a1 2 Research South, Nestle Research Center St Louis (NRC-STL), Checkerboard Square, St. Louis, MO 63164, USA
a2 Department of Clinical Studies, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA
a3 Veterinary Pathology Services, Aliso Viejo, CA 92656, USA
a4 Department of Pathobiology, College of Veterinary Medicine, University of Illinois, Urbana, IL 61801, USA
a5 College of Veterinary Medicine (emeritus), Michigan State University, East Lansing, MI 48823, USA
This report reviews decade two of the lifetime diet restriction study of the dog. Labrador retrievers (n 48) were paired at age 6 weeks by sex and weight within each of seven litters, and assigned randomly within the pair to control-feeding (CF) or 25 % diet restriction (DR). Feeding began at age 8 weeks. The same diet was fed to all dogs; only the quantity differed. Major lifetime observations included 1·8 years longer median lifespan among diet-restricted dogs, with delayed onset of late life diseases, especially osteoarthritis. Long-term DR did not negatively affect skeletal maturation, structure or metabolism. Among all dogs, high static fat mass and declining lean body mass predicted death, most strongly at 1 year prior. Fat mass above 25 % was associated with increasing insulin resistance, which independently predicted lifespan and chronic diseases. Metabolizable energy requirement/lean body mass most accurately explained energy metabolism due to diet restriction; diet-restricted dogs required 17 % less energy to maintain each lean kilogram. Metabonomics-based urine metabolite trajectories reflected DR-related differences, suggesting that signals from gut microbiota may be involved in the DR longevity and health responses. Independent of feeding group, increased hazard of earlier death was associated with lower lymphoproliferative responses to phytohaemagglutinin, concanavalin A, and pokeweed mitogen; lower total lymphocytes, T-cells, CD4 and CD8 cells; lower CD8 percentages and higher B-cell percentages. When diet group was taken into account, PWM responses and cell counts and percentages remained predictive of earlier death.
(Received June 20 2007)
(Revised October 01 2007)
(Accepted October 25 2007)
p1 Present address: Kellogg Company, 8291 South Cedar Creek Road, Battle Creek, MI 49050, USA.
p2 Present address: Monsanto Company, 800 N. Lindbergh Blvd, St Louis, MO 63167, USA.
Abbreviations: CF, control-feeding; DR, diet restriction; ME, metabolizable energy; MER, metabolizable energy requirement; OA, osteoarthritis