What You Were Never Told About Milk

what you may not know about milk

It’s no wonder that milk is our sole source of nutrition during the first 4 to 6 months of life when you look at what a nutritional powerhouse it is, specifically human breast milk. This may just be Nature’s most perfect food because it’s rich in high-quality protein, omega-3 fatty acids, and unique prebiotics (i.e. fermentable fiber). This helps to establish and maintain the ideal microbial composition in the gut of an infant.  The down side is you’ll be hard pressed to find human breast milk in your local dairy aisle. However, there is a potential alternative, the high-tech version of old-fashioned dairy milk. It’s called lactose-free milk.

The History of Dairy Milk

To explain my statement you have to understand the history of dairy milk and genetics.  All newborn children have the enzyme (lactase) in their gut that allows them to breakdown the disaccharide lactose found in human breast milk to simple sugars (galactose and glucose) that can be absorbed.  This is important since if the lactose makes its way to the colon, it is often the cause of gastric disturbances (i.e. lactose intolerance).   Furthermore, galactose is not a very common carbohydrate.  It has recently been shown that higher levels of galactose in the blood appear to be important in reducing insulin resistance (1).

Children and other mammals nourished by maternal milk are genetically programmed to lose the lactase enzyme activity with time (2,3).  In children, the lactase activity is usually gone by age 7, whereas other mammals lose this enzyme activity in a much shorter period of time (2,3).

Lactase: If You Don’t Use It You Lose It

If there is no compelling reason to maintain gene expression for a particular enzyme, the body will divert its resources to other proteins that increase the chances for survival. This is why there is little evidence to show that Paleolithic populations had lifelong lactase activity since it gave them no evolutionary advantage (4).

With the advent of dairy farming, a change took place in the ability to produce lactase. For those that continued to keep producing the lactase enzyme, they actually had a survival advantage over those who didn’t because milk could be used as a source of nutrition in times of famine, was a secondary protein supply (5,6) and an uncontaminated source of liquid.

Today about 35% of the world’s population is lactose-persistent (meaning milk is an excellent source of nutrition for them), whereas the other 65% of the world’s population will have a difficult time consuming any dairy at all.  Considering 10,000 years virtually no one carried this gene for lactose-persistence, this is a dramatic increase. The development of lactose-tolerant individuals has become the best example of natural genetic selection in humans induced by a cultural change (7).

The Evolution of Lactose-Free Dairy Products

One of the first applications of biotechnology some 6,000 years ago was to reduce the lactose levels in dairy products.  This provided new food sources for those individuals that were still genetically lactose-intolerant.  Two of these early biotechnology products were yogurt and cheese. Yogurt was only a partial solution since the lactose concentration was still relatively high being reduced from about 5% in whole milk to about 3-4% lactose.  However for many, that reduction was enough for them to tolerate the remaining lactose.  Yogurt production uses live bacteria (i.e. probiotics) to partially reduce the lactose levels in yogurt by converting lactose into lactic acid giving yogurt its bitter taste.  On the other hand, cheese production was much more efficient in lactose removal from dairy milk. This process used rennet (a complex of enzymes isolated from the stomachs of ruminants) to digest the lactose to galactose and glucose instead of using probiotics as in yogurt production.  This is why some hard cheeses are nearly lactose-free depending on the production method and extent of aging.  Unfortunately, all cheeses are also devoid of one of the key benefits of dairy milk: complex fermentable fiber.

Benefits of Lactose Free Milk







Milk: Not Just a Source of Protein and Calcium

We still think of milk as primarily a source of protein and calcium.  However, it may be the complex oligosaccharides (polymers of sugar molecules) in dairy milk that may have generated its significant survival benefits in ancient populations who continued to carry the gene for lactose-persistence (8).  Human breast milk is the richest source of complex fermentable fibers, which determines the composition of the gut microbes in the infant (9).  The microbes in the gut that breakdown the complex oligosaccharides in human breast milk into simple sugars unique to them, would have provided a very significant evolutionary advantage for colonization over their other microbial competitors for the prime real estate in the gut.  If you are a microbe that doesn’t get fed correctly, you simply don’t survive in the gut. That dietary advantage can only be maintained if those newly established microbe colonies are being continually provided their “super-food”. Although many plants are rich in fermentable fiber, those plant oligosaccharides are simply not as complex in structure compared those found in human breast milk.  These less complex forms of fermentable fiber in plants would potentially allow for more unwanted microbial intruders to try and set up shop in the gut.  Of course, eating a fiber-poor diet like the typical Western diet or following a ketogenic diet (both virtually absent in any complex fermentable fibers) gives greater access to even less desirable microbes to potentially take up residence in the gut.

