Grain-free diets are becoming much more commonplace in the pet food aisle. There are a number of reasons for this growing trend, such as the belief that grains are harmful for pets or that grain-free diets are more appropriate for dogs and cats from an evolutionary perspective.

Also, gluten — a protein found in wheat, barley and rye — has been touted as a substance to be feared in many popular human nutrition diets, and pet and human nutrition trends usually go hand-in-hand. With so many grain and grain-free options available, what do you need to know about the great grain debate?

Grains are an important source of complex carbohydrates, which have three or more sugar molecules joined together so they are more slowly digested than simple sugars that only have one or two molecules. Although carbohydrates are not considered essential nutrients in the diets of dogs and cats, and are often considered "fillers," they do play a critical role in your pet's body.

In particular, carbohydrates provide a highly digestible, readily available energy source. Foods rich in complex carbohydrates are also an important source of essential nutrients. The shape, texture and density of kibble depends on the carbohydrate (starch) content of the food. This is important, as mouth feel and the structure of the kibble help to determine palatability.

Recent genetic research suggests that one of the important steps in the domestication of dogs was their adaptation to a diet high in carbohydrates relative to the diet of carnivorous wolves. Carbohydrates are often considered to be detrimental to cats, but research suggests that moderate amounts may actually be beneficial in promoting insulin sensitivity.

Some of the grains commonly found in pet foods include barley, corn, rice, oats and wheat. Whole grains include all parts of the grain, while refined grains have the nutrient-rich germ and bran layers removed.

Whole grains promote digestive health since they are not only an excellent source of complex carbohydrates, but are also rich in fiber. Dietary fiber is a unique type of carbohydrate that cannot be digested by your pet's digestive enzymes, but nonetheless provides many benefits.

For example, oats and barley contain a special type of fiber called beta-glucan, which has been shown in numerous human studies to fight heart disease and diabetes. Beta-glucan may also be beneficial in pet foods to control blood glucose and prevent obesity.

Grain-free does not mean carbohydrate-free, as complex carbohydrates can be sourced from nongrain ingredients such as peas, lentils, chickpeas, tapioca, potatoes and sweet potatoes. Some pets may have allergies to one or more specific grains, but it might not be necessary to eliminate all grains.

Gluten-free diets are necessary for humans diagnosed with celiac disease or nonceliac gluten sensitivity, but this is not a common problem in pets and most tolerate gluten without any difficulty. The exception is some Irish Setters with inherited gluten sensitivity.

Many grain-free pet foods are higher in protein than conventional diets and, while extra protein is typically not a problem for most healthy pets, it can be problematic in certain medical conditions such as kidney disease. Since all foods contain a balance of carbohydrates, fat and protein, decreasing the amount of carbohydrate in a food will increase the fat and/or protein content.

What are some of the benefits of grain-free carbohydrate sources? Peas are an excellent source of carbohydrates, fiber, vitamins and minerals, and provide most of the essential amino acids required by dogs and cats. Peas also provide an added environmental benefit in that they are used as a tool in sustainable agriculture to add nitrogen back into the soil.

Tapioca does not contain protein, so it is not considered a potential allergen or source of food sensitivity. This is especially important in limited ingredient diets that are designed for food hypersensitive pets.

Potatoes are a rich source of vitamins and minerals, particularly vitamin C and potassium. Sweet potatoes are a major source of vitamin C and beta-carotene, which act as antioxidants, as well as manganese and potassium.

One of the primary benefits of grain-free diets is the increased variety of new and unique pet food recipes available. This allows pet parents to choose a diet with or without grains that works best for their dog or cat.