbohydrate beverages consumption on metabolism and performance during
exercise is the most researched topic in sports nutrition. The main aims of sports beverages ingested
during exercise are to replace sweat loss and to reduce the problems associated with dehydration and
to provide a source of energy in the form of carbohydrates, which can supplement the limited stores
of muscle and liver glycogen (Coombes and Hamilton 2000).
In order to thermoregulate during exercise, the human body loses substantial amounts of water
and electrolytes through sweat. If these losses are not replaced, excessive dehydration occurs,
which not only degrades performance but can also increase the risk of heat illness (Casa et al.
2005). The goal of drinking sports beverages during exercise is to prevent water loss that exceeds
2% of the body weight (American College of Sports Medicine 2007). However, this is not always
an easy task, because sweat rate is inluenced by many factors such as the duration and intensity of
exercise, the environmental conditions, the type of clothing or equipment worn, and the character-
istics of the individual (body weight, genetic predisposition, acclimatization state, and metabolic
eficiency). Therefore, it is not surprising that sweat rates may vary from 0.3 to 2.6 L h -1 (American
College of Sports Medicine 2007). Under these circumstances, general guidelines are dificult
to give. Athletes are advised to record their body weights preexercise and postexercise in order
to estimate individual sweat loss, which will help in designing individualized luid replacement
programs.
Many studies have reported an ergogenic effect when sports drinks are ingested during short
term (up to 1 h; Below et al. 1995; Jeukendrup et al. 1997; Millard-Stafford et al. 1997), prolonged
intermittent (1-4 h; Hargreaves et al. 1984; Murray et al. 1989, 1991; Davis et al. 1997), prolonged
continuous (Maughan et al. 1989; Wright et al. 1991; Tsintzas et al. 1993; Febbraio et al. 1996;
McConell et al. 1996; Tsintzas et al. 1996), or ultraendurance (>4 h; Brouns et al. 1989) exercise.
These studies are some of the many investigations that have shown an improvement in perfor-
mance. Several reviews offer a more detailed presentation of the topic (Coombes and Hamilton
2000; Kerksick et al. 2008; American College of Sports Medicine 2009).
In terms of quantity and timing, ingesting 200-450 mL of sports beverages (depending on
body weight) every 15-20 min should deliver about 30-60 g of carbohydrates per hour (American
College of Sports Medicine 2009).