Chronic experience with unpredictable food availability promotes food reward, overeating, and weight gain in a novel animal model of food insecurity.

Ubiquitous, easy access to food is thought to promote obesity in the modern environment. However, people coping with food insecurity have limited, unpredictable food access and are also prone to obesity. Causal factors linking food insecurity and obesity are not understood. In this study we describe an animal model to investigate biopsychological impacts of the chronic unpredictability inherent in food insecurity. Female rats were maintained on a 'secure' schedule of highly predictable 4x/day feedings of uniform size, or an 'insecure' schedule delivering the same total food over time but frequently unpredictable regarding how much, if any, food would arrive at each scheduled feeding. Subgroups of secure and insecure rats were fed ordinary chow or high-fat/high-sugar (HFHS) chow to identify separate and combined effects of insecurity and diet quality. Insecure chow-fed rats, relative to secure chow-fed rats, were hyperactive and consumed more when provided a palatable liquid diet. Insecure HFHS-fed rats additionally had higher progressive ratio breakpoints for sucrose, increased meal size, and subsequently gained more weight during 8 days of ad libitum HFHS access. Insecurity appeared to maintain a heightened attraction to palatable food that habituated in rats with secure HFHS access. In a second experiment, rats fed ordinary chow on the insecure schedule subsequently gained more weight when provided ad libitum chow, showing that prior insecurity per se promoted short-term weight gain in the absence of HFHS food. We propose this to be a potentially useful animal model for mechanistic research on biopsychological impacts of insecurity, demonstrating that chronic food uncertainty is a factor promoting obesity.