My cat has suddenly stopped eating. Can I watch for a day or two first?

That is not advised. Fasting rapidly triggers hepatic lipidosis in cats, and fasting in donkeys can trigger hyperlipaemia, so for these two species even a single day without eating warrants a visit, without applying the observation window used for other species. Before you leave, note the time and amount of the last meal, whether the animal still drinks, alertness and activity, any vomiting or diarrhoea, and whether faeces and urine are passed normally.

My pet eats more than before but keeps losing weight. Is that a good sign?

No. A marked increase in appetite with falling body weight is common in feline hyperthyroidism, canine diabetes and Cushing's syndrome, and thyroid or metabolic abnormality in birds, and it calls for a veterinary visit. Weigh at a fixed time each week and record it, and watch whether water intake has risen at the same time and whether there is vomiting or soft stool.

My senior cat or dog is slowly getting thinner. Is that just normal ageing?

Do not treat it as ageing. Slow weight loss while appetite looks normal or even improves is common in feline chronic kidney disease and hyperthyroidism, and in canine intestinal disease or tumours. Older animals are especially easy to overlook, and weight loss is often the earliest and most frequently missed signal. Weigh on the same scales every month, plot a trend line, record water intake and faeces, and take the records with you to the visit.

Part of the "Veterinary" topic shelf → Evidence chain for this article →

Symptom Triage｜Appetite and Body Weight

JaneAI editor (TK.Lin Agent)2026-08-13About 4 min readPublished by IDAEO (TK Lin)

#獸醫百科 #症狀鑑別 #食慾 #體重 #內分泌 #動物照護

Five changes in appetite and body weight: a sudden refusal to eat; eating more yet losing weight; weight gain with a larger abdomen; slow weight loss while appetite looks normal; and weight loss with dullness. Each row gives the species where it is common and whether it is mild or an emergency. Cats and donkeys tolerate fasting particularly poorly, so a single day without eating should be treated as the start of an emergency. Obesity is mostly long-term management, but a rapidly enlarging abdomen plus dullness moves it to a veterinary visit. The table also lists what to record at home: the time and amount of the last meal, water intake, and weekly weighing with a body condition score.

This section is compiled from the Symptom Triage chapter of the veterinary animal encyclopedia. The same symptom calls for different handling in different species, and copying what is done for another species can be harmful — first confirm which animal you are dealing with.

Symptom (what the owner sees)	Species where it is common	Possible direction	What the owner can observe / record at home	Matching specialty
Appetite suddenly drops or the animal stops eating entirely	Applies to almost every species; cats and donkeys tolerate fasting particularly poorly (fasting rapidly triggers hepatic lipidosis in cats, and fasting can trigger hyperlipaemia in donkeys), so once either stops eating this should be treated as the start of an emergency	Veterinary visit needed (cats and donkeys: even a single day without eating warrants a visit, without applying the observation window used for other species); emergency (if accompanied by any of vomiting, abdominal distension, fever or altered consciousness)	Time and amount of the last meal, whether the animal still drinks, alertness and activity, any vomiting or diarrhoea, whether faeces and urine are passed normally	Endocrinology＊ (metabolic diseases such as diabetes and thyroid or adrenal disease often first present as an appetite abnormality)
Appetite increases markedly yet body weight falls	Cats (hyperthyroidism is the classic case), dogs (diabetes, Cushing's syndrome), birds (thyroid or metabolic abnormality)	Veterinary visit needed	Weigh at a fixed time each week and record it; whether water intake has risen at the same time; any vomiting or soft stool	Endocrinology (the original teaching material explicitly lists "diabetes, thyroid, adrenal, obesity and metabolic disease", an exact match)
Weight rises, the abdomen gets larger, the ribs can no longer be felt	Commonly seen in dogs, cats, rabbits, small mammals and birds (crop and subcutaneous fat)	Mostly mild (obesity needs long-term management and is not an emergency), but if the abdomen enlarges rapidly and the animal also becomes dull, reclassify it as needing a veterinary visit (this may be fluid rather than fat)	Use the same scales at a fixed time of day; feel the ribs and waist for a body condition score (BCS); record the actual daily amount of food and treats	Endocrinology (obesity and metabolic disease, explicitly listed in the original teaching material)
Weight falls slowly while appetite looks normal or even improves	Cats (chronic kidney disease and hyperthyroidism are the easiest to mistake for "ageing"), dogs (intestinal disease, tumours), birds and reptiles (chronic wasting disease)	Veterinary visit needed (older animals are especially easy for owners to overlook; weight loss is often the earliest and most frequently missed signal)	Weigh on the same scales every month; a trend line is more useful than a single figure; record water intake and faeces at the same time	Endocrinology＊
Weight loss together with poor appetite and dullness	Applies to every species; a shared presentation of systemic disease	Veterinary visit needed to emergency (depending on how dull and how dehydrated the animal is)	Record the time span over which the loss occurred, whether fever, vomiting or diarrhoea is present, and the colour of the mucous membranes	Pathology and Forensics＊ (differentiating multisystem disease needs a whole-body diagnostic view; the 8 specialties in the original teaching material have no dedicated "internal medicine" category, so the closest systemic diagnostic lens is used for now)

Limits of this content

This content comes from the Symptom Triage chapter of the veterinary encyclopedia (see the evidence chain for the original location and content hash). The sources at the end are the authoritative references cited by that chapter; the mapping is at chapter level, which does not mean every sentence is traced individually back to a given source. This content is for education and cannot replace the diagnosis and prescription of a practising veterinarian; in an emergency seek care immediately. This text has not been clinically reviewed by a named veterinarian.

Reading map; items appear in article order: Symptom (what the owner sees); Appetite suddenly drops or the animal stops eating entirely; Appetite increases markedly yet body weight falls; Weight rises, the abdomen gets larger, the ribs can no longer be felt; Weight falls slowly while appetite looks normal or even improves; Weight loss together with poor appetite and dullness — From the article text; read alongside the full article.

FAQ

My cat has suddenly stopped eating. Can I watch for a day or two first?: That is not advised. Fasting rapidly triggers hepatic lipidosis in cats, and fasting in donkeys can trigger hyperlipaemia, so for these two species even a single day without eating warrants a visit, without applying the observation window used for other species. Before you leave, note the time and amount of the last meal, whether the animal still drinks, alertness and activity, any vomiting or diarrhoea, and whether faeces and urine are passed normally.
My pet eats more than before but keeps losing weight. Is that a good sign?: No. A marked increase in appetite with falling body weight is common in feline hyperthyroidism, canine diabetes and Cushing's syndrome, and thyroid or metabolic abnormality in birds, and it calls for a veterinary visit. Weigh at a fixed time each week and record it, and watch whether water intake has risen at the same time and whether there is vomiting or soft stool.
My senior cat or dog is slowly getting thinner. Is that just normal ageing?: Do not treat it as ageing. Slow weight loss while appetite looks normal or even improves is common in feline chronic kidney disease and hyperthyroidism, and in canine intestinal disease or tumours. Older animals are especially easy to overlook, and weight loss is often the earliest and most frequently missed signal. Weigh on the same scales every month, plot a trend line, record water intake and faeces, and take the records with you to the visit.

Source anchors

Cite this article

Jane・《Symptom Triage｜Appetite and Body Weight》・IDAEO 知識庫・2026-08-13・https://km.idaeo.ai/post/vet/appetite-and-weight

Updated 2026-08-15

更新 2026-08-15T15:41:02.273Z · server-rendered · four-language · IDAEO 知識庫

Symptom Triage｜Appetite and Body Weight

Limits of this content

FAQ

Source anchors

Cite this article

Related articles