Intentional Weight Loss During Lactation: Recommendations for Dietitians

Supporting postpartum breast/chest feeding clients in balancing energy needs and milk supply can be a complex challenge for dietitians. 

Many individuals want to return to their pre-pregnancy weight in the least amount of time possible, but restrictive eating patterns may compromise milk supply, nutrient status, and overall infant and maternal health. 

This article reviews energy requirements during lactation, the safety of weight loss through diet and exercise postpartum, and the impact of caloric restriction on milk supply, quality, and maternal health.

*Note on inclusive language:

We recognize that not all individuals who lactate identify as mothers or use the term “breastfeeding.” Throughout this article, we use "breast/chestfeeding" and "lactating individuals" to reflect inclusivity. However, some of the referenced research studies and guidelines use gendered terms like "mother" or "breastfeeding" in alignment with their original source material. When citing these studies, we maintain their original language while acknowledging the need for inclusive terminology in clinical practice.

Energy Requirements During Lactation

Lactation increases energy demands due to milk production. The average energy content of breastmilk is 67 calories per 100 g. Energy recommendations: 

• 0 to 6 months (exclusive breast/chest feeding): An additional 540 calories is needed to support an average milk output of 800 mL/day. 140 calories is mobilized from maternal tissue stores, drawing from the weight gained during pregnancy. An additional intake of 400 calories is recommended from diet  

  
  

• 7-12 months: Around an additional 380 calories/day to support continued milk output of approximately 570 mL/d alongside complementary feeding​

Milk production can be resilient, even under suboptimal nutritional conditions. However, prolonged inadequate intake can lead to maternal nutrient depletion, particularly of fat-soluble vitamins​.

Weight Loss and Lactation: Is It Safe?

The research on lactation and weight loss is surprisingly limited, with most studies having small sample sizes and dating back to the early 2000s. 

From the limited data that we have, it appears that moderate weight loss during lactation is generally safe for both parent and infant. Gradual weight loss, achieved through mild caloric restriction and exercise, does not compromise milk production or infant growth.

Here is what studies have found:

One of the most cited on weight loss during lactation is the randomized controlled trial conducted by Lovelady et al. (2000). The study examined whether a caloric deficit combined with exercise could promote safe postpartum weight loss without negatively affecting infant growth. 

• Individual energy needs of the participants was estimated using the Harris-Benedict equation, multiplying the basal metabolic rate (BMR) by an activity factor of 1.35 to account for moderate activity levels.

• To account for lactation energy demands, they added 630 calories/day, based on the assumption that breast milk contains 70 calories per 100 ml and that daily production is around 750 ml with an 80% efficiency rate.

• Participants were then randomized and divided into intervention and control groups

  
  

• The intervention group was prescribed:

  • An energy intake that was 500 calories less than the average of their reported baseline intake and the estimated requirement

  • A minimum caloric intake of 1800 calories/day to ensure adequate nutrient intake

  • Macronutrient distribution was set at 55% carbohydrates, 25% fat, and 20% protein

  • Participants were provided with six low-fat, low-calorie frozen meals per week 

  • Additionally, they followed a structured exercise program of four 45-minute sessions per week, gradually increasing duration over five weeks. The activities included brisk walking, jogging, and aerobic dance

Results from this study showed:

• The intervention group lost an average of 4.8 kg over 10 weeks, compared to only 0.8 kg in the control group, which maintained their usual diet and exercised less frequently

• No significant differences were observed in infant weight gain or length, indicating that moderate caloric restriction paired with exercise does not negatively affect infant outcomes

Another 16-week study investigated whether moderate energy restriction combined with resistance training affected weight loss and bone mineral density (BMD). Bone loss during lactation is driven by the increased demand for calcium in breast milk and mobilization from maternal stores. However, most studies show that maternal BMD returns to baseline after weaning. 

The study included 27 fully breastfeeding participants, randomly assigned to either an intervention group or a control group. Participants in the intervention group were placed on:

• A 500 calories/day deficit while engaging in resistance training three times per week 

• A minimum intake of 1800 calories/day was maintained to avoid excessive restriction

• Methods for calculating energy needs and macronutrient ratios were not detailed in the study 

The results showed that moderate energy restriction lead to significantly greater weight loss than the control with no adverse effects of BMD.

Impact of Severe Caloric Restriction on Milk Supply

Findings from multiple studies have shown that milk volume can decrease by approximately 15% when energy intake dropped below 1500 calories/day. However, milk composition remained relatively stable, suggesting that while the body prioritizes milk production.

Severe carbohydrate restriction may also pose risks, such as lactational ketoacidosis, but this is rare. Additionally, prolonged severe restriction may deplete maternal nutrient stores, increasing the risk of bone loss, fatigue, and micronutrient deficiencies. 

While mild-to-moderate caloric deficits are generally safe, excessive restriction should be avoided to prevent a decline in milk production and maternal health complications.

Nutrients to Monitor

Nutrient needs are greater with lactation. Whether or not individuals are looking to lose weight during lactation, it is essential to focus on nutrient-dense foods to support both maternal and infant health. Key nutrients to prioritize include:

• Carbohydrates 

• Protein 

• Fats 

• DHA 

• Vitamin B12 

• Folic acid 

• Calcium  

• Vitamin D 

• Vitamin C

• Iron 

• Zinc 

A multivitamin/mineral or prenatal supplement may be beneficial during lactation to meet increased micronutrient needs.

Summary and Recommendations

• Energy needs increase by 350-400 calories per day during lactation 

• Moderate caloric restriction, around 500 calories/day, can support safe postpartum weight loss

• Minimum intake should not fall below 1800 calories/day to ensure adequate nutrient supply. Even 1800 calories/day may reduce milk output for some, which is why it is recommended that individuals who wish to pursue weight loss during lactation consult with a Registered Dietitian 

• Diets below 1500 calories/day increase the risk of milk supply reduction and maternal nutrient depletion

• Exercise, particularly aerobic and resistance training, can support weight loss and maternal health without harming lactation

Conclusion

Dietitians play a critical role in supporting lactating individuals by providing evidence-based, individualized nutrition plans. By addressing energy needs, promoting safe weight management, and avoiding severe restriction, dietitians can help optimize outcomes for both parent and infant.