ORIGINAL ARTICLE The effects of increasing water content to reduce the energy density of the diet on body mass changes following caloric restriction in domestic cats K. M. Cameron 1 , P. J. Morris 2 , R. M. Hackett 2,3 and J. R. Speakman 1 1 Institute of Biological and Environmental Sciences, University of Aberdeen, Aberdeen, UK, 2 WALTHAMÔ Centre for Pet Nutrition, Leicestershire, UK, and 3 Institute of Grocery Distribution (IGD), Hertfordshire, UK Introduction Obesity results from a chronic imbalance between energy intake and energy expenditure. The preva- lence of human obesity has dramatically increased in recent decades and is also the most common nutri- tional disorder in companion animals (German, 2006). Factors implicated in companion animal obes- ity include neutering, inactivity and feeding energy dense food (Scarlett et al., 1994; Lund et al., 2005; German, 2006). Estimates of feline obesity in the United States vary from 25% to 35% (Scarlett et al., 1994; Lund et al., 2005). Caloric restriction is the most frequent self- and physician-prescribed treat- ment to promote body mass loss for both humans and companion animals, but is rarely successful in the long-term and the lost mass is often regained. This trend has been widely observed in humans (Anderson et al., 1999), dogs (Laflamme and Kuhlman, 1995), cats (Villaverde et al., 2008) and laboratory mice (Hambly et al., 2007). Several die- tary and behavioural strategies aimed at promoting maintenance of mass loss have been identified in human subjects, such as consumption of low fat Keywords energy density, cats, body mass, food intake, caloric restriction, digestibility, physical activity, diet Correspondence Kerry Cameron, Institute for Ageing and Health, Newcastle University, Campus for Ageing and Vitality, Newcastle-upon-Tyne, NE4 5PL, UK. Tel: 0191 248 1219; Fax: 0191 248 1101; E-mail: kerry.cameron@newcastle.ac.uk Received: 12 July 2010; accepted: 12 November 2010 Summary Caloric restriction induces body mass loss that is often regained when restriction ends. This study aimed to determine if dietary energy density modulates the extent of post-restriction body mass regain. Water (20% wt:wt) was added to a standard dry commercially available feline diet. Twenty-seven domestic short-haired cats underwent a 20% caloric restriction on this diet. Following restriction, cats were offered the same dry diet ad libitum either without additional water or with 40% added water, therefore maintaining macronutrient composition whilst manipu- lating energy density. Despite no significant difference in energy intake during ad libitum consumption, post-restriction body mass regain was greater on the high energy dense (0% hydrated), compared to the low energy dense (40% hydrated) diet. The same protocol was repeated with a separate cohort of 19 cats with additional measures of physical activ- ity, gut transit time and energy digestibility. Activity levels on the low energy dense diet were significantly higher than in cats on the high energy dense diet (p = 0.030) and were similar to those recorded during caloric restriction. These results suggest that body mass gain following caloric restriction is ameliorated, and physical activity enhanced, by feeding a diet which is low in energy density due to the addition of 40% water. DOI: 10.1111/j.1439-0396.2010.01107.x Journal of Animal Physiology and Animal Nutrition 95 (2011) 399–408 ª 2010 Blackwell Verlag GmbH 399