Question: How much protein do babies need?

Infant nutrition

Infant Nutrition is the description of the dietary needs of infants. A diet lacking essential calories, minerals, vitamins, or fluids is considered inadequate. Breast milk provides the best nutrition for these vital first months of growth when compared to formula. For example, breastfeeding aids in preventing anemia, obesity, and sudden infant death syndrome; and it promotes digestive health, immunity, and intelligence. The American Academy of Pediatrics recommends exclusively feeding an infant breast milk, or iron fortified formula, for the first twelve months of life. Infants are usually not introduced to solid foods until four to six months of age.[1] Historically, breastfeeding infants was the only option for nutrition otherwise the infant would parish. Breastfeeding is rarely contraindicated, but is not recommended for mothers being treated for cancer, those with active tuberculosis, HIV, substance abuse, or leukemia[2]. Clinicians can be consulted to determine what is best for each baby.  
Infant nutrition requirements

Proper infant nutrition demands providing essential substances that support normal growth, functioning, development, and resistance to infections and diseases. Optimal nutrition can be achieved by deciding to breastfeed or bottle-feed the infant before birth and preparing for either decision[2].  
Birth to six months
The World Health Organization (WHO) and the Pan American Health Organization currently recommend feeding infants only breast milk for the first six months of life[3]. If the infant is being fed formula, it must be iron-enriched. An infant that receives exclusively breast milk for the first six months rarely needs additional vitamins or minerals. However, vitamins D and B12 may be needed if the breastfeeding mother does not have a proper intake of these vitamins. In fact, the American Academy of Pediatrics suggests all infants, breastfed or not, take a vitamin D supplement within the first days of life to prevent a deficiency or rickets. Exclusively breastfed infants will also require an iron supplement after four months, because the iron is depleted at this point from the breast milk[2].  
It is important to know that some foods are restricted for infants. For example, whether breast- or bottle-fed, infants do not need additional fluids during the first four months of life[2]. Excessive intake of extra fluids or supplements can have harmful effects. Fluids besides human breast milk or iron-enriched formula are not recommended. These substitutes, such as milk, juice, and water do not require what the infant needs to grow and develop, cannot be digested correctly, and have a high risk of being contaminated. Water is acceptable only for mixing formula. Honey also must be avoided because there is a high risk of botulism[2]. Breast milk is the safest thing to give, unless the mother is advised against it by a health care professional.  
The frequency of breastfeeding varies amongst each mother-infant pair. Contributing factors are the age, weight, maturity, stomach capacity, and gastric emptying of the infant; as well as the storage capacity the mother has of breast milk. Typically, feedings occur eight to twelve times per day for breastfed infants. Early on, infants may not signal when they are hungry, so parents are taught to feed the infant every three hours during the day and every four hours during the night, even if waking the infant is required. The feedings will last 30-40 minutes in the beginning, or 15-20 minutes per breast if breastfeeding. As the infant matures, the feeding times shorten[1]. Feeding often is important to promote normal growth, development, and milk production in mothers who are breastfeeding.  
Solid foods should not be introduced until four to six months of age. This is delayed because the infant is not able to digest solid foods properly. Infants are born with a reflex to suck milk in, they do not have the ability to push food away. So, if solids are given, it is considered forced feeding[2]. Giving solid foods prematurely can lead to weight gain and obesity, this is why breast milk or formula is preferred.  
Six to twelve months

Solid foods should be introduced from six months onward. Salt, sugar, processed meat, juices, and canned foods should be avoided. Breast milk or formula continues to be the primary source of  nutrition during these months, in addition to solid foods[3]. Solid food can be introduced during this age because the gastrointestinal tract has matured. Solids can be digested more easily, and allergic responses are less likely. The infant has begun teething by now, which will aid in chewing of solid food. Another milestone that the infant has hit by now is properly supporting and turning their head. They may do this to express a dislike in certain foods. The infant has also developed enough to participate in feedings by grasping bottles and pieces of food to feed themselves[2]. When all of these developmental milestones are considered, it is easy to understand why introducing solid foods before six months is not recommended.   
When choosing which solid to introduce first, it is important to understand what the infant actually needs. Iron-fortified infant cereal is typically the first solid introduced due to its high iron content. Cereals can be made of rice, barley, or oatmeal. Foods must be introduced one a time over a five- to seven-day period, to be able to detect any allergic responses. Orange juice is the best thing to mix with the cereal, because the vitamin C enhances the absorption of iron. Juices like apple, pear, prune, peach, and grape need to be avoided because of the risk of gastric upset[2]. Overall, solids can be introduced in any order after the cereal is introduced. It is important to know that solids cannot completely replace formula or breast milk until after twelve months of age.  
Health benefits of breast milk

