Improved glucose tolerance with lifetime diet restriction favorably affects disease and survival in dogs.

Labrador retrievers (42 of original 48) were used to assess the effects of lifetime diet restriction on glucose tolerance at ages 9-12 y. Restricted-fed (RF) dogs were fed 75% of the same diet consumed by control-fed (CF) pair-mates. An intravenous glucose tolerance test was done annually (maximal stimulation, nonsteady-state). Diet treatment, age, and interactions were fixed effects. Statistical procedures used included mixed-model, repeated-measures ANOVA; least-squares means; Tukey's multiple comparison; paired t tests; and Spearman rank correlations. Glucose k-value and half-life, and insulin sensitivity (total, and 9, 10, 11 y, and per lean mass) were higher (P < 0.05) in RF than in CF dogs. Late-phase insulin release [area under the curve (AUC) 30-120 min] was less (P < 0.05) in RF than in CR dogs. Early-phase insulin release (AUC 0-5 min), y 12 insulin sensitivity and insulinogenic index did not differ between RF and CF dogs. Insulin peak, delta and total AUC increased (P < 0.05) with age, whereas the glucose k-value and glucose half-life were not affected by age. Insulin sensitivity was negatively, and insulin AUC 30-120 min, peak and delta glucose were positively correlated with body weight, body condition score, fat mass, percentage of fat and abdominal fat/total tissue. Higher insulinogenic indices tended (P = 0.053) to be associated with greater median survival and dogs with higher insulin sensitivity were at lower (P < 0.05) risk of dying or receiving chronic disease treatment. Time to first osteoarthritis treatment or death was greater with lower basal glucose and higher insulin sensitivity (P < 0.05), but diet restriction explained most of this relationship's variation. Glucose disposal efficiency and insulin response were associated with increased quality and length of life in diet-restricted dogs.