Breastmilk is the gold-standard nutrition for an infant and the World Health Organization (WHO) recommends exclusive breastfeeding for at least the first six months of life.
Despite the importance of human milk in infant nutrition, there is a lack of robust knowledge about its nutritional composition and this is even more evident in donor human milk (DHM), according to the authors of the current study, from Octubre University Hospital, Madrid.
The findings in maternal milk should not be generalised to DHM due to additional variation caused by expression, freezing, storage, pooling, mixing, multiple container transfers, and pasteurization.
One of the many factors that influence the composition of human milk is the mother’s diet yet no previous study has focused on comparing the human milk nutritional composition of DHM between omnivorous and vegetarian women.
The objective of the new study therefore was to compare the maternal intake, nutritional status, and nutritional composition (i.e., macronutrients, water-soluble and fat-soluble vitamins, minerals, fatty acid profile, lipid class profile, molecular species of triacylglycerols, and the relative composition of phospholipids) of human milk from omnivore human milk donors and vegetarian/vegan lactating mothers.
The researchers developed a detailed and comprehensive description of micronutrients and lipids in human milk from both groups of women, concluding that there are notable differences in the content of omega-3 fatty acid DHA and vitamin B12.
The report concludes: "There are no previous studies on vegetarians/vegans in which such a quantity of nutrients has been determined in their milk or in which they have been compared with milk donors....
"Of particular concern is the lower DHA content in the milk of our vegetarians/vegans’ group. However, raising awareness and administering proper supplementation could bridge this gap, as has been the case with vitamin B12."
Milk donor conundrum
Vegetarians without proper dietary advice are at a high risk of inadequate intake of and an inadequate status for several nutrients, mainly vitamin B12, vitamin D, iron, iodine, zinc, calcium, selenium, and docosahexaenoic acid (DHA).
Consequently, human milk banks have been faced with the challenge of determining whether these women are suitable to be milk donors, with the aim of ensuring the safety and quality of DHM via donor selection processes.
Following the recommendations of the European Milk Bank Association, a vegan diet with an adequate supplementation of vitamin B12 is not an exclusion criterion for donor candidates. Nevertheless, certain countries do not accept milk donations from vegans, regardless of their vitamin B12 supplementation status.
The subjects of study were as follows: (1) human milk donors with an omnivore diet and with full-term infants (Donors) who donated milk at least once in the last 2 months to the Regional Human Milk Bank Aladina MGU (RHMB); and (2) healthy vegetarian/vegan lactating mothers (Veg) with a milk expression routine who were lactating 3 weeks or more postpartum.
A total of 112 participants completed the study: 92 Donors and 20 Veg. In the Veg group, there were 11 vegans and 9 vegetarians.
An early morning meeting at the RHMB was arranged for each of the women who agreed to participate in the study. At this appointment (day 0), the participant’s blood and urine samples for biochemical studies, somatometric measurements, informed consent for the study, health and socio-demographic survey, and food frequency questionnaire (FFQ) were collected. Women were weighed and measured, and their body mass index (BMI) was also calculated
Within the following 15 days after their visit to the RHMB, participants were asked to choose 6 days in a row to conduct the second part of the study. During the first 5 days (days 1 to 5) they filled in a dietary record. In parallel, from days 2 to 5, they collected a milk sample of 25 mL from each expression (at least one per day) for vitamin and mineral studies. On the sixth day (day 6), they collected a complete milk sample from one of their breasts for the lipid studies. Participants were requested to bring their dietary records and milk samples to the RHMB within the following 15 days after study’s completion.
The vitamins and lipids were determined in the plasma, erythrocytes, and milk. Minerals were determined in milk and urine.
Resulting data indicated the DHA intake by the Veg group (110 mg/day) was less than one-half of the DHA intake by the Donors (380 mg/day), which resulted in a DHA concentration in the milk of the Veg group that was less than half that of the Donors (0.15% vs. 0.33%, respectively).
This is in line with the findings of another study comparing milk DHA content from non-donor vegetarians, vegans, and omnivores. It is recommended that breastfeeding women consume at least 200 mg of DHA per day, which should translate into a milk DHA content of 0.30%.
"As only 25% of women in the Veg group reported taking DHA supplements, there is an important opportunity for improvement in this area," note the researchers.
In terms of micronutrients, the greatest concern among vegetarians is the vitamin B12 content of their milk but this study found that supplementation made up for this.
"The vitamin B12 content in the milk of our Veg group is a perfect example that the vegetarian/vegan diet can be suitable for lactating women if sufficient supplementation is provided. Our results support the approach of most worldwide milk banks, which recruit vegetarian/vegan mothers as donors on the condition that they regularly supplement vitamin B12, as well as other micronutrients if necessary.
"In the Veg group, with a vitamin B12 supplementation rate of 85% and an average daily dose of 312 mcg/day, their plasmatic levels were similar to those of the Donors."
The authors emphasise that the studied milk was subjected to the usual procedures in the donation process, such as extraction, freezing, and thawing. All these processes can affect the composition of the milk so the results are not superimposable to those of mothers’ own milk.