Lisa M. Freeman, DVM, PhD, DACVN
Although aging, in itself, is not a disease, it often is 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 dog or cat can be a difficult decision. Animals are individuals so just because a pet turns 7 or 12 years old doesn't necessarily mean it's old. The aging process depends on a variety of factors including breed, genetics, and concurrent diseases. Therefore, just because a food is marketed for older animal, doesn't mean it is right for every older dog or cat.
Individual differences aside, there are certain changes that occur with aging that can affect nutritional requirements. Unfortunately, many of our assumptions are based on research in other species since minimal research has been conducted in dogs and cats. In other species, digestion and absorption of nutrients can be impaired with aging. Dogs tend to have decreased energy requirements, decreased activity, and 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 also appear to occur in older dogs and cats, minimal research has been done on changes in nutritional requirements that can result. In people, requirements for the elderly can be very different from younger adults. In the current dietary reference intakes (DRIs) for people, people are separated into the age groups: 19–30 years, 31–50 years, 51–70 years, and > 70 years for men and women. Currently, in cats and dogs, adults are considered as a single group, whether the animal is 2 years old, 7 years old, or 17 years old. More specific requirements for elderly animals would be beneficial as the requirements of older dogs and cats are most certainly different from a young adult.
So, while much additional work is needed on the specific requirements of older dogs and cats, not all animals require major changes in the foods they're eating as they age. Many older dogs and cats would be best served by continuing to eat a high quality commercial diet designed for adults. Others, however, will benefit from changing to a "senior" diet. However, 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. In fact, there is a huge range of levels of key nutrients, such as protein, phosphorus, sodium, and fat, in commercial senior diets. Therefore, some foods will meet the needs of an individual animal better than others.
"Senior" foods vary depending upon the manufacturer, but there are a number of nutritional adjustments that are common to many:
1. Reduced protein. Although there is a common belief that protein restriction is helpful for older animal, there is little scientific evidence to show that low protein foods are beneficial for the healthy older dog or cat. In fact, foods highly restricted in protein may actually be too low in protein for many older animals and can contribute to muscle loss. Therefore, dogs and cats should not be fed a low protein diet just because they are old (if moderate to severe renal disease is present, then some protein restriction may be beneficial). The "optimal" protein level for older dogs and cats, however, is still controversial. Some companies manufacture "senior" diets with low protein, some have moderate protein, and some senior pet foods actually contain higher levels of protein than for younger adults. Much additional research is needed but for older animals without significant renal or hepatic disease, it is wise to avoid reduced protein diets.
2. Phosphorus. Phosphorus can contribute to the progression of renal disease, so phosphorus restriction is recommended for animals 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 dogs and cats.
3. Sodium. Sodium restriction is unnecessary for the general population of older dogs and cats, but may be recommended if cardiac disease is present. Most people (pet owners and veterinarians alike) believe that "senior" diets are low in sodium but, in fact, this is not always true. Some senior diets are actually very high in sodium! Therefore, it is important to evaluate the individual food for its sodium content if a sodium restricted food is desired.
4. Calorie adjustment. Many dogs and cats (and people) tend to gain weight as they age. In these obesity-prone animals, 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 animals gain weight as they age. If a patient is one that is gradually losing weight or muscle with aging and there is no underlying medical condition, a more calorically dense food (and possibly also one with some adjustments in other nutrient levels) should be selected to help to prevent weight loss.
5. Fiber. Increased soluble or insoluble fiber intake may be useful for dogs and cats that have decreased intestinal motility and are prone to constipation, but high fiber foods may not be appropriate for animals with trouble maintaining weight since high fiber foods are generally low in calories.
6. Supplemental vitamins and minerals. If a good quality, complete and balanced commercial food 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 older companion animals 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 geriatric dogs and cats. Unfortunately, pet food manufacturers will never be able to design a single food that meets the needs of every older animal. Therefore, it is important to do a careful nutritional assessment of the individual patient 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 animal, the first thing to consider is overall health. If the animal is healthy, in good body condition and eating a good quality adult food, there is no reason to change foods. If the patient has one of the diseases often seen with aging such as arthritis, diabetes, cancer, dental problems, cardiac disease, or kidney disease, dietary adjustments may help improve clinical signs or even slow progression of the disease. For cats with chronic kidney disease, for example, dietary modifications such as reduced phosphorus, avoiding acidifying diets, and omega-3 fatty acid supplementation may help to slow progression of the disease. Reduced sodium foods may be useful in dogs with congestive heart failure and can help reduce the diuretic dose required. The best diet (or diets) should be based on the individual animal'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 dog and cat and to modulate disease as animals age. The large variety of commercial diets and their variable nutrient contents provides many choices for optimizing the health of the elderly patient.
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