Generally, 100 ml of mature breast milk consist of 90 g water and contain 0.8 – 1.3 grams of protein, 6.9 – 7.4 grams of carbohydrate, 3.0 – 5.0 grams of fat. In total, mature breast milk provides 60 – 75 kcal per 100 ml 3923. Nevertheless, the compostion of human milk is still being studied since it differs among mothers and populations as well as during different times of lactation 222425.

There is little research done about breast milk composition among lactating women in Latvia 2122. Research 22 is only a recent study conducted in Latvia about breast milk composition. However, samples were taken from mothers, whose children were not full term healthy infants. In research 22, breast milk samples were obtained from the mothers (on the 5th–7th and 11th–28th day of lactation), whose neonates were treated in the Neonatal Care Unit, Children’s Clinical University Hospital, Riga. Protein, fat and lactose content as well as pH and density were determined from the milk samples. Study 21 was done according to the National Implementation Plan on Persistent Organic Pollutants (POPs) for the years 2004–2020. Mothers were selected from a presumably polluted area in Latvia (Olaine) to assess the contamination of breast milk with polychlorinated biphenyls, polychlorinated dibenzodioxins, dibenzofurans and some pesticides.

The previously mentioned studies 2122 were conducted in particlar areas so it is difficult to judge if the human milk of Latvian women differs from other populations and what are the factors that mostly affect it.

Human milk proteins contribute to the optimal growing and development of an infant and also secure against infections 26. Proteins provide ~8% of the exclusively breastfed infant’s energy requirements; however, the concentration of protein changes as lactation progresses.

Higher concentration of protein was noticed in the milk among Latvian women in comparison to the samples from the USA and the UK, but it can be explained by sampling period which was from 5th to 7th day of lactaction representing the transitory milk 22.

The total protein content decreases as lactation progresses mainly due to the diminution in whey protein concentration. However, it seems that, in general, concentration of protein in human milk is not affected by the protein content in a mother’s diet 2326.

100 ml of mature breast milk contains 6.9 – 7.4 grams of carbohydrates, which mostly consist of disaccharide lactose (90 – 95%) and count for approximately 40% of the total breast milk energy content. The lactose content remains constant during the colostrum transition to mature milk 39.

Study done in Latvia 22 suggests that the concentration of lactose is higher for mothers who had a neonate with low birth weight (<2.5 kg), which could be explained by lactose positive effect on gastrointestinal microflora 27. However, since the studied samples represent the milk composition from the mothers with unhealthy young ones, the results cannot be used as a reference for the general Latvian population 22.

Fat is the most variable macronutrient and the main source of energy in human milk contributing ~50% of the total energy 3. Some researchers conclude that the quantity of the total fat in breast milk is quite stable and does not correlate to the fat intake of a mother 925282930. Others, among them Latvian researchers as well, observe a large variability between milk samples 12222431 and suggest that fat content could depend on mother’s nutrition 122231.

The study about the milk composition among lactating women in Latvia showed a large variability in the fat content (1.605-5.470 and 2.427-4.560 on the 5th – 7th and 11th – 28th lactation day respectively). The concentration of fat on the the 11th – 28th day of lactation among Latvian women was also significantly higher than among British women 22. However, samples were taken from the mothers of infants treated at hospital during the study so results cannot be attributed to a general population. There is also no mention if the samples were taken on a specific time of the day (for instance, in the morning) and if the milk samples where expressed in the beginning or in the end of the feeding. This information is important because the milk composition (especially the fat content) differs not only during a day but also during a feeding 923. Authors 22 emphasize that it would be advisable to perform an individual milk analysis among the infants with poor weight gain to evaluate if it is influenced by the fat content in milk and therefore by the fat content in a mother’s diet. The studies conducted to determine relations between the infant feeding practices and antropometrical traits in Latvia 3233 reveal that the breastfed intfants tend to have a higher body weight in the first month of life in comparision with the formula fed ones. Yet, the formula fed infants have a higher weight starting from 2 months of age. However, in those studies no effort was made to analyse the impact of the composition of human milk on infant’s weight gain. Therefore, a mother’s low fat diet could affect the weight gain of an infant 122231.

A lot of attention in recent years is drawn to the trans fat content in different foodstuffs, including milk. Humans do not synthesize trans isomers of fatty acids but accumulate them via diet 34353637383940. The trans fatty acid content of human milk reflects the mother’s trans dietary intake from the previous day 38. The content of TFA in milk among women from different countries varies from ~1% to ~11% of the total fatty acids 617, 3536, 3839, 414243. Although dairy and meat fats are a natural source of TFA, intake of foods that contain greater concentrations of trans fat such as processed foodstuffs made with partially hydrogenated vegetable oils leads to greater intakes of trans fatty acids, which are then incorporated into milk fat. Therefore, the total amount and composition of trans fatty acids in milk may be attributed to the differences in womens’ diet 6, 36373839, 41, 4445.

Knowing that TFA in breast milk leads to possible adverse effects on the infant’s growth and development, their level in breast milk should be kept as low as possible 617194446. Legislation is a way to reduce the negative influence of TFA. The TFA content in human milk in Canada has declined with the introduction of the trans fat declaration in food labelling 46. However, the mandatory declaration of the TFA content had no effect on reducing the content of TFA amount in a lactating woman’s diet in Brazil 42. Latvia has become the latest European Union country to set the maximum amount of trans fats in foodstuffs. The new regulations entered into force on May 20, 2016. However, there is a transition period until June 1, 2018 18. The new requirements will cause food industries to produce foods with lower levels of TFA and might result in lower maternal consumption and concentration in milk 42. The ceilings of TFA in foodstuffs is a more rigorous approach of legislation than mandatory labelling; therefore, it would be a novel idea to study if the TFA content also declines in milk among Latvian women after the introduction of the new Cabinet Regulation 18.

Persistent organic pollutants (POPs) are chemicals that accumulate in the food chain and are toxic to humans. Due to their high stability and lipophilic properties, they accumulate in fat-containing foodstuffs 14748. For most people, exposure to POPs comes from the ingestion of food such as fish, meat, and dairy products 48. WHO has considered human milk as an important matrix for monitoring POPs because high levels of POPs have resulted in serious adverse health effects for children. Breastfed infants developed pink sore, weakness, seizures and an annular rash because their mothers’ ingested bread was prepared from grains treated with high dose of fungicides. There was also an extremely high rate of mortality 49. Fortunately, the assessment of the exposure of breast milk to POPs in Latvia corresponds to the lowest levels detected in the European countries and is not a cause of health disorders 2149.