Can your diet and health change your breast milk? Review uncovers the key maternal and birth factors

By Tarun Sai LomteReviewed by Susha Cheriyedath, M.Sc.Aug 3 2025

From diet and geography to delivery mode and preterm birth, discover how a mother’s journey shapes the unique nutritional profile of her breast milk, potentially influencing lifelong health.

Diagram of factors that may affect macronutrient and energy content of breast milk. Abbreviation: IUGR, intrauterine growth restriction. Factors That May Affect Breast Milk Macronutrient and Energy Content: A Critical Review

In a recent study published in the journal Nutrients, researchers in Portugal reviewed the factors affecting energy and macronutrient content of breast milk.

Breast milk composition may adapt to maternal factors, neonatal characteristics, and obstetrical factors. The impact of changes in breast milk composition on offspring growth and health remains unknown. In the present study, researchers reviewed the factors affecting the energy and macronutrient content of breast milk. They searched medical literature databases using relevant terms and identified 35 studies for a comprehensive review using Levels of Evidence (LOE) classification and focusing on studies published after 2006 for methodological consistency. The factors affecting macronutrient and energy content of breast milk were stratified as maternal, obstetrical, and neonatal.

Maternal factors affecting breast milk energy and macronutrient content were maternal age, socioeconomic status, geographical location, dietary intake, nutritional status, and lactation stage. A study observed that milk from mothers with a lower socioeconomic status was richer in monounsaturated and n-9 fatty acids, while milk from mothers with a higher socioeconomic status was richer in polyunsaturated, n-3, and n-6 fatty acids (PUFAs). Milk from self-employed mothers or those working in the private sector was found to have a higher fat and protein content than that from unemployed mothers or those working in the public sector. Older maternal age has been reported to correlate with more fat in colostrum, transitional, and mature milk.

A study found consistent evidence that breast milk fatty acid content varies by geographical location, likely due to dietary differences. For instance, Swedish mothers’ breast milk was found to have higher eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA; n-3) but lower linoleic acid (n-6) content than Chinese mothers’ breast milk. Maternal obesity has been associated with elevated fat content in breast milk, though transitional milk may show lower fat, with evidence for higher lactose being less consistent and primarily observed in colostrum.

A systematic review found that higher maternal body fat was associated with increased fat content in breast milk. Lower maternal fat intake has been associated with higher eicosapentaenoic acid and docosahexaenoic acid content in breast milk. Higher maternal protein intake has been linked to increased energy, carbohydrate, fat, and protein content. Higher maternal intake of PUFAs has been found to correlate with higher PUFA content in breast milk.

Different lactation stages influence breast milk macronutrient content. A cross-sectional study found lower protein and higher fat content in mature milk than in transitional milk. A meta-analysis of preterm milk reported that during the first 12 weeks postpartum, there is a progressive increase in fat content and a progressive decline in protein content, with carbohydrate and energy content increasing initially before achieving a steady state. This pattern is most consistent for preterm milk, while term milk shows variations (for example, energy may increase continuously).

Obstetrical factors that may impact the energy and macronutrient content of breast milk include parity, preterm delivery, mode of delivery, and pregnancy morbidities (gestational diabetes and hypertensive disorders). Studies have suggested associations between the parity number and the macronutrient content of breast milk. Fat content is reported to increase with parity number up to three, beyond which the trend may reverse.

The extent of prematurity may impact breast milk's energy and macronutrient content. A study found higher true protein and total energy content in breast milk with increasing prematurity. Another study found higher energy and fat but typically lower carbohydrate content in milk from mothers with preterm delivery than in milk from those who gave birth at term. Breast milk composition could also vary by the mode of delivery.

Milk from mothers who underwent cesarean section had elevated fat content, while milk from those with vaginal delivery had increased carbohydrate content. A systematic review found that mature milk and colostrum from hypertensive mothers had higher protein content compared to normotensive mothers. Hypertensive disorders were also linked to higher energy content (chronic hypertension) and lower DHA (preeclampsia), whereas gestational hypertension was associated with lower milk energy and fat.

A different study reported higher true protein and total energy content in milk from mothers with chronic hypertension. On the other hand, mature milk from mothers with gestational diabetes was found to have a lower energy and fat content compared to euglycemic mothers. A systematic review reported lower lactose and fat content in milk from mothers with diabetes mellitus.

Neonatal factors that affect breast milk’s energy and macronutrient content include sexual dimorphism and anthropometrics. Multiple studies conflict on sexual dimorphism: some report higher energy and fat content in milk for males, while others show the opposite for females. Lower carbohydrate content in milk for males is more consistently observed. Higher birth length was independently correlated with higher energy and fat content in breast milk.

In sum, various obstetrical, maternal, and neonatal factors affect the energy and macronutrient content of breast milk. Milk from obese and overweight mothers has been reported to be fat- and energy-rich, though transitional milk may differ. Increased energy and protein content have been reported in milk from mothers with earlier preterm delivery, especially extremely preterm births. Higher protein and energy content and variable fat changes were reported in milk from mothers with hypertensive disorders, while lower fat characterized milk from diabetic mothers. Though sexual dimorphism findings conflict, male infant sex may be associated with lower milk carbohydrate. The review acknowledges limitations, including heterogeneity in study designs and methodology.