Low carbohydrate diets and breastfeeding

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Feature article
Month and year: 
Jan 2017
Dr Susan Tawia, Manager Breastfeeding Information and Research team

Low carbohydrate (carb), high fat diets continue to be popular and women of reproductive age are following them. They will often change their diet to a more ‘conventional’ one during pregnancy, but are often keen to return to a weight-loss diet, that they have had success with, after the pregnancy. So, what do we know about the effect of low carb, high fat diets on breastmilk composition and on the metabolism of the breastfeeding woman?

The lack of research on this type of diet, and the possible effect on breastmilk composition, breastfeeding women and their infants, was highlighted by both breastfeeding experts and dietitians in 2004 (Heinig & Doberne, 2004; Wood & Hilldebrandt, 2004) at the height of the popularity of the low carb, weight loss diet advocated by Dr RC Atkins — the Atkins diet.

Research on low carb, high fat diets has been undertaken, but surprisingly, only one study has been done. Mohammad, Sunehag, & Haymond (2009) looked at maternal breastmilk production, infant intake and maternal glucose metabolism and broadly looked at the macronutrients in breastmilk.

Two moderate hypocaloric diets (1785 ± 22 kcal/day) were assessed in a cross-over design: seven, healthy lactating mothers and their infants were studied on 2 occasions in random order for 8 days separated by 1 to 2 weeks. On one occasion, the subjects received the low carb, high fat (LCHF, 30% of energy as carbohydrate and 55% as fat) and on the other occasion received the high carb, low fat diet (HCLF, 60% of energy as carbohydrate and 25% as fat). It is important to note that the amount of carbohydrates consumed during the LCHF was around 150 g per day (Table 1). This is not considered a true low carb diet — during a strict low carb diet around 20 g of carbohydrates are eaten, increasing to 40 g to maintain health (Dashti et al., 2006).

Table 1. Daily intake of macronutrients during the HCLF and LCHF diets




Energy intake (EI, kcal/d)

1782 ± 16

1787 ± 31




51 ± 1

107 ± 2*

 (% of EI)

26 ± 0

54 ± 0*




265 ± 4

137 ± 2*

 (% of EI)

59 ± 1

31 ± 0*




69 ± 2

69 ± 1

 (% of EI)

16 ± 0

15 ± 0

* Significantly different from HCLF, p < 0.01 (paired t test).

The researchers found that:

  • daily breastmilk production was the same regardless of diet: 829 ± 41 mL/d (HCLF) and 821 ± 33 mL/d (LCHF)
  • daily infant breastmilk intake was the same regardless of diet: 611 ± 41 mL/d (HCLF) and 612 ± 41 mL/d (LCHF)
  • there was no effect of diet on either breastmilk lactose or protein
  • there was no difference in infants' intakes of carbohydrate (lactose) or protein between the two diets.
  • the milk fat concentration (4.8 ± 0.3 and 4.3 ± 0.3 g/dL, p = 0.01) and the corresponding daily milk fat content (39 ± 2 and 34 ± 2 g/d, p = 0.02) were higher during the LCHF diet
  • the energy content of milk was higher (p = 0.02) during the LCHF diet (654 ± 24 kcal/d) than during the HCLF diet (619 ± 23 kcal/d)
  • infants' energy intakes expressed as kcal/d (486 ± 24 compared with 452 ± 23) or as kcal/kg/d (87 ± 4 compared with 81 ± 3) was higher (p < 0.05) during the LCHF diet
  • the estimated average maternal energy expenditure was higher (P < 0.03) during the LCHF diet (1368 ± 15 kcal/d) than during the HCLF diet (1283 ± 24 kcal/d)
  • the sum of maternal energy expenditure plus milk energy content was higher (P < 0.01) during the LCHF diet (2022 ± 35 kcal/d) than during the HCLF diet (1910 ± 40 kcal/d)
  • the deficit in energy balance [intake — (energy expenditure + milk output)] was greater (P < 0.01) during the LCHF diet (−235 ± 39 kcal/d) than during the HCLF diet (−119 ± 48 kcal/d)
  • lactating mothers who consumed the LCHF diet decreased carbohydrate oxidation and increased fat oxidation to liberate glucose.

This study, the only good-quality study of a LCHF diet in breastfeeding women, has shown that maternal diet had no short-term effect on milk volume or its water-soluble components, such as protein and lactose. However, it did show that the LCHF diet increased the milk fat concentration and content by about 13% and 15%, respectively, when compared with the HCLF diet. This resulted in an increase in the calorie content of the milk by an average of 35 kcal, leading to increased fat and calorie intakes by infants. The increase in calories was statistically significant, but it is not known whether it is biologically significant.

