Let me start by saying, the most important thing is that you feed your baby, whether it is breast or bottle. Do what is right for you and your baby. I breast fed my first born until he was 14 months old and my second born for only 5 months. In retrospect, I wish I had breastfed my second for longer but tiredness (my kids are 18 months apart) and low milk supply got the better of me.
The World Health Organisation (WHO) recommends exclusive breast-feeding for the first 6 months of life. WHO also recommend continuing breast-feeding into the second year of life, alongside solid foods. Unfortunately, breastfeeding isn't always an option for every mother. There are ranges of reasons why some women can't breast feed their babies, from infections or medications, to rare metabolic disorders in the infant. It's important not to judge one way or another and all efforts to feed your baby should be supported. My personal recommendation is for those who can, to breastfeed as long as you enjoy it and to draw upon as much support as you can to assist you in feeding as long as you feel comfortable.
Breast milk contains proteins, fats, carbohydrates, vitamins and minerals plus non-nutritional components including antimicrobial factors, digestive enzymes, hormones, immune-related compounds and growth factors. The main carbohydrate in breast milk is lactose. Lactose not only acts as a source of energy for baby but also as fuel for bacteria in helping to establish a healthy gut flora. The fats found in breast milk are predominately essential fatty acids (EPA & DHA) and long chain polyunsaturated fatty acids. These fats are essential for the development and health of the brain as well as structure and function of cell membranes in every part of the body.
While the macro-nutrient profile of infant formula has been designed to be similar to breast milk, it lacks all the digestive enzymes, immune and growth factors that breast milk contains. Formula fed babies in general suffer more upper respiratory infections, diarrhoea and, later in life, higher rates of allergies and asthma than breastfed babies. You can read more about this in the Allergies and Sensitivities chapter of "Starting Solids" [p23].
As infant formula lacks probiotic bacteria, I always ensure that fermented foods rich in probiotic bacteria are included as first foods for these babies. Bacteria in the gastrointestinal tract are responsible for digesting foods, creating enzymes and synthesising some vitamins. A lack of good bacteria can leave baby open to infections, a compromised immune system, potential allergies and constipation or diarrhoea. Fermented foods such as natural yogurt and milk kefir are great sources of good bacteria for you and your baby. If your baby was delivered by c-section or antibiotics were used by the mother prior to vaginal birth, I would consider a baby probiotic and absoluetly encourage breast feeding. If the infant has cradle cap, eczema or has taken antibiotics, I would recommend supplementing with a baby probiotic containing bifidobacterium species. Please seek a health professional’s advice before starting your baby on a probiotic.
Breastfed babies’ requirements are dependent on the mother’s nutrition status, her gut flora at time of birth, mode of delivery (C-section or vaginal), and time of year (for vitamin D). In general, mothers tend to be low in iron, vitamin D and sometimes iodine by the time your baby is 6 months old. Calcium can be leeched from the mother’s bones to supply adequate amounts in the breast milk. Taking a prenatal or breastfeeding multi will help ensure adequate nutrient status in the breastfeeding mother.