The Benefits of Milk Come From its Fermentable Fiber

Although dairy oligosaccharides are not as complex as those in human breast milk, they are far more similar to those in human breast milk than fermentable fibers from plants (10,11).  With our growing knowledge of the importance of microbial composition of gut to human health, it may be that the significant survival advantage of dairy products in lactose-persistent populations, may have much to do with their positive effects on the gut microbiota composition.  This would also explain why yogurt has more perceived health benefits than cheeses.  Although the yogurt is richer in lactose than hard cheese, yogurt is also far richer in dairy oligosaccharides than cheese. This is because the first step of cheese production (the precipitation of casein to make curds) also removes much of fermentable fiber in the milk.  So perhaps the trade-off of greater lactose levels (a problem for lactose-intolerant individuals) is outweighed by the increased retention of complex diary oligosaccharides in yogurt.  This hypothesis is reinforced by recent research that has indicated dairy oligosaccharides may be powerful agents in reducing inflammation just as are the more complex oligosaccharides in human breast milk (12,13).

The Development of Lactose-Free Dairy 

It was one of biotechnology’s first uses that gave many humans (those who maintained lactase production) a vastly improved survival advantage.  These individuals had a greater chance for survival not only because they had a more consistent and plentiful source of high quality protein, but also because they had access to complex fermentable fibers that gave them a superior advantage in gut health and overall control of inflammation.

Today modern biotechnology can take this a step further through the development of lactose-free milk.  Using a similar enzyme technology compared to cheese making, it is possible to reduce the lactose level in dairy milk to zero without losing its unique oligosaccharides.  Now you have a renewable source of high-quality protein as well as the complex oligosaccharides that significantly improve gut, and all readily available at your local grocer. In addition lactose-free milk contains readily available free galactose for easy absorption to reduce insulin resistance. Most importantly, you don’t need a have a genetic mutation (only 35% of humans do) to enjoy these benefits as long as you are consuming lactose-free dairy milk.

Omega-3s: The Missing Piece in Lactose-Free Milk

As I said earlier, human breast milk is the ultimate super-food because it supplies high-quality protein, unique fermentable fiber, and omega-3 fatty acids such as EPA and DHA. Unfortunately, lactose-free dairy milk doesn’t contain any EPA or DHA. However, those omega-3 fatty acids can easily be supplemented with your diet to increase the resolution of existing inflammation to a far greater degree than the levels of the same fatty acids found in human breast milk.  The combination of lactose-free milk plus high-dose fish oil as a dietary supplement may represent the next super-food applicable for everyone.

