Is whey protein safe during pregnancy?

We found no trial of whey shakes in pregnant women in general, so nobody can call them proven safe. The strongest warning comes from protein supplements as a group. In a Cochrane review, a high-protein supplement raised the risk of a small-for-gestational-age baby by 58 percent in one trial of 505 women, and the reviewers concluded it may harm the fetus. Whey itself has been tested only in women with gestational diabetes. In 62 such women, 20 g of whey isolate before breakfast lowered blood sugar after the meal and caused no more side effects than placebo.

Unsettled. Whey in pregnancy is unsettled because the only direct evidence is two small, short Danish trials in women with gestational diabetes, run by the same group and part funded by a whey ingredient maker. They were built to measure blood sugar, and a trial of 55 women cannot see rare harms to the baby.

What the trials found

Whey and blood sugar, in gestational diabetes

In a double-blind randomized trial, 62 Danish women with gestational diabetes took 20 g of whey protein isolate or a placebo 30 minutes before breakfast through the third trimester. One hour after breakfast, glucose was 20 percent lower with whey early in the trimester (95% CI 11 to 28) and 15 per cent lower late (95% CI 5 to 24). The trial was part funded by Arla Foods Ingredients, and fasting glucose, HbA1c and insulin resistance did not change.

A crossover trial by the same authors and sponsor gave 24 pregnant women 20 g of whey 30 minutes before a glucose drink. The peak glucose fell by 18 mg/dL (95% CI 7.2 to 29; metric: 1.0 mmol/L, 0.4 to 1.6) in the 12 women with gestational diabetes and by 13 mg/dL (95% CI 1.8 to 23; metric: 0.7 mmol/L, 0.1 to 1.3) in the 12 without. That was the effect of a single dose, measured on the day.

Whey and the baby

In the 62-woman trial, the 55 women who finished it had no difference in stomach or bowel side effects or in obstetric outcomes between whey and placebo. Newborn birthweight did not differ either. The babies in the whey group averaged 3461 g against 3611 g with placebo, a gap of 5.3 oz (150 g) that did not reach significance (95% CI 399 g lighter to 100 g heavier). Cord blood C-peptide was higher with whey, a difference that also did not reach significance and was measured in only 19 samples.

Protein supplements in general

The Cochrane review that carries the warning above split protein supplements by type. Adding protein without extra calories, the design closest to stirring a protein powder into a normal diet, did not change birthweight in two trials with 184 women (mean difference 108 g, 95% CI 221 g lower to 437 g higher), on very low-quality evidence. Balanced energy and protein supplements cut the risk of a small-for-gestational-age baby by 21 percent across 7 trials with 4,408 women, mostly in low-income settings, on moderate-quality evidence.

A 2026 analysis of individual data from 8 trials with 10,252 women in low- and middle-income countries found balanced energy-protein supplements cut the risk of a baby born at term, small and of low birthweight by 20 percent. The comparison groups differed between trials, and the result cannot be carried over to well-fed women. In undernourished women, a meta-analysis of 7 trials with 2,367 women found these supplements raised birthweight with a small standardized effect of 0.20 (95% CI 0.03 to 0.38). A meta-analysis of 62 randomized trials of animal-source protein in mothers and young children found that supplementing mothers raised birth weight by 0.13 lb (0.06 kg), and the abstract gives no interval or number of maternal trials for that figure.

Established. Protein with extra food helps babies grow in women who are not eating enough. That benefit comes from balanced food supplements in poorer countries, and none of these trials used whey powder in women who already eat well.

Who should be careful

Not for everyone. A high-protein supplement is the one form of extra protein in pregnancy with a randomized signal of harm: a 58 percent higher risk of a small-for-gestational-age baby (RR 1.58, 95% CI 1.03 to 2.41) in one trial of 505 women, on moderate-quality evidence. It was a single trial of a high-protein supplement, not whey powder. WHO does not recommend high-protein supplements for pregnant women in undernourished populations.

Whey is a milk protein, and the US FDA lists milk among the nine major food allergens, so whey powders are not for anyone with cow's milk allergy. The US NIDDK lists whey among the label words that mean a product contains lactose, which matters if you are lactose intolerant. Surveys of heavy metals in protein powders are covered on the protein powder and pregnancy page.

Myth. Cutting out milk protein in pregnancy does not protect the baby from allergy. A Cochrane review of 5 trials with 952 women at high risk of having an allergic child found an avoidance diet is unlikely to reduce the child's risk, and it may harm the nutrition of mother or baby. A USDA systematic review of trials and cohort studies judged with moderate evidence that restricting cow milk products in pregnancy does not lower the child's risk of eczema.

