pregnant woman eat for baby

Maternal magic - how your body secretly adapts during pregnancy (without even telling you)

Would you believe us if we told you that your energy and nutrient requirements don’t really change much during pregnancy? 

What about if we said that you and your little babe can get exactly what you need just from your regular diet? That your body is so perfectly designed that it changes the way you absorb, handle and get rid of nutrients, meaning you really don’t need to do anything differently (providing what you’re starting with is good!)

You’d be forgiven for not believing us, because there is so much to contradict that statement - growing numbers of prenatal supplements, recommendations to increase nutrients such as folate, vitamin D, protein, iron, the misnomer that you need to 'eat for two' and so on. 

Here is where we step in to translate the wonders of female physiology.

We make more blood during pregnancy, both the liquid part (plasma- ~50% increase) and the red blood cells (~20%). This increases the oxygen carrying capacity of our blood and the amount of blood that can be moved through our body. Like some sort of physiological magic, we are even protected from blood clots at this time due to the fact that our plasma volume increases by more than the red blood cell volume. This increased blood volume can make it look like our blood nutrient levels are low (because the same amount of nutrient is now diluted in a larger volume of blood) - but in fact most nutrients actually increase in concentration during pregnancy.

This happens because the hormone progesterone acts on our gastrointestinal tract and slows down the movement of our food through the small intestine (this is where we start to breakdown and absorb nutrients). Because the food sits in the small intestine for longer - and the villi, the thin finger-like projections in the small intestine get longer - there is a greater opportunity for nutrients to be absorbed. 

More nutrients from the same amount of food? We’ll take it. Every day of the week please.

Ok, let’s take stock here. 

We know we’ve got extra blood which can transport more oxygen and we’ve also got more nutrients in our blood. How does the body move all of this extra stuff around and where do we get the extra oxygen from? 

Well, pregnancy changes the way our heart and lungs work of course! Here’s how this magic happens.

The amount of blood we move around our body is determined by our cardiac output, which is the amount of blood our heart can push out each minute. During pregnancy, this increases by up to 1 litre / minute, which means for every minute of the day, we are moving an extra litre of blood around our body. You know that carton of milk you used for your coffee this morning? That’s likely to have been a litre. That’s how much extra blood you have coursing around that multitasking system of yours while you grow a small human. Amazing.

So how is this even possible? Well, in addition to relaxing the gastrointestinal tract to slow it down, progesterone also relaxes our blood vessels as both of these are smooth muscles. This means the blood vessels dilate (relax / open) more easily and can carry more blood. There is also the addition of the placenta which is described as a low resistance vascular bed, which basically means lots of blood can go there and just sit. This is excellent for our babies as it means the nutrients have plenty of opportunity to be taken from OUR blood and moved across the placenta to THEIR blood for growth. 

So what about the extra oxygen we mentioned earlier? Well, that comes from our lungs. As the blood passes through the lungs on its way around the body, it picks up more oxygen. Early in gestation this is pretty passive, but later in gestation, particularly as the fetus gets bigger and occupies a lot more of our abdominal cavity, this requires us to breathe more deeply than normal. And listen to this! Within our normal lung function there is a part of the organ that we don’t normally use - called the residual volume. A very sciencey term for what is really a reserve or unused part of the lung. During pregnancy, we access this reserve, breathing into parts of it that we don’t normally need.

Have you noticed you also change the way you breathe when pregnant?

This is the job of your clever little walnut shaped organ - the brain. Those pregnancy hormones reset the breathing centres of our brain and trigger us to breathe earlier than we normally would. To understand this properly, let's take a step back. For all of us, there is a threshold level of carbon dioxide in our blood that triggers us to breathe. When we are pregnant, this threshold is moved to lower levels of carbon dioxide, so we breathe earlier than we normally would. This is important because it allows us to breathe off excess carbon dioxide more readily (remember we are dealing with our baby’s excess carbon dioxide now too, not just our own), it allows us to carry more oxygen in our blood (which we and our baby need) and it allows the oxygen to be offloaded more easily at the placenta for our baby to access. 

If that wasn’t enough amazingness, you might be surprised to know that your kidneys change too! These guys are responsible for excreting our body's waste products. Because we are pumping a whole heap more blood, the kidney sees this (~80% more) and drives our glomerular filtration rate to increase. Glomeruli are the little units in our kidney that filter the blood, reabsorb solutes we aren’t ready to let go of yet, and excrete the ones we are done with.

Let’s finish on a myth that we might bust for you right here, right now. 

Eating for two. That’s true, isn’t it? Nope. Here’s why.

The last major change in our bodies during pregnancy, impacting on our nutrient requirements, is a change to our metabolism. Our babies love glucose for energy, so they can use protein and fat to build their body. Our metabolism shifts to rely predominantly on fat as our own energy source, so that more glucose is available for our baby. 

Progesterone and estrogen are responsible for triggering this metabolic shift, which is why we experience an increase in storage of body fat during the second trimester of pregnancy. As the fetus demands more and more glucose later in pregnancy, our plasma glucose levels fall, triggering lipolysis - the process of releasing lipids from storage for use. 

So what does this all mean for you?

First up, the old rules don’t apply anymore. The way nutrient requirements are determined for the general population are not applicable for pregnant or lactating mothers. Secondly, because of our BS ‘fragile’ and ‘vulnerable’ mentality around pregnant women, the research that would inform these things is scarcely done. And lastly, and perhaps most importantly, mother nature and our survival and evolution as a species are unlikely to favour an environment whereby it is near impossible for a pregnant woman to achieve her nutrient requirements from her regular diet. Nature just isn’t that dumb. 

Eat for You is not here to encourage you to eat more, but instead to eat well. Your body is resourceful and clever - it will get everything it can out of everything you eat, and use it to build your baby. We encourage you to start (or keep) thinking about the building blocks you put in. Make a baby using nature's bounty; vegetables, fruits, wholegrains, legumes, meat and fish. 

Don’t be fooled into thinking you need to eat for two. Or three. Or four. You don’t. 

Need inspiration? We’ve created a beautiful e-book filled with recipes for every stage of a pregnancy journey. And we have delicious, nutritious, safe bars and bites inspired by the nutritional and safety needs of pregnant women.


Back to blog

Leave a comment