Many parents ask why they can't just feed their baby regular cow's milk. The answer is simple: Young infants cannot digest cow's milk as completely or easily as they digest formula.
Also, cow's milk contains high concentrations of protein and minerals, which can stress a newborn's immature kidneys and cause severe illness at times of heat stress, fever, or diarrhea. In addition, cow's milk lacks the proper amounts of iron, vitamin C, and other nutrients that infants need. It may even cause iron-deficiency anemia in some babies, since cow's milk protein can irritate the lining of the stomach and intestine, leading to loss of blood into the stools. Cow's milk also does not contain the healthiest types of fat for growing babies. For these reasons, your baby should not receive any regular cow's milk for the first twelve months of life.
Once your baby is past one year old, you may give him whole cow's milk or reduced-fat (2 percent) milk, provided he has a balanced diet of solid foods (cereals, vegetables, fruits, and meats). But limit his intake of milk to 1 quart (about 32–36 oz.) per day. More than this can provide too many calories and may decrease his appetite for the other foods he needs. If your baby is not yet eating a broad range of solid foods, talk to your pediatrician about the best nutrition for him.
At this age, children still need a higher fat content, which is why whole vitamin D milk is recommended for most infants after one year of age. If your child is overweight or at risk for being overweight, or if there is a family history of obesity, high blood pressure, or heart disease, your pediatrician may recommend 2 percent milk (reduced-fat) instead.
Do not give your baby 1 percent (low-fat) or nonfat (skimmed) milk before his second birthday. Also, nonfat, or skimmed, milk provides too high a concentration of protein and minerals and should not be given to infants or toddlers under age two. After two years of age, you should discuss your child's nutritional needs, including choice of low-fat or nonfat milk products, with your pediatrician.