Neonatal Caloric Requirements
Selia asked me an interesting
question about a recent post from the FIB folks about neonatal stomach
volume. It seems that J. Seagrave RN,
IBCLC wrote a provocative piece about how our neonatal stomach volume models of
the marble and the nut, and egg are not evidence based and therefore everything
that we think we know about neonatal feeding is wrong. As we usually find on the internet she is
half-right, and biased, but she makes a very good point. Our neonatal feeding estimates are probably
wrong and our understanding of neonatal feeding in the first 48 hours is almost
certainly wrong, but that doesn’t mean we have to change anything. It also doesn’t mean that the babies are
starving or suffering either. To defend
this, I’ll use basic nutritional theory and a little microbiome science for
back up. So, let’s dive in and I’ll tell
you what I have discovered.
First, Seagrave is 100% correct,
the estimate of neonatal stomach volume that suggests a size of 5-7 mL are not
measures of actual stomach volume, they are a mathematical calculation where
researchers took the average 24-hour intake and divided by number of feeds and
came up with a number that is incorrect.
I won’t go so far as to say that they based their findings on one flawed
study, but I will say that assumptions on neonatal stomach volume are
flawed. I agree with Bergman (cited by
both Seagrave, and me). The neonatal stomach
volume, at which the stomach is “full” but not bloated is probably about 20 mL
and rapidly expanding as amniotic fluid is replaced, first with colostrum, and
eventually with breast milk. In my
practice I usually use a rough estimate of 15 mL/kg during the first month for
what I can expect from a baby who is totally full. I also understand that the average newborn
between 7-21 days takes about 30 mL in a “good feed”. Unfortunately, that last observation comes
from my own practice where I have monitored about 250 adequately growing
neonates. That isn’t to say it is made
up out of whole cloth, Kent and the good folks at the Hartmann lab have said
the same thing in numerous studies (bibliography). So where is the disconnect? Neither stomach volume nor average intake
tells the whole story.
I’d like to start with stomach
volume. I have no reason to disagree
with Bergman or Seagrave, the average neonatal stomach volume is approximately
20 mL., but if you read the works they cite it is actually between 10-35 mL and
that is an important distinction. The
stomach is an organ with a tremendous capacity to stretch, the difference
between empty and full is tremendous. In
adults, the average stomach volume varies tremendously and is ultimately based
on the volume of food habitually eaten (Lutz et al., 2015). Actual measurements show that the empty adult
stomach holds about 50 mL but can stretch to approximately 4 liters (Hoffman
& Sullivan, 2017). That is a stretch
capacity of 8,000% (80-fold). In his
work on neonates Bergmann shows that the stretch capacity is about 350% (from 10-35
mL). Can you imagine attempting to
assess how much food you should eat based entirely on your stomach volume? It would be impossible! Would we limit your intake to 50 mL per
feeding, or would we force you to eat 4,000 mL of food at every feeding? Both are laughable in their simplicity. Also,
it would be foolish to even suggest that you eat the same amount at every
single feeding. Imagine, the same amount for all three meals and all three
snacks. Nonsense, as adults we
understand that sometimes we want a snack and sometimes we want a feast. It has nothing to do with how much is
available, and everything to do with appetite.
Why then would we suggest that a neonate must eat the same thing at
every feeding? Why would we attempt to
predict every single feed? Newborns are
not robots. No, they are like us they eat according to appetite, not some mathematic
calculation discovered by research studies.
My answer to both the ABM and the FIB folks is that neonatal stomach
volume is a useless predictor for required volume or calorie intake.
So let’s talk about actual
caloric requirements. Unfortunately, I
don’t have a good estimate of calorie requirements for a neonate in the first
48 hours. I agree with FIB, what we
think we know is based on myth and bad science (both ours and theirs). But if we expand that to the first month,
there is some pretty interesting stuff out there. Seagrave reported the estimated neonatal
caloric requirement of about 100 kcal/kg/day.
That is lower that the Food and Agriculture Organization (FAO- a
division of WHO), which reports 113 kcal/kg/day for male neonates and 107
kcal/kg/day for female neonates, for simplicity we can average that to 110
kcal/kg/day for both male and female (FAO, 2004). They also report that the TEE (Total Energy Expenditure)
for Breast fed infants is lower than what is required for formula fed infants. In other words, formula fed infants require
more calories to survive and grow than breastfed infants. The actual report is 12% more at 3 months,
then gradually getting closer over the first year and becoming equal by 12 – 18
months (FAO, 2004). That means that the
average formula fed infant needs approximately 500 kcal/day where the average
breastfed neonate needs only 430 kcal/day (FAO, 2004). The two sets of numbers a little different,
but they end up being close enough for our purposes. If we can assume that both breastmilk and
formula is 20 kcal/ounce (which is close enough), that means that the average
(3.5 kg) breastfed neonate needs 385 kcal/day (3,500 g x 110 kcal = 385) or
19.25 ounces per day. And the average
formula fed needs up to 12% more (431 kcal/day or 21.5 ounces).
