Impact of Maternal Body Composition, Hydration, and Metabolic Health on Breastfeeding Success: A Comprehensive Review

Introduction

The term “breastfeeding” refers to the practice of an infant receiving mother’s milk, either directly from the breast or expressed and given by other means [1]. Breastfeeding is a natural method of providing essential nutrients, and breast milk plays a crucial role in ensuring the proper growth and psychophysical development of the infant [2,3].

The basic definitions defining breastfeeding practices, according to current World Health Organization (WHO) standards, include: (1) exclusive breastfeeding, by which the child receives only mother’s milk, either directly from the breast or expressed, and oral administration of pharmaceutical products, such as vitamins and medicines, is allowed; (2) predominant breastfeeding, in which the baby receives mother’s milk and water, tea, or fruit juice; (3) complementary or partial breastfeeding, in which the baby is given mother’s milk and semi-liquid milk foods; (4) full or complete breastfeeding, which is exclusive and dominant breastfeeding; and (5) “any” breastfeeding, in which the child is breastfed or receives breast milk at least once [4].

According to the guidelines of the WHO, the European Society of Pediatric Gastroenterology, Hepatology and Nutrition (ESPGHAN), and the American Academy of Pediatrics (AAP), exclusive breastfeeding is recommended for the first 6 months of life. After this period, complementary feeding is advised for the next 18 months. However, guidelines from other organizations vary [5].

Breastfeeding has a positive impact on the child’s health and intellectual development [6]. Increasing emphasis is being placed on the role of breastfeeding in prevention of various maternal diseases and the potential consequences of avoiding breastfeeding [7,8]. Mothers benefit from breastfeeding both in the postpartum period and in the long term. Immediately after childbirth, breastfeeding accelerates uterine contractions, reduces excessive blood loss, protects against iron deficiency anemia, helps prevent postpartum depression, strengthens the mother-child bond, and improves the quality of sleep, which is often disrupted during this period [9–12]. The long-term benefits include a reduced risk of certain cancers (eg, breast cancer, endometrial cancer, ovarian cancer), cardiovascular diseases (eg, ischemic heart disease, hypertension), and metabolic disorders (eg, diabetes, glucose intolerance, obesity, hyperlipidemia, hyperinsulinemia), as well as a decreased risk of rheumatoid arthritis or osteoporosis [13–16].

The electrical properties of tissues have been recognized for over a century. In the mid-20th century, the relationship between bioelectrical impedance measurements and the total amount of water in the body was first observed by Barnett and subsequently by Thomasset, who employed 2 subcutaneous electrodes. This was followed by Hoffer et al, who utilized 4 electrodes placed on the skin surface. In the 1970s, Nyboer et al conducted pioneering research in impedance plethysmography, demonstrating the relationship between changes in the body’s impedance and fluctuations in pulsatile blood flow, arterial pulse, and respiration [17]. Bioelectrical impedance analysis (BIA) has become an increasingly prevalent, non-invasive method for assessing body composition. This technique involves measuring the impedance (electrical resistance) of body tissues through which a low-intensity, specific-frequency electric current is passed [18].

Therefore, this article aims to review the effects of maternal body composition, hydration status, and metabolic and social factors on lactation and breastfeeding. The influence of postpartum body composition on breastfeeding effectiveness has been under-explored in the scientific literature. Methods such as BIA may prove to be valuable and safe tools for supporting lactation.

Methods for Measuring Maternal Body Composition and Hydration Status

Human body composition testing is crucial in determining the nutritional status of individuals and populations. Mothers experience benefits not only early, in the postpartum period, but also long term [19–21]. Currently, there are numerous methods available for assessing body composition. Laboratory methods such as hydrodensitometry, computed tomography (CT), magnetic resonance imaging (MRI), electrical conductivity, isotope dilution, assessment of the isotope content, total potassium-40 (40K) isotope content analysis, and neutron activity analysis for total calcium and nitrogen content provide valuable insights but are costly and not typically accessible in routine clinical practice. Alternative methods employed in population-based epidemiology, such as anthropometry, skinfold thickness measurement, and infrared impact assessment, are less practical. Generally, the anthropometric method is used in clinical practice. Emerging technologies such as bioelectrical impedance analysis (BIA) and dual-energy X-ray absorptiometry (DXA) are also increasingly used in clinical settings and research trials [22–26].

