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  • Writer's pictureDr Meredith Wall

Underweight cats: feeding for weight gain

Updated: Apr 19

Older cats shouldn’t inevitably become underweight, but unfortunately it is a common problem. Scrolling through Facebook, I frequently see photos of cats that are in very poor body condition, and so I wanted to share some thoughts on how to best to prevent weight loss, and how to feed your cat to achieve weight gain.

A senior ginger cat sleeping

Is it normal for older cats to be underweight?

Research has shown that the prevalence of obesity plateaus and then declines in cats after seven years of age, whereas the prevalence of underweight cats increases significantly after eleven years of age, so from ten years of age is the time when we really need to be increasingly vigilant, with respect to body weight and body condition.

Identifying weight loss is really important, because underweight cats are more likely to have greater mortality. It can also help with earlier diagnosis of disease.


What causes older cats to lose weight?


Studies have shown that approximately one-third of cats greater than 12 years of age have decreased fat digestibility and approximately 20% of cats greater than 14 years of age have reduced protein digestibility, so feeding a senior cat the same diet as a young adult cat, may result in weight loss. Older cats often need more protein and more fat, as well as appropriate amounts of fibre, essential fatty acids and vitamins and minerals. The most fundamental concern, though, is to ensure adequate energy intake (meaning adequate calories fed per day).


Older cats may sometimes lose weight due to physiological changes that occur due to ageing, like decreased sense of smell and decreased taste perception. This is why it is commonly recommended to gently warm an older cat’s food, to increase the aroma of the meal and make it more appealing.


How to monitor your cat’s weight


There are many strategies to help an underweight cat gain weight. However, the most important thing you can do is to monitor your cat’s weight on a regular basis, so that you know what is normal and so that you can promptly detect even slight weight loss.

Weight loss of more than 10% of body weight is typically concerning, however in senior cats, weight loss of 5% may be abnormal, especially if the cause for this is not obvious.


The best way to monitor your cat’s weight is:

  1. Weigh your cat at home, at least once a week. Don’t wait for it to be done at vet visits, because they are too infrequent.

  2. Purchase a digital baby scale. These are not too expensive; there are plenty of options on Amazon, or at stores like Kmart or Target.

  3. Be sure to place the scale on a steady surface, and then gently lower your cat onto the scale. Have a favourite treat handy, to reward your cat for standing still on the scale.

  4. Be sure all of the cat is on the scale (no paws off the side!), and then make a note of the weight. Keep a diary or spreadsheet of the results.

A digital baby scale
Digital baby scales are perfect for at-home monitoring of body weight

If your cat’s weight is stable – that’s fine, no further action is needed. Cats gaining weight may need a weight loss plan, but that’s a topic for another day. If your cat has lost weight, re-check this a few days later. Trends over 3-4 weigh-ins are most important, so review your records. If you have noticed a downward trend in weight over several weigh-ins, then it is probably time to book a visit to your veterinarian.


Next steps for a cat that is losing weight


There are many medical conditions that can cause weight loss in cats, so it’s really important to visit your vet as promptly as possible. It is much better to prevent weight loss, than to have to try and reverse it, because weight gain in older cats can be slow, and require diligent feeding practices.


Some common conditions in cats that cause weight loss include:

  • Diabetes mellitus

  • Hyperthyroidism

  • Dental disease

  • Gastrointestinal diseases like inflammatory bowel syndrome

  • Chronic kidney disease

Many of these conditions can be diagnosed via a physical exam and blood tests, so it’s not too expensive or invasive to reach a diagnosis most of the time.


If no medical reason for the weight loss can be found, it may be helpful to quantify caloric intake for a week, to see if decreased food intake is the cause of the weight loss. Practically, this means keeping a diary of food offered, and food consumed (e.g. one 95 gram can of ‘Weruva’ Steak Frites; 90% consumed). This can help us to work out whether the cause of the weight loss is simply inadequate food intake.


The cause of the weight loss will often affect the choice of diet going forward. For example, cats with kidney disease will require a renal diet, and diabetic cats may need a diabetic diet.

Regardless of this, there are some basic points to consider when selecting a diet for weight gain, such as energy density, digestibility, protein and fat content, and palatability.


Diet selection for an underweight cat


Here’s some general guidelines, in terms of diet selection:

Select an energy-dense diet (and treats)


Inaba churu cat treats in different flavours

Energy density is perhaps the most important consideration when choosing a diet for weight gain. Energy density is the amount of energy (calories) per gram of food.

