Most grains found in a lot of commercial, pet grade foods, are grains that are unfit for human consumption. This means they are filled with mold, aflotoxins and bacteria. They are also poor quality as most are by-products of the milling process. This means that they are left overs of the milling of corn, wheat or barley and are stripped of their inherent nutrients. So many dogs are experiencing allergies and even seizures due to the quality of raw ingredients in their diet. The grains themselves are not the issue, the quality and toxicity are.
Grains have many health benefits providing they are whole grains such as brown rice, whole wheat pasta and barley. Once cooked, they are well absorbed and well digested by dogs. Whole grains provide a myriad of vitamins and minerals and provide soluble fiber to feed the good bacteria in the gut. They also provide the nutrients the body needs to manufacture its own vitamin K.
Whole grains are digested slowly, which keeps blood sugar levels low, reducing stress on the pancreas and liver. They are also an excellent form of protein when combined with the amino acids found in vegetables.