Anthropometric measurements, including height, weight, and body mass index (BMI), are among the most common methods for assessing body composition [27,28]. Body height is defined as the distance from the base to the highest anatomical point on the head, known as the vertex. Body weight value provides information about a patient’s total protein, body fat, water content, and bone mass. However, changes in body composition may not always be reflected by changes in body weight alone, as body weight can remain constant despite alterations in composition. Body weight should be measured using a standardized scale [28,29]. In clinical practice, waist circumference and hip circumference measurements are used to estimate intra-abdominal fat. Waist circumference should be measured at a horizontal level between the lower edge of the last rib and the top of the iliac crest. Hip circumference should be measured around the largest protrusion of the buttocks and at a horizontal level. According to WHO guidelines, waist circumference should not exceed 80 cm in women and 94 cm in men [27,28,30].

BMI, also known as Quetelet’s index, is calculated by dividing body weight (in kilograms) by the square of height (in meters) [kg/m2]. The National Institutes of Health (NIH) uses BMI to classify individuals as underweight, normal weight, overweight, or obese, replacing traditional height vs weight charts. These classifications are applicable to White, Hispanic, and Black populations; however, they may underestimate obesity risk in Asian and South Asian populations, which necessitates slight adjustments in their classification. Although BMI is useful, it has limitations and should not be used as the sole indicator of obesity or malnutrition. In specific populations, such as elite athletes and bodybuilders, elevated BMI may not accurately reflect health status due to increased muscle mass. In pediatric populations, BMI facilitates comparisons among children of the same sex and age [23,27,28,31].

The waist-to-hip ratio (WHR) is another indicator used to assess body fat distribution. It is calculated by dividing the waist circumference (in centimeters) by hip circumference (in centimeters). Values equal to or greater than 0.85 in women indicate abdominal obesity, while values less than 0.85 suggest thigh-buttock obesity. For men, a WHR of 0.9 or greater is considered indicative of abdominal obesity [27,28].

BIA is a reliable, non-invasive, safe and effective method for assessing body composition. This technique measures the total resultant electrical resistance of the body, which is determined by both resistance (passive resistance) and reactance (active resistance). The measurement is conducted using a set of surface electrodes connected to a computerized analyzer through which a current of a specific frequency and intensity is passed [17,23]. BIA provides estimates of total body water (TBW), intracellular body water (ICW), and extracellular body water (ECW), as well as body cell mass (BCM). From these measurements, it is possible to derive the mass of adipose tissue (ATM) and muscle tissue (lean body mass, LTM) [18].

Although BIA is sufficiently reliable for estimating TBW at a single point in time, its methodology may be less effective for accurately quantifying changes in hydration status over time. Hypo- and hyperhydration often occur alongside alterations in intra- and extracellular fluid and electrolyte content. Consequently, variations in electrolyte content can confound BIA measurements when assessing concurrent fluid changes. BIA is useful for monitoring changes in body composition during dietary interventions and for adjusting dietary plans accordingly. However, the results of BIA are influenced by various factors, including proper device handling and appropriate preparation of the individual being tested. BIA is employed in a range of settings, from clinics and medical offices to fitness centers. It is applicable to individuals of all sexes and ages, regardless of health status. The results obtained from BIA are generally easy to obtain and are highly reproducible, and the required equipment is portable and relatively inexpensive [32]. BIA tests are considered completely safe; the frequencies used do not cause irritation to nerves or cardiac muscle, and the current intensity is harmless [33].

DXA was originally developed for measuring bone mineral density (BMD). It has been recognized by the WHO as the criterion standard for diagnosis and monitoring of osteoporosis [34]. Advances in this technology have expanded its application to body composition analysis, enabling comprehensive assessments that include the measurement of regional fat mass (FM), fat-free mass (lean mass, LM), and bone mineral content (BMC). Additionally, DXA has improved the precision of the trabecular bone score (TBS) for assessing trabecular bone structure, enhanced the identification of vertebral fractures through vertebral fracture assessment (VFA), facilitated the measurement of hip joint geometry, and provided the capability to estimate a 10-year fracture risk using the Fracture Risk Assessment Tool (FRAX) [34,35].

