top of page

Does Breast Milk Lose its Nutritional Value Over Time? The Evidence on Breastfeeding Beyond Age One.

The benefits of extended breastfeeding

We all know breastfeeding is good for both, baby and mom. There are many studies out there investigating all the nutritional components of breast milk - macronutrients (protein, fats, lactose), micronutrients (vitamins and minerals) and bioactive factors (immune factors, hormones etc.) and showing there is not a formula in the world that can replicate all the magical components that are in breast milk.

But there's something else about breast milk that formula can't replicate: It changes composition over time! Not only does the composition of breast milk change throughout the day to adjust for your baby's needs (for example, there is more melatonin in night time breast milk to help baby sleep), but it also changes as your baby gets older.

Yes, it's true. Breast milk's nutritional components change over time. But does it get 'less nutritious' or even 'lose its nutritional value' over time, as some claim? Is there still a benefit to breastfeeding a toddler or even a 4 or 5 year old?

Thankfully, more studies have come out over the past few years to look into the possible benefits (and downfalls) of long term breastfeeding so we actually have some scientific evidence to go by.

Let's look at some of those studies:

Study 1: Breast Milk Macronutrient Components in Prolonged Lactation

This study from 2018 published in the reputable journal "Nutrients" looked into the macronutrient composition (proteins, fats and carbohydrates) and calories in breast milk from month one all the way to month 48 (4 years postpartum). What they found can be summarized as follows:

  • The fat and protein content of breast milk is significantly higher after 18 months of breastfeeding, whereas the carbohydrate (lactose) content is lower.

  • This change to the macronutrient composition then stays relatively constant between 2 and 4 years of breastfeeding.

  • The amount of calories in breast milk, or the calorie density, increases over time and is highest in breast milk from mothers who are 2 years or more postpartum.

The authors of this study conclude that breast milk changes over time to adapt to the child's higher energy needs. They also speculate that longer breastfeeding may very well change a child's metabolic programming lifelong.

My take on this study:

This study shows us there is a definite and significant change in the composition of breast milk after about 2 years of breastfeeding. There is more protein and fat and less carbohydrate (lactose) in breast milk after 2 years. There are also more calories per ounce in breast milk after 2 years. This means a toddler can get the same amount of calories from drinking less breast milk. So, even if you think your child must not be getting much from the little breast milk they drink at that age, remember there are more calories, more protein and more fat per ounce in your milk now. There will also be more fat soluble vitamins (Vitamin E, D, K and A) in your breast milk that come with a higher fat content. On top of that, the gradual change towards more protein and fat and less carbohydrates in your breast milk could very well program their bodies towards a stronger metabolism that is less prone to obesity, diabetes and other metabolic diseases later in life.

On a personal note, my breasts didn't even change anymore 2 years postpartum. You wouldn't be able to tell I still produced milk. It was nothing like breastfeeding in the first few months postpartum where you go from an inflated to a deflated balloon within minutes of nursing your baby. You just couldn't tell a difference between a full and an empty breast. But even though my breasts didn't change size anymore, my breastfeeder received valuable nutrition through my breast milk, in a more concentrated form.

Study 2: Lactoferrin in Human Milk of Prolonged Lactation

This study from 2019 was also published in the journal "Nutrients". It looked into whether one of the important immune factors in breast milk, lactoferrin, was still present in breast milk of mothers after 1 year. Lactoferrin is an important component of the immune system and can protect a baby from bacterial infection, viral infections, yeast overgrowth and more. It has even shown anticancer properties. It's one of the reasons breast milk is so special and beneficial.

This study shows that

  • The amount of lactoferrin in breast milk significantly increases 12 months postpartum.

  • Even after 24 months postpartum, lactoferrin was still significantly higher (4.9 grams per liter) compared to the amount in breast milk from mothers who were 12 months or less postpartum (3.39 grams per liter).

  • The amount of lactoferrin was tied to how much protein was in breast milk, which explains why its concentration is higher after 12 months (see Study 1).

  • The lactoferrin concentration in breast milk after 12 months of breastfeeding is close to that in colostrum, which is known for being a superfood for immunity!

The authors of this study conclude that breast milk from prolonged breastfeeding has 'high immunological potential" and that this evidence should make us question whether we should wean as early as we usually do.

My take on this study:

This study is clear evidence that breast milk does NOT lose it's beneficial properties after year 1. On the contrary, it has MORE of some bioactive factors which can protect your (now) toddler or young child from all of those yucky germs and viruses they are exposed to at daycare or at the playground. Biologically, this makes a lot of sense because we all know that a toddler can get into all kinds of dirty mess, and continuing to breastfeed can help them stay protected and train their immune system.

