Are mice calorically restricted in nature?

Area of Science:

• Gerontology
• Animal Ecology
• Evolutionary Biology

Background:

• Caloric restriction (CR) extends lifespan in laboratory animals.
• The mechanism behind CR's anti-aging effects is debated: is it a return to normal intake or below natural levels?
• Understanding mouse food intake in labs versus nature is crucial for interpreting CR studies.

Purpose of the Study:

• To compare energy intake of laboratory mice, wild-derived mice, and wild mice.
• To determine if CR in lab mice represents a return to normal or below-natural food intake.
• To clarify the role of overeating in CR's anti-aging effects.

Main Methods:

• Comparative analysis of energy consumption across three mouse groups: lab mice, wild-derived mice (4 generations from wild), and wild mice.
• Standardized housing conditions for lab and wild-derived mice.
• Body mass correction applied to energy intake data.

Main Results:

• Ad libitum fed laboratory mice consume no more energy than wild mice, after body mass correction.
• Wild mice in natural environments consume more energy than ad libitum fed laboratory mice.
• Laboratory mice consume more than wild-derived mice under similar captive conditions, suggesting selection for increased intake during domestication.

Conclusions:

• Laboratory mice have been selected for higher food intake compared to captive wild mice but not compared to wild mice in nature.
• CR in laboratory settings restricts energy intake below levels experienced by mice in their natural environment.
• The anti-aging effects of CR are unlikely due to eliminating detrimental overeating, as lab mice do not overeat relative to wild counterparts.