Interesting in Reading More: Milk and Milk Substitutes 

1. Stahel P, Kim JJ, Xiao C, and Cant JP. “Of milk the sugars, galactose, but not prebiotic galacto-oligoscaccharide, improves insulin sensitivity in male Sprague-Dawley rats.” PLoS 12: e0172260 (2017)
2. Kretchmer N. “Expression of lactase during development.” Am J Human Genet 45:487-488 (1989)
3. Murry RD, Ailaboui AH, Powers PA McClung HJ, Li Bu, Heitlinger LA, and Sloan HR. “Absorption of lactose from the colon of the newborn piglet.” Am J Physiol 261:G1-8 (1991)
4. Burger J, Kirchner M, Bramanti B, Haak W, and Thomas MG. “Absence of the lactase-persistence-associated allele in early Neolithic Europeans.” Proc Nat Acad Sci USA 104:3736-3741 (2007)
5. Gerbault P, Libert A, Itan Y, Powell A, Currat M, and Burger J. “Evolution of lactose persistence: an example of human niche construction.” Phil Trans Royal Soc B 366:863-877 (2011)
6. Itan Y, Powell A, Beaumont MA, Burger J, and Thomas MG. “The origin of lactase persistence in the Europe.” PLoS Comput Biol 5:e1000491 (2009)
7. Troelsen JT. “Adult-type hypolactasia and regulation of lactase expression.” Biochim Biophys Acta 1723:19-32 (2005)
8. Kunz C and Rudloff S. “Potential anti-inflammatory and anti-infectious effects of human milk oligosaccharides.” Adv Exp Med bio 606:455-465 (2006)
9. Blaser MJ. “The theory of disappearing microbiota and the epidemics of chronic disease.” Nat Rev 17:461-463 (2017)
10. Mehra R, Sarie D, Marotta M, Lebrille CB, Chu C, and German JB. “Novel high-molecular weight fucosylated milk oligosaccharides identified in dairy streams.” PLoS One 9:e96040 (2014)
11. Dong Z, Zhou S, and Mechef. “LC-MS/MS analysis of permethylated free oligosaccharides and N-glycans derived from human, bovine, and goal milk samples.” Electrophoresis 37: 1532-1548 (2016)
12. Boudry G, Hamilton MK, Chicholwski M, Wichramasinghe S, Barile D, Kalaneta KM, Mills DA, and Raybould HE. “Bovine milk oligosaccharides decrease gut permeability and improve inflammation and microbial dysbosis in diet-induced obese mice.” J Dairy Sci 100:2471-2481 (2017)
13. Hamilton MK, Ronveaux CC, Rust BM, Newman JW, Hawley M, Barile D, and Raybould HE. “Prebiotic milk oligosaccharides prevent the development of obese phenotype, impairment of gut permeability, and microbial dysbiosis in high-fat fed mice.” Am J Physiol Gastrointest Liver Physiol 312:G474-G487 (2017)

About Dr. Barry Sears

Dr. Barry Sears is a leading authority on the impact of the diet on hormonal response, genetic expression, and inflammation. A former research scientist at the Boston University School of Medicine and the Massachusetts Institute of Technology, Dr. Sears has dedicated his research efforts over the past 45 years to the study of lipids. He has published 40 scientific articles and holds 14 U.S. patents in the areas of intravenous drug delivery systems and hormonal regulation for the treatment of cardiovascular disease. He has also written 14 books, including the New York Times #1 best-seller, The Zone, which have sold more than 6 million copies in the U.S. and have been translated into 22 different languages.


  1. Ken Storch

    1) How about Kefir Barry?
    2) What about the association between Casein and western disease (e.g. China Study)?

  2. Anita

    If I choose to use a Soy Protein Shake base with NO flavour and/or additives (versus Whey) into which I add some berries, nut butters and Cows Milk/Coconut Milk, am I ingested a higher load of Omega 6?

    I’m not allergic to either, it’s just hard to find a Whey Protein Shake Base that has NO additives or flavourings including sugar etc.

    Thank you for your thoughts.

  3. Kimberly

    Dr. Sears, thank you for this thoughtful discussion. I have been using flax milk so I can up the berries in my smoothies. However, I feel a tinge of guilt for not using dairy since I live in Wisconsin. I think what I will try to do is use 2% organic milk for my cocoa zone shake and flax for my berry zone shake.

  4. judy

    If I am unable to drink milk, soy or nut products what would you suggest for a protein supplement. Is the whey in your protein power likely to cause allergic reactions in those who have a milk allergy? I use rice protein powder but heard it may be more likely to have heavy metals from the water in which it is grown…depending on what country grows the rice (and they don’t tell you that).

  5. Leslie C Stevens

    Several years ago I was experiencing a great deal of gastric distress. My blood was submitted for the ALCAT test process and it came back that I was highly reactive to milk proteins. Milk products were my “go to” comfort food. Since then I have avoided milk products as much as possible and a great majority of that distress went away. How common is this type of protein sensitivity? I am insulin resistant and mildly diabetic and I am looking for other sources of protein besides eggs, meats, and nuts, for snack purposes. I am also reactive to soybeans and their products. Is it time to reintroduce milk products to my diet and observe the reactions?

