Senior Cat Diet: More Protein, Not Less, After 11

The diet that keeps a 12-year-old cat going looks close to the one for a 4-year-old, with three changes: more protein rather than less, more water, and more calories per mouthful. Switching a healthy cat to a low-protein "senior" formula at 7 costs muscle that never comes back.

Why the low-protein senior formula is backwards

Cats lose lean mass from about 8 years old onward, and the loss is not inevitable aging so much as a protein supply problem. Two things happen at once. Muscle protein turnover becomes less efficient, and the apparent digestibility of protein and fat drops by roughly 5–10% in cats over 11. A food that met a 4-year-old's requirement now delivers less usable protein to a 13-year-old, at exactly the age when muscle is hardest to rebuild.

Most veterinary nutrition texts therefore treat senior protein requirement as equal to or slightly above adult maintenance, not below it. Kidney disease is the exception, and it is a diagnosis, not an age.

Protein in numbers

Aim for 40% or more protein on a dry-matter basis, and about 30–35% of calories from protein. For a 4.5 kg cat eating 220 kcal a day that works out to roughly 17–19 g of protein, or 3.8–4.2 g per kg. Feed the top of that range if the cat has lost weight or muscle, and add about 10% to cover the digestibility drop.

Check the body condition score and, more importantly, the muscle score along the spine and hips every month. Ribs you can feel but not see, with muscle either side of the spine, is the target. A cat that is thin with a bony spine is losing protein even if the scale has not moved much.

Phosphorus: only when the kidneys say so

Phosphorus restriction is a treatment for chronic kidney disease (CKD), staged by creatinine, SDMA and urine specific gravity. In a cat with normal renal values there is no evidence it prevents anything, and it comes bundled with protein restriction and lower calorie density, both wrong for a healthy old cat. Maintenance food sits at 0.8–1.2% phosphorus dry matter; renal formulas at 0.3–0.6%.

The practical rule: check creatinine, SDMA and phosphorus once a year from age 8, twice a year from 11. Restrict only when the numbers say CKD, and then restrict early rather than late, because the benefit is largest at IRIS stage 2.

Potassium and the drooping neck

Low potassium is common in older cats, in CKD, and in cats eating highly acidifying diets. It shows as hind-limb weakness, a neck that droops forward when the cat is lifted, poor coat and reduced appetite. Serum potassium can look normal while total body potassium is low, so a cat with those signs deserves a recheck even after one normal result.

Renal formulas are supplemented to roughly 0.6–0.9% potassium dry matter. Outside a therapeutic diet, potassium gluconate at 2–6 mEq a day, divided and titrated against bloodwork, is the usual correction. Do not supplement on a guess: too much potassium is dangerous in Addison's disease and in some urinary obstructions.

Calories per mouthful, and why smell decides

Olfaction declines with age, and appetite with it. A senior cat often eats 10–20% less volume but needs the same or more energy, so the food has to be denser. Canned food at 70–100 kcal per 100 g and dry at 350–450 kcal per 100 g is normal; a senior formula should sit at the upper end, and recovery diets at 1.3–1.6 kcal per mL exist for cats losing weight.

Three habits carry most of the difference: warm wet food to about 37°C to release aroma, offer 4–6 small meals rather than 2, and never leave food out more than 30 minutes if the cat is a grazer who walks away. A cat that eats 40 g three times a day holds weight better than one offered 120 g once.

Water before anything else

Thirst drive weakens with age while the kidney's ability to concentrate urine falls, so the same cat needs more water and asks for less. Canned food at 75–80% moisture against 8–10% for dry is the single largest lever: a cat eating 200 g of canned takes in about 150 mL from food alone. Total intake target is roughly 45–60 mL per kg per day, which for a 4.5 kg cat is 200–270 mL.

Add a fountain, a wide bowl filled to the rim, and water placed away from the food. Measure intake over 3 days before assuming it is adequate: cats are poor at asking.

B12 and omega-3

Cobalamin deficiency turns up in chronic enteropathy, pancreatitis and untreated hyperthyroidism, and it drags appetite and weight down further. Serum cobalamin below about 290 ng/L is the usual cutoff for supplementing; methylcobalamin at 250–1000 µg by injection or orally once weekly for 6–12 weeks is the standard course, then recheck.

Omega-3 at roughly 40 mg/kg a day of combined EPA and DHA supports renal and joint health and reduces inflammatory signalling. Read the EPA and DHA line, not the "fish oil" line, because 1000 mg of fish oil may carry only 300 mg of the two that matter.

Weight loss over 5% a year is a symptom

Losing more than 5% of body weight in 12 months, or any visible muscle loss, needs a workup rather than a richer food. The shortlist: hyperthyroidism, CKD, diabetes, dental disease, chronic enteropathy, and gastrointestinal lymphoma. Hyperthyroid cats often eat well and still lose weight, which is why appetite is a poor guide.

Target (dry matter, unless stated)	Healthy senior, 11+	Senior with CKD
Protein	40%–50%	26%–32%
Phosphorus	0.8%–1.2%	0.3%–0.6%
Potassium	0.6%–0.9%	0.6%–0.9%, supplemented
Calorie density	≥1.2 kcal/mL wet	≥1.2 kcal/mL wet
Moisture	75%+ (canned)	75%+ (canned)
Meals per day	3–5	4–6

1. Weigh monthly on the same scale and record it; 5% in a year means a vet visit, not a new food.
2. Do not cut protein for age alone; cut it only with a CKD diagnosis on paper.
3. Feed canned as the base, warm it to body temperature, and split into 3–5 meals.
4. Check creatinine, SDMA, phosphorus, potassium and cobalamin at least yearly from age 8.
5. Score muscle along the spine every month, not just body weight.

Handling, grooming and home changes for this age group are in senior cat care. The protein arithmetic is set out in how much protein cats need, and staging in early signs of kidney disease.

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