Pet Nutrition Primer
All animals have basic nutritional needs that must be met for them to live long, healthy lives. “Essential nutrients” are called such because our bodies and our pets’ bodies are incapable of making enough of them on their own and so we must get what we need from food. Inadequate or excessive amounts of these nutrients can cause health problems, so it’s important to make sure that your pet’s diet contains nutrients in the appropriate amounts. The easiest way to do this is to feed a commercial diet made by a reputable manufacturer, but a carefully designed home-cooked diet can also meet nutrition needs.
To maintain a healthy body weight, pets needs to consume enough calories. In animal nutrition, a Calorie, the unit that we see on the Nutrition Facts label for human foods, is typically called a kilocalorie, or just “kcal”. Calorie needs vary between pets, just like they do with people. One Labrador retriever may need 800 kcal per day where another Labrador retriever of similar size may eat 1000 kcal per day and also be at an ideal body weight, just like you may be able to eat much more or less food than a friend or family member to maintain weight. There are basic equations to help you calculate how many calories a dog or cat should need, but these are only starting points, just like the 2,000 kcal per day that is commonly recommended for people. (LINK to how many calories does my pet need post)
All calories in food come from one of three nutrients, called macronutrients, because they are present in the diet in pretty large amounts: protein, fat, and carbohydrates.
Protein is made up of building blocks called amino acids. Dogs and cats need a certain amount of protein every day, but they also need adequate amounts of each amino acid in the correct proportions to each other to use them most efficiently. Both dogs and cats can utilize amino acids from both plant and animal proteins, but animal proteins usually have a better combination of amino acids so at least some animal proteins are desirable in dog and cat foods. The body can’t store protein, so any extra that is eaten above the requirement for general health is broken down and excreted by the kidneys.
Fat, like protein, is made up of smaller units called fatty acids and while all animals need some fat in their diet for good health, certain fatty acids are critical to good health and body function. Fat contains twice the calories of protein and carbohydrates, so it is way that the body stores energy. There is almost no limit to how much fat an animal can store if it is fed too many calories. In addition to making the diet higher in calories, too much fat can upset some pet’s gastrointestinal systems.
While adult dogs and cats do not have a strict requirement for carbohydrates in the diet, moderate levels of carbohydrates are well-tolerated by both species. Adding carbohydrates to the diet allows for lower fat, lower calorie diets, and provides important compounds such as fiber. Dogs generally do well on higher amounts of carbohydrates in their diets than cats, as they have developed as omnivores whereas cats are true carnivores. Even so, the amount of carbohydrates found in typical dry cat diets are generally well tolerated. Most animals can store very small amounts of carbohydrate in their liver, but it generally is only enough to last for a few hours of fasting.
A diet of just protein, fat, and carbohydrates will not provide everything an animal needs for good health, however. While vitamins and minerals do not provide any calories, they are of critical importance for normal body function.
Minerals are the main components of bone and are also critical for normal muscle contraction, including the heart. They are also critically important as components of the red blood cells. They include calcium, phosphorus, potassium, sodium, iron, zinc, and magnesium, as well as some lesser known ones.
Vitamins are critically important for normal body functioning – they help the cellular machinery to work to breakdown protein, fat, and carbohydrates. They are generally only needed in small amounts, but too little can result in serious, sometimes even fatal health conditions. Some of the vitamins that dogs and cats require include thiamine (B1), riboflavin (B2), niacin, B12, choline, and Vitamin A, D, and E.
Water provides no calories and only small amounts of minerals, but it must be consumed in appropriate amounts every day for normal body function. Animals die of dehydration due to lack of water before they die of lack of food.
The National Resource Council of the National Academy of Sciences has prepared some nice booklets that discuss essential nutrients for dogs and cats in more depth: http://dels.nas.edu/global/banr/petdoor