    • Barry Sears

      The vast majority of problems with dairy products come from the lactose content. However, about 1% of individuals have a senistivity to milk protein. You might think about trying a new type of dairy product using A2 casein instead of the A1 casein found in almost all dairy milk. These A2 products are now appearing in supermarkets. I would suggest moving to other protein sources and then after about 30 days trying some A2 milk. Unfortunately, there is no lactose-free A2 milk. If you do well on A2 milk, then try some lactose-free milk to see how you respond to it. If you do well, then you probably had developing lactose intolerance as opposed to a milk protein allergy.

      • Leslie C Stevens

        Thank you for this information. I will see if I can find any dairy products in my area using A2 casein.

  6. BJ

    There’s a reduced-carb milk produced by Fairlife. It’s 100% milk but has 13g protein and 6g carbs per cup. It’s not organic, but they have both skim and 2%, and I think it’s great for allowing one to use more berries (thus more polyphenols and fiber, plus flavor) when making a Zone shake.

    Kroger also puts out an even lower carb milk that only has 3g per cup, but they only have (that I’ve seen) a skim version that’s flavored with vanilla, and includes sweetener and stabilizer. I’m not opposed to these things, but you can’t really do anything else in terms of food preparation than to make something sweet.

    As long as the cows were not treated with antibiotics then I’m not really concerned about it being organic. Maybe the feed will affect the fatty acids in their fat, but I personally don’t like the taste of milkfat so always buy skim. I’m also not aware of any organic low-carb milks being on the market.

    • Barry Sears

      Low carb milks are intermediate between dairy products and isolated dairy protein that have no carbs. Unfortunately the processes of making isolated dairy protein can sometimes leave the isolated dairy protein with a slightly off taste. That is why they add flavoring agents to cover that off-taste.

      You are correct that using the Fairliife milk would allow you to use greater levels of berries for making a Zone shake.

      One of the benefits of organic grass-fed milk is potentially higher levels of certain isomers of conjugated linoleic acid in the milk fat. But you are drinking skim milk, then that potential benefit would not be present.

  7. Peggy MacPhee

    If I understand you correctly it is not necessary for people with adequate lactase to drink lactose-free milk? Just let it be organic? Is that correct?

  8. Denise

    I live in a rural area with a dairy farmer 10 minutes away. We currently drink whole milk from the grocery, as the heat process to reduce fat out of the milk also takes away many important nutrients. I am insulin resistant. Would it be better to drink milk from the dairy farmer?

    • Barry Sears

      The most important nutrients in milk are the protein and fermentable fiber. The heat process is only for pasteurization of the milk. The fat is removed by centrifuges operating at low temperatures. That removal of fat would not effect the levels of protein or fermentable fiber in the defatted milk. If you have a dairy farmer that close, then consider yourself lucky. However, it is likely that the only milk he can offer is whole milk. The higher levels of palmitic acid in whole milk compared to lower fat versions will likely have an adverse on insulin resistance.

  9. Jimbo

    Here I was right in the middle of a big, thick milkshake while eating a triple cheeseburger with cheese curds on the side and then I was shown this article. Boy, you sure just killed my appetite!

    Seriously, after reading this article, I was wondering if there are any benefits left when baking or cooking with milk, especially lactose-free milk.

    Also as a testimony on being in The Zone, ever since I kept a proper intake of heart-healthy oils (in this instance olive oil) with each meal I no longer have a craving for ice-cream (and I have always LOVED ice-cream in the past) and other omega-6 laden products (hard to call ice-cream a food). It’s only when I eat a meal without them that these cravings return.

    • Barry Sears

      I believe for recipes calling for milk would be best served by using lactose-free milk especially for those with lactose-intolerance.

      One of the reasons that healthy fats to decrease cravings is because they don’t cause inflammation in the hypothalamus. Once you have inflammation in the hypothalamus, you lose significant control over satiety signals.

  10. madeleine laffont

    There’s a lot of talk about milk being inflammatory: its designed to make babies grow. continuing to ingest growth promiting milk past childhood is therefore asking for trouble in that it may stimulate growth where you don’t want it? (I have thyroid nodules which I have checked every 6 months. Ive been on the zone for six months and not only have I lost weight and increased my energy levels – but my nodules have shrunk – although not statistically significantly). I’m thinking about cutting out all things dairy for the reasons above – do you have thoughts?