If you have gestational diabetes, the whey trials above were done in women like you, under a study team's supervision, with 20 g a day. Whether that fits your own treatment plan is a question for the team managing your diabetes.

What expert bodies say

WHO's antenatal care guideline states that in undernourished populations, high-protein supplementation is not recommended for pregnant women to improve maternal and perinatal outcomes. The US recommended protein intake in pregnancy is 71 g a day, which the FDA adopted as the label reference for pregnant and lactating women. In the US dietary survey database a scoop of one brand of whey protein powder weighs 20 g, the dose used in the trials. None of the agency sources we checked addresses whey powder in pregnancy itself.

How we searched

What would change this answer

• We found no systematic review of whey in pregnancy. A trial of whey shakes in well-nourished pregnant women without gestational diabetes, followed to birth, would answer the question most people are asking.
• Results from NCT06170905, the completed trial of a whey pre-load and blood sugar in pregnancy.
• A trial testing whether whey before a meal delays the mother's own insulin response in gestational diabetes, which the authors of the 62-woman trial propose.
• An updated Cochrane review of high-protein supplementation in pregnancy. The warning on this page rests on one trial.

More on whey as a food: the whey page. Protein powders in general have their own evidence page for pregnancy, and protein needs are in the protein guide.

Sources

1. ev-whpreg-01 · Randomized controlled trial(s) · double-blinded randomized placebo-controlled parallel trial · n = 62
   In the WP group, the 1 h postprandial glucose following breakfast was -20% (95% CI -28%, -11%) lower in the early and -15% (95% CI -24%, -5%) lower in the late third trimester compared with the placebo group under controlled conditions.
   
   Who: women with gestational diabetes, normotensive, aged 18 or over, singleton pregnancy, given 20 g whey protein isolate or placebo daily 30 min before breakfast throughout the third trimester, Denmark
   Effect: 1 h postprandial glucose after breakfast -20% (95% CI -28% to -11%) early and -15% (95% CI -24% to -5%) late third trimester under controlled conditions
   Certainty: Partly funded by Arla Foods Ingredients. HbA1c, fasting glucose, and HOMA-IR did not change; whether it delays insulin was not tested.
   Diabetologia, 2026 · checked 2026-10-07 · we read the abstract
2. ev-whpreg-02 · Randomized controlled trial(s) · double-blinded randomized placebo-controlled parallel trial · n = 55
   There were no differences in gastrointestinal side effects or obstetrical outcomes (ESM Fig. 1, ESM Table 4).
   
   Who: women with gestational diabetes given 20 g whey protein isolate or placebo daily in the third trimester (30 and 25 completers)
   Effect: no between-group differences in gastrointestinal side effects or obstetrical outcomes
   Certainty: Small sample, third trimester only, 20 g isolate only; such an RCT will not see rare harms.
   Diabetologia, 2026 · checked 2026-10-07 · we read the fulltext
3. ev-whpreg-03 · Randomized controlled trial(s) · double-blinded randomized placebo-controlled parallel trial · n = 55
   Newborn birthweight and z score did not differ between groups.
   
   Who: newborns of women with gestational diabetes given whey protein (30) or placebo (25) in the third trimester
   Effect: birthweight 3461 g vs 3611 g, difference -150 g (95% CI -399 to 100), p=0.235; cord blood C-peptide p=0.093
   Certainty: Weight numbers from table 2 of the full text; C-peptide in cord blood was measured in only 19 samples.
   Diabetologia, 2026 · checked 2026-10-07 · we read the fulltext
4. ev-whpreg-04 · Randomized controlled trial(s) · placebo-controlled single-blinded randomized crossover trial · n = 24
   Intake of premeal whey resulted in lowered peak glucose by -1.0 mmol/L (95% CI -1.6 to -0.4) in women with GDM and -0.7 mmol/L (95% CI -1.3 to -0.1) in women without GDM compared with placebo.
   
   Who: 12 women with gestational diabetes and 12 pregnant women with normal glucose tolerance at 20-36 weeks' gestation
   Effect: peak glucose -18 mg/dL (95% CI -29 to -7.2; metric: -1.0 mmol/L, -1.6 to -0.4) with GDM, -13 mg/dL (-23 to -1.8; metric: -0.7 mmol/L, -1.3 to -0.1) without; at home 30 g whey up to -36 mg/dL (-45 to -27; metric: -2.0 mmol/L, -2.5 to -1.5)
   Certainty: Acute effect of a single dose; the same authors and sponsor as in ev-whpreg-01.
   Diabetes Care, 2025 · checked 2026-10-07 · we read the abstract
5. ev-whpreg-05 · Meta-analysis or systematic review · Cochrane systematic review and meta-analysis of randomized controlled trials · n = 505
   High-protein supplementation does not seem to be beneficial and may be harmful to the fetus.
   
