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Trying to lose weight whilst breastfeeding

by Rachel Anne Hobbs R.D. Pg.Dip mHCPC

As I sat down for my final midwife appointment I saw a sign that said “Benefits of Breastfeeding”, I scanned through the list hesitantly waiting to see IT - “reduces risk of infection, decreases chance of ovarian cancer, osteoporosis and cardiovascular disease” AND there it was … “supports weight loss after birth”

breastfeeding weight loss

I am huge advocate for body autonomy, it is your body and therefore your choice, BUT trying to encourage women to breastfeed by implying that weight loss will happen if you do plays into the toxic narrative that diet culture creates of the thin ideology ie. “the smaller, the better”. How your body looks is the very last thing a woman should be concerned about as you adapt to life as a new mum with a fresh baby. “The more nurtured, the better” is what we should be advocating for new mothers. 

Regardless of the ethical implications of promoting weight loss as a benefit of breastfeeding, it is also not necessarily true if we look at both the evidence and very importantly, the experience of new mothers. If you are someone who has tried and struggled to lose weight whilst breastfeeding or perhaps you have  gained weight, you are certainly not alone and very importantly this is not a willpower issue. 


Weight loss fundamentals

The  fundamentals of weight loss lead us to look at the equation:

Weight loss = energy in (kcals) < energy out (kcals)

To break this down a little further, we measure energy in (kilo)calories, which on the back of packets you will see written as “kcals”. When energy into the body, which comes from food and drinks, is less than the energy out of the body,  otherwise referred to as energy expenditure, then the body has to break down it’s own fat and muscle to metabolise and create energy to perform essential bodily process’ and complete every tasks, including a lot of baby rocking in those early days! This breakdown and utilisation of fat and muscle stores leads to weight loss. 

Energy expenditure (energy out)  is broken down into different components, firstly there is the Basal Metabolic Rate or BMR, this is the amount of energy the body uses per day for essential processes such as breathing, digestion and keeping the heart beating; this remains pretty similar day to day but can adapt overtime depending on health, hormones and lifestyle factors. This accounts for approximately 60-80% of total daily energy expenditure (TDEE). 

Then there is the energy the body expends in order to break down the food you eat so it can be used, this accounts for around 10% of TDEE and is called diet induced thermogenesis. Next there is the energy expended through planned physical activity, such as running, going to the gym, dancing and so on. This is variable daily and often decreases for the last few months of pregnancy and first few months postpartum (or if you are like me, first few years!). Finally there is the amount of energy expended through the day to day activities, popping to the shops, taking a shower, doing the washing, we refer to this as NEAT (non exercise activity thermogenesis); and this varies depending on what you are doing each day. 

When we add breastfeeding into the mix, this is a form of energy expenditure, this study suggests that breastfeeding expends about 450-500kcals per day. 

Although the message energy in needs to be less than energy out” or in other words, you need to “eat less and move more” to create an energy deficit and lose weight seems pretty simple on the surface and is true, it doesn’t not explain the nuance, complexity and wonderfulness of the human body. 


Things that impact weight loss 

There are many factors that have an effect on the basal metabolic rate (BMR), which is often referred to as metabolism and thus body weight. If metabolism decreases as a result of any of these factors then it may mean that energy expenditure is equal to or more than energy in from food, preventing weight loss during the postpartum period. Online calculators are only able to offer an estimate of energy expenditure and do not take into account metabolic factors. 

Hormones are one factor that can influence metabolism and thus body weight; these include oestrogen, progesterone, testosterone and prolactin. 

After birth oestrogen and progesterone levels plummet and depending on the individual and the length of breastfeeding this effectively acts like a mini menopause within the body - hot flushes, low sex drive, vaginal dryness anyone? This is why women often won’t ovulate and have a period whilst they are exclusively breastfeeding. 

This study suggests that the decrease in oestrogen as a natural result of breastfeeding can lead to what we refer to in the world of eating behaviours as “hyperphagia” or an increase in eating, it also suggests that lower oestrogen makes you more fatigued and thus decreases energy expenditure through being less active. Less activity and more food prevents weight loss. They found that supplementing oestrogen in those in natural menopause lead to a reduction in food intake and increase in physical activity, which may be due to oestrogen’s impact on different hunger and fullness hormones such as leptin and peptide Y. This study also found that lower oestrogen alters where body fat is stored too, when oestrogen is lower it is natural to store more around the belly compared to when it is higher and stored around the hips and bottom. 

Breastfeeding causes low oestrogen, this often leads to an increase in hunger, decrease in activity and more fat storage around the belly. When breastfeeding reduces or stops and oestrogen levels return to normal, appetite, activity levels and body fat storage also return to normal. 

Next the hormone progesterone; it’s primary function is to support reproduction and pregnancy, but it also has roles in making you feel good and relaxed. After pregnancy and during breastfeeding progesterone levels drop; so if you are not feeling too relaxed, then the lower progesterone levels may very well be contributing. This study suggests that in general higher people with higher body weights are associated with lower progesterone levels; although it is not thought that progesterone has a direct effect on body weight, but rather than low levels can increase feelings of tiredness which in turn can increase intake of food, decrease activity and prevent weight loss. 

Breastfeeding causes low progesterone, this often leads to an increase in fatigue which causes a higher intake of food and less movement. When breastfeeding reduces or stops and progesterone levels return to normal, appetite, activity levels and body fat storage also return to normal. It is not about will power.