The estimated average daily energy expenditure was higher during the LCHF diet than during the HCLF diet. When increased milk energy output is added to the maternal energy expenditure, the deficit in energy balance was twice that during consumption of the LCHF diet when compared with the HCLF diet. The researcher suggests that breastfeeding women may lose more weight while consuming an LCHF diet than a HCLF diet.

Ketosis and ketoacidosis
Ketosis is a mild form of ketoacidosis and it’s not necessarily harmful. You can be in ketosis if you’re on a low carb diet or fasting, or if you have consumed too much alcohol. If you have ketosis, you have a higher than usual level of ketones in your blood or urine. Ketones are a chemical your body produces when it burns stored fat.
Normally the body uses glucose from ingested carbohydrates or from glucose stores in the body as the primary energy source. Starvation ketosis is a metabolic state in which the body breaks down fat and produces acids known as ketones, which are then used as a primary energy source. In most cases, people only use ketones for energy when they aren’t getting adequate glucose from food.
People sometimes intentionally trigger this state as a means of burning fat to lose weight by following low carb diets. Ketones can supply energy to the body, but an abnormally high level (ketoacidosis) can cause a number of problems, including organ damage, coma and even death.

Lactation ketoacidosis
There have been a few accounts in the literature of breastfeeding mothers who were admitted to hospital with starvation ketoacidosis from intentionally or unintentionally ingesting a low carb diet and/or fasting (Table 2). In all instances, diabetic and alcoholic ketoacidosis were ruled out and lactation ketosis diagnosed.
Lactation ketosis (starvation ketoacidosis during lactation) was first recognised and described in milking cows (bovine ketosis). It occurs in cows when the animal is unable to maintain sufficient energy intake coupled with the release of stored glucose (gluconeogenesis) to match the increased demand for glucose during lactation. If energy intake and gluconeogenesis cannot be maintained, then fat is utilised as the energy source and ketones are formed (Gleeson, Mulroy and Clarke, 2016).
Table 2.



Laboratory results

Weight loss and/or diet and/or unwell and not eating


Breastfeeding outcome


Case 1

31-year-old woman breastfeeding a 10-month-old-infant


nausea fatigue vertigo malaise and had vomited once

pH 7.26

pCO2 31mmHg

Serum anion gap 32.3 mmol/L

Blood glucose 3.8 mmol/L

Serum ketones ++

Urinary ketones +++

No specific illness or event described, other than lactation.

2L iv sodium chloride

Next day feeling better, tolerating normal diet and pH, anion gap and blood ketones had returned to normal.

Advised to ensure sufficient energy intake and to avoid prolonged fasts while breastfeeding.

Stopped breastfeeding for 12 hours.

Gleeson, Mulroy and Clarke (2016)

Case 2

32-year-old woman breastfeeding a 3-week-old infant

tachypnoea tachycardia

pH 6.99

pCO2 8mmHg

Serum anion gap 28 mmol/L

Blood glucose 3.8 mmol/L

Urinary acetone +++

Had not eaten solid foods for days because of nausea and vomiting.

Infusion of sodium bicarbonate (8.4%), potassium phosphate (50mmol/50ml), glucose 20% and saline and refeeding.

Discharged from hospital after 10 days.

Breastfeeding discontinued.

Hudak et al., (2015)


32-year-old woman breastfeeding a 10-month-old infant



pH 7.20

pCO2 2.8 kPa

Blood glucose 3.8 mmol/L

Blood ketones 7.1mmol/L

Followed a low carb, high fat diet for 10 days, lost 4kg.

10% glucose infusion (3L in 48 hours)

Insulin (4 units in 24 hours).

Discharged after 3 days.

No mention of advice around breastfeeding.

Von Geijer & Ekelund (2015)

Case 4

36-year-old woman breastfeeding a 5-week-old infant

nausea and

vomiting for 48 hours


pH 6.90

pCO2 19mmHg

Serum anion gap 35 mmol/L

Blood glucose 133 mg/dL

Urinary ketones <80 mg/dL

Limited her diet to several small high-protein, carbohydrate-free meals in an attempt to return to her pre-partum weight.

Had intentionally lost 30 lbs (13.6 kg) since birth.

Fluid resuscitation with 3 ampoules of sodium bicarbonate per litre of D5W was initiated for 24 hours

Improvement in laboratory results occurred within 12 hours.

Started 1800 kcal diet during hospital stay, supplemented with food from home.

Breastfeeding ceased on advice from lactation consultant.