Advancements in camera technology have enhanced image quality, which has increased the interpretability of DXA results. DXA is a precise, non-invasive method that requires a short examination time (3–10 minutes) and exposes patients to very low radiation doses (1–6 μSv) [35–38]. Consequently, DXA is suitable for use across all age groups, from infants to the elderly. Its applications are expanding beyond traditional osteoporosis monitoring to include uses in sports medicine, obesity assessment, oncology (eg, evaluating adverse effects of chemotherapy, hormonal treatments, and radiotherapy), and other medical conditions. The results from DXA are strongly correlated with fat tissue measurements obtained through CT, MRI, and BIA [39–41].

Effect of Maternal Body Composition on Effectiveness of Breastfeeding

Adipose tissue research has grown over the past few decades in response to the increase in obesity worldwide. Studies support the hypothesis that adipose tissues function as a sizable organ with endocrine and plastic capabilities. Adipose tissue is composed of lipid-rich adipocytes. White adipocytes are grouped in white adipose tissue (WAT), which serves as a source of energy between meals. Brown adipocytes are organized in brown adipose tissue (BAT) and burn lipids for heat production. The unique structure of adipose tissue contributes to its plasticity. Increased thermogenesis is required in specific circumstances, such as chronic exposure to cold (where the plasticity of the organ allows the browning phenomenon) or increased energy storage for metabolism (where the plasticity of the organ allows the whitening phenomenon). As a result, organ plasticity enables the adaptation of its function to specific requirements. It is commonly acknowledged that the biological process underlying this flexibility is caused, at least in part, by direct differentiation of white adipocytes into brown adipocytes and vice versa. This phenomenon is known as trans-differentiation [42].

In addition to its importance for survival, adipose tissue is crucial for mammalian reproduction, particularly in females. Adipose tissue depots can secrete a variety of signaling molecules known as adipokines, which function as hormones and pro- and anti-inflammatory cytokines. Compared with other adipose depots, visceral adipose tissue appears to be more endocrinologically active. In many mammalian species, including humans, endocrine function is important for long-term regulation of energy metabolism and adaptation during lactation [43]. By analyzing the mRNA expression pattern of potential implicated adipokines in adipose tissue, Josephs et al conducted a study using rat models. Over the course of pregnancy and breastfeeding, WAT had 2.2–2.5 times higher levels of fasting-induced adipose factor (FIAF) mRNA. This adipokine can regulate the metabolic changes that occur during pregnancy and breastfeeding because of the significant induction of FIAF [44].

Therefore, in addition to WAT and BAT, the female body transforms white adipocytes into follicular cells, known as pink adipocytes, during pregnancy as they gear up for nursing through noradrenergic nerve fibers and hormonal factors. Throughout pregnancy, the mother’s adipose tissue is redistributed. The adipose tissue is not only a storage site; it is also a metabolically active tissue that secretes adipocytokines with endocrine and paracrine effects, including leptin, resistin, adiponectin, retinol binding protein-4 (RBP4), and Visfatin [45–47]. In summary, adipose tissue enables the division of energy into 3 fundamental requirements: metabolism, thermogenesis, and lactation [42].

During a healthy pregnancy, the mother’s body undergoes significant changes in body composition. There is a significant increase in the maternal blood volume and total adipose mass, although there was no change in the quantity of lean tissue. Depending on race, ethnicity, dietary status, and metabolic parameters, there is a wide range of individual variance in the accumulation of FM, ranging from 2 to >10 kg/woman. In the first half of pregnancy, maternal energy is mainly stored as triglycerides (TG) in her adipose tissue. However, as the pregnancy progresses, the lipids are mobilized to be utilized by peripheral tissues. In physiological pregnancy with sufficient weight gain, fat deposition begins in the second trimester and proceeds until delivery [48].

Trivett et al demonstrated that there is a shift from the lower body to the upper abdomen during pregnancy. The increase in abdominal fat during pregnancy has been shown to be related to the accumulation of visceral adipose tissue rather than subcutaneous adipose tissue, and there is an increase in visceral adipose tissue accumulation throughout pregnancy [49]. A study by Selovic et al, involving 400 pregnant women, revealed that throughout pregnancy, the average levels of preperitoneal adipose tissue and the abdominal wall fat index increased, whereas subcutaneous adipose tissue decreased. These results agree with the hypothesis that visceral adipose tissue expands during pregnancy [50].

