A recent study reveals that limiting calorie intake does not prevent mice from exercising, thus questioning the common notion that dieting reduces exercise energy.
A new UC Riverside study reveals that limiting calorie intake does not prevent mice from exercising, thus questioning the common notion that dieting reduces workout energy.
The research, featured in the journal Physiology & Behavior, shows that a 20% decrease in calorie intake did not greatly affect the distance mice opted to run daily.
The aim of the study was to explore the effects of reduced food availability on mice. The researchers believed that their results could be applicable to wild animals who might not have consistent food access and to humans, who often follow calorie-restricted diets prescribed by their healthcare providers.
Assessing the amount of voluntary exercise in humans can be complex. While activities like gym workouts are easy to recognize, other instances—such as walking to get lunch instead of eating from a packed meal—fall into a gray area that is challenging to measure.
In contrast, observing lab mice is much simpler; they generally enjoy running on wheels for extended periods. The study indicated that mice maintained similar running levels, regardless of their food consumption.
“Voluntary exercise showed surprising resilience even with a 20% and 40% reduction in calories,” stated UCR biologist and lead author Theodore Garland, Jr. “They just kept on running.”
The researchers monitored the baseline running activity of the mice for three weeks, then conducted a week with a 20% calorie reduction followed by another week with a 40% reduction. This research was conducted with both typical mice and “high runner” mice specifically bred for their love of running.
While the high runners showed a slight decrease in total distance with the 40% calorie cut (an 11% reduction), this was minimal since they initially ran three times farther per day than the average mice. “They are still running at very high levels,” Garland noted. The regular mice did not decrease their daily running distance, even when facing a 40% calorie reduction.
Given that running can create a “runner’s high” by boosting dopamine and cannabinoid levels in the brain, the researchers think this motivated the mice to continue their activity even with less food. “Wheel running is an inherently rewarding behavior,” added Garland.
Surprisingly, the researchers also found that body mass was not notably affected by the 20% calorie reduction in either type of mouse. Although there was a minor decrease in body mass with a 40% caloric cut, it was lower than expected.
“Typically, people lose about 4% of their body mass when dieting, which aligns with what we observed in these mice,” Garland remarked.
This study enhances our understanding of why some individuals enjoy exercising while others do not. The researchers plan to conduct further studies to uncover why both the levels of voluntary exercise and body weight resist reduction despite decreased caloric intake.
“There must be some form of compensation at work when food intake drops by 40% without significant weight loss,” Garland noted. “This could involve reducing other physical activities or becoming metabolically more efficient, which we have not yet analyzed.”
As habitats are destroyed and food becomes scarce for wildlife, this information could prove invaluable for conservation efforts. Moreover, it may have important implications for individuals looking to enhance their health.
“We don’t want individuals on a diet to think, ‘I lack energy, so I won’t exercise.’ That would be counterproductive, and we’ve found that it doesn’t necessarily have to be this way,” Garland concluded.