Sandhu, Michelis & DeVita, 2009

Case 5

35-year-old woman breastfeeding and formula supplementation of 12-week-old twins

Two day history of progressive fatigue and shortness of breath followed by palpitations and light-headedness with light exertion

pH 7.24

pCO2 16mmHg

Blood glucose 68 mg/dL

Serum ketones moderate

Urinary ketones >80mg/dL

Reported attention to diet selection but denied fasting, carbohydrate avoidance, ketogenic diet and attempted weight loss or meal intolerance.

Initial intervention included iv isotonic saline, thiamine 100mg, magnesium sulphate 2 g and 5% dextrose in normal saline infusion, followed by a meal.

Symptoms improved within 6 hours and patient tolerated a normal diet within 24 hours

Nutritional consultation calculated caloric requirements of lactation and discovered mild carbohydrate and protein dietary deficiency. The patient was discharged home on a normal diet and multi-vitamin supplements.

Limited lactation was continued via breast pump on day 1.

Heffner & Johnson 2008

Mothers who are considering low carb, high fat and/or other weight loss diets should be informed of the potential risks, educated about how to avoid risks and reminded that one of the benefits of breastfeeding is a more rapid return to pre-pregnancy weight (Neville et al., (2014) undertook a systematic review and found that, of the five studies that were considered to be of high methodological quality, four studies demonstrated a positive association between BF and weight change). One of the unintended consequences of dieting which leads to hospitalisation may be the discontinuation of breastfeeding.
Gleeson, Mulroy and Clarke (2016) also highlighted the need to ensure adequate and proper nutrition whenever breastfeeding women are admitted to hospital, particularly if they are fasting for medical reasons eg preoperatively.
Note: A recent publication by Bravi et al., 2016 summarised the best available evidence of the impact of maternal nutrition on breastmilk composition and included the Mohammad, Sunehag and Haymond, 2009 paper. They looked at the effect of diet on total energy, total protein, fat, fatty acids (the focus of most studies), carbohydrate and some vitamins and minerals and concluded that: ‘The available information on this topic is scarce and diversified. Most of the evidence currently used in clinical practice to make recommendations is limited to studies that only reported indirect associations.’
Bravi, F., Wiens, F., Decarli, A., Dal Pont, A., Agostoni, C., & Ferraroni, M. (2016). Impact of maternal nutrition on breast-milk composition: a systematic review. The American Journal of Clinical Nutrition, 104, 646-662.
Dashti, H. M., Al-Zaid, N. S., Mathew, T. C., Al-Mousawi, M., Talib, H., Asfar, S. K., & Behbahani, A. I. (2006). Long term effects of ketogenic diet in obese subjects with high cholesterol level. Molecular and Cellular Biochemistry, 286(1-2), 1-9.
Gleeson, S., Mulroy, E., & Clarke, D. E. (2016). Lactation ketoacidosis: an unusual entity and a review of the literature. The Permanente Journal, 20(2), 71-73.
Heffner, A. C., & Johnson, D. P. (2008). A case of lactation “bovine” ketoacidosis. The Journal of Emergency Medicine, 35(4), 385-387.
Heinig, M. J., & Doberne, K. (2004). Weighing the risks: the use of low-carbohydrate diets during lactation. Journal of Human Lactation, 20(3), 283-285.
Hudak, S. K., Overkamp, D., Wagner, R., Häring, H. U., & Heni, M. (2015). Ketoacidosis in a non-diabetic woman who was fasting during lactation. Nutrition Journal, 14(1), 1.
Mohammad, M. A., Sunehag, A. L., & Haymond, M. W. (2009). Effect of dietary macronutrient composition under moderate hypocaloric intake on maternal adaptation during lactation. The American Journal of Clinical Nutrition, 89(6), 1821-1827.
Neville, C. E., McKinley, M., Holmes, V., Spence, D., & Woodside, J. (2014). The relationship between breastfeeding and postpartum weight change—a systematic review and critical evaluation. International Journal of Obesity (London), 38(4), 577-590.
Sandhu, H. S., Michelis, M. F., & DeVita, M. V. (2009). A case of bovine ketoacidosis in a lactating woman. NDT plus, 2(4), 278-279.
von Geijer, L., & Ekelund, M. (2015). Ketoacidosis associated with low-carbohydrate diet in a non-diabetic lactating woman: a case report. Journal of Medical Case Reports, 9(1), 1.
Wood, S., & Hildebrandt, L. A. (2004). Use of low‐carbohydrate diets during lactation: implications for mothers and infants. Topics in Clinical Nutrition, 19(4), 286-296.