I would argue the most impactful hormone on body weight when breastfeeding is prolactin. This is our miracle hormone, it supports women to produce all the nutrients their baby needs for the first six months of life - it is also the hormone to thank, or not thank for the extra couple of cup sizes. Prolactin is high throughout the breastfeeding journey, this study suggests that prolactin excess is known to promote weight gain through increasing hunger levels and therefore increasing food intake. This study suggests that high prolactin also impacts the way food is metabolised and stored and this study is exploring the hypothesis that higher prolactin also reduces the ability of the body to break down fat for energy. 

Breastfeeding causes high prolactin, this often leads to an increase in hunger, increase in fat storage and less fat breakdown. When breastfeeding reduces or stops and prolactin levels return to normal, appetite, activity levels and body fat storage also return to normal. It is not about willpower. 

The very normal impact of breastfeeding on hormones means that creating an energy deficit is more challenging during this time, due to their role on both energy expenditure through reduced BMR and NEAT; and also due to increased food intake. This means that you may think you are in an energy deficit because that is what an online calculator or coach has recommended, but actually due to these temporary and natural changes, you are in energy balance, meaning weight does not decrease. 

Weight loss is possible when breastfeeding but more challenging; this is an act of love and survival from the body, it is protecting both mother and baby to ensure adequate milk is produced and there is enough energy to cope with sleepless nights. If you attempt to drop food intake too low, milk supply will sadly be negatively affected because the body will prioritise your survival over your baby’s at this stage. 

Other than hormones there are also SO many other reasons the promised weight loss with  breastfeeding may not happen during those first postpartum months. These are predominantly lifestyle factors which are very natural changes that occur when you become responsible for a new little life.

Sleep, that new little life is not a big fan of sleep, which means that you won’t be getting much either, to begin with at least. This study  looked at weight gain over a 10 year period and found that women who get less than five hours sleep per night gained the most weight; the link between sleep restriction and weight gain is thought to be through altering leptin, our fullness hormone, and ghrelin, our hunger hormone. When someone is sleep deprived their hunger hormones increase and fullness hormones decrease, naturally causing higher food intake. This increase in food intake takes away any energy deficit and prevents weight loss. Low sleep does not make it impossible to lose weight, but it definitely makes it harder and you probably won’t feel your best self either. After a sleepless night the type of food people tend to  eat often changes too, this study shows how low sleep impacts blood glucose negatively which means we are more likely to choose foods that increase glucose quickly and are easy to make; chocolate, toast, sweets, popcorn, ice cream, cereal are all examples. 

Breastfeeding a new baby means a reduction in sleep. Low sleep increases levels of hunger hormones whilst decreasing fullness hormones as well as reducing blood glucose leading to increased food intake. When sleep is restored hormones and glucose levels return to normal. It is not about willpower. 

Due to the rather large and life changing responsibility of having a new baby, it is more likely that food choices will be slightly, or hugely different and you may forget to take your vitamins (I definitely did!) This can lead to a reduction in vitamins and minerals and potentially may cause deficiencies. This study suggests that deficiencies in vitamin D, found in sunlight; as well as deficiencies in magnesium, found in leafy greens and wholegrains; and zinc, found in red meat and poultry can impact glucose metabolism and influence body weight. 

Breastfeeding also puts a demand on the wonderful body and means it needs MORE of certain nutrients to support both mother and baby. This study suggests breastfeeding mothers need to increase:

  • Protein + 15g/d

  • Vitamin A + 600ug

  • Vitamin E + 4mg

  • Biotin + 5ug

  • Folic Acid + 100ug

  • Niacin + 3mg

  • Vitamin B2 + 0.5mg

  • Vitamin B1 + 0.3mg

  • Vitamin C +45mg

  • Iodine + 105ug 

  • Zinc +4mg

  • Magnesium 0.8mg 

There are many more important consequences of not increasing these than a potential deficiency impacting metabolism, fatigue, appetite and thus body weight; but a nutrient deficiency may also make weight loss more challenging. A deficiency is more likely when breastfeeding due to the increased demands of both breastfeeding itself and of caring for a tiny human.

Breastfeeding increases the risk of nutrient deficiencies due to an increase in demands on the body, which in turn can impact metabolism, appetite and activity levels. When nutrient deficiencies are treated, and levels return to normal metabolism, appetite and activity also return to normal. It is not about willpower. 

This study found that activity levels are lower in breastfeeding mothers, this may be due to the initial unpredictability of feeding schedules making it more challenging to exercise, I often start to do a little training and then get interrupted by my very own milk monster! This means that energy expenditure is often lower over those first few months. This is very normal, it is not about willpower. 



Final remarks

If you do or do not choose to breastfeed you are phenomenal and your baby adores you. If you choose to breastfeed and have a desire to lose weight, this is possible AND it is often more challenging when you are breastfeeding. This is not a willpower issue; breastfeeding impacts the hormones oestrogen, progesterone and prolactin, it reduces sleep quality and quantity and increases nutrient needs. 

These natural, normal and temporary changes as a result of breastfeeding can easily prevent an energy deficit through impacting food intake, activity levels and metabolism. When you choose to stop breastfeeding, hormone levels return to normal and creating an energy deficit becomes easier IF you choose to pursue weight loss. 

During breastfeeding the body is protecting you and your beautiful little bundle of joy, so if you cannot love your body right now, try to respect it, try to care for it, because it is doing its best to keep you and your baby nurtured. 

You absolutely can pursue weight loss during this chapter, but evidence shows it is harder, so perhaps just ask … is this the right time? Is this what is best for me and my baby? Does this feel like an act of self care? Are deep rooted diet culture beliefs making me fight my body’s natural state? Can I trust my body to find it’s natural weight slowly? Perhaps like much of motherhood, our bodies are teaching us to surrender to what is, to sit with the discomfort of the unknown, to hold space for change, to breathe in presence

It is time we stop promoting weight loss as a benefit of breastfeeding. 

Rach xx


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