Abstract
Dear Editor:
Human milk contains volatile food odors and varies depending on maternal food intake. 3 In contrast, formula milk has a uniform flavor. Some studies have shown the acceptance of basic taste in weaning is different among breastfeeding and formula-feeding infants.4,5 However, it is not known if these taste preferences are present before weaning, especially around 3–4 months of age, the period of optimal acceptance for new taste described as a developmental window. The aim of our study was to compare preferences to basic taste among breastfed and formula-fed infants.
This cross-sectional study was developed at the Instituto de Medicina Integral Prof. Fernando Figueira Hospital (Recife, PE, Brazil) between August 2011 to March 2012. This study was previously approved by the Instituto de Medicina Integral Prof. Fernando Figueira Ethical Committee in Research, and written informed consent was obtained.
Sixty-three healthy infants 3 months of age, all born full-term, were studied. Exclusively breastfeeding infants were according to the World Health Organization definition. Other infants were habitually fed only on cow's milk formula (NAN® I; Nestle, Vevey, Switzerland). Infants with diseases that could impair growth were excluded.
Each child was tested at the same time of day (9:00 a.m.) accompanied by his or her mother in an isolated room (at a temperature of 23°C). All children received their previous meal an hour before the test. The stimulus was given in the following sequence with an interval of 1 minute: glucose (0.3 M), sodium chloride (0.3 M), sodium citrate (0.001 M), and urea (0.18 M). A 1-mL disposable syringe was used to apply 0.2 mL of solution on the dorsal surface of the tongue. All infants were held upright facing forward during the test and had their face videotaped during a 1-minute interval.
The facial responses were coded into nine action units according to the Baby Facial Action Coding System: A1 represents no distinct mouth action or sucking on the face; A2 is A1 with a negative expression on the mid-face; A3 is A1 with a negative expression on the mid-face and brows; B1 represents the facial response of a pursing mouth; B2 is B1 with a negative expression on the mid-face; B3 is B1 with a negative expression on the mid-face and brows; C1 represents a mouth-gaping action; C2 is C1 with a negative expression on the mid-face; and C3 is C1 with a negative expression on the mid-face and brows. Two trained professionals who were unaware of the study aims watched the videotape recordings to classify facial responses. Reliability for scoring was 88% (p<0.001).
The data were analyzed by SPSS software (SPSS, Inc., Chicago, IL). The frequency of the facial action units was compared between breastfeeding and formula-feeding infants. The χ2 test was used, and significance was considered at p<0.005.
We studied 60 infants, 27 exclusively breastfeeding and 33 formula feeding. Both groups did not differ in age, gender, birth weight, and delivery: the average age was 3.3 months (SD, 0.2 months); 46.6% were male; birth weight ranged from 2,980 g to 4,010 g (average, 3,241±332 g); and 40% were born by cesarean section.
Facial responses to taste solutions showed differences; more liking responses were shown to sweet (88.3%), followed by salty (51.7%), sour (30.0%), and bitter (28.3%) tastes.
Facial responses to basic tastes showed no difference among breastfed and formula-fed infants in our study (Table 1). Despite the importance of exclusive breastfeeding for health, both in the period of breastfeeding and in later stages of life, there are few studies that had assessed taste responses in early infancy. Formula-fed infants are exposed to a constant flavor, a predominantly sweet taste, whereas breastfed infants can be exposed to different flavors, also a predominantly sweet taste, depending on the maternal diet. To the best of our knowledge this is the first study to assess preferences to basic tastes comparing breastfeeding and formula-feeding infants at 3 months of age. Most of the studies have been done during weaning, and some differences in food acceptance were found among breastfed and formula-fed infants.3,4
Data are number of infants (percentage of total).
We detected a similar pattern of facial responses to newborns during the first hours of life: predominantly indifferent or liking responses to a sweet flavor and negative responses to sour and bitter tastes. Taste development is not yet completely understood, and it seems to occur in a period of plasticity around 3–4 months of age, the period of optimal acceptance for new tastes. 2 We studied infants at this age, and facial responses to basic tastes may be not sensitive enough to detect differences at this age. Besides, breastmilk and formula milk have a predominance of sweetness and could not cause different stimulation like hydrolysate formulas, which have more pronounced bitter and sour tastes. Both of these two reasons could explain our results.
Our study has some potential limitations. First, we studied a small group of children and used only a single concentration. Milk has a predominant taste of sweetness, and it is known that the response to the stimulus can be modified with different concentrations. However, we used standard solutions in a concentration usually used in other studies. Second, we did not investigate maternal food habits. Breastmilk has volatile food odors that change according to maternal diet and vary from mother to mother.
In conclusion, our findings suggest that breastfed and formula-fed infants at 3 months of age have the same pattern of facial response to basic tastes. Our results need to be confirmed, and further studies should be conducted to evaluate taste responses in breastfed infants over 3 months of age.