Lisa M. Freeman, DVM, PhD, Diplomate ACVN
It has often been said that aging, in itself, is not a disease. However, aging is often associated with a variety of diseases. Nutrition can be a powerful tool in maintaining health, preventing disease, and in helping to manage disease. However, deciding on the "best" diet for an older cat can be a difficult decision; there is no one best diet for every older cat. Cats are individuals so just because a cat turns 7 or 10 or even 13 years old doesn't necessarily mean it's old. The aging process depends on a variety of factors including breed, genetics, and health problems. Therefore, just because a food is marketed for older cat, doesn't mean it's right for every older cat.
Individual differences aside, there are a number of changes that occur with aging that can affect nutritional requirements. Unfortunately, little research on feline aging and nutritional requirements has been done so much of our assumptions are based on research in other species. In other species, digestion and absorption of nutrients can be impaired with aging. Changes seen in other species, including dogs, are decreased energy requirements, decreased activity, and the tendency to gain fat and lose muscle.Immune function and kidney function also decline with age, although the degree to which this occurs depends upon the individual animal. While these structural or functional changes are thought to occur in older cats, minimal research has been done on changes in nutritional requirements that can result. In humans, there has been a great deal of work on specific requirements for the elderly and these can be very different from younger adults. In the new dietary reference intakes (DRIs) for people, people are now separated into additional age groups: 19-30 years, 31-50 years, 51-70 years, and >70 years for men and women. When enough information is available, recommendations are made for each age group. If there are not enough data to distinguish differences in requirements between these age groups, information is given for a larger, combined age group. Therefore, the direction is to have established requirements for each age group, including people >70 years. Currently, in cats (and dogs), adults are considered as a single group, whether the cat is 2 years old, 8 years old, or 15 years old. More specific requirements for elderly cats would be beneficial as the requirements of older cats are most certainly different from a young adult.
Even if requirements are altered in older cats, adjustment of the diet may or may not be necessary or even desirable in the average older cat. Many older cats do very well by continuing to eat a good quality commercial diet designed for adult cats. Others, however, will benefit from changing to a "senior" diet. It is important to understand that there is no legal definition for "senior" or "geriatric" foods. Although the title generally implies lower protein, lower phosphorus, and a lower caloric content, the levels vary with each company and each company's senior food will have different properties. Therefore, some foods will meet the needs of an individual cat better than others.
"Senior" foods vary depending upon the manufacturer, but there are a number of nutritional adjustments that are common to most:
Reduced protein. Although there is a common belief that protein restriction is helpful for older cats, there is little scientific evidence to show that low protein foods are beneficial for the healthy older cat or that moderately high protein foods contribute to the development of kidney disease. Therefore, cats should not be fed a low protein diet just because they are old (if renal disease does develop, dietary modification may be beneficial). In fact, foods highly restricted in protein may actually be too low in protein for many older cats and can contribute to muscle loss. The "optimal" protein level for older cats, however, is still controversial. Some companies manufacture "senior" diets with low protein, some have moderate protein, and some nutritionists actually recommend that older cats eat a higher protein level than younger cats. The jury is still out but for older cats without significant kidney disease, it is wise to avoid low protein diets unless there is a specific indication such as severe renal or hepatic disease.
Phosphorus. Phosphorus can contribute to the progression of renal disease, so phosphorus restriction is recommended for cats with significant renal disease. It is not known, however, whether high dietary phosphorus directly contributes to the development of renal disease. Nonetheless, high phosphorus foods may not be ideal for older cats.
Sodium. Sodium levels are often reduced in "senior" foods. Sodium restriction is unnecessary for the general population of older cats, but if a cat has cardiac disease or hypertension, salt restriction can be beneficial.
Calorie adjustment. Many cats tend to gain weight as they age. In these obesity-prone cats, decreasing the number of calories eaten (either by feeding less or changing to a food with a lower caloric density) will help to prevent weight gain. Those extra pounds around the middle are not innocuous and can cause or exacerbate other diseases. On the other hand, not all cats gain weight as they age. If a cat is one that is gradually losing weight or muscle with aging, a more calorically dense (and possibly also with some adjustments in other nutrient levels) should be selected to help to prevent weight loss.
Fiber. Increased soluble or insoluble fiber intake may be useful for cats that have decreased intestinal motility and are prone to constipation, but high fiber foods may not appropriate for cats with trouble maintaining weight since high fiber foods are generally low in calories.
Supplemental vitamins and minerals. If a good quality commercial food that is tested by feeding trials is being fed, supplementation is unnecessary. Some nutritional supplements may be helpful in certain diseases, and future research will help to better define where they can be beneficial and where they can cause problems.
There is an increasing interest in geriatrics among the pet food companies. A new niche has developed for special diets for geriatric cats so more and better research into their unique requirements will be done. Hopefully, this will provide the necessary information to develop separate nutritional profiles for elderly cats. Unfortunately, pet food manufacturers will never be able to design a single food that meets the needs of every older cat. Therefore, it is important to evaluate the individual cat's condition and health status to determine an appropriate food that will maintain a proper body weight and provide optimal nutrient levels.
In selecting the optimal diet for an older cat, the first thing to consider is the cat's overall health. If the cat has one of the diseases often seen with aging such as arthritis, diabetes, cancer, dental problems, heart disease, or renal failure, dietary adjustments may help improve clinical signs or even slow progression of the disease. For cats with diabetes mellitus, for example, dietary modifications such as increasing fiber or using a high protein, low carbohydrate food may help to control the disease and reduce insulin requirements. Reduced sodium foods may be useful in cats with congestive heart failure and can help reduce the diuretic dose required. The best diet (or diets) should be based on the individual cat's clinical signs, laboratory results, and stage of disease. As the disease progresses and medication adjustments are required, further dietary changes also may be necessary. Dietary modification can help to optimize health in the healthy cat and to modulate disease in cats as they age. The large variety of commercial diets and their variable nutrient contents provide many choices for optimizing the health of the elderly cat.
References are available upon request.