Metabolic availability of carbohydrates ingested during, before, or after muscular exercise

Hydrogen breath test as a simple noninvasive method for evaluation of carbohydrate malabsorption during exercise

The aim of this study was to examine hydrogen (H2) production with the hydrogen breath test (HBT) after ingesting primarily digestible carbohydrate (CHO) during 3 h of 75% maximal oxygen consumption exercise. This was done to indicate CHO overflow in the colon which may occur when gastric emptying, intestinal transit and CHO absorption are not matched and CHO accumulates in the colon where it is subject to bacterial degradation. Further, this study was designed to assess breath H2 production as a function of the type of CHO ingested and the type of exercise. A group of 32 male triathletes performed three exercise trials at 1-week intervals with either a semisolid (S) intake, an equal energy fluid intake (F) or a fluid placebo (P). Each trial consisted of cycling (sessions 1 and 3) and running (sessions 2 and 4). The mixed-expired H2 concentrations in the resting and "recovery" periods (5 min after each session) did not change significantly in time and did not differ among intakes. There were also no significant differences in H2 concentrations between resting and "recovery" conditions. During exercise, H2 concentrations decreased three to six-fold in comparison to resting and recovery levels and differed among intakes (ANOVA; P < 0.05). The H2 concentrations were almost continuously lower with P than with F and S. The H2 concentrations were significantly higher during running than during cycling. During exercise, we found that CHO overflow could be compared among intakes and between exercise types by using the HBT, provided the influence of other factors on H2 excretion--ventilation and intestinal blood flow--was similar for each condition.

Child and Adolescent Athletes With Diabetes

In brief: The common desire to participate in sports can be harnessed to encourage children and adolescents with type 1 diabetes to participate actively in controlling their disease. This is partly because the diabetic who successfully learns to control blood glucose during exercise by wise regulation of diet and insulin is rewarded with enhanced athletic performance. Age, duration of the diabetes, insulin dosage, hypoglycemia, seasonality, training, duration of training periods, and calorie intake must be considered in prescribing specific exercise regimens for diabetic youngsters. To participate in endurance sports, persons with diabetes must manage the effects of exogenous insulin on their normal triphasic metabolic fuel supply derived from muscle, liver, and adipose tissue. If educational guidelines are followed and potential risks due to complications are taken into account, the benefits of regular exercise early in the course of the disease outweigh potential disadvantages.

The effects of consuming carbohydrate-electrolyte beverages on gastric emptying and fluid absorption during and following exercise

A variety of beverages formulated to provide fluid, carbohydrates, and electrolytes during and following exercise are commercially available. Such 'sport drinks' commonly contain 4 to 8% carbohydrate (as glucose, fructose, sucrose or maltodextrins) and small amounts of electrolytes (most often sodium, potassium, and chloride). The efficacy of consuming such beverages has been questioned primarily because of concern that beverage carbohydrate content may inhibit gastric emptying rate and fluid absorption during exercise, thereby jeopardizing physiological homeostasis and impairing exercise performance. Gastric motor activity, and consequently gastric emptying rate, is governed by neural and humoral feedback provided by receptors found in the gastric musculature and proximal small intestine. Gastric emptying rate may be influenced by a variety of factors including, but not limited to, the caloric content, volume, osmolality, temperature, and pH of the ingested fluid, diurnal and interindividual variation, metabolic state (rest/exercise), and the ambient temperature. The caloric content of the ingested fluid appears to be the most important variable governing gastric emptying rate, providing a mean caloric efflux from the stomach of 2.0 to 2.5 kcal/min for ingested fluid volumes less than 400 ml. At rest, gastric emptying is inhibited by solutions containing calories in a manner independent of the nutrient source (i.e. carbohydrate, fat or protein). Consequently, plain water is known to empty from the stomachs of resting subjects at rates faster than solutions containing calories. Gastric emptying is increasingly inhibited as the caloric content of the ingested fluid increases. During moderate exercise (less than 75% VO2max), gastric emptying occurs at a rate similar to that during rest; more intense exercise appears to inhibit gastric emptying. When fluids are consumed at regular intervals throughout prolonged exercise (greater than 2 hours), postexercise aspiration of stomach contents reveals that solutions containing up to 10% carbohydrate empty at rates similar to plain water. There is ample physiological justification for the addition of glucose, fructose, sodium, potassium and chloride to fluid replacement beverages. Fluid absorption in the small intestine is stimulated by glucose and sodium (and to a lesser extent by fructose and other electrolytes). Glucose and sodium are absorbed via a common membrane carrier in the mucosal epithelium of the proximal small intestine. The potentiation of sodium uptake by glucose establishes an osmotic gradient for fluid absorption.(ABSTRACT TRUNCATED AT 400 WORDS)