The postpartum period is divided into 3 phases: the acute phase, which lasts for the first 24 hours after placenta delivery; the early phase, which can last up to 7 days; and the late phase, which lasts between 6 weeks and 6 months. The evacuation of gestational products, along with blood loss, leads to a weight loss of 5–6 kg [51–53]. Brisk diuresis is responsible for additional weight loss of 2–3 kg. Diuresis-related weight loss may continue for up to 6 months after birth [51]. Uterine and mammary tissues, body water (ICW and ECW), and fat are a few components of postpartum weight. It is unclear which components contribute to weight retention; however, they all change postpartum to varying degrees, which has a noticeable impact on how weight retention is interpreted in each individual. Cho et al found about 4.0 kg postpartum weight gain in women from pre-pregnancy to 6 weeks after delivery. Postpartum reduction in ECW, ICW, TBW, and fat-free mass are some of the body composition components [54]. However, the elements that were altered the most throughout pregnancy were the visceral fat area and FM. Our findings show that even if the body’s overall weight decreases throughout the postpartum period, visceral compartments tend to accumulate more adipose tissue than in other areas. Postpartum fat-free body mass decreases, while FM, in particular visceral fat, increases [54]. Janumala et al discovered no weight retention at 59 weeks postpartum, but visceral adipose tissue in women increased by approximately 30% [55].

During pregnancy, a mature breast undergoes anatomical and physiological changes. The ductal system expands and branches into adipose tissue in response to an increased estrogen level during the first trimester. High estrogen levels also lead to a decrease in adipose tissue and cause ductal proliferation and elongation. In addition to stimulating the pituitary gland, estrogen elevates prolactin levels. As a result of prolactin’s stimulation, the mammary glands are sufficiently developed to produce milk components by the twentieth week of pregnancy [56]. During breastfeeding, women need approximately 500 kcal per day to produce milk. Therefore, the mobilization of fat depots that develop during pregnancy may be aided by lactation [11,57]. The involution of the breast occurs in 2 stages: first, the lactocytes are eliminated through apoptosis; then, the stroma around them is remodeled, and the adipocytes redifferentiate [58,59]. In summary, the ability of adipocytes to adapt to the different temporal requirements of the mammary gland throughout pregnancy, lactation, and involution is exemplified by their remodeling potential of mammary adipocytes. Interestingly, this remodeling occurs mostly in mammary adipose tissue and to a much lesser extent in other subcutaneous or visceral adipose depots [60].

Maternal health can be significantly impacted by breastfeeding, which can reduce the risk of a variety of metabolic and physiological problems in women, including type 2 diabetes, metabolic syndrome, and cardiovascular disease. Jayasinghe et al stated that population-level education on breastfeeding should be supported by simultaneous body composition evaluations to better understand factors influencing infant and maternal health [61].

A summary of the studies assessing the amount and role of adipose tissue in breastfeeding and maternal adipose tissue distribution is shown in Table 1.

Effect of Hydration Status and Social Factors on Breastfeeding Efficiency

Water is the main component of the human body – its functions include modulating osmotic pressure, maintaining proper body temperature, and regulating biochemical metabolism [62]. Water is considered one of the critical factors in determining both physical and mental health [63]. During pregnancy, a woman’s body undergoes significant physiological changes. The TBW volume increases by 20% compared to the pre-pregnancy levels, which is an increase of approximately 7 L [64]. Plasma osmolality decreases, and the osmotic threshold for vasopressin release is reset [65]. After childbirth, changes in body weight composition occur. A longitudinal study conducted in 2011 by Cho et al, involving an exploratory group of 41 healthy pregnant women, aimed to assess changes in body composition during the postpartum period and examine their impact on weight maintenance [54]. ICW and ECW content decreased by 16.12% and 11.32%, respectively, from day 2 to week 6 postpartum, with a reduction in TBW of 4.70±2.24 kg, which was the main factor responsible for the observed postpartum weight loss [54].