   Who: pregnant women given high-protein supplementation, one trial
   Effect: small for gestational age RR 1.58 (95% CI 1.03 to 2.41), moderate-quality evidence
   Certainty: A single RCT of a high-protein supplement, not whey powder; but this is the only randomized signal of harm from excess protein.
   Cochrane Database Syst Rev, 2015 · checked 2026-10-07 · we read the abstract
6. ev-whpreg-06 · Meta-analysis or systematic review · Cochrane systematic review and meta-analysis of randomized controlled trials · n = 184
   Isocaloric protein supplementation (two trials, 184 women) had no significant effect on birthweight (MD 108.25, 95% CI -220.89 to 437.40) and weekly gestational weight gain (MD 110.45, 95% CI -82.87 to 303.76, very low-quality evidence).
   
   Who: pregnant women given isocaloric protein supplementation, two trials
   Effect: birthweight MD 108.25 g (95% CI -220.89 to 437.40); weekly weight gain MD 110.45 g (-82.87 to 303.76), very low-quality evidence
   Certainty: The design closest to "just add protein powder"; very little data.
   Cochrane Database Syst Rev, 2015 · checked 2026-10-07 · we read the abstract
7. ev-whpreg-07 · Meta-analysis or systematic review · Cochrane systematic review and meta-analysis of randomized controlled trials · n = 4408
   There was also a significant reduction in the risk of small-for-gestational age (RR 0.79, 95% CI 0.69 to 0.90, I² = 16%, seven trials, 4408 women, moderate-quality evidence).
   
   Who: pregnant women given balanced energy and protein supplementation, mostly in low-income settings
   Effect: small for gestational age RR 0.79 (95% CI 0.69 to 0.90), I2 16%, moderate-quality evidence
   Certainty: Food supplements with protein under 25% of energy, not whey; benefit where women are undernourished.
   Cochrane Database Syst Rev, 2015 · checked 2026-10-07 · we read the abstract
8. ev-whpreg-08 · Meta-analysis or systematic review · systematic review and individual participant data meta-analysis of randomized controlled trials · n = 10252
   In the 10-group categorization of SVNs, on average, prenatal BEP supplementation led to a 30% lower risk of preterm-SGA-LBW (RR: 0.70; 95% CI [0.53, 0.91]; P = 0.009), a 25% lower risk of preterm-AGA-LBW (RR: 0.75; 95% CI [0.60, 0.93]; P = 0.009), and a 20% lower risk of term-SGA-LBW (RR: 0.80; 95% CI [0.72, 0.90]; P < 0.001).
   
   Who: pregnant women in low- and middle-income countries, 8 RCTs of prenatal balanced energy and protein supplements
   Effect: term-SGA-LBW RR 0.80 (95% CI 0.72 to 0.90); preterm-SGA-LBW RR 0.70 (0.53 to 0.91)
   Certainty: Controls differed (standard, iron-folate, micronutrients); cannot be transferred to well-nourished women.
   PLoS Med, 2026 · checked 2026-10-07 · we read the abstract
9. ev-whpreg-09 · Meta-analysis or systematic review · systematic review and meta-analysis of randomized controlled trials · n = over 30,000 (all 62 trials)
   Maternal supplementation increased birth weight by 0.06 kg, and both formula and food-based supplementation in term infants/young children increased weight by ≤0.14 kg.
   
   Who: mothers, preterm infants and young children in 62 RCTs of animal protein supplementation across 5 continents
   Effect: maternal supplementation birth weight +0.13 lb (0.06 kg)
   Certainty: The interval for the maternal subgroup is not given in the abstract; no full text in PMC.
   Am J Clin Nutr, 2019 · checked 2026-10-07 · we read the abstract
10. ev-whpreg-10 · Meta-analysis or systematic review · systematic review and meta-analysis of randomized controlled trials · n = 2367
    Balanced protein energy supplementation significantly improved birthweight (seven randomised controlled trials, n = 2367; d = 0.20, 95% confidence interval, 0.03-0.38, P = 0.02).
    
    Who: undernourished pregnant women in low- and middle-income countries, 7 RCTs
    Effect: birthweight SMD 0.20 (95% CI 0.03 to 0.38); no benefit for birth length or head circumference
    Certainty: Standardized difference, grams not given; undernourished women only.
    Matern Child Nutr, 2015 · checked 2026-10-07 · we read the abstract
11. ev-whpreg-11 · Meta-analysis or systematic review · Cochrane systematic review of randomized and quasi-randomized trials · n = 952
    Prescription of an antigen avoidance diet to a high-risk woman during pregnancy is unlikely to reduce substantially her child's risk of atopic diseases, and such a diet may adversely affect maternal or fetal nutrition, or both.
    
