Why are mice overweight? - briefly
Overconsumption of energy‑dense feed and limited movement, typical of laboratory conditions, drive adiposity in mice. Additionally, genetic susceptibility and disruptions in leptin signaling amplify weight gain.
Why are mice overweight? - in detail
Mice develop excess body fat when energy intake consistently exceeds energy expenditure. High‑calorie diets, especially those rich in sugars and fats, provide readily absorbable nutrients that promote rapid adipose accumulation. Laboratory rodent chow formulated with elevated protein or carbohydrate levels can induce weight gain if portion size is not restricted.
Genetic predisposition influences susceptibility. Mutations in genes regulating leptin signaling, such as ob/ob or db/db, impair satiety cues, leading to hyperphagia and reduced metabolic rate. Strains with altered melanocortin receptors exhibit similar patterns of uncontrolled feeding.
Environmental factors contribute significantly. Limited cage space reduces voluntary locomotion, lowering daily energy output. Ambient temperature near thermoneutrality eliminates the need for thermogenic heat production, decreasing basal metabolic demand. Continuous access to food eliminates natural fasting periods, further tilting the energy balance.
Hormonal dysregulation reinforces obesity. Elevated insulin levels promote lipogenesis, while decreased adiponectin impairs fatty‑acid oxidation. Chronic stress activates the hypothalamic‑pituitary‑adrenal axis, increasing corticosterone, which can stimulate appetite and fat deposition.
Microbiome composition modulates nutrient extraction. Colonization by Firmicutes‑dominant communities enhances caloric harvest from otherwise indigestible polysaccharides, contributing to weight gain even without increased food intake.
Key mechanisms can be summarized:
- Excess caloric intake from nutrient‑dense diets
- Genetic mutations affecting appetite and metabolism
- Reduced physical activity due to confinement or temperature
- Hormonal imbalances promoting fat storage
- Gut microbial profiles increasing energy extraction
Addressing mouse obesity requires controlling diet composition, limiting unrestricted feeding, providing environmental enrichment to encourage movement, and, when appropriate, selecting strains without known metabolic defects. Monitoring hormonal and microbiome markers can guide interventions and prevent progressive weight gain.