Study 3: Prolonged breastfeeding protects from obesity by hypothalamic action of hepatic FGF21

This study from 2022 is going to be an interesting one. Many studies show how breastfeeding protects babies against obesity later in life, but is there a benefit to breastfeeding for longer? Is there a minimum amount of time a child should be breastfed to protect them against obesity and all the diseases that come with it?

I have to point out, this study was done on rats so we are still missing some real life human studies on this topic. However, a big benefit of studying on a rat model is that you can control, down to the gram, how much and what a rat is fed and when they are weaned. You just can't ethically do this to a human. Rats are also generally considered a pretty good comparison to humans in terms of their metabolism, so let's look at the results of this study.

This study shows that

  • Rats who are weaned later have a lower body weight than rats who are weaned earlier, even on the same high fat/high calorie diet.

  • Rats who are weaned later have a higher energy expenditure compared to rats who are weaned earlier and they also have an easier time maintaining a constant body temperature when exposed to cold temperatures.

  • Rats who are weaned later have a better blood lipid profile (lower cholesterol, lower triglycerides etc.) and better glucose tolerance compared to rats who are weaned earlier.

  • The mechanism for all of this is thought to be through "enhanced brown adipose tissue thermogenesis and energy expenditure", a fancy way of saying their body is more efficient at turning excess calories into energy and body heat.

The authors conclude that the findings from this study in rats could mean that prolonged breastfeeding protects against obesity later in life by making the body more efficient at turning excess calories into energy and heat instead of storing them as harmful fat.

My take on this study:

Some of us are more prone to gaining weight than others. Why is that? Well, our metabolism works differently. Some of us turn excess calories into energy and heat more easily, and some of us turn it into inactive fat deposits instead, which are harmful to the body, lead to inflammation and cause metabolic disease. It's unfair, I know. But contrary to what we've believed, it's not necessarily even mainly a genetic issue. It may be something that is programmed during pregnancy and lactation.

This study shows there may be a pathway through which breastfeeding and extended breastfeeding in particular can protect your baby against obesity and its associated metabolic diseases later in life. Even though this is a study on animals, it is a highly controlled and thorough study. It also lays out and studies the pathway through which prolonged breastfeeding may protect against obesity, namely through activation of certain endocrine growth factors in the liver which then reach the central nervous system where neurons are activated which can change dopamine signaling which in turn change thermogenesis and the food reward system and so on and so forth. It's a complicated pathway, but if you are science-inclined, I absolutely recommend reading this study. Hopefully, we will have more research come out on this topic soon because I thoroughly believe the obesity epidemic in the western world is partially due to our insufficient breastfeeding practices, early weaning or no breastfeeding at all.

Does breast milk lose its nutritional value over time?


In summary, not a lot of research is out yet on the benefits of long term breastfeeding but the studies we have are very interesting and show that extended breastfeeding has its own set of benefits! One study shows the macronutrient composition of breast milk adjusts to the needs of an older child, with breast milk having more protein, fat and calories but less carbohydrates per ounce after 18 months of lactation. Another study shows that immune factors such as lactoferrin actually increase after a year of lactation, which is just about the time most babies start to walk and explore their surroundings and are exposed to more germs and viruses. Lastly, a very thorough study on rats shows that longer breastfeeding may protect your child better against obesity later in life by programming the body to be more efficient at turning excess calories into energy and body heat.

I didn't cover some other studies for the sake of keeping this article brief and manageable. For example, one study shows a reduced risk of ovarian cancer in women who breastfed for longer, another suggests extended breastfeeding may help to naturally space out children. On the other hand, one study showed extended breastfeeding may have a negative effect on weight and nutrient stores in women who are food insecure, so it's important to highlight there may be some downfalls to extended breastfeeding as well. Maybe this is a topic for a later blog post.

I breastfed my own two children for a little over 3 years each, my son actually closer to 4. It's sad to say, most people in the country where I live (United States) would consider this weird and inappropriate when prior to the 'industrialization' of our nations, this was the norm. There wasn't much research on the topic of extended breastfeeding back when I breastfed my children, but my intuition told me that "extended" (aka full term) breastfeeding was natural and the way to go for me and my kids.

Nonetheless, it's important to mention that extended breastfeeding may not be possible or desired by everyone, and that's ok, too. Any breast milk is better than none, and we all do what we believe is best for us and our children.

Much love to you & your loved ones. Take care & spread the word by sharing this article!


bottom of page