    • Barry Sears

      Most would assume that human breast milk is the ideal “super-food”. There is no indication that human breast milk is pro-inflammatory. Thus much of the discussions about milk protein being pro-inflammatory most be taken with a grain of salt. As in human breast milk, dairy milk is an excellent source of essential amino acids that are necessary for growth. In particular, it is the amino acid leucine that stimulates the growth factor known as mTOR necessary for muscle growth. mTOR can also play in role in tumor growth. That fact is counter-balanced by the need for continued muscle stimulation to maintain muscle mass to prevent sacropenia as we age. Sacropenia is a primary cause of frailty. In fact, our needs for protein to maintain muscle mass in the elderly are significantly greater than they are for young adults. What I would suggest to be an reasonable approach to ensure adequate intake of protein balanced with large amounts of polyphenols coming from non-starchy vegetables and fruits as the polyphenols will stimulate the production of AMP kinase that inhibits mTOR activity. This is one the foundations of the Zone Diet. This way you maintain your muscle mass as you age without concern about potentially stimulating growth in abnormal locations in the body like thyroid nodules. However, the best way to prevent abnormal growth is the increase the strength of the resolution response in the immune system and that can only be accomplished if you have adequate levels of EPA and DHA on a daily basis.

  11. John D Pilla

    What about the very helpful, nutritious, and beneficial whole raw milk,? Also you assume evolutin is a fact, it was only a theory, never proven, and too many holes to make it viable!

    • Barry Sears

      All theories simply help explain the world around us. It takes only one example of a theory not working to force us to find new theories that better explain observations. This is why quantum physics theory was developed to explain some of the problems in Newtonian theory of physics. Likewise evolutionary theory is also constantly evolving.

      The two problems with whole fat raw milk is the high saturated fat content and the potential for bacterial growth as it provides an excellent nutrient source for microbes. Unfortunately most of Americans live a considerable distance from dairy farmers so that the potential bacterial growth is a great concern in my opinion.

  12. Lee Stern

    I have been following the Zone Diet since you first published The Zone.

    My question has to do with pasteurized of milk versus raw milk. I have read that by pasteurizing milk (heat treating it) it harms or changes the shape of the milk proteins and this may be harmful. This is even more true of organic milk which is treated at higher temperatures. Should we be trying to find raw mil instead?

    Thanks for any thoughts on this subject.

    • Barry Sears

      Microbial contamination is the greatest potential problem with raw whole milk as well as it higher saturated fat content that can be pro-inflammatory. The scientific data for the benefits of raw milk compared to pasteurized milk is not compelling. This is coupled with the fact that most of the population country is a considerable distance from site of actual dairy production. Since whole raw milk provides an excellent nutrient environment for microbial growth, I would still stick to pasteurized milk. In my opinion, organic, pasteurized 2% lactose-free milk will provide the best taste and performance with the least potential for microbial contamination.

    • Jimbo

      If I’m correct, the high temp. organic milk you are talking about is UHT (Ultra High Temperature) milk or ultra-pasteurized milk. While a very large percentage of organic milk is produced in this manner (unless you live in a rural area) you can find regular pasteurized organic milk if you check around for it. Try at a local health/natural food store or search online. I worked at a chain grocer that carried it in their natural food section (select stores). It is the bane of retailers because it has the same shelf life of conventional milk (or less) but with much lower sales, hence more discarding and lower profits. This is probably one of the main reason why UHT and ultra-pasteurized organic milk (with its much longer shelf life) is the only type found among most grocers today.

  13. Bob K

    A lot of people have switched to Almond or Soy milk products. Are these valid replacements for whole milk products?

    • Barry Sears

      Both almond and soy milks are lower in saturated fats and are lactose-free compared to whole milk, they have other problems. First, almond milk is virtually devoid of protein. Although soy milk is slightly higher in protein than is almond milk, it is still less than dairy milk. Soy milk also contains isoflavones that can bind to thyroid hormone receptors and is richer in omega-6 fats compared to dairy milk as well as having a “beany” taste. I believe that organic 2% lactose-free dairy milk is the best overall compromise for taste and performance.


Leave a Reply

Your email address will not be published. Required fields are marked *