That is, of course, assuming the
calories taken in and the calories used are the same thing, which microbiome
theory would suggest, is not actually correct.
When we look at neonatal feeding, we know that the average newborn takes
only 37 mL in the first 24 hours (25 kcal), 100 mL in the second 24-hours
(60-70 kcal), gradually increasing to 450 mL/day by 14 days (300 kcal) and
750-1250 mL/day from 30-180 days of life (500-833 kcal). For references I highly recommend that you
look up the collected works of the Hartmann lab from 1976-2016, but if you are
lazy, they can all be found in the latest LEAARC Core Curriculum (2019). That means that newborns are seriously
lacking in calories for the first 1-2 days and even for as much as the first
month of life, and yet… they thrive. How
do they do that? It seems a mystery, but
it really isn’t. The simple answer is
“because”, for a more complete answer, we will have to turn to theory.
[I want to spend a second
explaining the two different concepts, TEE vs. Total caloric requirement. There is a world of difference between the
100-113 kcal/kg/day that is required for growth and the TEE. The TEE is what the body expends to promote
survival, not growth. It is remarkably
lower than you normally hear when talking about calorie needs. The TEE of the average neonate is only
108-110 kcal per day (not per kilogram/day).
The TEE is calculated by a pretty high-tech method (Doubly Labeled Water
or DLW, which I don’t have space to go into here, but just know that they use
mass spectrometry to measure actual energy use over a period of time, rather
than attempting to measure calorie intake).
Just understand that there is a difference, and that difference will be
important later.]
I hope you have been keeping up
so far because from here on out, we are forced to rely more on theory than
actual research, because there is no reliable research out there. First, we will talk about the normalcy of
mammalian physiology. That means that
all things considered equal, the mammalian neonate is designed to survive, and
that normal physiology can support that survival. That means that even if we don’t understand
it at a scientific level (and FIB certainly doesn’t not understand it), what
happens naturally, is probably what is
supposed to happen. When we see
that the average newborn takes in 37 mL of 18.7 kcal/ounce colostrum in the
first 24 hours, we have to assume that there is a reason for that. After all, mammalian physiology rules the
known world, it must be doing something right. My theory (and it is just that, a theory of
MINE, take it or leave it). My theory is
that babies are not eating in the first 24-72 hours, they are transferring the
mother’s immune system in the form of colostrum. We all should know by now that colostrum contains
almost no lactose (which is to say calories), that it is made up almost
entirely of proteins, immune proteins like sIgA, and restorative proteins like
human Breast Milk Stem cells (Bode, 2014).
All the calories that a healthy, term, newborn needs are delivered by
their body fat through gluconeogenesis, not through breastmilk (ABM, 2016, AAP,
2012). Like hibernating animals, they
get nice and fat, then they fast for a while and live off that fat. It is normal to lose weight in the immediate
newborn period. That isn’t a failure of
the American health care system, it is normal mammalian physiology.
Second, we need to look at basic nutrition theory. We have all met that person who can eat whatever they want and not gain weight, and we all know those poor unfortunate souls who look at a piece of cheesecake and end up looking like the Sea Witch from Disney’s “Little Mermaid”. I’m no Dietician, but I understand nutrition well enough to know that our daily caloric requirements and our TEE do not tell the whole story. That manipulating daily caloric needs is a game of estimation and trial and error. We increase or decrease our estimates by 10% until we reach the desired outcome. For most western adults that is weight loss, for most infants that is weight gain. That is a long-winded way of saying that we know that infants are eating “enough” when they gain weight. The actual volume of intake is irrelevant if it doesn’t achieve the ultimate goal which is growth over time.
Let’s go back
and look at that last bit a little more deeply.
Why do some people get fat when others don’t, even when they eat the
same amount of food? Microbiome
scientists have discovered that the bacterial content of our gut is ultimately
responsible for the efficiency of our caloric absorption. To put it simply, fat people have bacteria
that is very good at getting calories out of food and skinny people have
bacteria that is not very good at extracting calories from food. (for a very
good explanation of this, I recommend Robert Knight’s TED talk on the subject,
found at: https://youtu.be/i-icXZ2tMRM
) To dig a little deeper, a team of researches in Israel discovered that they
could use stool samples to predict the speed and efficiency of carbohydrate
uptake. In pregnant women there is an
overgrowth of a wonderful little bacteria called methanobrevibacter smithii.