Lactation presents a unique challenge to the water homeostasis of a breastfeeding woman. Adequate hydration during this period is particularly crucial, as a woman produces approximately 780 ml of milk per day [66]. Breast milk is composed of nearly 87% water, with its osmolality ranging from 290 to 300 mOsm/kg, and this osmolality is not correlated with maternal dehydration [66,67]. Lactating women are prone to dehydration due to milk production, which may have adverse effects on maternal health [63,67]. Therefore, regulatory authorities recommend increased water intake for pregnant and lactating women to compensate for fluid loss [68,69]. In 2010, the European Food Safety Authority (EFSA) set the total fluid intake (TFI) for breastfeeding women at 3.300 ml/d [68]. According to recommendations by Polish experts from 2009, the daily water intake norm is 3.700 ml for adult men, 2.700 ml for women, increasing to 3.000 ml during pregnancy and 3.800 ml during lactation [69]. The sensation of thirst during lactation may be mediated by oxytocin, which is structurally similar to vasopressin, with prolactin possibly also playing a role [70]. However, there is no substantial evidence that increased fluid intake enhances lactation [63].

The effect of a high level of hydration on the body and metabolism of a breastfeeding woman has yet to be thoroughly investigated. The recommendation to increase water intake during breastfeeding is primarily based on theoretical expectations of increased physiological water requirements during lactation [68,69,71]. However, the impact of additional fluid intake by breastfeeding mothers remains uncertain due to the lack of reliable randomized trials. Animal studies have demonstrated several prolactin-mediated physiological changes in the kidneys during lactation, such as increased glomerular filtration rate (GFR), enhanced renal plasma flow, and greater salt and water reabsorption in the proximal tubules [71]. These adaptations enable lactation to proceed without interruption, even under conditions of limited water intake [71]. A 2009 study by Alamer on 9 lactating Aardi goats found that a reduction in water consumption, combined with high environmental temperatures, did not significantly decrease milk production or its quality, owing to mechanisms that conserve body water in those mammals [72].

Numerous studies have failed to show that increased fluid intake by breastfeeding women has any effect on lactation efficiency [66,73,74]. A 1980 observational study of 21 women conducted by Horowitz et al found no difference in lactation efficiency between those with restricted and those with excessive fluid intake [73]. Similarly, a 1981 study by Dearlove et al reported no changes in serum prolactin levels or lactation efficiency in women who were given increased amounts of hypotonic fluids [74]. In a 2016 study, Soto-Méndez et al examined 31 women aged 18–49, between 30 and 365 days postpartum, and found no association between maternal hydration status, as indicated by urine osmolality, and the osmolality of human milk [66]. It is noteworthy that the osmolality of human milk is similar to that of plasma; therefore, infants consuming fortified milk or infant formula with an osmolality exceeding 400 mOsm/kg are at risk of developing osmotic diarrhea [66].

Although increasing fluid intake during lactation is unlikely to directly impact lactation efficiency, it is crucial for compensating water loss in breastfeeding women and thus preventing dehydration. A 2017 study by McKenzie et al involving 18 pregnant women found a correlation between urinary hydration biomarkers and TFI in both pregnant and breastfeeding women [65]. The study also observed that breastfeeding women maintain consistent milk secretion volumes over a wide range of TFI; however, this leads to higher urine concentrations in these women compared to non-breastfeeding women with similar TFI [65]. Despite recommendations for increased water intake among pregnant and breastfeeding women, research indicates that many do not adhere to these guidelines [67,75]. For instance, a survey of 308 pregnant or breastfeeding women in Mexico revealed that 41% of pregnant women and 54% of breastfeeding women consumed less water than recommended [75]. Similarly, a survey conducted in Indonesia reported that 42% of pregnant women and 54% of breastfeeding women consumed less water than suggested by regulatory authorities [67]. These findings underscore the need for effective interventions to encourage increased fluid intake during pregnancy and lactation. A 2017 study by Rigaud et al demonstrated that an illustrated tool based on a urine color scale can be effectively used by healthcare professionals to help pregnant and lactating women self-assess their hydration status and adjust their water intake as needed [64]. Similar conclusions were drawn in the 2017 study by McKenzie et al, which suggested that urine color assessment should be used to ensure that breastfeeding women consume adequate daily fluids [65]. Dehydration during pregnancy and lactation is associated with adverse outcomes, such as an increased risk of spontaneous miscarriage, preterm labor, low birth weight, and heightened levels of maternal aggression [68,74,76].

