US nutrition researchers have collaborated on a new study that pours cold water on the claim that lactation cookies boost breast milk production.

A randomized controlled trial comparing breastfeeding parents who ate the 'milk-stimulating' cookies daily with those who did not found no evidence that consumption has the advertised effect.

Often expensive and usually high in calories and added sugar, lactation cookies are marketed with ingredients that are said to increase milk production, but researchers warn that this could mislead vulnerable new parents.

"Despite being a physician and nutrition scientist focused on early-life nutrition, I still remember how difficult breastfeeding was for me with both of my children," says lead author and nutrition scientist Ana Palacios from Georgia Southern University.

"Purchasing lactation cookies to increase milk production may pose an unnecessary cost and may have additional implications for parents, such as limiting post-pregnancy weight loss and reducing consumption of healthier foods."

Palacios and her colleagues from four US universities looked at how well lactation cookies helped produce milk in 176 participants who were exclusively breastfeeding (only feeding with breast milk and no other formula or other drink) a healthy 2-month-old baby.

"Products with claims that may be deceptive are populating the market," they write in their published paper. "A variety of commercially available products claim to improve lactation and maternal/infant health; however, little evidence supports the purported benefits."

To test the claims, study participants were randomly assigned to either lactation cookies containing ingredients said to boost milk production, or regular cookies similar in calories and presentation but lacking these ingredients. Without knowing the type they had, the parents were instructed to consume an approximately 57-gram (2-ounce) pack of their designated cookies each day for a month.

After a month of daily cookie consumption, there was no discernible difference in breast milk production between the control and experimental groups. In addition, two other parameters – perceived insufficient milk and breastfeeding self-efficacy – measured with previously validated participant questionnaires, showed no differences between groups.

"Our research highlights that lactation cookies, which include added sugars and saturated fat, may not have the said purported benefits of increasing milk production," explains Palacios.

The World Health Organization advises exclusive breastfeeding for the first six months of life and continuing breastfeeding in combination with complementary foods until age two or later.

There are many reasons that cause parents to stop breastfeeding earlier than recommended or personally desired. One reason for this is that some parents feel they do not have enough milk to feed their baby.

Perhaps taking advantage of this lucrative market – lactation cookies are made with galactagogues, ingredients purported to increase milk production. Oatmeal, flaxseed meal, fenugreek, brewer's yeast, and blessed thistle extract are just some of the many galactagogues commonly used in these cookies.

The research team notes that there has been a lack of high-quality research on the effects of galactagogues on human milk production, and previous studies have varying methods making it difficult to draw broad conclusions or establish a causal relationship.

"Too often in the field of nutrition and food, strong beliefs – sometimes even well-reasoned conjectures based upon some scientific knowledge – are mistaken for demonstrated facts," says David Allison, an epidemiologist and biostatistician at Indiana University.

"Conjecture is good, but knowing is better. We come to know about the effects of nutrition and dietary supplements through rigorous, randomized, controlled trials. Having conducted such a study on lactation cookies, we found no evidence for their effectiveness."

The authors suggest there needs to be more research on other lactation cookies and on parents whose milk supply is low. This study used one brand of lactation cookies, and the people who took part thought they had enough milk to start with.

"This does not mean that it is impossible for any lactation cookie to affect human milk production. This study does suggest that the cookies we studied – under the conditions we studied them – have no discernible effect.

"The burden of proof seems to now be on those who claim there is an effect," Allison concludes.

The research has been published in The American Journal of Clinical Nutrition.