Resistin in Urine and Breast Milk: Relation to Type of Feeding and Anthropometry at 1-Month

Round 1

Reviewer 1 Report

The authors evaluated resistin levels in breast milk and urine at a single time-point and assessed correlations with maternal and infant anthropometry. Strengths include lack of confounding differences in maternal and neonatal factors and measurement of both breast milk and urinary resistin levels. The major weaknesses are limited statistical power and lack of wide demarcation in breast milk intake between the two groups given the lack of a formula only cohort.
Specific Comments:
1.    The final 2 paragraphs of the introduction are unfinished with incomplete sentences and no citations.
2.    Please provide the power calculation that was used to determine target enrolment or a post-hoc determination of statistical power.
3.    Were the samples analyzed in duplicate to improve accuracy?
4.    What were the lower limits of quantification for the two hormones, and how many samples were below those levels?
5.    Table 1: The asterisk for significant difference in formula volume should be placed in the breast-fed column.
6.    Please provide the correlation coefficients for the data in Figures 2 and 4.
7.    Clarify if body weight gain is based on the difference between current weight and birth weight or discharge weight.
8.    Clarify in methods if leptin was only measured in breast milk or also in urine
9.    Did leptin concentration in breast milk correlate with maternal weight or BMI?
10.    What is the speculation for the lack of correlation between adipokine levels in breast milk and maternal weight or BMI?
11.    Line 142: add “urinary” before “resistin” and add the reference number.
12.    Line 175: The statement that determination of urinary resistin could be a surrogate for serum resistin is not supported by the presented data.

Author Response

Thank you for the comment and here below are the answer for each specific comment:

1. I revised the two final paragraphs in the introduction section and added the related citations
2. The power calculation to determine target enrollment can't be done because as far as we know this is a pilot study, in which the anticipated level of resistin in urine is not known.
3. Yes, the samples were analyzed in duplicate.
4. The range is between 20-1.000 pg/mL. There were no samples below those lower limits.
5. We changed the study groups into 3 groups so the asterisk mark is not relatable anymore.
6. Each correlation coefficient was added next to each figure.
7. Bodyweight measured on a one-month check-up day will be used to count the body weight gain by subtracting it with the birth weight and was divided by the days from birth to one-month check-up day. (added to the Methods section)
8. It was only measured in breastmilk (and additionally explained in the method section)
9. Leptin in breastmilk did correlate with the BMI of mothers (r=0.395, p=0.03).
10. This might be caused by a non-standardized sampling. We asked the mother to collect the breastmilk at home before coming for a one-month check-up, so it can be either fore-milk or hind-milk, some a whole breast expression. 
11. The word 'urinary' has been added.
12. We deleted the statement that urinary resistin can be a replacement for serum resistin in conclusion.

Author Response File: Author Response.pdf

Reviewer 2 Report

Appreciate the invitation to review this paper, that is well structures and is easily read.

Congratulate the authors because on the thematic selection since the relation between adipokines and anthropometric parameters can contribute to obesity development knowledge.

 

Line 71 - Authors divided the sample in 2 groups according to the intake of more or less of 100ml of formula/day in the last 7 days of the study. What was the rational for that cutoff value? Please explain.

Line 76 - “only when the breast milk was inadequate” – How was accessed (by nutritional composition? by inadequate anthropometric evaluation of the RN? Please provide detail information);

There is also same abuse when authors say the breast feed group (BF), since as you know breast feed infants are those without any amount of formula. Suggest give a small justification that the nomination BF is just to simplify.

Line 78 – Newborn were split in two to groups by the last 7 days formula, this small amount of time could not be sufficient to reflect the anthropometric parameters;

Table 1:

-Suggest include BMI of mother before pregnancy since is more important then the weight, with this information easily the reader understand if the weight gain during pregnancy is adequate. Since the BMI of the mother can affect the levels of leptin (Nicholas J. et al) other adipokines could be also affected, so mention of maternal BMI before pregnancy is important.  

-Suggest adding the Z-score classification of children anthropometric data

-Information on body weight gain, can be tricky, even when groups are proportional in sex and (apparently) in z-score. As we know, the expected weight gain is variable according to sex and z-score, so better present the adequacy of weight gain (example in %) according to these factors.  

Line 166: Limitations In a 4-4,4kg child (Z-score aprox 0), the >100ml intake of formula can represent 100% or around 25%. This amplitude in a sample of 13 newborn could be important bias. Also in BF group, give information if there were any infants with exclusive breast milk.

 

Effect of Maternal Body Mass Index on Hormones in Breast Milk: A Systematic Review

Nicholas J. Andreas, Matthew J. Hyde, Chris Gale, James R. C. Parkinson, Suzan Jeffries, Elaine Holmes, Neena Modi. PLoS One. 2014; 9(12): e115043.

Author Response

Thank you for the kind words and constructive comments.

Line 71: We changed the groups into 3 divided groups. (Breastfed, breastmilk dominant mix-fed, formula dominant mix-fed). We found local data (only published in Japanese) that stated the average amount of intake in the 1-month old infant is 195 mL/kg/day. Based on these we divided mix-fed into breastmilk and formula dominant (< 100 mL/kg and ≥ 100 mL/kg, respectively).

Line 76: The decision was made solely by the mother, although we gave the education that it is better to do exclusive breastfeeding.

Line 78: A support study might be needed for this. And another limitation in this study, the compliance level was low.

Table 1: Added the BMI before pregnancy and z-score for anthropometric data.

Author Response File: Author Response.pdf