Each year in the U.S. roughly 27% of infants and children are affected by disease[4]. Breastfeeding can lower the risk of respiratory, gastrointestinal, and other potentially life-threatening diseases. It offers protection against obesity and diabetes later in life, too[5]. Breast milk is proven to be chemically different for each mother and infant pair. For example, a premature infant's mother will have different milk than a mature infant's mother. Breast milk can also change if an infection is detected in the infant[6]. This natural prevention is tailored to each infant.   
Preventing anemia
Breastfed infants are at a lower risk for acquiring iron-deficiency anemia. Infants that only consume cow’s milk become deficient in iron and are 50% more likely to lose blood in their stool. If the infant is allergic to cow’s milk, it causes inflammation of the digestive system, resulting in chronic blood loss and decreased absorption of iron. This is why formula must be iron-enriched if breastfeeding is not possible[2]. Breast milk naturally contains lactoferrin, an iron binding protein that allows better iron absorption and digestion[7]. Allowing the baby to absorb more iron leads to a better gut health of the infant.  
Preventing obesity
Breastfed infants tend to have lower incidences of obesity later in life. Breast milk leads to a slower weight gain in early infancy, and is protective against obesity and development of type 2 diabetes[2]. Diabetes is a serious health problem where the body does not use insulin correctly. This diagnosis can cause many complications of the skin, eyes, feet, nervous system, heart, and kidneys[8]. Therefore, it is important to prevent diabetes when possible, because it goes hand-in-hand with obesity.   
When an infant is breastfed, they are exposed to a variety of flavors due to the mother’s changing diet and breast milk[9]. A study showed that later in life breastfed children are more likely to eat a variety of healthy foods; this happens because food preferences are ingrained early in life. So, when an infant is exposed to a variety of flavors early on, they are less likely to be picky later. Another study confirmed a decrease in obesity at ages two and four if the infant is exclusively breastfed for at least four months[10]. Therefore, breast milk is proven again to be the best nutrition without causing obesity.   
Preventing sudden infant death syndrome (SIDS)

SIDS is an unexplained death occurring in an infant who is one year of age or younger. Most deaths occur when the infant is sleeping[11]. Breastfeeding will help reduce the risk of SIDS when done exclusively for any length of time [2]. It is recommended to breastfeed the infant from birth to 6 months exclusively to decrease the risk of SIDS by 50%[12]. Diarrhea and upper respiratory illnesses, both linked to a higher risk of SIDS, occur less frequently for infants who are breastfed when compared to babies that are not breastfed, thus reducing the risk. Also, breast milk provides necessary nutrition for the infant's brain to develop. This allows the brain of the baby to mature quickly enough so that he or she will have the response to gasp for air when needed. Lastly, breastfed babies tend to sleep for shorter periods at a time and awaken more easily. Research has shown that babies who sleep shorter and awaken from their sleep easily tend to have a lower risk of SIDS[13]. Conclusively, most incidences happen when the infant is asleep, so it is important to exclusively breastfeed in order to reduce the incidence of SIDS. 
Promoting digestive health
Breast milk is important for the infant’s digestive system. It is the best substance to give, especially over cow's milk. Infants cannot properly digest fats, which cow's milk is full of. Breast milk contains a lot of fat, too, but it also contains lipase, a substance to help break down fat to aid in digestion. This leads to infants passing softer stools, so constipation is rare in breastfed infants[2]. Human milk also allows beneficial bacteria to grow in the infant’s intestines, which protects the mucosal barrier of the infant's stomach. This prevents harmful pathogens from harming the infant’s intestinal lining. The infant’s digestive mucosa is unable to produce antibodies until they are about four to six months old, which makes the infant susceptible to many infections. However, breast milk provides the antibodies needed for the infant to stay protected until they are able to produce their own antibodies[7]. Breast milk also stimulates a microbiota, which results in the production of IgA. IgA is an immunoglobulin that is a first line of defense to protect the digestive tract of the infant. This immunoglobulin is much higher in infants that are breastfed than in infants that were formula-fed[7].  
Promoting immunity