    Who: pregnant women at high risk of having an atopic child, prescribed avoidance of cow milk, egg or other antigens
    Effect: no protective effect on atopic eczema in the first 18 months; slightly lower gestational weight gain with the restricted diet
    Certainty: An argument against the myth "give up dairy protein so the child does not develop allergy"; 2012 review.
    Cochrane Database Syst Rev, 2012 · checked 2026-10-07 · we read the abstract
12. ev-whpreg-12 · Observational data · agency systematic review of RCTs and prospective cohort studies (USDA NESR), plain language summary · n = —
    Moderate evidence indicates that lower or restricted consumption of cow milk products during pregnancy does not reduce the risk of atopic dermatitis/eczema in the child.
    
    Who: pregnant women and their children, RCTs and cohort studies
    Effect: moderate evidence: restricting cow milk products in pregnancy does not reduce child atopic dermatitis risk; evidence for food allergy insufficient
    Certainty: Concerns dairy products in general, not whey powder.
    USDA Nutrition Evidence Systematic Review, 2020, Maternal Diet during Pregnancy and Lactation and Risk of Child Food Allergies and Atopic Allergic Diseases: A Systematic Review · checked 2026-10-07 · we read the section
13. ev-whpreg-13 · Position of an expert body · WHO guideline recommendation · n = —
    In undernourished populations, high-protein supplementation is not recommended for pregnant women to improve maternal and perinatal outcomes
    
    Who: pregnant women in undernourished populations
    Effect: recommendation against high-protein supplementation (WHO ANC guideline 2016)
    Certainty: Two independent requests: WebSearch returned the sentence verbatim from WHO eLENA; WebFetch of the BIGG/PAHO register confirmed it, source WHO ANC 2016.
    WHO, 2016, WHO recommendations on antenatal care for a positive pregnancy experience (eLENA: high-protein supplementation during pregnancy) · checked 2026-10-07 · we read the section
14. ev-whpreg-14 · Position of an expert body · regulatory reference value · n = —
    In the preamble to the proposed rule (79 FR 11879 at 11943), we noted that the IOM established 71 grams/day protein as the RDA for pregnant and lactating women based on the needs for maternal and fetal development and human milk production.
    
    Who: pregnant and lactating women, US labeling
    Effect: RDA 71 g/day protein in pregnancy (IOM)
    Certainty: A protein norm, not an upper limit; whey in pregnancy is not addressed.
    FDA, 2016, Food Labeling: Revision of the Nutrition and Supplement Facts Labels, final rule (FR Doc. 2016-11867) · checked 2026-10-07 · we read the section
15. ev-wpm-13 · Position of an expert body · FDA consumer and industry page on food allergies, content current as of 11 March 2026 · n = -
    The major food allergens are milk, eggs, fish, Crustacean shellfish, tree nuts, peanuts, wheat, soybeans, and sesame.
    
    Who: people with food allergy in the United States
    Effect: milk listed as a major food allergen requiring declaration on labels
    Certainty: Allergy to milk protein differs from lactose intolerance; whey isolate still contains milk proteins.
    Food Allergies, US Food and Drug Administration, 2026 · checked 2026-10-06 · we read the full text
16. ev-wpc-13 · Position of an expert body · agency patient guidance · n = —
    The following words mean that the product contains lactose: milk, lactose, whey, curds, milk by-products, dry milk solids, nonfat dry milk powder
    
    Who: people with lactose intolerance reading food labels
    Effect: whey named as a lactose-containing ingredient
    Certainty: whey isolate carries far less lactose than concentrate; the page does not split them
    NIDDK (NIH), Eating, Diet, & Nutrition for Lactose Intolerance · checked 2026-10-07 · we read the section
17. whyr8-14 · Position of an expert body · USDA survey food dataset · n = —
    Nutritional powder mix (EAS Whey Protein Powder) (FNDDS 95201200): 1 scoop EAS Whey 20 g; 1 tablespoon 10 g; Quantity not specified 39 g
    
    Who: FNDDS record Nutritional powder mix (EAS Whey Protein Powder)
    Effect: 1 scoop 20 g; 1 tablespoon 10 g; quantity not specified 39 g
    Certainty: one brand; a serving is a measure, not the amount consumed
    USDA FNDDS 2021-2023, FNDDS 95201200, FDC 2710731 · checked 2026-10-03 · we read the dataset