Despite claims sometimes made about the health benefits of drinking raw milk, evidence does not suggest that drinking raw milk will relieve or lessen the symptoms of lactose intolerance, according to a study conducted by nutritionists at Stanford University and published this week in Annals of Family Medicine.
But, according to the dairy owner who supplied the raw milk and aided in the study, the design had several limitations that were not obvious until after the data had been collected. As a result, he says, the study raises more questions than answers and should be seen as paving the way for a more complete analysis.
The relatively small study required 16 individuals with the clinical definition of lactose intolerance to drink raw milk, pasteurized milk and soy milk exclusively over eight-day periods, separated by a week of zero milk consumption each time. As each phase progressed, the test participants reported on their level of physical discomfort as they went through bouts of diarrhea, cramping, flatulence and audible intestinal sounds.
The results found no noticeable difference between the severity of lactose-intolerance symptoms faced when participants drank raw milk compared to pasteurized milk, said Christopher Gardner, Ph.D., professor of medicine at the Stanford Prevention Research Center and senior author of the study.
Gardner said, however, that the test did not account for whether or not the eight-day phase of drinking raw milk was a long enough time for bodies to adjust to the bacteria in raw milk, as theorized by Mark McAfee, the owner of Organic Pastures, a prominent raw milk dairy and the supplier of raw milk to the study.
Gardner said that he became personally interested in the subject of raw milk and lactose intolerance when a student in one of his nutrition classes said that drinking raw milk did not cause him to suffer from symptoms of lactose intolerance such as diarrhea and abdominal cramping, but he did suffer those symptoms when he drank pasteurized milk. In fact, the student said he had developed severe intestinal problems from drinking pasteurized milk since moving to the U.S. from Africa, but was able to nurse himself back to health with raw milk, which he was accustomed to drinking back home.
At first, that claim didn’t make sense to Gardner. Raw milk and pasteurized milk contain the same amount of lactose and should therefore both require a person to produce the lactase enzyme in order for them to digest it.
“Raw milk has just as much lactose in it, but it also has probiotics,” Gardner said, explaining his thought process. “Does that make a difference? It sounded like something I could test.”
Gardner told Food Safety News that he is personally a big proponent of whole foods and studying how whole foods influence nutrition, as opposed to studying isolated nutrients. He said that he understands the attraction to whole foods as a response to the abundance of refined and highly processed foods found in grocery stores, and that’s why his nutrition studies focus on whole foods.
How the study worked
Participants were asked to rate the severity of their symptoms on a scale of 0 to 10 for each of the eight days they drank progressively larger servings of each type of milk. A rating of 10 indicated “unbearably severe” symptoms.
The ratings of symptom severity for raw milk and pasteurized milk matched up almost identically on day seven of each phase – the day when participants consumed the largest serving of milk.
On average, participants rated the severity of their flatulence at a little more than 4 out of 10 after drinking both raw and pasteurized milk. For diarrhea, severity averaged around 3 for both, while it also averaged around 3 for intestinal sounds and 2.5 for abdominal cramping.
By comparison, when the participants drank soy milk for a week, on average they rated flatulence at less than 2, while diarrhea, intestinal sounds, and cramping hovered around 1. Soy milk has no lactose.
To prevent participants from easily identifying which milk they were drinking during each phase – and therefore potentially influencing the results – the milk samples were supplemented with sugar-free maple syrup flavoring, provided in unlabeled containers, and distributed in a randomized order.
At the end of each phase, participants were asked to try to identify which milk they had just consumed. When it was over, 40 percent (6 participants) correctly guessed each of the dairy milks, while 80 percent (12 participants) correctly guessed the soy milk.
Finding real lactose-intolerant participants
One of the biggest challenges of the study, Gardner said, was finding participants who fit the clinical definition of lactose intolerance by proving with a hydrogen breath test that they could not digest lactose.
While Gardner said that lactose intolerance is not a binary condition and there are degrees to which someone can or cannot digest milk, the clinical definition of lactose intolerance occurs when a person is a malabsorber of lactose, along with exhibiting the usual symptoms of digestion problems such as diarrhea and cramping. When someone does not produce enough lactase enzymes to break down the lactose in milk, the lactose passes on to the colon, where bacteria feed on it and produce hydrogen as a byproduct.
