Pregnancy proves that calories in, calories out is a gross oversimplification

Prometo fazer uma versão em português deste artigo – aguardem!

A
remarkable paper, that’s how I would describe Caloric cost of normal
pregnancy
. Obstet Gynecol. 1972 Dec;40(6):786-94, by Emerson K
Jr, Saxena BN, Poindexter EL. As you can see, it is not a new one. As a matter
on fact, it is hard to find such well done research papers these days.

The study
sets out to measure what is the extra metabolic requirement of a normal
pregnancy. And they did it not the usual way (fail-prone questionnaires), they
did it in a metabolic ward setting. How the authors were able to find 11
pregnant women (before 20 weeks of pregnancy) willing to spend 1 every 4 weeks
locked in a hospital, with a constant diet, weight and fluid balance control,
nitrogen balance, and (after 3 days of dietary equilibrium) 2 consecutive days
of expired air collection for 2 hours, 3 times a day, is simply astonishing. But
they did it, and what they found out is really interesting, useful and, in some
ways, counterintuitive.

First,
let’s take a look a the table describing patient’s characteristics:

7 patients
were in positive caloric balance – they had normal weight before getting pregnant.
Four patients, on the other hand, were deemed overweight and were put in a low
calorie diet to prevent excess weight gain. As you can see in the table, they
had a measured caloric deficit around 200 Kcal/day. However, not only
these overweight women gained weight on a calorie-restricted diet, but they
gained more weight (10 Kg) than the lean mothers that had a positive
calorie balance around 200 Kcal (7.36 Kg). In other words, if you are
pregnant, you will gain close to 8 Kg, whether you overeat or undereat by 200
Kcal/day
. How is that for calories in, calories out?? Maybe hormones are
driving the process? You bet they are. By the way, the 4 heavier women were
eating a very restrictive diet in order to produce the aforementioned caloric
deficit – only 1440 kCal/day (ranging from 1200-1600). Yet, all these starved
mothers managed to gain weight, so did their offspring (not a single baby was
born underweight, and these babies were actually heavier). Again, how is that
for calories in, calories out?

Now, table
2 is pure gold (see below). Why? One could speculate that the 4 overweight
women overate while outside of the hospital, so that they would really be in
positive caloric balance. It may be true, but here enters the VO2 measure. It
is a measure of the metabolism, by way of measuring how much oxygen is being
consumed per Kg.
Remember, this was measured after 3 days in the
hospital, eating controlled food portions and resting – same (low) level of
physical activity for every woman. In table 2
you can see that the calorie restricted women had a mean VO2 of 3.2 ml/Kg/min,
versus 4.06 for the positive caloric balance ones. Those of you that specialize
in exercise physiology please correct me if I am wrong, but I understand from
these numbers that the starved moms’ basal metabolism was running 21% slower
than that of the well fed ones. If this is correct, this would mean that Nature finds a
way. Starve a pregnant woman and the calories will be partitioned towards
maintaining a healthy pregnancy, even if it means slowing down metabolism as a
whole.

Finally,
the authors have calculated the total extra caloric expenditure from conception
to delivery: it is 27,120 +/- 2175 Kcal. It seems a lot, but is it?

The mean
daily increase for all subjects amounts to 100 Kcal for the whole pregnancy.
The median value was 9 Kcal for the first trimester, 84 for the second, and 216
for the 3rd trimester. Interestingly, the authors observed sparing of fat
tissue even when the caloric balance was negative. The fact that pregnant women
tend to be insulin resistant makes this observation even more interesting.

Now, let’s
think about this for a moment. 100 Kcal is really nothing. It is one cereal
bar. It is a single banana. So, if you really believe the calories in, calories
out paradigm, this is what you would get: just eat one extra banana a day, and
you will be 10 Kg fatter 9 moths later. But if you undereat by 2 bananas a day,
you will still be 10 Kg fatter later. How? May be photosynthesis, who knows?

There is
more to the paper (nitrogen balance, and esoteric concepts like “non-protein
respiratory quotient”), and I recommend those interested to
take a look at the original. But table 1 of this paper is
enough to bring down the whole edifice of calories in, calories out. In fact,
pregnancy itself already  proves that
point: one (usually) will be in a positive caloric balance for the pregnancy to
advance, but the positive balance is a consequence, not a cause
(conception and hormones, of course, are causal). Or else, one could just eat
an extra banana a day, and get a baby after nine months!