Weight loss in an old dog is a symptom, not just an appetite problem
Older dogs lose weight for different reasons, and the fix depends on which one is yours. Sore teeth or gums can make chewing dry food painful, so he leaves the bowl while still hungry. Muscle wastage along the back and hind legs is common with age and arthritis, so the scales can fall even when he eats well. Digestive changes can mean less of each meal is absorbed, and conditions affecting the kidneys, thyroid, liver, or gut can all pull weight off quietly. That is why adding a second dinner before a vet check can mask a problem that needed finding.
Rule out pain and illness first
Book a vet visit if the loss is new, rapid, or paired with drinking more, vomiting, loose stools, bad breath, or dropping food from one side of the mouth. A dental look, a hands-on feel of muscle condition, and routine blood work answer most of the common questions. Weigh him at that visit and ask what weight the vet wants him held at — a target matters more than a vague aim to fatten him up, because some old dogs are correctly lean and only look thin as muscle changes.
Feeding changes that genuinely help
Once causes are checked, smaller meals more often usually beat one large bowl: three or four modest portions are easier on an older stomach and less likely to be left half-finished. Choose a complete food formulated for senior dogs or one your vet suggests for his situation, and warm it slightly or add a little warm water to release smell and soften the texture for sore mouths. Feed in a quiet spot away from younger, faster dogs who may crowd him, and give him unhurried time — an old dog who eats slowly can look like a poor eater simply because the bowl is lifted too soon. Add extras only on veterinary advice, since rich scraps can trigger stomach upsets that cost more weight than they add. If he walks away from meals but returns to the bowl an hour later, leave food down in his quiet feeding spot rather than following him with it — grazing suits many older stomachs, and hovering owners can turn a slow eater anxious, which suppresses the appetite you are trying to protect.
Track the trend, not single days
Weigh him on the same scales, at the same time of day, every week or two, and note appetite, stool quality, and energy beside the number. A stable line over a month is success even if he never regains his younger bulk, while a continuing slide despite good meals means the vet needs another look rather than another portion increase. Sudden loss, a swollen belly, or complete refusal to eat for more than a day should not wait for the next routine weigh-in. Keeping those dated notes in KinsLe Pet Passport means his weight history, dental findings, and blood results travel together as one portable packet, so any vet who sees him can spot the trend at a glance.