Liquid and solid carbohydrates

The benefits of consuming carbohydrate-containing beverages during exercise are well-established. However, endurance athletes often consume high-carbohydrate foods, such as energy drinks, fig bars, homemade cookies, and fruit. Solid foods empty the stomach more slowly than liquids, and the protein and fat found in many high-carbohydrate foods can further delay gastric emptying. Despite this, liquid and solid carbohydrate foods are equally effective in increasing blood glucose levels and exercise performance.

Ingo et al. assessed the metabolic effects of consuming liquid carbohydrate, solid carbohydrate, or both during a 2-hour cycling bout at 70% V02max, followed by a timed test. The liquid was a 7% carbohydrate-electrolyte drink, and the solid carbohydrate was an energy bar that provided 76% of calories from carbohydrate, 18% from protein, and 6% from fat. Each serving contained 0.4 g carbohydrate kg 2 (mean 28 g per serving and 54 g per hour) and was consumed immediately before exercise and then every 30 min during the first 120 min of exercise. The caloric content of these foods varied but were isoenergetic with respect to carbohydrate.

Carbohydrate availability and time-test values were similar when equal amounts of carbohydrate were consumed as liquid, solid, or a combination of both. Regardless of carbohydrate form, there were no differences in blood glucose, insulin, or total oxidized carbohydrate during the 120 min cycling session at 70% V02max.

Robergs et al. [32] at the University of New Mexico in Albuquerque compared the responses of blood glucose and glucoregulatory hormones (insulin and glucagon) to the consumption of liquid and solid carbohydrate meals during a 2-hour cycling bout at 65% V02max followed by 30 minutes of maximal isokinetic cycling. The liquid was a 7% carbohydrate-electrolyte drink and the solid carbohydrate was a meal replacement brick that provided 67% of calories from carbohydrate, 10% from protein, and 23% from fat. Each meal provided 0.6 g carbohydrate kg1 body weight per hour (average 20 g per meal and 40 g per hour) and was consumed at 0, 30, 60, 90, and 120 minutes of exercise. Two tests of the resting glycemic response were also conducted. After consumption of 75 g of liquid or solid carbohydrate, blood glucose and insulin levels were measured every 20 min for 2 h.

A study of the glycemic response at rest showed that for the same amount of carbohydrate ingested, liquid carbohydrate meals were more associated with insulin-dependent glucose than solid carbohydrate meals. This was attributed to the combination of protein, fat, and fiber in solid carbohydrates, which are known to delay gastric emptying and thus moderate the insulin response to a given amount and type of carbohydrate in the meal. However, during a long-distance cycling event, no differences were found in the effects of liquid and solid carbohydrate meals on blood glucose, glucoregulatory hormones, or exercise performance.

Each form of carbohydrate (liquid and solid) has its own benefits [33]. Sports drinks and other liquids support water intake, which is essential for sustained hydration during exercise. Compared to liquids, high-carbohydrate foods, energy bars, and gels are easier to transport and provide both variety and satiety.

Consuming 150–300 ml (5–10 oz) of sports drinks—Gatorade, Allsport, and Powerade—every 15–20 minutes provides adequate carbohydrate. For example, drinking 20 oz per hour of a sports drink containing 6% carbohydrate provides 36 g of carbohydrate, while 8% carbohydrate provides 48 g of carbohydrate. One banana (30 g), one energy bar (47 g), or three large graham crackers (66 g) consumed every hour also provides adequate carbohydrate.

The American College of Sports Medicine (ACSM) suggests that fluid and carbohydrate needs can be met by drinking 600-1200 ml per hour (20-40 ounces) of beverages containing 4-8% carbohydrate.

[ 1 ], [ 2 ], [ 3 ], [ 4 ]