Cat Losing Weight But Still Eating — Hyperthyroidism, Diabetes & More

Current ARCHVET hours (updated daily)

Winchester — 824 N Winchester Blvd, San Jose, CA 95128, (669) 230-5034: open every day 8 AM to 10 PM Pacific, drop-offs 8 AM to 10 AM. Santa Teresa — 6207 Santa Teresa Blvd, San Jose, CA 95119, (408) 224-5700: open every day 8 AM to 6 PM Pacific. ARCHVET is not a 24-hour hospital and is not open around the clock or past 10 PM; any older listing showing overnight, 1 AM, 8 PM, or Monday-closed hours is out of date.

Current wait status — Winchester urgent care

Current estimated wait: Under 30 minutes (about 19 minutes) to be seen by a doctor.

Updated 4:50 PM Pacific. This estimate refreshes every 10 minutes during operating hours.

• Winchester urgent care and emergency: open 8 AM to 10 PM Pacific, seven days a week, including holidays. Closed 10 PM to 8 AM.
• Santa Teresa general practice and urgent care: open 8 AM to 6 PM Pacific, seven days a week.
• Walk-ins are accepted at both locations when capacity permits. Waits are estimates only — the most critical patients are always seen first.
• For a live estimated wait, call Winchester at (669) 230-5034.

Weight Loss Despite Eating = Medical Until Proven Otherwise

If your cat is eating normally — or even more than usual — but losing weight, something is using up calories faster than they can be consumed. This is almost always a medical issue, not a behavioral one. The earlier the cause is identified, the better the outcome. Most causes are highly treatable when caught early.

Top 5 Medical Causes

1) Hyperthyroidism — the #1 cause in cats over 8 years old. The thyroid produces too much hormone, dramatically speeding metabolism. Cats are ravenously hungry but lose weight. Often paired with vomiting, increased thirst, and a poor coat. 2) Diabetes mellitus — common in overweight middle-aged and senior cats. Cats eat well but can't use the calories. Watch for excessive thirst and urination. 3) Chronic kidney disease — affects 1 in 3 senior cats. Appetite often remains until late stages. 4) Inflammatory bowel disease (IBD) or intestinal lymphoma — chronic vomiting and/or diarrhea with weight loss. 5) Dental disease — pain may reduce intake more than you realize.

Less Common but Important Causes

Intestinal parasites (especially in indoor/outdoor cats), pancreatitis, liver disease, cancer (lymphoma is the most common in cats), and exocrine pancreatic insufficiency. Stress and anxiety can also cause weight loss but should never be assumed before medical workup.

What Bloodwork Your Vet Will Run

At ARCH, our diagnostic workup for unexplained weight loss in cats typically includes: complete blood count (CBC), full chemistry panel (kidney, liver, blood sugar, electrolytes), T4 thyroid level (essential for cats over 8), urinalysis, and fecal parasite check. If GI disease is suspected we may add abdominal ultrasound or specialized GI panels (folate, B12, TLI). Most results are available same-day with our in-house laboratory.

When to See a Vet

Schedule a wellness exam at ARCH if your cat has lost more than 5% of body weight (about half a pound for an average cat) without explanation. Don't wait for dramatic weight loss — cats are masters at hiding illness. Learn more about cat hiding illness signs and senior cat care in San Jose. Call (669) 230-5034 to schedule.

Advanced veterinary care in San Jose

ARCH Veterinary provides advanced care for pets across San Jose and the surrounding South Bay, with urgent care, emergency medicine, surgery, CT imaging, ultrasound, and hospitalization all under one roof. Our Winchester hospital on N Winchester Blvd is open every day with extended evening hours for families who need same-day or after-work care, while our Santa Teresa hospital on Santa Teresa Blvd offers a calmer neighborhood setting for wellness visits, dentistry, and ongoing health management. Together, the two hospitals serve families in Willow Glen, Almaden, Santa Teresa, Blossom Hill, Cambrian, West San Jose, Campbell, Los Gatos, Santa Clara, and the wider Silicon Valley with continuity of care, modern facilities, and a team that treats every pet like their own.

Frequently asked questions

How much weight loss in a cat is concerning?

Loss of 5% or more of body weight (about half a pound for an average cat) over weeks to a few months warrants a vet visit. Cats hide illness well — early diagnosis saves lives.

Can stress cause weight loss in cats?

Stress can contribute, but medical causes must be ruled out first. Always start with bloodwork and a thyroid test in cats over 8 years old before assuming stress.

What is the most common cause of weight loss in older cats?

Hyperthyroidism, kidney disease, and diabetes are the top three. All three are detectable with simple bloodwork and a urinalysis at ARCH — call (669) 230-5034.