Let’s look at some examples:


Fancy Feast Royale Broths Tuna, Surimi and Whitebait broth 0.30 kcal per gram

Inaba Churu chicken recipe tubes 0.43 kcal per gram

Weruva 'Grandma’s chicken soup' canned diet 0.68 kcal per gram

Hill’s Prescription Diet a/d canned diet 1.17 kcal per gram

Feline Natural lamb feast canned diet 1.21 kcal per gram

Hill’s Prescription Diet m/d GlucoSupport dry diet 3.98 kcal per gram

Ziwi Peak chicken recipe air-dried diet 5.00 kcal per gram

Feline Natural beef feast freeze-dried diet 5.33 kcal per gram

Orijen Original freeze-dried cat treats 5.43 kcal per gram


What you can see is that the energy density (or kcal per gram) of different diets and treats for cats varies a lot!

If you would prefer to feed a high moisture diet, try to choose a canned diet with more than 1 kcal per gram. Broths are great for adding water to the diet, but not energy. Canned diets with a lot of gravy will typically have a lower energy density.

Here are some examples of canned and raw diets with a higher energy density you can consider:

Zealandia beef pate 1.23 kcal per gram

Feline Natural chicken and lamb pouch 1.31 kcal per gram

Tiki Cat® After Dark™ Paté Lamb & Beef Liver recipe 1.28 kcal per gram

Koha Limited Ingredient Diet Duck Pâté for cats 1.35 kcal per gram

Viva Raw beef for cats recipe 1.58 kcal per gram

Please be sure to check that these diets suit your cat's needs (for example, some are higher in phosphorus than others). There are many other options available; usually beef, lamb and duck diets are more energy dense than diets made from lean meats like kangaroo, chicken breast, or turkey breast.

Generally, we don’t recommend long-term feeding of a dry diet, however what you can see is that many dry diets have 4 to 5 times the energy density of most wet diets. What this means is that you have to feed 4 to 5 times the amount of a canned diet, compared with a dry diet, to provide the same calories. This can be difficult to achieve for some older cats.


So, an appropriately chosen dry diet (kibble or air-dried) can sometimes be used as a clinical tool, to achieve weight gain, until an ideal weight has been reached. This will normally take 2-6 months. The dry diet can be fed alongside a canned diet, or even as a small supplement to the diet.

Hill's Prescription Diet m/d dry diet in a white bowl

For example, 4 x 8 grams (32 g) per day of Ziwi Peak chicken recipe air-dried diet will provide 160 kcal, which is about 50% of a 5 kg cat’s daily requirement.

If fed alongside a canned diet with a high moisture content of about 80%, adding a small amount of dry food to each meal can add a lot of calories while only reducing the overall moisture content of the diet to 74%.

The best dry diets to use for this purpose are high protein, high fat kibble like prescription diabetic diets, or air-dried diets. Some clients are happy about being able to leave the dry diet out overnight; this can be a bit more challenging with a raw, fresh-cooked or canned diet.

For clients that would prefer not to feed kibble, air-dried diets can be a good alternative because they are often high in protein and fat, and very energy-dense. They may contain less fibre than prescription diabetic diets though, so this can increase the risk of constipation in some older cats. Some air-dried diets are more palatable than others, so you may need to trial a few options. Remember, the goal is to use the dry diet to achieve significant weight gain, and then gradually return to a more moisture-rich diet for long-term feeding.

Be careful with freeze-dried diets, because they are very energy-dense when dry, but when rehydrated to 75-80% moisture, they have the same energy density as most canned diets. We don’t recommend feeding these diets dry/not rehydrated, except in small amounts as an occasional treat or topper.

Select a high protein, high fat diet:


A diet that’s high in protein may help to maintain existing muscle mass and promote formation of muscle during weight gain. It can also increase the palatability of the diet, which is obviously very important.

Fat is more calorie-dense per gram, compared with carbohydrate or protein – the fat content of the diet is predominantly what determines energy density (along with the moisture and fibre content of the diet). Higher fat diets are generally more energy-dense – for example, a high fat canned diet will typically be more energy-dense than a low-fat canned diet. For cats, as mentioned previously, canned supermarket diets containing mainly or only tuna and shredded chicken breast are often very low in fat, and not an ideal choice as the sole diet for an underweight cat.

A can of Rawz 96% duck and duck liver cat diet

Some examples of high fat, high protein canned diets include:

Feline Natural chicken and venison canned diet, Ziwi Peak venison canned diet, and Rawz 96% duck and duck liver pate canned diet.

