Breastfeeding can lead to weight gain for some women, largely due to hormonal shifts and increased appetite.
The common expectation is that breastfeeding helps melt away pregnancy weight. Many new parents hear this long before their baby arrives, so when the scale instead creeps up or stays stubbornly still, it can feel confusing and isolating. It’s easy to assume something is wrong, or that your body isn’t responding the way it should to the demands of nursing.
The truth is more nuanced. While breastfeeding burns significant calories and helps some women return to their pre-pregnancy weight, research shows it can also be associated with weight gain in others. Factors like hormonal shifts, sleep deprivation, and changes in appetite all play a role. This article walks through what the science actually says and why your experience might not fit the common narrative.
What The Research On Breastfeeding And Weight Actually Shows
You might expect a clear answer—breastfeeding either leads to weight loss or weight gain—but the data is surprisingly mixed. One notable study published in the American Journal of Clinical Nutrition found that women who breastfed gained about one kilogram (roughly 2.2 pounds) more over time than women who never breastfed, even after adjusting for activity and pre-pregnancy BMI.
That finding may sound discouraging, but it’s not the whole picture. Another trial tracking women over 24 months postpartum concluded that the relationship between breastfeeding and weight loss remains unclear. For many women, breastfeeding did seem to help shed pregnancy weight. For others, it didn’t make a measurable difference, and some actively gained.
The bottom line from these studies: there isn’t one universal metabolic response. Your genetics, your baby’s nursing patterns, and your overall health all contribute to how your body handles postpartum weight changes.
Why The Old Expectation Of Effortless Weight Loss Sticks
The idea that breastfeeding guarantees weight loss is deeply embedded in postpartum culture. It comes from a real place—breastfeeding does burn around 300-500 calories a day—but it ignores the complex biological and lifestyle changes happening simultaneously. These are the factors that often get overlooked.
- Hormonal shifts and prolactin: Prolactin is essential for milk production, but may indirectly contribute to appetite increase and water retention, potentially offsetting the calorie burn.
- Sleep deprivation: Broken sleep raises cortisol, a stress hormone that can encourage the body to hold onto visceral fat, particularly around the midsection.
- Increased appetite: The body needs extra fuel for milk production, and that hunger can sometimes outpace actual calorie needs, leading to unintentional overeating.
- Reduced physical activity: Recovery from birth, coupled with the demands of round-the-clock feeding, often means less movement and exercise than before pregnancy.
- Thyroid changes: Postpartum thyroiditis is common and can affect metabolism, making weight management harder regardless of breastfeeding status.
When these factors stack together, it becomes easier to see why the scale doesn’t always cooperate. The calorie burn of breastfeeding doesn’t happen in a vacuum—it’s just one piece of a much larger hormonal and lifestyle puzzle.
Unpacking The 1-Kilogram Study Finding
The study showing a small average weight difference raises an important question: why would breastfeeding be linked to slightly more weight? The answer likely involves prolactin, the primary hormone driving milk production. Prolactin levels surge with every nursing session, and higher prolactin has been associated with increased appetite centers in the brain, along with changes in how the body stores fat.
University of Utah Health clinicians note that many women find it difficult to lose weight after giving birth—see their postpartum weight insights for more on this common struggle. This expert perspective confirms what many new parents suspect: the body holds on to weight despite the extra energy being spent on milk production.
The 1 kg finding is an average. It doesn’t mean you will gain weight; it means the metabolic math is more complicated than “calories out exceed calories in.” Some women lose significant weight while breastfeeding because their bodies respond differently to prolactin or because their appetite stays in check. The variation is enormous.
| Factor | How It May Affect Weight | Why It Matters |
|---|---|---|
| Prolactin Levels | May encourage fat storage / appetite | High prolactin can shift metabolism toward conservation |
| Sleep Quality | Can cause weight gain | Elevated cortisol promotes visceral fat retention |
| Calorie Intake | Variable | Increased hunger can lead to eating above energy needs |
| Physical Activity | Usually supports weight loss | Lower activity levels postpartum slow energy expenditure |
| Genetics | Variable | Some women are genetically predisposed to hold weight while nursing |
| Infant Feeding Frequency | Mixed | More nursing equals more prolactin, but also more calories burned |
Understanding these variables helps explain why two women with similar feeding routines can have completely different weight outcomes in the first year postpartum.
Steps To Navigate Postpartum Weight Changes
If you’re gaining or not losing weight while breastfeeding, a few targeted steps can help you understand what’s happening and support your body without resorting to harsh restrictions that could affect milk supply.
- Prioritize protein and fiber over calorie cutting. Breastfeeding requires adequate energy. Focus on protein-rich foods and vegetables to stay full without drastic calorie drops that can tank milk supply.
- Focus on sleep hygiene where possible. Since sleep deprivation raises cortisol, aiming for longer stretches (even if it means a partner gives a bottle of pumped milk) can help regulate appetite and stress hormones.
- Move your body gently and regularly. Walking, postpartum yoga, or light strength training can support mood and metabolism without the stress of high-intensity workouts.
- Monitor your thyroid. Ask your provider to check TSH, T3, and T4 if you have other symptoms like hair loss, fatigue, or feeling cold, as postpartum thyroiditis is common.
- Track your intake without judgment. Keeping a brief log for a few days might reveal that portion sizes crept up or that stress eating is a factor, giving you a starting point for change.
These aren’t guaranteed fixes, but they address the most common underlying issues. If weight gain continues despite these efforts, a registered dietitian or your OB can help look deeper at hormones or other medical factors.
The ‘Postpartum Myth’ Perspective
Healthline directly addresses this topic by calling the expectation that breastfeeding will lead to weight loss a breastfeeding weight loss myth. For some women, this myth creates pressure and disappointment when their body doesn’t conform to the expected timeline.
The article points out that while breastfeeding burns calories, it also stimulates hormone release that can increase appetite and encourage fat retention. This doesn’t mean breastfeeding is bad for weight—it just means that losing weight is not guaranteed, and for a subset of women, the hormonal effect may outweigh the calorie burn.
This framing can be freeing. It validates the experience of women who didn’t lose weight or who gained while nursing. Releasing the expectation that breastfeeding must transform your body can reduce stress, which in itself may help with weight regulation over the long term.
| Goal | Typical Calorie Range | Notes |
|---|---|---|
| Maintain weight while exclusively breastfeeding | 2,000–2,500 kcal/day | Varies heavily by height, activity, and baseline weight |
| Gentle weight loss while breastfeeding | 1,800–2,000 kcal/day | Should not dip below 1,800 without professional guidance |
| Gain weight intentionally if underweight | 2,500+ kcal/day | Prioritize nutrient-dense whole foods and healthy fats |
The Bottom Line
Breastfeeding’s effect on weight is highly individual. While many women experience gradual weight loss, research shows that some women gain weight due to hormonal shifts, sleep deprivation, and increased appetite. The 1 kg average weight difference found in studies highlights that weight retention is possible, but not guaranteed.
Your obstetrician or primary care provider can help assess whether hormonal imbalances, like a thyroid issue or high prolactin, are contributing to unexpected weight gain in your specific situation.
References & Sources
- University of Utah Health. “Why Am I Gaining Weight After Giving Birth” Clinicians at University of Utah Health note that many women find it difficult to lose weight after birth, even with breastfeeding, and some continue to gain weight.
- Healthline. “Breastfeeding Made Me Gain Weight” A dietitian notes that the idea that breastfeeding causes weight loss is a “postpartum myth” and that some women experience weight gain instead.