Dieting while breastfeeding

Can I diet while breastfeeding?

Should mothers choose to diet, it should be combined with exercise to promote weight loss and maintain muscle strength. Studies have shown that short-term weight loss of about half a kilogram (one pound) a week has no effect on milk production. Intense exercise and starvation, however, may change the quality of the milk and will leave the mother with little energy to care for her children. They may also reduce her milk supply and release toxins from her body fat into her milk. Mothers who choose to diet need to consider that they burn calories producing milk. A diet should include food from all the groups, including carbohydrates.

A) Describing dieting

When breastfeeding, the mother’s body uses fat, other components, and energy to make milk. Breastfeeding mothers with average weight loss will lose half of their baby weight by 6 weeks after delivery and return to their pre-pregnant weight by 6 to 12 months after delivery.

Studies have shown that breastfeeding can encourage weight loss after delivery. Consider that a well-nourished mother will put over 6 kg (13 pounds) of fat into breastmilk during a 6-month period of exclusive breastfeeding (McManaman 2021). 

Some mothers may decide to diet. Ideally, healthy dieting is combined with exercise to promote weight loss and maintain muscle strength and strong bones (Colleran 2019; Dodd 2018). Short-term weight loss of 0.5 kg (about one pound) per week has been shown to have no effect on milk production (Lovelady 2011). Mothers who have had a Caesarian delivery may find it more difficult to lose weight (Legro 2020).

If you choose to diet, remember to consider the calories you burn to produce milk. The total number of calories required depends on how much milk you make.

On average, a woman uses about 85 calories to make 100 millilitres (3 1/3 U.S. fluid ounces) (Butte  2005). To breastfeed a three-month-old baby, a woman would make roughly 800 ml (27 oz) of milk and use about 700 calories. Mothers breastfeeding twins would need to double this amount and mothers of triplets would increase this by a further 700 calories.

B) Risks of dieting

More intense exercise and starvation, however, may cause changes in milk proteins and other milk components (Gregory 1997; Zimmerman 2009). Extreme dieting also leaves a mother with little energy to care for her children and may reduce her milk supply.

Another concern with a very low-calorie diet is the release of environmental contaminants from the mother’s body fat into her milk (Fénichel 2021; Jansen 2018).

There is a small risk of dieting causing major and dangerous imbalances in the acidity level of the blood (lactation ketoacidosis). To prevent this, the mother’s diet should not be extremely limiting and the food should include all groups, including carbohydrates.

C) Fasting

Fasting for religious reasons or around the time of surgery can result in minor changes in breast milk but is unlikely to impact the baby’s health (Allegaert 2020).

After fasting, breastfeeding mothers should taking in only water as this will not provide any necessary salt and may result in low blood salt (sodium) levels. This can be avoided by eating food along with drinking water (Rosen 2021).


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