Nutrition of aging cats

Figure 1. Our population of pet cats is aging; approximately 20-40% of cats in the United States are now estimated to be classed as “senior” and “super senior”.

Figure 2. It has been suggested that the senses of smell and taste diminish as cats age, which may lessen their food intake. Strategies to help with this include providing diets with varying aromas and flavors, and by providing food at the optimal temperature of 37°C/98.6°F. 

Therefore, senior, even healthy, cats may require a higher caloric intake to maintain weight, and a diet that has higher digestibility might result in improved nutrient absorption. Feeding guidelines are provided by manufacturers to give an average estimate of requirements, but individuals may vary up to ±50% from average. Assessment of body weight, body condition score and muscle condition score, and appropriate caloric, and potentially diet, adjustments should be done regularly for all cats that are considered senior or super senior (Figure 3).

Figure 3. All cats that are considered senior or super senior should be regularly assessed for their body weight, body condition score and muscle condition score, and their dietary requirements revised as necessary.

Dietary moisture

Dehydration can occur in aging animals due to a decreased thirst drive, decreased mobility and/or a disease process, but it can be difficult to assess the hydration status of a patient, as clinical signs of dehydration are not consistent despite significant water loss. Therefore, it is important to encourage water intake in senior cats, even if they do not appear overtly dehydrated (Figure 4). Ensuring clean, fresh water is a central tenet in this endeavor, but providing dietary moisture by feeding a wet diet can also improve intake. Dental disease is common, with one study reporting it to be present in over 50% of senior cats, so if there is evidence of oral discomfort or a reduced ability to chew kibble, feeding a wet diet may be of some benefit (alongside other appropriate measures for the underlying problem) (Figure 5). Other conditions where dietary moisture is important for management include CKD and all forms of urolithiasis. However, it is essential to remember that increasing dietary moisture also decreases the caloric density of a diet. Therefore, it is important to ensure feeding amounts are appropriate for the cat’s daily needs and that intake levels remain sufficient. If the cat has difficulty consuming the daily volumes required, mixed feeding or a dry diet may help to meet energy needs.

Figure 4. Dehydration can occur in aging animals due to various factors, but it can be difficult to assess the hydration status of a patient, and it is therefore important to encourage water intake in senior cats even if they do not appear overtly dehydrated. 

Protein 

While we know that some senior cats have reduced protein digestibility, it is less clear what level of protein should be recommended for older individuals that are otherwise considered healthy. Given that CKD is a fairly common diagnosis in older cats, with one estimate suggesting 30-40% of animals over 10 years of age being affected, and because decreased dietary protein is generally recommended for cats in the later stages of the disease, it is sometimes believed that an early reduction in dietary protein for all older cats might be of benefit. However, there is insufficient evidence to confirm that reducing dietary protein as cats age will reduce the occurrence of CKD. In addition, as mentioned above, sarcopenia is documented in cats as early as 7 years of age, so given the compromised protein digestive capacity in older cats, a reduced protein diet may increase the risk of developing sarcopenia. Therefore, as cats are obligate carnivores and have a high dietary protein requirement, these factors suggest that feeding lower levels of protein should be reserved for cats with active renal disease and is not recommended prophylactically for healthy older cats.

Figure 5. Senior and super senior cats will often suffer with dental problems, which can in turn affect their food intake. Cats in this these categories should undergo a full dental examination regularly. 

Fat 
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As previously noted, senior cats can have reduced fat digestibility which can contribute directly to decreased caloric absorption, as fat has more calories than either carbohydrate or protein per gram. Feeding foods with a higher fat content, particularly diets which also have higher protein and carbohydrate digestibility, can be good options for cats that might be otherwise healthy but that are losing weight and body condition over time. Conversely, if a cat is overweight, using a diet that is lower in fat and thus lower in calories would be preferred. The Association for Pet Obesity Prevention in the United States estimated in 2022 that 61% of pet cats are overweight or obese, and with many cats living longer, it is likely that this statistic includes those in the senior category. Cats with obesity are more likely to have respiratory, dermatological, musculoskeletal and/or dental problems, as well as urinary tract disease and diabetes, therefore while higher levels of fat might be recommended for cats that are unintentionally losing weight, there may be situations where weight loss is the goal, requiring lower levels of fat intake.

Figure 6. Older cats may have special dietary needs, such as the cat with diabetes mellitus; in this situation the digestible carbohydrate component of their diet may need to be carefully evaluated.

