Intermittent Fasting While Breastfeeding

Losing the extra weight from pregnancy is something a lot of new mums think about once the initial newborn haze starts to settle. It’s completely normal to want your body back, or at least something close to it. Weight gained during pregnancy varies enormously from one woman to the next, and for some it can be more than expected. Because of this, intermittent fasting has become a popular option for mums looking to shift the extra pounds without a complicated diet plan. But if you’re breastfeeding, it’s worth understanding what fasting actually does to your body before you try it, because your baby’s nutrition is tied directly to yours right now.

What Intermittent Fasting Actually Is

Intermittent fasting isn’t a specific diet in the way something like keto or Weight Watchers is. It’s an eating pattern built around when you eat rather than what you eat. Instead of three meals plus snacks spread across the day, you compress your eating into a shorter window and fast for the rest of the time.

The most common versions are:

• 16:8, where you eat within an 8 hour window and fast for the remaining 16 hours (often overnight and into the morning)
• 5:2, where you eat normally five days a week and significantly reduce calories on two non-consecutive days
• Alternate day fasting, where you cycle between normal eating days and very low calorie or no calorie days

During the fasting window, plain water, black coffee and unsweetened tea are usually fine. Anything with calories, including milk in your tea or a splash of juice, technically breaks the fast. The idea behind all versions is the same: by limiting your eating window, you naturally reduce total calorie intake and encourage your body to draw on fat stores for energy.

Is Intermittent Fasting Safe While Breastfeeding?

This is where things get more complicated than most fasting guides let on. Breastfeeding itself is metabolically demanding. Your body is using energy and nutrients to produce milk on top of everything else it needs to keep you going day to day.

There isn’t strong research showing that intermittent fasting causes immediate harm to breastfeeding mothers or their babies, but there also isn’t much research proving it’s safe either, especially for longer or more restrictive fasting protocols. Harvard Medical School has noted that intermittent fasting generally isn’t recommended for breastfeeding women unless it’s being done under medical supervision. The concern isn’t usually about a single skipped breakfast. It’s about what happens when calorie restriction is sustained day after day while your body is also trying to make milk.

If your calorie intake drops too low or too often, a few things can happen:

• Your milk supply may drop, particularly if you’re also not drinking enough fluids during your eating window
• You may feel dizzy, shaky, unusually tired or nauseous, especially in the first week or two while your body adjusts
• In more extreme cases, low milk volume can affect your baby’s hydration, feeding pattern and weight gain

None of this means fasting is automatically dangerous for every breastfeeding mum. It means it needs to be approached carefully, with realistic expectations, and ideally with your GP, midwife or health visitor aware of what you’re doing so they can flag anything concerning early.

How Many Extra Calories Do You Actually Need?

The CDC advises that breastfeeding mothers typically need somewhere around 330 to 400 extra calories a day compared with their pre-pregnancy needs, though this varies depending on how often and how exclusively you’re breastfeeding, your activity level and your own body size. If you’re exclusively breastfeeding a young baby, this isn’t a number to ignore.

If you do want to try a form of intermittent fasting, the general principle is to make sure you’re still hitting your total daily calorie and fluid needs within your eating window, rather than simply eating less overall. That’s a fairly narrow line to walk, and it’s easy to underestimate how much you’re actually eating once your window shrinks. Keeping a rough note of what you eat for the first week or so can help you see whether you’re genuinely meeting your needs or quietly under-eating.

When Might Fasting Be More Reasonable to Consider?

Most lactation professionals suggest waiting until breastfeeding is well established before making any significant changes to your eating pattern. That usually means at least the first few months, once your milk supply is settled and your baby has a predictable feeding routine.

It also tends to be a more reasonable option once your baby is partially weaned or eating solids and relies less heavily on breast milk for their full nutritional needs, generally from around six months onwards. Trying to fast in the early newborn weeks, when supply is still being established and your baby is feeding frequently, is generally not a good idea.

Your own health background matters too. Things like your BMI, whether you have a history of low milk supply, your age and any underlying health conditions can all change how appropriate fasting is for you. This is exactly the kind of decision worth running past your doctor or health visitor rather than working out on your own from an app or a forum post.

Signs You Should Stop

Pay attention to both how you feel and how your baby seems. In yourself, watch for persistent dizziness, headaches, extreme fatigue, irritability beyond normal new-parent tiredness, or a noticeable drop in milk supply when pumping or feeding. In your baby, keep an eye on wet and dirty nappies, general alertness, and weight gain at check-ups. Fewer wet nappies than usual, unsettled feeding, or your health visitor flagging slow weight gain are all reasons to stop fasting and go back to eating normally straight away.

Safer Ways to Approach Postpartum Weight Loss

If fasting feels like too much of a gamble while you’re breastfeeding, you’re not out of options. A steady, balanced approach tends to work just as well over time and carries far less risk to your milk supply.

Some practical, lower risk approaches:

• Eat regular, balanced meals built around protein, whole grains, vegetables and healthy fats rather than skipping meals
• Keep portions sensible rather than restrictive, and try not to eat out of stress or exhaustion, which is easy to fall into with a new baby
• Add in gentle movement once you’ve been cleared for exercise at your postnatal check, building up gradually from walking to more structured activity
• Prioritise sleep where you can, since poor sleep is linked to slower weight loss and stronger cravings

Breastfeeding itself also burns a meaningful amount of energy. Mayo Clinic notes that many women lose pregnancy weight gradually over the following months simply through a combination of breastfeeding and a normal, balanced diet, without needing to add any specific weight loss method on top. For most women, the extra weight gained in pregnancy comes off over roughly six to nine months, though this timeline is different for everyone and isn’t something to compare too closely with friends or what you see online.

If You Do Decide to Try It

Talk to your GP, midwife or health visitor first, particularly if your baby is under six months old or exclusively breastfed. If you get the go ahead, start gradually rather than jumping straight into a strict schedule. A shorter fasting window, like 12 hours overnight, is a much gentler starting point than 16:8 or 5:2.

Drink plenty of water throughout the day, not just during your eating window, and make sure the meals you do eat are genuinely nutrient dense rather than an afterthought. Iron, healthy fats and a good variety of vegetables matter more than usual right now. Try not to swing between under-eating during the fast and overeating once the window opens, since that pattern won’t help your energy levels or your milk supply.

If you notice your supply dropping, your mood dipping more than usual, or your baby seeming unsettled or feeding less well, stop and go back to normal eating. There’s no prize for pushing through it. Weight loss will still happen with patience, and your baby’s needs come first while breastfeeding is still their main source of nutrition.