Obesity
Excess body fat associated with negative health effects. Around 60% of dogs and 50% of cats in many countries are overweight or obese. Major lifespan and disease driver.
Obesity is the most common nutritional disorder in pets. It is also one of the most reversible causes of premature illness — every kilogram off an overweight pet reduces strain on joints, heart, pancreas, kidneys, and the immune system.
Causes are simple in principle (calories in > calories out) and complex in practice (over-feeding, treats and table scraps, de-sexing-driven metabolic shift, inactivity, ageing, the unintended cumulative effect of "just a bite"). The most common owner-side cause is using treats as love.
Health consequences: arthritis, diabetes, hepatic lipidosis in cats, pancreatitis, heart disease, kidney disease, urinary disease, multiple cancers, exercise intolerance, anaesthetic risk, and shortened lifespan (1.8 years in the landmark Labrador study).
Weight loss must be gradual — 1–2% body weight per week in dogs, 0.5–1% in cats. Crash dieting in cats triggers hepatic lipidosis. Use a vet-supervised plan: prescription weight-loss food, measured portions, fewer treats (or treats as part of the daily calorie allowance), increased low-impact activity.
The hardest part of weight loss in pets is the household — multiple feeders, kids slipping treats, the older relative who can't bear to see the dog "starve." Family consensus is the actual lever.