On the other hand, excessive fluid intake in pregnant and breastfeeding women can be associated with adverse health outcomes. Exercise-associated hyponatremia (EAH) is a complication observed in highly active individuals who engage in intense physical activity [77]. The pathogenesis of EAH involves the consumption of excessive amounts of fluids combined with osmotically inadequate secretion of antidiuretic hormone [77]. In severe cases, EAH can lead to encephalopathy, which is invariably linked to the excessive intake of large amounts of hypotonic fluids and exercise-induced non-osmotic vasopressin secretion. This effect may also be mediated by oxytocin [77]. Frequent oxytocin release during breastfeeding could contribute to a sustained antidiuretic effect by either directly acting on or by up-regulating vasopressin receptors 2 (V2R), making lactating women a group particularly susceptible to severe forms of exercise-related hyponatremia [77].

In developing countries with warm climates, where access to clean water may be limited, water availability is a critical factor influencing infant breastfeeding [70,78,80]. A 2020 survey by Schuster et al in 2020 (n=3303), conducted across 19 sites in 16 low- and middle-income countries (including Ethiopia, Malawi, Uganda, Pakistan, and Tajikistan), found that water insecurity contributes to reduced breastfeeding rates, decreased milk production, increased infant exposure to pathogens, and less frequent breast washing by mothers [78]. These factors collectively lead to higher infant mortality, malnutrition, dehydration, hunger, and increased morbidity [78]. Furthermore, environmental and water pollution, particularly in countries such as the United States, exacerbates perceived stress among breastfeeding women [79]. This stress often leads to a reduction in breastfeeding frequency due to health concerns and prompts mothers to substitute breast milk with formula [79]. A 2014 study by Rosinger et al., involving 54 women in the Amazon, demonstrated that environmental conditions, such as high temperatures, adversely affect women’s hydration status [80]. The study found that a significantly higher proportion of lactating women were dehydrated compared to non-lactating women (78% vs 50%), with breastfeeding women being 4–6.4 times more likely to experience dehydration than their non-lactating counterparts [80]. Women living in conditions with limited water access have developed some behavioral adaptations to conserve water, such as reducing physical activity and carrying water supplies with them [70].

The quality of water consumed during pregnancy and lactation is important. It is recommended to consume natural spring water that is non-carbonated, as carbonated beverages may cause a rapid sense of thirst quenching before proper hydration is achieved, and can also lead to bloating [69]. Once bottled water is opened, it should be consumed within a few hours to ensure its microbiological safety for both the mother and infant [69]. The consumption of beverages containing caffeine and alcohol is discouraged due to their diuretic effects, and the intake of hypertonic energy drinks containing taurine is also not recommended [81]. Chlorine, commonly used in water treatment processes, reacts with organic molecules to form products such as trihalomethanes, halogenated acetic acids, halogenated ketones, halogenated nitriles, trichlorobenzene, trichlorophenols, and hydroxyfurans [81]. These compounds can negatively impact fetal and infant development, as well as increase the risk of miscarriage and congenital anomalies. Therefore, pregnant and breastfeeding women are advised to avoid consuming tap water [81].

The amount of water consumed by breastfeeding women has not been shown to directly affect breastfeeding effectiveness. However, adequate water intake is crucial for preventing dehydration. Breast milk secretion remains consistent across a wide range of TFI, primarily due to the vasopressin-like effects of oxytocin. For self-monitoring hydration status, urine color scales may be effective; darker urine color indicates higher urine density and potential dehydration, signaling the need to increase fluid intake.

A summary of the studies assessing the effects of hydration status and social factors on breastfeeding efficiency is shown in Table 2.

Impact of Selected Metabolic Factors on the Effectiveness of Breastfeeding

The lactation process is influenced not only by the body’s adaptation during pregnancy and childbirth, but also by the mother’s metabolic conditions and hormonal balance. In addition, various diseases can disrupt the water-electrolyte balance and lipid metabolisms. The next paragraph discusses the relationship between lactation effectiveness and thyroid hormone levels, polycystic ovary syndrome (PCOS), prolactin levels, body weight, diabetes, and hypertension.

