One of the common themes of SBM is that our public health decisions, and individual health decisions, should be based on the best evidence currently available evaluated as much as possible within a thorough scientific context. Unfortunately, many segments of society do not operate under this paradigm. Rather, they operate under one or more other approaches: what emotionally feels right, what is ideologically convenient, conspiracy thinking, or the demands of marketing. Often these threads weave together.

For example, industry often tries, and succeeds, to create a health halo around their product, so that people feel they are being smart and healthy when they use it, regardless of the science. They may also exploit an existing health halo, such as the notion that a product is “natural”. Conspiracy theories can always be invoked to fend off science-based criticism or refutation of their claims.

In essence alternate narratives to the scientific evidence can be manufactured, or can emerge spontaneously, and then take on a life of their own. Social media makes this process faster and easier, and can create virtual “rabbit holes” that curious people can fall into if they use social media to satisfy their interest in the topic.

One such rabbit hole is the “raw” food narrative. This is the notion, completely divorced from reality, that raw food is healthier than cooked or heated food. There was even a movement to sell “raw water”, which was essentially contaminated water. The “raw” health halo is especially pernicious, however, when applied to milk.

Most milk consumed in the US and industrialized nations is pasteurized and homogenized. Pasteurization is the process of flash heating raw milk in order to kill bacteria, making the milk safer and extending its shelf life. The process involves heating milk in stainless steel containers to 161° F for 15 seconds then rapidly cooling down to 39°F. This creates milk with a refrigerated shelf life of 10-21 days. There is also ultra-pasteurized milk, which involves heating to 280-300°F for 2-3 seconds and storing in a more sterile condition, which results in milk that still needs to be refrigerated, but can last 30-90 days.

Then there is UHT – ultra-high temperature pasteurization, which uses the same high temperature process as ultra-pasteurized, but then the milk is stored in sterile and hermetically sealed conditions. This produces shelf-stable milk that can last for 6 months without refrigeration.

Of course, regardless of the process, as soon as the container is opened there is the potential for contamination, and therefore it is recommended that the milk be consumed within 7-10 days.

Pasteurization undeniably works as advertised. As Mark Crislip summarized previously, the widespread use of pasteurization has reduced milk as a source of human bacterial infection outbreaks from 25% to 1%. Many studies have shown that consuming raw milk is a risk factor for bacterial infection. So why would raw milk proponents claim it is better? They believe that raw milk is more nutritious and tastes better, and contains healthy probiotics.

I am skeptical of the taste claim, because of the mountain of scientific evidence that taste is extremely subjective and amenable to other sensory clues and expectations. Therefore I only trust blinded taste tests. Having participated in these myself, it is often shocking how much expectation plays a role in perceived taste. To be generous, though, I will grant this point to anyone who has a personal preference, but I will just caution everyone that you really don’t know until you have done a blind test. Heating does chemically change the milk and therefore the flavor, but whether or not the result is “better” is personal choice.

The questions that have more scientific evidence behind them regard safety and benefits. Is raw milk better? The nutrition question has been answered. Here is one study that compares raw milk to standard “Holder” pasteurization and shelf-stable (retort processing or SS) milk:

Macronutrient content is relatively unaffected by processing; Holder pasteurization and retort processing maintain similar fat, lactose, and total protein levels. Lysine and thiamine were significantly decreased by retort processing, but not by Holder pasteurization. Thiamine losses are clinically significant, and fortification may be necessary if SS donor milk is a long-term feeding choice.

For regular pasteurized milk, therefore, there is no significant nutritional difference. Any minor differences are clinically irrelevant. Ultra-pasteurized or shelf stable milk has reduced thiamine, which is only an issue if milk is your primary source of thiamine, which is likely not true for most people. Milk doesn’t even crack the top ten in terms of sources of thiamine, which you can get from a variety of meats, vegetables, and legumes.

So the nutrition claim is bogus. What about the claim that raw milk contains beneficial probiotics? That is partially the topic of a recent study. They examined raw and pasteurized milk for bacterial content at baseline and over time if left at room temperature vs refrigeration at 4 C. They found:

Despite advertised “probiotic” effects, our results indicate that raw milk microbiota has minimal lactic acid bacteria.

The claim to health benefits from routine use of probiotics is problematic at best in any case. The best conclusion we can make from existing data is that there is no benefit for healthy people routinely consuming probiotics. There is some open question when it comes to those suffering from irritable bowel syndrome or similar conditions, and also with the use of high culture count probiotics in the early treatment of diarrhea produced by antibiotic use. Even there the data is thin, but a benefit is plausible. But there is clearly no benefit from routine use.

This is a double-whammy for the raw milk claim – routine consumption of probiotics is probably not beneficial, and raw milk doesn’t contain them anyway.

What raw milk does contain in abundance is pathogenic bacteria, those capable of causing infection. Further, raw milk is loaded with antibiotic resistant genes (residing in those bacteria). Consuming raw milk not only risks infection, it is potentially seeding the bacteria already in your body with antibiotic resistant genes. This study does not establish a specific health risk to consuming the resistant genes, but they are a potential hazard.

Unsurprisingly, leaving raw milk at room temperature quickly and dramatically increases the number of bacteria and resistant genes. People do this when they are making a culture for certain products. The authors recommend that a starter culture be used instead of starting with raw milk. Incidentally, at refrigeration temperatures the bacterial counts were stable (but still higher in raw milk).

The bottom line is that there is no health benefit to drinking raw milk vs pasteurized milk, but there is a clear increased risk from pathogenic bacteria and now possibly from increased spread of antibiotic resistant genes.


Posted by Steven Novella

Founder and currently Executive Editor of Science-Based Medicine Steven Novella, MD is an academic clinical neurologist at the Yale University School of Medicine. He is also the host and producer of the popular weekly science podcast, The Skeptics’ Guide to the Universe, and the author of the NeuroLogicaBlog, a daily blog that covers news and issues in neuroscience, but also general science, scientific skepticism, philosophy of science, critical thinking, and the intersection of science with the media and society. Dr. Novella also has produced two courses with The Great Courses, and published a book on critical thinking - also called The Skeptics Guide to the Universe.