Breastfeeding, Weight Loss & Weight Gain

I share this post because I get asked about breastfeeding and weight loss all the time, not because I believe any lactating mother should be dieting or trying to lose weight.

I personally did not weigh myself for at least a year postpartum, because I did not have the time, energy, or desire to track my weight. My weight fluctuated throughout my breastfeeding journey, as did my energy levels - and my stress levels.

The relationship between breastfeeding and weight is a complex one. It is a commonly held belief that breastfeeding helps mothers lose weight. Whilst that is true for some, it simply isn’t the case for all. Here’s why.

Your body needs more, not less

Lactation demands significantly more calories than your body requires at baseline - between 300 and 700 extra calories per day, depending on your metabolism and activity levels.

Paradoxically, if you do not eat enough, your body may actually hold onto excess weight, because your nervous system perceives a state of survival and conserves your energy stores. This underscores the importance of eating a nourishing, nutritious diet whilst breastfeeding - I know that can feel impossible at times, but eating enough is not optional when you are feeding another human being.

The hormone cascade

Breastfeeding suppresses oestrogen and progesterone. This hormonal shift can either dramatically increase or suppress your appetite - particularly if you are also under stress. The result can be weight loss or weight gain, depending entirely on your unique body and circumstances.

If you are breastfeeding on demand, you are also likely being woken frequently overnight. Sleep deprivation causes your body to produce higher levels of cortisol, the primary stress hormone. In a prolonged state of elevated cortisol, your body may hold onto excess weight or struggle to maintain a healthy weight. Sleep deprivation also causes ghrelin - the hunger hormone - to rise, meaning you feel hungrier, often for calorie-dense foods.

On top of this, every single time you breastfeed, your blood sugar levels drop. This can drive hunger pangs, cravings, and energy crashes throughout the day.

This is why weight management whilst breastfeeding is not as straightforward as counting calories and moving more. Lactation has a profound impact on the hormones that regulate appetite, hunger, fat storage, and satiety.

Leptin resistance: the hormone nobody talks about

Leptin is your satiety hormone. It is produced by fat cells and travels to the brain to signal that you have eaten enough and that your energy stores are adequate. When leptin is functioning well, it helps regulate both appetite and body weight.

But here is the problem: chronic sleep deprivation and sustained stress - the lived reality of early motherhood - can cause leptin resistance. This means your brain stops receiving the “I’m full” signal clearly, even when your body has had enough to eat. You may find yourself eating past the point of fullness, or feeling hungry again very shortly after a meal, despite having eaten well.

Leptin resistance is not a character flaw or a lack of willpower. It is a physiological response to the conditions of new motherhood. Eating regular, nourishing meals - particularly those rich in protein and healthy fats - can support leptin sensitivity over time, as can prioritising rest and reducing your cortisol load wherever possible.

POPs: what rapid weight loss whilst breastfeeding can release

There is another dimension to this conversation that is less widely known, but important.

Weight loss whilst breastfeeding - whether intentional or not - is relatively common. But rapid weight loss carries a specific consideration for nursing mothers: the release of Persistent Organic Pollutants, known as POPs.

POPs are environmental pollutants - including certain pesticides, industrial chemicals, and flame retardants - that accumulate in body fat over time through the food chain. They are widespread in our environment and found at low levels in almost everyone. During periods of rapid fat loss, POPs stored in your adipose tissue can be released into your bloodstream and, because breast milk is rich in fat, potentially into your breast milk at higher concentrations.

Research suggests that losing more than 1–2 pounds (approximately 0.5–1kg) per week whilst breastfeeding may release more POPs than your body can process and eliminate safely. This is one of the key reasons why crash dieting, extreme calorie restriction, and rapid weight loss approaches are not recommended whilst nursing.

It is worth noting that POPs are also found at low levels in infant formula, because they are present in animal milk and are an environmental reality. This information alone is not a reason to avoid breastfeeding - the benefits of breastfeeding are well established and the levels found in breast milk, even during gradual weight loss, are generally considered low. But it is an important reason to avoid drastic dietary approaches whilst nursing.

What actually supports your body whilst breastfeeding

Eat enough and eat regularly.

Focus on nutritionally dense whole foods - fruit, vegetables, protein, healthy fats, nuts, seeds and complex carbohydrates. Setting a phone timer to remind yourself to eat and drink throughout the day can help, as can eating every time your baby nurses or you pump.

Prioritise rest.

Sleep deprivation elevates cortisol, raises ghrelin, and blunts leptin sensitivity - three mechanisms that all work against your body’s ability to regulate weight. I know sleep feels impossible in the early months, but going to bed at the same time as your baby - genuinely - is one of the most impactful things you can do for your overall wellbeing.

Regulate your nervous system.

Your body needs to feel safe in order to release stored weight. Breathwork, walking outdoors, and meditation are all accessible, evidence-supported ways to bring your cortisol levels down. A particularly effective technique is box breathing - inhale for four counts, hold for four, exhale for four, hold for four - which can be practised anywhere, even whilst nursing. Regular nervous system regulation can also support leptin sensitivity over time.

If weight loss is a goal, aim for gradual change.

Research supports 1–2 pounds per week as the safest rate of weight loss whilst breastfeeding - sufficient to see progress, but slow enough to protect your milk supply and minimise the release of POPs from fat tissue.

Move your body gently and with love.

Gentle movement - walking, swimming, postnatal yoga - supports blood sugar regulation and nervous system health without placing excessive demands on a body that is already working hard.

A final note

I know that many of us feel disconnected from our bodies postpartum, because of the profound changes that pregnancy, birth, and breastfeeding bring. Whatever your size, and however you feel about your body right now, you are doing something extraordinary. Your body grew a life, brought that life into the world, and is now sustaining it. Weight is the least interesting thing about you in this season (or any, for that matter!).

My mantra has always been: empowered and supported is best. I hope this post helps you feel both.

For evidence-based, heart-led support in all things nursing, pumping, and beyond, my Penguin debut The Breastfeeding Survival Guide is available now.

With love,

Danielle

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