Thyroid hormones have a crucial role in regulation of lipid synthesis and catabolism, since they modify both cholesterol and fatty acid metabolism. Thyroid insufficiency results in increased low-density lipoprotein (LDL), high-density lipoprotein (HDL), and TG levels, and in this matter hyperfunction has the opposite effect [82]. Thyroid dysfunction can also alter hydration status, and cause renal manifestations, since thyroid gland insufficiency may cause elevated levels of creatinine in serum and GFR reduction, while hyperthyroidism causes decreased GFR [83]. During lactation, lower levels of thyroid hormones and thyroid-stimulating hormones (TSH) are commonly observed. In the past, the impact of maternal hormones on lactation was investigated, and studies showed that higher levels of thyrotropin-releasing hormone (TRH) stimulate lactation via higher prolactin secretion. Therefore, it was hypothesized that mothers with mild hypothyroidism, compensated by higher TRH release, could have higher milk secretion. Lactation intensity is also positively correlated with 5-deiodinase activity, which is the enzyme responsible for transition of thyroxine (T4) to triiodothyronine (T3) and is present in lactating mammary glands [84,85]. Interestingly, acute iodine deficiency is linked with vasodilation and increased blood flow in breast tissue during lactation [86].

Prolactin, as a principal lactogenic hormone, is crucial for milk production that occurs following reduction of progesterone and estrogen levels. Prolactin is 1 of 3 hormones essential for lactation occurrence, besides insulin and hydrocortisone [87]. As long as pituitary secretion is inhibited, the lactogenesis process is delayed. However, plasma levels do not positively correlate with milk secretion levels; therefore, the role of the hormone is believed to be permissive and does not increase lactation [85]. Hence, hypopituitarism, present in Sheehan’s syndrome, which is defined as ischemic pituitary necrosis after postpartum hemorrhage, results in absence of lactation [88]. The role of prolactin in fat remains unclear. Several papers showed no significant differences in prolactin levels between obese and lean individuals, but there is also evidence for a positive correlation of prolactin levels with weight gain, visceral fat, and lipogenesis [82,89], whereas extrapituitary prolactin, present in adipose tissue macrophages, induces weight loss [82]. Prolactin also participates in regulation of water and electrolyte balance by increasing water and salt absorption in the bowels, with decreased sodium and potassium kidney secretion [90,91].

The incidence of PCOS in reproductive-age women is estimated at over 18% of the described population [92]. Studies on the topic report that hyperandrogenism and insulin resistance are the key factors leading to impaired breastfeeding in PCOS patients [92]. In breast tissue during milk synthesis, insulin, synergistically with prolactin, promotes cell proliferation [92]. Vanky et al found that compared to controls, the PCOS patients had lower breastfeeding rates. Elevated androgen levels, including dehydroepiandrosterone sulfate (DHEAS) can act as lactation inhibitors. Androgens are hypothesized to be one of the main substances involved in this phenomenon since levels tend to be higher in PCOS patients, and this thesis was also supported by their study, where higher (DHEAS) levels were linked to lower breastfeeding rates in the early post-partum period [93]. Additionally, hyperandrogenemia observed in PCOS is associated with increase of plasma TG, LDL and cholesterol levels, and lowered HDL cholesterol [82]. Joham et al discovered shortened breastfeeding time in PCOS patients, but the results were inconclusive, since BMI was the main factor affecting the breastfeeding duration, and not PCOS itself [94]. Thatcher et al reported that PCOS patients had poor milk production, but the tested group was very limited [95]. Rassie et al reported that breastfeeding time in PCOS patients was shorter compared to patients without the condition, while a study by Riddle et al showed that low milk supply was not influenced by diagnosis of PCOS in women with diabetes during pregnancy [92,96,97].

Overweight and obese women account for over 60% of reproductive-age women, and this group is more vulnerable to breastfeeding problems [92,98]. For the purpose of this paragraph, BMI calculation was used as weight in kilograms divided by height in meters squared, and the following BMI classification: normal BMI for BMI 18.5–24.9 kg/m2, overweight for BMI 25–29.9 kg/m2, and obesity for BMI 30–34.9 kg/m2 (grade I), 35–39.9 kg/m2 (grade II) or >40 kg/m2 (grade III) [99,100]. Maternal obesity strongly is associated with lower probability of breastfeeding initiation and delayed onset of lactogenesis (lack of lactation within first 72 hours postpartum) [101,102]. Among the possible factors prolonging lactation initiation are lower prolactin levels within the first days after birth [92].