Select a highly digestible, palatable diet:


Many factors can affect digestibility – these can relate to the individual cat, or the diet in question. Factors affecting the digestibility of protein in the diet include protein quantity and quality; the presence of any anti-nutritional factors such as phytates or fibre; and the storage and processing of the diet. Factors affecting fat digestibility include animal age, fat and calcium concentrations in the diet, and type of fat.


From a practical perspective, to choose a highly digestible diet for an underweight cat, pay attention to the ash content of the diet, the fibre content, and the quality of the diet. Higher ash and fibre in the diet may decrease digestibility – although constipation can be a common problem in senior cats, so fibre should be appropriate but not excessive. Higher quality diets often contain more protein, and better-quality protein, ultimately increasing protein digestibility.


With respect to processing, in one study, higher dry matter and protein digestibility was observed for two commercial raw diets, compared with a heat-processed (canned) diet. Heat treatment in general decreases protein bioavailability through a variety of biochemical reactions, including proteolysis, protein cross-linking, oxidative reactions and browning or Maillard reactions.

Feeding practices: how much and when?


Multiple small meals per day are a sensible choice for an underweight cat, because this gives them every opportunity to eat throughout the day and slowly gain weight. As mentioned previously, it is useful to have food available overnight for grazing, although it’s important to be mindful of food safety (for example, raw diets shouldn’t be left out of the fridge for 8 hours overnight).


Underweight cats can be fed ad lib (as much as they would like per day), however it is important to keep a record of what and how much is fed, and how much is actually eaten. This is because ad lib feeding actually often makes it difficult to tell whether a cat is eating enough, especially in a multi-cat household.


Make sure you work out how much your cat needs to eat per day; this can be done using online calorie calculators (for example, Pet Nutrition Alliance has a calorie calculator for cats available here.) If your cat has a poor appetite and is not eating enough, again, it's important to see your vet as soon as possible, to work out why.

Screenshot of Pet Nutrition Alliance's calorie calculator for dogs and cats

Supplements and high calorie toppers for weight gain


There are a number of high calorie supplements and topper available for cats. Some of these are quite high in carbohydrate, and some do contain simple sugars.

Here are some examples:

Troy Nutripet high calorie supplement for dogs and cats

4.39 kcal per gram

Includes vitamins and minerals; but not complete and balanced.


3.58 kcal per gram

Includes vitamins and minerals; but not complete and balanced.


Available as a paste or powder

3.85 kcal per gram

Includes vitamins and minerals; but not complete and balanced.


If you want to supplement your cat’s canned diet with a palatable, high calorie topper, you can also consider adding a small amount of cooked or raw meat with a higher fat content (for example, ground beef, pork or lamb with 20% fat). Avoid very lean meats like chicken breast or turkey breast, unless the goal is to add predominantly protein to the diet. If you find that the added meat is high palatable, you could consider a balanced raw or cooked homemade diet, using a meal completer or human vitamin and mineral supplements.


Toppers and treats should make up no more than 10% of daily calories, otherwise the diet may become deficient. Freeze-dried treats are energy-dense and can be crumbled over a meal to encourage eating and provide a calorie boost.

Other examples of additives or toppers to improve palatability include:

  • Purina Proplan FortiFlora

  • AnimalBiome® Fish Bits High-Protein Food Topper

  • Inaba’s broths, purees and mousses

  • Bonito flakes

  • Nutritional yeast and brewer’s yeast

  • Certain amino acids like glycine

  • Freeze-dried toppers like those made by Primal Pet Foods


Be very careful to avoid supplements that make the cat’s food taste horrible! Many popular supplements can taste quite horrible, and cats can be very sensitive to unusual additives. Medications that taste nasty should not be mixed into meals, but rather given separately or compounded to facilitate administration.

Key points:

  1. Be vigilant with your senior cat's weight. Have a digital scale at home for monitoring body weight once or twice weekly. Keep records.

  2. If you observe weight loss over 3-4 weigh-ins, be sure to visit your vet to address this as soon as possible.

  3. Energy-dense, highly digestible diets are a good choice for underweight cats. Be careful with broths, purees and canned diets with a lot of gravy, as the kcal per gram can be very low. Dry diets can be used as a tool to achieve weight gain, and then discontinued.

  4. Feed frequent, small meals and make sure you are feeding enough calories per day by using a calorie calculator to work out your cat's requirement.

  5. Toppers, treats and palatability enhancers can be used to increase the appeal and energy density of meals.

If you have any questions, comments or suggestions:

A senior tabby cat

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