In short, when clinically lactose-intolerant people drink milk, they exhale hydrogen. When people can digest lactose, they don’t.
More than 400 people who said they suffered digestion problems from drinking milk expressed interest in participating in the study. Out of 63 people who were ultimately tested, only 27 passed the hydrogen test for clinical lactose intolerance. Of those 27 qualifiers, 11 chose to drop out of the study when they learned they would be asked to drink milk for several weeks. That left behind the relatively small sample size of 16 lactose-intolerant participants.
Gardner said he could not say why more than half of the people who claimed to have lactose intolerance proved to not be lactose malabsorbers. They could have just had a bad experience with milk and misdiagnosed themselves, or they could be affected by milk in another way that isn’t related to lactose.
“I couldn’t explain it, but I’m not going to look someone in the eye and tell them they don’t have cramps and diarrhea when they drink milk,” Gardner said.
McAfee questioned the high selectivity of the criteria for the participants. With so many people complaining of problems when they drink pasteurized milk, he said, there is reason to believe that lactose may not be the only thing wrong. That, or the hydrogen breath test may not be the definitive way to diagnose if someone has problems digesting milk.
From McAfee’s personal observations, he said that new raw milk customers who cite pre-existing symptoms of lactose intolerance usually say that they experience the same symptoms when they begin drinking raw milk, but the symptoms fade away after several weeks on raw milk. To him, that suggests that it may take some time for lactose-degrading bacteria to colonize the intestines and ease the symptoms.
Criticism about study’s flaws and limitations
The study was funded in part by the Weston A. Price Foundation, an organization which promotes traditional practices of food, farming and healing arts, including the consumption of raw milk for health benefits. When contacted by Food Safety News, a spokeswoman for the foundation referred questions to McAfee.
But the spokeswoman did cite a survey conducted by the foundation in 2007 that found that 81 percent of Michigan raw milk drinkers who say they were diagnosed with lactose intolerance reported that they did not suffer from symptoms after switching to raw milk.
McAfee said that conducting this study identified two main flaws, which Gardner agreed were limitations. The first was that the hydrogen breath test may have excluded a number of participants who have legitimate digestion problems when it comes to drinking milk. The second was that eight days on raw milk was not enough time to judge whether or not the body could adapt to any new bacteria.
“If the study would have continued for another two or three weeks, I propose you would see a decline in the severity of symptoms from raw milk,” McAfee said. “That’s exactly what we see happening in the marketplace.”
Gardner said his study could not account for those limitations, in part because he wasn’t willing to ask participants with clinical lactose intolerance to drink raw milk for weeks or months. Participants were asked to drink 16 ounces on days one and eight of each phase, while, on days two through seven, they drank progressively larger servings, starting with four ounces on day two and working up to 24 ounces on day seven.
Participants were permitted to quit drinking the milk at any time if their symptoms ever became too unbearable. To Gardner’s surprise, however, 13 of the 16 participants drank all the way up to the 24-ounce level for both raw and pasteurized milk.
Of course, experiences varied, and some participants couldn’t handle the symptoms.
“One guy wrote us a very graphic email explaining how he soiled everything in his house,” Gardner said.
Taking what they have learned from this study, McAfee expressed interest in conducting a similar study in the future that would involve participants drinking the milk over a longer duration.
“This study has taken us to a place where we can ask the right questions,” McAfee said. “I have a theory that there’s some sort of maldigestion syndrome going on here that should be analyzed and evaluated. There’s something going on with the people who complain of tummy aches that isn’t indicated by the hydrogen breath test.”
The study was turned down by four peer-reviewed journals before finally making it into Annals of Family Medicine. The two main reasons given for rejection were that the sample size of 16 participants was too small and that the study was answering too obvious of a question, implying that there should be no expected difference in effects between raw milk and pasteurized milk since the lactose levels would be the same.
“At the end of the day, it’s a small study and not intended to be the final word on the issue,” Gardner said. “Maybe I recruited 13 freaks out of the whole population of lactose-intolerant people.”