Higher pregestational BMI negatively correlates with breastfeeding time in general and exclusive breastfeeding time [98,101–103]. Normal-weight women breastfeed on average 4 weeks longer than overweight women, and 7.5 weeks longer than obese women [98]. These differences progressed as the BMI of the patients increased [96,99]. Ballesta-Castillejos et al observed that women with obesity grades I, II and III had lower breastfeeding initiation rates within the first hour after birth with adjusted odds ratios (AOR) of 0.8, 0.66 and 0.58, respectively. The authors described that the number of exclusively breastfeeding women with grade III obesity was significantly reduced compared to normal-weight mothers (0.57%) by the time of the hospital discharge [104]. They reported that women with grade II and grade III obesity had less breast engorgement and there was insufficient weight gain in their offspring, with more cases of delayed breast milk production in all 3 classified groups. Moreover, there is a negative correlation between BMI and percentage of patients who started breastfeeding within the first hour and those who breastfed exclusively. Due to breast composition, excessive fat tissue can mechanically constrict the ducts and compromise lactation [104]. Pèrez-Escamilla presented 4 possible geneses of altered lactation in mothers with higher BMI. Among them are obesity-related fat and glucose metabolic changes and chronic inflammation; mechanical latch difficulties resulting from excessive amounts of fatty breast tissue; psychoemotional factors and early introduction of prelacteal feeding [102]. Keyes et al comprehensively explored the impact of various factors mediating the pre-pregnancy maternal BMI on breastfeeding duration, which was associated with dietary inflammatory index (DII), C-reactive protein (CRP), and cesarean section delivery [98].

Patients with type 2 diabetes mellitus, besides having delayed lactation and struggles with milk supply, are at risk of breastfeeding-related hypoglycemia. Compared to the healthy patients, fewer diabetics are breastfeeding exclusively at the time of hospital discharge [105]. Also, type 1 diabetes mellitus patients have lower breastfeeding rates compared to healthy females [106]. A meta-analysis by Bortoli and Amir shows that data collected from 10 studies consistently confirms the higher probability of delayed onset of lactation (DOL) in pregnant diabetic women [107]. A study by Suwaydi et al revealed that females with gestational diabetes are more susceptible to delayed secretory activation and low milk supply [108]. Glucose intolerance is a cause of impaired mammogenesis, differentiation of lactocytes, delayed onset of lactogenesis, and impeding milk secretion in mature lactation [101]. During lactation, the insulin-sensitive gene expression was found to be up-regulated and the insulin itself is now linked to secretory differentiation, activation, and mature milk production [101]. Cordero et al found that type 1 and type 2 diabetes mellitus, obesity, and excessive gestational weight gain (GWG) are associated with lower rates of exclusive breastfeeding and breastfeeding overall at discharge, but negate the independent role of excessive GWG in this event [100].

The literature suggests that high blood pressure also affects lactation, since it affects mammary gland development and breast milk composition [107]. A recent study observed that patients with chronic hypertension (CHTN) and CHTN superimposed on pregestational diabetes mellitus had breastfeeding initiation rates of 82%, and 63%, respectively, but exclusive breastfeeding rates were significantly lower in both groups [109]. However, the mechanisms behind these phenomena are unclear, and various conditions can lead to each other and frequently coexist, which could bias research results. A summary of the studies investigating the impact of selected metabolic conditions on breastfeeding is shown in Table 3.

Future Directions

Further research is needed to validate advanced body composition technologies, specifically for use in lactating women. Conclusions should be based on studies that incorporate long-term measurements, diverse and multi-ethnic samples, and appropriate comparison groups of non-lactating women. Future research should not only refine body composition measurement techniques but also investigate the various factors influencing these changes throughout the reproductive cycle. The ultimate objective is to enhance maternal and child health outcomes. Comprehensive studies should integrate nutritional assessments, mental and general health evaluations, metabolic markers, and the woman’s ecological context. There is a need for collaboration among key stakeholders to promote optimal breastfeeding practices on a global scale.

Conclusions

A mother’s body composition after childbirth affects breastfeeding effectiveness. Maintaining proper hydration and a balanced diet during this time can improve breastfeeding, benefiting both mother and child. Breastfeeding supports the child’s development and immune system while reducing future disease risks. For mothers, it lowers the risk of postpartum depression, chronic diseases, cancer, and osteoporosis. However, conditions like diabetes and obesity can negatively impact breastfeeding.