This is an issue I've been blindly trying to find an answer for recently, finding all sorts of opposing views from all different people on forums, with no authoritative answer on the subject, so I set about trying to solve it myself. Here is the result:
The problem:
Baby formula guidelines are given by various medical authorities. The NHS recommends 150-200ml per kg of bodyweight per day, the AAP (American Association of Pediatrics) recommends a maximum of 32oz per day. Various other sources claim that a baby should be having around 2.5oz, per lb of bodyweight, per day.
The issue arises in how the volume of a bottle feed is calculated. Instructions for powdered formula usually equate 1 oz to 1 scoop of powder, meaning that if you want a 5oz feed, you pour 5 oz of water into a bottle, and add 5 scoops. Once you’ve shaken the bottle, most parents will find that this 5oz feed now measures around 6oz in volume, according to the markings on the bottle. If your baby finishes this feed, do you count it as a 5oz feed or a 6oz feed? This may seem arbitrary, but in fact, if your baby is having 5oz, 6 times per day, that extra oz will equate to more than an entire additional feed.
There is a lot of contention online between parents as to how the volume of a bottle should be calculated. Some claim to only count the water volume before the powder is added, and ignore the extra volume introduced by the powder. Others claim that you should be more concerned by the resulting volume of actual infant milk rather than ignoring the powder.
We are told that bottle-fed babies are prone to overfeeding, leading to potential health problems such as reflux and childhood obesity, so not being able to account for 15-20% of your child’s daily milk intake is a significant issue for a lot of parents.
The solution:
If you want a quick solution, all you need to know is that it doesn’t make a huge difference. Personally, I have decided to count the water volume before the powder is added. This is absolutely contrary to my original stance, and if you want to know why I’ve made this decision, please read on…
The first step I took to try and understand how I should be measuring infant formula was to speak directly to the manufacturers. I contacted the three largest formula brands in the UK (SMA, Aptamil and Cow & Gate), to find out what their recommendations were, in regards to how I should be calculating feeds.
SMA recommended that I measure their formula based on the final volume of powder + water.
Cow & Gate recommended that I measure their formula based on the initial water volume, disregarding any powder.
Aptamil recommended the same as Cow & Gate, so I mentioned to them that SMA had said otherwise and asked why that was. They said they needed to consult their nutritionist and get back to me. A few days later, they replied saying that they’ve changed their stance and, in fact, I should calculate based on the final volume of water + powder.
I then contacted Cow & Gate again, told them about what SMA and Aptamil had said and asked their reasoning. They didn’t reply.
When looking at Cow & Gate products, I discovered something interesting in their nutritional information. On the Cow & Gate formula powder container, the nutritional info states that per 100ml of pre-prepared feed (read: water + powder), it contains 66 kcal. On a bottle of Cow & Gate pre-mixed, ready to drink formula, the nutritional info states exactly the same thing. This means there is no difference in nutrition between the two in their final forms, which directly illustrates that Cow & Gate’s recommendation to only count the water volume in a powdered formula feed is completely wrong.
This would mean that a 5oz feed of powdered formula would contain approx 97 kcal, and a 5oz feed of powdered formula, assuming the final volume appeared to be 6oz would contain 115 kcal. Over 6 feeds per day, this would equate to a difference of 108 kcal per day.
I decided to test this. With the help of my lovely OH, we set about measuring 1oz of water, adding 1 scoop of formula and measuring the resulting volume, very precisely, using a medicine syringe. The result was a 5.28% increase in volume after adding a scoop of formula. This was WAY less than the 20% increase we were expecting. The difference? Bubbles. Lots and lots of bubbles, which we had inadvertently settled during the process of syringing the milk.
The result is that your 5oz feed that looks like 6oz is actually around 5.25oz, meaning that over the course of 6 feeds, your baby is only having 1.5oz (approx 44ml) more than you measured, if you measured by water volume before adding powder. In fact, it also showed us that there really is no easy and accurate way to measure the volume of a feed after mixing formula, unless you want to painstakingly remove all the bubbles before doing so.
Since the amount is so negligible, we have decided to measure by water volume from now on, simply because it makes our lives easier.
We hope this settles the debate once and for all!