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SAN DIEGO – People who chowed down on protein bars as a way to avoid overeating actually took in an extra calories and saw no lessening of appetite, but did experience a rise in fat-mass levels.

In a small trial, non-athlete participants who consumed one protein bar a day for a week boosted their calorie intake by a mean 170 calories a day, while their appetites remained stable. But their fat mass levels rose by an average of 3% at the end of the 7 days, according to Carol S. Johnston, PhD, RD, of Arizona State University in Phoenix.

"We expected to see that the increased satiation would decrease 24-hour calorie intakes. But rather, they increased on the days of bars were consumed at an average of about 170 calories a day, which could contribute over time to weight gain," said Johnston, who presentation the study at the ObesityWeek annual meeting.

In the winter and spring 2022, Johnston and colleague , of the Shanghai American School in China, assigned 21 non-athlete participants (majority female, mean age 22, BMI 18.5-30, 30% overweight) to eat one of the following for 7 days:

• Pure Protein bar: 21 g protein, 15 g carbohydrate, 5 g fat, 2 g fiber, 180 calories
• Quest protein/fiber bar: 20 g protein, 10 g carbohydrate, 7 g fat, 14 g fiber, 180 calories

After a week-long washout period, participants crossed over to eat the other kind of protein bar each day. were calculated using five 100-mm Visual Analog Scales (VAS).

They reported that composite weekly appetite scores didn't change significantly at 58.3, 57.9, and 55.6 mm for baseline, high protein, and high protein/fiber bars, respectively. Nor did these scores differ between the kinds of bars after 1 hour at 36.0 and 35.6 mm, respectively.

But the average daily calorie intake jumped by 7%-13%: 1,776 kcals during the washout week, 1,902 kcals with the high-protein bar, and 1,998 kcals for the high protein/fiber bar. The researchers also found that body fat mass grew by a mean 3% after 1 week of consumption of both types of bars. And fat mass was significantly higher with the high protein/high fiber bar versus baseline (18.8 kg vs 18.3).

The increase in adipose tissue "suggests that over time, you would see gains in body mass," Johnston said. However, waist circumference and body mass didn't change significantly during the study period.

"Individuals need to be counseled that ingestion of a protein bar needs to substitute for other calories that they're consuming during the day and can't just be added to the daily caloric intake," Johnston said.

The North American market for protein bars and it's expected to continue on that trajectory.

"People are consuming these protein bars because they perceive them as healthy," Johnston said. "And we know that the literature shows that protein is satiating in the diet."

Johnston explained that she and Pang " were interested in examining whether consumption impacted satiety and thereby would decrease 24-hour caloric intake and potentially help with weight management through the satiety effect."

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