Vitamins and minerals 

Phosphorus and calcium:phosphorus

While there is insufficient evidence that higher protein diets can cause CKD in senior cats, there is evidence that diets with higher amounts of phosphorus may do so. In two recent studies, diets with differing phosphorus content and calcium:phosphorus ratios were tested in a cohort of healthy cats. 
The diets with the highest phosphorus level (the majority of which was from inorganic sources) and lowest calcium:phosphorus ratio induced renal changes in the cats. Further testing of different diets with varying levels of total phosphorus, inorganic phosphorus sources and calcium:phosphorus ratios indicated that a high level of inorganic phosphorus leads to a dose-dependent peak in plasma phosphorus concentrations which is higher than what occurs with organic phosphorus. However, not all forms of inorganic phosphorus cause the same postprandial rise in plasma phosphorus concentrations. While more work in this area is needed, avoiding diets that have high levels of soluble, inorganic phosphates and those with a calcium:phophorus ratio of less than 1:1 is advised.

However, it must be acknowledged that in the manufacturing of pet food, the levels of protein and organic phosphorus tend to run together; that is, the higher the level of one of these nutrients is, the higher the likelihood that the other one will be as well. We are seeing newer diets on the market (particularly therapeutic diets targeted for early kidney disease) where this is less likely, due to careful ingredient selection, but for many maintenance diets it may not. Thus, maintaining high dietary protein levels whilst avoiding the highest phosphorus levels might be challenging when evaluating regular, maintenance-type diets for older cats.

Other minerals and vitamins

While it is a given that cats of all ages require complete and balanced diets with appropriate vitamin and mineral content, there may be some further considerations for aging cats. Because of the decreased fat digestibility capacities of these animals, vitamins that are fat-soluble may have compromised absorption. To date, we have no data on deficiencies of these vitamins in older cats due to poor absorptive capacity. However, should a cat be eating a diet that is not being properly absorbed, or is not complete and balanced, and is losing body and muscle condition, deficiencies of these key nutrients may be a consideration.

Antioxidants in vitamin form, such as vitamins C, E, and the provitamin beta-carotene, may be of benefit in older animals. While vitamin C is not an essential nutrient for cats (as they can synthesize it endogenously), there is some evidence that higher levels of vitamin E and beta-carotene in feline diets can contribute to increased longevity. While not necessarily an issue for healthy older cats, water-soluble vitamins such as vitamin B12 can be lost if there is increased water loss through polyuria or through malabsorption, and supplementation may be considered for those animals.

Figure 7. One study has shown that cats with osteoarthritis which receive supplemental fish oils are likely to have higher activity levels and are more able to cope with climbing and jumping. 

Nutrients for cognitive decline

As there are increasing numbers of cats falling into the “senior” and “super senior” categories, cognitive decline and cognitive dysfunction are becoming more common and easily recognized, even in cats that are otherwise deemed healthy. In fact, this is often considered part of the normal aging process. One study showed 36% of owners of cats aged 7-10 years (mature adult and senior categories), and 88% of owners with cats between 16-19 years (super senior category) reported that their pets had developed age-related behavioral problems. These changes can lead to a decreased quality of life for the cat and the owner, and as such there is a great deal of interest in finding diets and/or supplements that can slow this process. 

A number of additives have been studied, with mixed results. Some evidence has been seen for supplementary S-adenosyl-l-methionine (SAMe), and there are anecdotal reports on other additives such as melatonin, L-theanine, milk protein hydrolysates, and pheromones. However, most of these supplements have been used to address general anxiety issues in cats and not cognitive decline specifically. Further clinical trials examining the effects of additives on cognitive decline are warranted. Medium chain triglycerides (MCTs) are another nutrient that has been used in dogs to address cognitive dysfunction, but further work needs to be done in cats. Previous studies using MCTs in this species had indicated there may be palatability challenges, although newer reports suggest this may not be the case. Recent research is targeting the gut-brain axis with the idea of improving brain function during aging. In addition to studies involving MCTs (which focus on the action of ketones and direct effects of the medium-chain fatty acids), prebiotics and probiotics are other considerations for future work that may address the cognitive needs of aging animals.

Conclusion

Many companies now offer diets or supplements labeled for senior cats based on their own considerations and beliefs without having the research or understanding about what is needed. While we are beginning to understand the nuances of some nutrients, the nutritional requirements for aging cats is still largely undefined. It is a broad category that encompasses consideration of several nutritional needs, even for seemingly healthy, older cats, so it is difficult to standardize recommendations for all; instead, dietary advice should be done on an individual basis. As our population of cats gets older, we continually look to better understand their needs and provide evidence-based recommendations to support them into their senior and super senior years.