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A recent study from UC Riverside has revealed that calorie restriction does not hinder the exercise habits of mice, presenting a challenge to the assumption that dieting diminishes energy available for physical activity.
The findings, published in the journal Physiology & Behavior, show that even when calorie intake was decreased by 20%, mice maintained their voluntary running distances without significant changes.
The objective of the research was to assess the effects of reduced food availability on animal behavior. The researchers aimed to draw parallels between their findings and the behavior of wildlife, which often face fluctuations in food supply, as well as to provide insights relevant to humans who are commonly advised to diet.
Measuring the amount of physical activity that humans engage in can be quite complex. While activities like gym workouts are easily categorized as exercise, many everyday movements—such as walking to a cafeteria for meals—often fall into a gray area that is difficult to quantify.
Conversely, studying lab mice offers a clearer picture of voluntary exercise behaviors, as these animals tend to run extensively on wheels. The researchers found that mice maintained consistent running levels regardless of their caloric intake.
“Voluntary exercise showed remarkable resilience, even when food intake was cut down by 20% and 40%,” stated Theodore Garland, Jr., a biologist at UCR and the lead author of the study. “The mice kept running.”
To gather data, researchers first established a baseline of running activity over three weeks. They then reduced calorie intake by 20% for a week, followed by a 40% reduction in the subsequent week. This research included both standard mice and a breed specifically selected for their high running ability.
The high-running mice did experience a slight decline in running distance—an 11% decrease during the 40% calorie restriction—yet they continued to run significantly more than their standard counterparts. According to Garland, “They’re still running at extremely high levels.” Interestingly, typical mice did not show any decrease in distance, even under the more extreme reduction.
The researchers hypothesized that the joy of running, linked to increases in dopamine and cannabinoid levels in the brain, drove the mice to continue exercising despite reduced food intake. “Wheel running is a self-rewarding behavior,” Garland explained.
Additionally, the study found that body mass was largely unaffected by a 20% reduction in calories for both mouse types. While there was a slight drop in body mass with the 40% reduction, it was not as pronounced as anticipated.
“People often lose about 4% of their body mass while dieting, which is similar to what we observed in these mice,” noted Garland.
This research adds to the existing knowledge regarding exercise motivations and why there is variability in exercise habits among individuals. Future studies are planned to further explore the resilience of voluntary exercise and body mass in response to calorie restriction.
Garland speculated, “There must be some compensation occurring if food intake decreases by 40% but weight remains relatively stable. This could involve reduced activity levels or improved metabolic efficiency, which we haven’t yet measured.”
As environmental changes lead to food shortages for many animal species, findings from this research could aid conservation efforts. Moreover, the insights gained may also have significant implications for individuals looking to enhance their health and fitness regimes.
Garland concluded, “Our findings indicate that individuals on diets shouldn’t feel they lack the energy to exercise. This perception could lead to counterproductive behaviors, as our study suggests that such a situation doesn’t necessarily have to occur.”
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