From the very first day of their life, humans are introduced to milk. They are exposed to breast milk or formula as the only sustenance until 6 months of age. Breastfeeding should then continue up to 2 years of age and beyond, but children should also begin to eat adequate complementary foods as recommended by the WHO (WHO, 2011). Human milk composition is dynamic and varies daily, during a feeding, based on the lactation stage, between mothers and populations. The mean macronutrient composition of mature milk is estimated to be approximately 0.9 to 1.5 g of protein, 3.2 to 3.6 g of fat, and 6.7 to 7.8 g of carbohydrates, mainly lactose (6.5g) in 100 ml. Energy is estimated to range from 65 to 70 kcal (270 to 295 kJ) in 100 ml and is highly correlated with the fat content of human milk. Macronutrient composition differs; preterm milk tending to be higher in protein and fat (Ballard and Morrow, 2013). Mineral content is approximately 0.2g, represented by calcium, phosphorus, sodium, potassium, magnesium, and iron. Vitamins present in the milk include A, D, E, C, and B vitamins, but human milk is deficient in vitamin K (Bernier, Adrian, and Vidon, 1988). Breastfeeding provides many positives for both infants and mothers: decreased postpartum bleeding and faster uterine involution caused by increased concentrations of oxytocin, decreased menstrual blood loss and increased child spacing attributable to lactational amenorrhea, earlier return to pre-pregnancy weight, decreased risk of breast cancer, decreased risk of ovarian cancer, and possible decreased risk of hip fractures and osteoporosis in the postmenopausal period (American Academy of Pediatrics, 2005). Known effects in infants include a decrease in child morbidity and mortality; protection against diarrhea, respiratory infections, and otitis media; and a possible 68% reduction of malocclusion in children (Victora et al., 2016). There are also positive effects on cognitive skills, which determine educational outcomes, and on knowledge and skill accumulation during both childhood and adult life. Longer breastfeeding duration is also associated with decreased autistic traits and decreases the risk of overweight and obesity in adulthood (Victora et al., 2016; Boucher et al., 2017). However, breastfeeding for longer than 12 months or during the night increases the risk of dental caries in deciduous teeth (Tham et al., 2015). Despite all the positive effects, many infants and children do not receive optimal feeding. WHO reports that only about 44% of infants aged 0 – 6 months worldwide were exclusively breastfed throughout 2015 – 2020 (WHO, 2020). Unfortunately, some mothers are not able to breastfeed. Known alternatives include human milk provided by milk banks or infant formulas. The main ingredient of an infant formula is usually cow milk, which must be modified because of its different composition than human milk (Blanchard, Zhu and Schuck, 2013). The composition of infant formula is defined by The European Union Commission Directive (2006) concerning infant formula that applies to all member states (European Commission, 2006). Nevertheless, formula-fed infants face a higher risk of diseases due to a lack of specific and innate immune factors present in human milk (Stuebe, 2009). Later in life, it is recommended that people continue to have milk intake, most frequently cow milk, because it contains several essential nutrients (Haas et al., 2019). Cow milk is proposed as a useful eatable, mainly during childhood and adolescence, when its content of calcium (125 mg per 100 ml), the protein of high biological value (3.5 g per 100 ml), phosphorus (100 mg per 100 ml), and other micronutrients promotes skeletal, muscular, and neurological development (Blanchard, Zhu and Schuck, 2013; Visioli and Strata, 2014). However, its relatively high-fat content (approximately 70% SFAs; myristic and palmitic acids combined account for ~50%, the remainder are mostly short- and medium-chain FAs and oleic acid) has marked it as potentially detrimental food, especially in connection to cardiovascular health (Visioli and Strata, 2014; Juráček et al., 2020). Furthermore, due to widespread health issues linked to milk consumption, such as lactose intolerance or milk allergies, and lifestyle changes, an alternative market for plant-based milk is emerging (Chalupa-Krebzdak, Long and Bohrer, 2018). Plant-based milk alternatives are fluids made from ground plant matter (cereals, pseudo-cereals, legumes, oilseeds, nuts) extracted in water. Further homogenization is necessary and results in particle size distribution in the range of 5–20 μm, which imitates cow milk appearance and consistency (Sethi, Tyagi and Anurag, 2016).

We examined the relationship between breastfeeding in childhood, milk and milk alternatives consumption, and body composition in adulthood. A questionnaire method was used to obtain information on breastfeeding in infancy and the current consumption of milk and milk alternatives. Each participant completed the questionnaire alone and anonymously. The survey involved 84 participants, 18 men (21%), and 66 women (79%). The average age of the participants was 23.26 ±1.36. The questionnaire consisted of questions on gender, age, educational level, health status, and certain anthropometric parameters, and 21 specific questions on milk consumption. Body composition data were obtained using InBody 720 (Biospace Co. Ltd., Seoul, Republic of Korea), a multifrequency bioelectrical impedance analyzer (BIA). Measured parameters included body weight (kg), FM (fat mass, kg), FFM (fat-free mass, kg), percentage of body fat (%), VFA (visceral fat area, cm²), WHR (waist-to-hip ratio), and BMI (body mass index). We compared the information from the questionnaire with the information from the body composition measurements. Participants undergoing measurements using BIA were healthy, without a pacemaker. None of the women were pregnant. All participants provided written consent to the bioelectrical impedance measurement.

We did not observe significant differences between breastfed and non-breastfed participants, but in those who were breastfed as infants, the duration of this period played a significant role. Significant differences were detected in VFA (p = 0.048) and WHR (p = 0.022) between participants breastfed for less than 4 months and breastfed for more than 12 months. This finding is consistent with the WHO recommendations and the benefits of breastfeeding. Participants that were formula-fed as infants showed a higher percentage of body fat (p = 0.047) when fed for less than 1 year (12 months). Consumption of milk did not cause significant differences in body composition. However, the fat percentage of milk was a significant factor for WHR (p = 0.026), refuting claims that whole milk is a detrimental food. Participants consuming plantbased milk alternatives showed significant differences in WHR (p = 0.031) and BMI (p = 0.015) and highly significant differences in weight (p <0.001) and FFM (p <0.001). Those differences are most likely due to the lower energy content of these beverages and various protein and fat compositions based on the raw materials used for production.