While he was an assistant professor of nutrition in the School of Family and Consumer Studies at Kent State University in Kent, Ohio, Hertzler studied the Web sites of two leading energy bars - Ironman PR Bar and PowerBar - which had different carbohydrate contents but made similar claims about not spiking blood-glucose levels.
Instead of researching how the bars affected athletic performance, Hertzler decided to look at how they affect glucose levels.
He used 10 female and two male subjects in a 15-week study, none of whom had diabetes. The test group consisted of dietetics students, most of whom were not athletes.
On four occasions, the subjects were fed either an Ironman PR Bar, a PowerBar, a candy bar or two slices of white bread after overnight fasts of 12 or more hours. The meals were consumed with up to 8 ounces of water.
Every 15 minutes for the first hour after eating, then at 30-minute intervals the second hour, blood was taken from the students' fingers to measure glucose levels. The results were published in the January 2000 edition of Journal of the American Dietetic Association.
The PR Bar had what Hertzler considered to be a moderate carbohydrate content - 40 percent of its energy came from carbohydrates - while PowerBar had a high carbohydrate content, with more than 70 percent of its energy from carbohydrates.
According to the study, blood-glucose levels peaked at the 30-minute mark for both energy bars but the level for the high-carbohydrate bar was significantly higher. Peak blood glucose levels for the white bread and the candy bar were reached by the 45-minute mark and were similar to those for the high-carbohydrate energy bar, the study showed. The glucose value for the moderate-carbohydrate bar was significantly lower than the other three.
Hertzler also found that the high-carbohydrate bar caused a more rapid peak in glucose level followed by a sharper decline. The energy content of the moderate-carbohydrate energy bar was higher than that of the other three meals, according to the study.
A quick rise in glucose levels usually causes a spike in insulin levels, which ties up fatty acids, preventing them from being released into the blood for fuel, Hertzler said. That can be bad news for athletes.
But Hertzler said he isn't against the use of energy bars.
"There's no such thing as a good or a bad energy bar," he said.
An individual taste
The type of energy bar people should eat depends on what they like and what response they want their body to have, said Douglas Lentz, director of fitness and wellness at Results Therapy & Fitness in Chambersburg, Pa.
Athletes participating in short-duration events likely want high-carbohydrate energy bars, while endurance athletes may be better served by moderate-carbohydrate bars, according to the study.
The market for such bars started with bodybuilders and has gone mass-market, said Jose Antonio, who has a Ph.D. in exercise physiology and works for Rexall Sundown Inc. in Boca Raton, Fla., which manufactures and markets vitamins, supplements, nutritional products and over-the-counter pharmaceuticals.
Antonio doesn't like the term "energy bars" because it suggests their content is primarily carbohydrate and sugar. Many have protein - some boast as much as 30 grams. Plus, unwrapping and eating a food in bar form is more convenient than cooking a chicken breast or preparing a healthful shake, he said.
"I believe in them," Lentz said. "I do think there's a benefit."
Antonio, who writes for Muscle & Fitness magazine, added that indulging in such healthful bars can prevent overeating during the day.
Perhaps the best solution to sagging energy levels is a healthful diet, said Brent Garrett, an exercise physiologist at The Wellness Center at City Hospital in Martinsburg, W.Va.
"If you can eat a regular diet, you don't necessarily need to supplement your diet with an energy bar," Garrett said.
Lentz is an advocate of consuming plenty of carbohydrates.
"I'm a firm believer in a complex-carbohydrate-type diet," he said. "Carbs give your body fuel."