This bacteria is actually why pregnant women are more gassy than
non-pregnant women. You see, it is more
efficient at fermenting and digesting carbohydrates in the maternal-child
gut. So where you may get 80 kcal from
your average slice of bread, the mother and baby may get 90 kcal. Simply put, they don’t need to eat as many
calories because they get more calories out of the food they eat. This certainly helps explain why so many
pregnant women gain excessive amounts of weight even when they stick to a
prescribed diet. In infants there is a phosphotransferase
transporter system (a group of bacteria) that enhances carbohydrate breakdown
and transport (Backhead, 2014). It helps
to explain why breastfed infants thrive with fewer calories than they should
need, and why formula fed infants need more calories than breast fed infants. Imagine what changes we may see in the future? While we agree that pregnant women NEED an
extra 300-500 kcal/day to support the increased metabolic needs of the
developing pregnancy, perhaps they don’t need to EAT an extra 300-500 kcal,
because they might actually get it through their enhanced digestion from good
old m smithii. It is too early to say, but there is evidence
that breastfed neonates benefit from the same bacteria, and perhaps formula fed
neonates do not (Backhead, 2014). You
might recall that the FAO reported that formal fed infants need extra calories
(FAO, 2004).
I know, this is
hopelessly long, but how can I explain sucha complicated problem in only 2,500
words? Let me try to sum it up for you
here. 1) Neonatal stomach volume
estimates are probably wrong, and almost certainly useless measures that have
nothing to do with caloric requirements, so both sides of the argument are
wrong. 2) Newborns are not supposed to
take large volumes of milk early on, they pack a lunch and take it with them. 3) Colostrum is not calories, so it is a
little pointless to try to use it as such.
4) Infants are not robots; their
intake is guided by appetite and ability and those change from feeding to
feeding. The assumption that every
feeding must be a specified volume is simplistic and will lead to errors. 5) The breastfed infant has a very efficient
carbohydrate digestion system which may enable them to take more than 20 kcal
from every ounce of 20 kcal breastmilk, so estimates of daily caloric
requirements may not be accurate. 6)
(AND THIS IS THE BIG ONE) Infants need “enough” calories to support growth over
time and estimates of required volume are just that… estimates. The proof is in the pudding, as they say, a
baby who isn’t growing well on X amount of breast milk needs more breast milk, and
vice versa. I hope that answers your
question. For me, it only creates more
questions. But that is the joy of
science, is it not?
References:
Backhed, Roswall…Dahlgren, & Wang (2015) Dynamics and stabilization
of the human gut microbiome during the first year of life. Cell Host & Microbe 17, 690-703.
Bergman, NJ (2013) Neonatal stomach volume and physiology
suggest feeding at 1-h intervals. Acta Paediatrica, 102, p 773-777.
Bergmann, RL., Bergmann, KE., vonWeizsacker, K., Berns, M.,
Henrich, W., Dudenhausen, JW. (2014). Breastfeeding is natural but not always
easy: intervention for common medical problems of breastfeeding mothers – a
review of the scientific evidence. Journal
of Perinatal Medicine; 42:1 9-18.
Bode L. (2012) Human milk oligosaccharides: Every baby
needs a sugar mama. Glycobiology, 22(9), 114-1162.
Food and Agricultural Organization of the WHO.
(2004). Human Energy Requirements. Chapter 3: Energy requirements of infants from birth to 12 months.
Retrieved from http://www.fao.org/docrep/007/y5686e/y5686e05.htm#bm05.3
Retrieved on 01 April 2017.
Hartmann, P. (2007) The lactating breast: An overview from
down under. Breastfeeding Medicine,
2(1) 3-9.
Hoffman & Sullivan (2017). Davis Advantage for Medical-Surgical Nursing:
Making connections to practice. FA Davis
Publishing. ISBN-13: 978-0-8036-4417-5
Kent, J.C., Hepworth, A.R., Langton, D.B., Hartmann, P.E.
(2015). Impact of measuring milk production by test weighing on breastfeeding
confidence in mothers of term infants. Breastfeeding
Medicine, 10(6), 318-325.
Kent, J.C., Prime, D.K., Garbin, C.P. (2012). Principles
for maintaining or increasing breast milk production. JOGNN, 41: 114-121.
Knight R (2016). How
our microbes make us who we are. TED talks. Retrieved from: https://youtu.be/i-icXZ2tMRM
Lutz, Mazur, & Litch (2015) Nutrition and Diet Therapy,
6th ed. FA Davis Publishing. ISBN-13: 978-0-8036-3718-4
Seagrave, J (2018). Newborn Stomach size myth:
its not 5-7 mL. retrieved from: https://fedisbest.org/2017/06/newborn-stomach-size-myth-not-5-7-ml/
