If you’ve been told to supplement or fortify your breast milk because your baby isn’t gaining weight, it can feel like someone just handed you a quiet accusation: your milk isn’t good enough.

So let me say this clearly: you do not have “skim milk.” Your breast milk is not low quality, low calorie, or weak. And most of the time, when a baby isn’t gaining well, it’s not a milk quality problem.

It’s a milk volume problem — meaning your baby isn’t getting enough total intake. In this post, we’ll break down supplementation vs. fortification, when fortification truly matters, and how to ask better questions before you assume something is wrong with your body.

Supplementation vs. Fortification: They Are Not the Same Thing

If you’ve been told to “supplement” or “fortify,” it can sound like the same advice — but these are two very different interventions.

And understanding the difference matters, because it changes what problem you’re actually trying to solve.

What supplementation means

Supplementation simply means giving your baby more milk.

That milk might come from:

• Your expressed breast milk
• Donor milk
• Infant formula

The goal is straightforward: increase total intake volume.

What fortification means

Fortification means adding something to milk to make it more calorie-dense.

Breast milk and standard infant formula both average around 20 calories per ounce.

Fortification is when we intentionally increase the calories by adding a measured amount of formula powder or a medical fortifier to breast milk.

The goal of fortification is not to increase volume.

The goal is to increase calories per ounce — so the baby can get more calories even if they can’t take in a large volume.

You Don’t Have “Skim Milk” 

If you’ve ever been told your breast milk is “low calorie,” “watery,” or “not fatty enough,” it can feel like your body is failing at the one job it’s supposed to do.

But here’s what I want you to hear:

Your milk is not low quality.

Human milk is designed to be dynamic. It changes throughout the day, throughout a feeding, and throughout the course of lactation.

But that natural variation is not the same thing as having “bad milk.”

Research shows that while breast milk calorie density can vary, most mature human milk still falls into a predictable range.

In other words:

Your milk is just fine for your baby.

What changes most from feed to feed is the fat content — and that is normal physiology, not a sign that something is wrong with your milk.

Real life matters more than one sample

One of the biggest problems with the “low-calorie milk” narrative is that it’s often based on incomplete information.

Because milk fat can shift depending on:

• time of day
• how full your breasts/chest is
• whether milk was collected at the beginning or end of a feeding
• how the milk was stored or measured
• whether the sample reflects your typical feeding pattern

So if someone tells you your milk is “low calorie,” the first questions should be:

• Compared to what?
• Based on what measurement?
• And does this match my baby’s real-world growth pattern over time?

Because one number from one moment in time is not the whole feeding story.

Weight Gain Is Calories In vs. Calories Out

This is the part that matters most — because it cuts through so much noise.

When a baby isn’t gaining weight well, parents often get stuck in the same fear spiral:

Is my milk bad?
Is my milk low-calorie?
Did my body fail my baby?

But weight gain is not about “good milk” or “bad milk.”

Weight gain is about whether your baby is taking in enough calories to meet their needs.

And yes — that’s as unromantic as it sounds.

Because this is just math.

There are really only 3 reasons babies don’t gain weight

• They aren’t getting enough volume of milk.
• They are getting enough volume, but the calorie density is lower than expected.
• They are getting enough volume and calories, but their metabolism or processing is not behaving as expected.

And here’s the clinical truth:

It is almost always #1.

Which means that most of the time, the problem isn’t your milk.

The problem is that your baby isn’t getting enough of it — whether because of feeding efficiency, latch issues, fatigue, milk transfer problems, or a feeding plan that isn’t matching your baby’s needs.

That’s why jumping straight to “just fortify” or “just add formula” without understanding intake can miss the real issue.

Because before we assume milk quality is the problem, we should always ask the most basic question first:

How much milk is actually getting into the baby?

If you have a baby who is slow to gain, the best way to figure out how much is getting into your baby is with a weighted feed. Here is a blog that gives you more information about what that is and how to do it. 

So why do professionals jump to “your milk is low-calorie”?

Sometimes it’s because it’s easier. Sometimes it’s because providers aren’t trained in breastfeeding mechanics.

Sometimes it’s because it feels like a simple fix.

And sometimes… it’s because blaming milk is culturally familiar.

Is it an intentional attempt to blame women?

Usually, no. But is it harmful?

Yes.

Because it places the problem inside your body before anyone has actually measured intake.

When Fortification Actually Makes Sense

Fortification is not wrong. It’s not harmful. And it can be absolutely lifesaving in the right context.

But it’s a tool — not a default assumption.

Fortification is most helpful when volume is limited

Fortification is most appropriate when a baby cannot take enough volume to meet their caloric and nutritional needs, such as when:

• The baby is premature
• The baby is medically fragile
• The baby fatigues quickly and cannot finish feeds
• The baby has cardiac, respiratory, or neurological issues affecting feeding stamina
• The baby cannot safely take large volumes

In these situations, fortification helps because it increases calories and nutrients without requiring the baby to drink more milk.

For Healthy Babies, Volume Is Usually the First Step

If your baby is otherwise healthy and term, and weight gain is slow, the first question should usually be:

Is my baby getting enough total milk volume in 24 hours?

Because if your baby is getting 18 ounces per day when they need closer to 25 ounces, the problem is not “low calorie milk.”

The problem is simply that they need more milk.

And there is also a standard way to figure out how much milk your baby needs.  Here is a blog that helps you understand how much milk your baby needs. 

You can increase calories by increasing volume

This is the part many parents aren’t told:

If you increase volume, you increase calories.

If your provider is recommending fortification “to increase calories,” you can ask:

Can we try increasing total intake volume first?

Because in many cases, adding an extra ounce of breast milk is the same caloric impact as fortifying a smaller bottle.

What to Ask Your Provider Before You Fortify or Supplement

If you’ve been told to fortify, supplement, or add formula, you deserve a clear explanation.

You are allowed to ask questions.

You are allowed to understand the plan.

These are some questions you can ask:

• How much milk do you think my baby is taking in per day?
• How did you estimate that?
• Are you concerned that my baby can't take in enough volume to meet their needs? Why do you think that is true?
• Is your primary concern calories or nutrients?
• What is the goal of fortification in this situation?
• What is the endpoint for fortification?
• Can we try increasing volume first before increasing calories per ounce?

If a provider cannot answer these questions, they cannot confidently claim this is a milk quality problem.

The Takeaway: Your Milk Is Not the Problem

If you’ve been told to fortify your breast milk or give supplementation, and you immediately felt panicked or ashamed, of course you did.

It’s so easy to feel that way.

And:

Fortification is a tool — not a judgment.

Supplementation is support — not failure.

But most importantly:

You do not have skim milk.

Your milk is not low quality.

Your baby’s weight gain is not proof that your body is broken.

Most of the time, when babies struggle to gain weight, the first problem is simply that they are not getting enough volume of milk.

And the solution is often not to change your milk — but to change how much of it your baby is able to get.

The problem isn’t you.

You just need better information — and a plan that actually matches what your baby needs.