Colostrum is a great source of nutrition for a newborn baby, it is a thick yellow fluid that a mother first produces after birth. It has valuable nutrition that aids the baby with building immunity because it helps destroy disease-causing viruses. Other benefits of colostrum include: prevention of jaundice, aiding the baby in passing their first stool, building a strong immune system, providing a great number of vitamins and protein, and prevents low blood sugar in babies[14]. Overall, the sticky, thick, yellow liquid called colostrum has many benefits for a newborn baby which can be only provided to the baby through breastfeeding. 
Breast milk also contains much more protein than cow's milk. It contains 60% protein whereas cow’s milk contains only 40% protein[7]. Protein is very important for infants because they need more protein per pound than adults do. For the first few months of their life, this protein must come from breast milk or formula, it cannot come from cow's milk [15]. One specific protein that breast milk has is lactoferrin, which is bacteriostatic[7], meaning it prevents the growth of harmful bacteria. Without protein, the baby cannot produce the immunity that its body desperately needs, resulting in a higher risk of disease and malnutrition. Breast milk provides the best source of protein for an infant.
Another immunoglobulin breast milk provides to the infant is known as IgG. IgG provides passive immunity from the mother to the infant. This means that antibodies for common childhood diseases like diphtheria, measles, poliomyelitis, and rubella are passed onto the infant naturally, if the mother was vaccinated for this in her lifetime. The infant is then protected for about 3 months, just enough time to protect them until they receive their first immunizations at 2 months[2].
Promoting intelligence
Parents generally want their child to be as smart as possible and to exceed in school. Breastfeeding an infant can increase their intelligence throughout life. Mothers who exclusively breastfed their child have a higher chance of increasing their child’s intelligence. Studies have shown that infants that are breastfed for six months versus infants who were only breasted for one month have a higher intelligence score. Those children tend to have a higher intelligence score in the third and fifth grade. Their intelligence scores are also higher at the age of 15[16]. Breastfeeding aids in the development of cognitive maturity which leads to a higher intelligence[17]. However, this only correlated to those children which were exclusively breastfed by their mothers as infants [16].  
History of breastfeeding

Breastfeeding, prehistorically, was the only way infants were nourished, there was no acceptable substitute for human milk for a long time. In 1 AD, philosophers were discovering the importance of breast milk versus any substitute. It was concluded that breastfeeding helped the mother and infant establish an emotional connection[3]. The nutritional value was still not fully understood, but it was believed that through suckling, the infant gained not only energy, but also the characteristics and personality of whoever they fed from. It was suggested that infants be breastfed as long as possible, and many were until two to three years of age. 
It was not until 16 centuries later that the importance of breast milk was truly understood. In 1748, in the book “An Essay upon Nursing, and the Management of Children, from Their Birth to Three Years of Age” by Cadogan, colostrum was recognized as a substance responsible for the elimination of meconium, and prevention of illnesses of mothers and children. Also, it was believed that a bond was established if the mother breastfed her child from the hour it was born. Wet-nurses and introducing solid food before the baby turned six months were now opposed, and mortality rates decreased once accepting the value of breastfeeding. Those that continued to feed their infants substitutes like cereals, cow’s milk, and broths too early, led to the infant's development of scurvy, rickets, gastrointestinal problems, and kidney stones[3].
Continuing on into the 19th century, scientists were relating high rates of mortality and malnourishment to the lack of infants being breastfed. At last, breastfeeding was seen as the best and only option for infant nutrition before six months. However, in 1847, when the first commercial formula was made, it promoted the use of bottles, partly due to breasts receiving a sexual connotation during this time. With the promotion of formula, the long fight for breastfeeding took a dive. Organizations that took notice came together to promote breastfeeding once again, they included Natural Childbirth Movement, Baby Friendly Hospital Initiative launched by WHO, and United Nations International Children’s Emergency Fund (UNICEF). In 1990, these organizations pushed to protect and promote “breast milk is the best food for infants[3].” This value still holds true today. Factors leading to increased breastfeeding rates recently include facilities encouraging mothers to have skin-to-skin contact with the infant after birth, cultivating the initiation of breastfeeding; and facilities encouraging rooming-in, where the mother can watch for feeding cues with the infant staying in her room[1]. 
See also
Infant formula
Breastfeeding