Obesity has become a major health issue in dogs. Obesity in dogs increases the risk of many chronic diseases and chronic low-grade inflammation. The objective of this study was to determine the effect of a therapeutic weight loss (TWL) diet on weight loss and metabolic health in overweight and obese dogs. Thirty overweight and obese dogs were randomized into two groups with 15 dogs per group based on key baseline (BSL) parameters and allotted to either a control or TWL diet for 6 mo. At the start of the study, the control group had six females and nine males with mean age of 9.12 ± 0.48 (mean ± SEM) yr; there were seven females and eight males with mean age of 9.73 ± 0.63 yr in the TWL group. The control group and the TWL group had comparable body weight (34.78 ± 0.76 and 34.63 ± 0.86 kg, respectively), % body fat (BF; 39.77 ± 1.18 and 39.89 ± 0.93, respectively), and body condition score (BCS; 7.80 ± 0.14 and 7.67 ± 0.16 on a 9-point BCS scale, respectively). The control (CTRL) diet was formulated based on the macronutrient ratio of a commercial metabolic diet, and the TWL diet was enriched with dietary protein, fish oil, and soy germ meal. Both diets were fortified with essential nutrients to account for caloric restriction during weight loss. Dogs were fed with 25% less than BSL maintenance energy requirement (MER) for the first 4 mo and if they did not reach a BCS of 5, they were fed 40% less than BSL MER for the last 2 mo. Body composition was determined by dual-energy x-ray absorptiometry. Postprandial glucose profiles were determined by continuous glucose monitoring devices. Serum samples were collected for analyses of blood parameters, hormones, and cytokines. All data were analyzed using SAS 9.3, with significance being P < 0.05. At the end of the study, the control group and the TWL group had comparable weight loss (-5.77 ± 0.31 and -6.14 ± 0.32 kg, respectively; P = 0.4080). But the TWL group lost significantly (P = 0.034) more BF (-13.27 ± 1.28%) than the control group (-9.90 ± 1.23%). In addition, the TWL diet completely prevented loss of lean body mass (LBM) in dogs compared with BSL. Dogs fed with the TWL diet had significantly lower fasting serum cholesterol, triglycerides, insulin, leptin, mean postprandial interstitial glucose, and pro-inflammatory cytokines compared with dogs fed with the CTRL diet. In summary, the TWL diet prevented loss of LBM, promoted weight loss and metabolic health, and reduced pro-inflammatory cytokines and chemokines in overweight and obese dogs during weight loss.