Your Personal Paleo Code: The 3-Step Plan to Lose Weight, Reverse Disease, and Stay Fit and Healthy for Life (18 page)

Dairy often gets a bad rap in the health and nutrition world. It’s been maligned by some for its high saturated fat content and condemned by others as unfit for human consumption. Let’s take a closer look at each of these criticisms.

In the conventional nutrition world, dairy is recognized as an important part of a healthy, well-balanced diet because it’s a good source of protein, calcium, and added nutrients like vitamins A and D. However, dairy fat is typically portrayed as being harmful, mostly due to its saturated fat and cholesterol. Mainstream organizations like the American Heart Association and the American Diabetes Association recommend using nonfat, low-fat, or reduced-fat dairy products and have steered consumers away from full-fat or whole dairy for the most part. But does the evidence support this recommendation?

A 2012 paper published in the
European Journal of Clinical Nutrition
reviewed sixteen studies examining the relationship between high-fat dairy intake, obesity, and cardiovascular and metabolic disease. In the majority of studies reviewed, high-fat dairy intake was either inversely associated with obesity and metabolic disease (meaning that those who ate the most high-fat dairy foods had the lowest risk for these conditions) or not associated with them at all.

Some compounds in high-fat dairy products—such as butyrate, phytanic acid, trans palmitoleic acid, and conjugated linoleic acid—have been shown to have beneficial effects. Butyrate provides energy to the cells lining the colon, inhibits inflammation in the gastrointestinal tract, and may prevent colonic bacteria from entering the bloodstream. In fact, butyrate’s anti-inflammatory effect is so strong that a dose of four grams per day for eight weeks induced complete remission in a group of Crohn’s disease patients. Phytanic acid, one of the fatty acids in dairy fat, has been shown to reduce triglycerides, improve insulin sensitivity, and improve blood-sugar regulation in animal models. In a study of 2,600 U.S. adults, another fatty acid in dairy fat, trans palmitoleic acid, was found to be associated with lower triglycerides, lower fasting insulin, lower blood pressure, and a lower risk of diabetes. Finally, conjugated linoleic acid (CLA), a natural trans fat found in dairy products, may reduce the risk of heart disease, cancer, and diabetes.

Dairy is also a good source of fat-soluble vitamins like retinol (active vitamin A) and vitamin K
₂
, which are difficult to obtain elsewhere in the diet.

One of the main arguments against dairy, advanced by vegans, raw-foodists, and even advocates of the Paleo diet, is that dairy isn’t an appropriate food for humans. They support this argument by pointing out that most humans don’t produce lactase after childhood and that no mammals other than humans consume the milk of other animals.

These may seem like compelling arguments on the surface, but they don’t hold up under scrutiny. As I mentioned in
chapter 1
, human evolution didn’t stop in the Paleolithic era. While it’s true that most of our genes are the same as they were hundreds of thousands of years ago, some of them have adapted in a relatively short time. Lactase persistence is perhaps the best example of this. Our hunter-gatherer ancestors were breast-fed until around age four. Mother’s milk was virtually the only food they consumed that contained lactose, or milk sugar, and there was
no need for the body to continue producing lactase (the enzyme that digests lactose) after early childhood. But when humans began consuming cow’s milk, natural selection went to work, and about eight thousand years ago, a genetic mutation that continued the production of lactase into adulthood began spreading through the population. Now a third of the world’s population produces lactase into adulthood (and that figure approaches 100 percent in some parts of Northern Europe).

Humans have also developed technology that addresses some of the potential disadvantages of dairy consumption. For example, fermentation of milk into yogurt and kefir can reduce the lactose content to less than 1 percent—an amount that even someone who doesn’t produce lactase should be able to tolerate. Some studies have even shown that consuming fermented dairy products like yogurt may reverse lactose tolerance by increasing levels of lactose-digesting bacteria in the gut.

What about the idea that humans shouldn’t drink milk because no other animal drinks the milk of another animal? By this logic, we humans should also avoid cooking our food and drinking coffee and alcohol. I don’t know of any other animals doing these things, but that alone is not a sufficient reason for us
not
to do them. We’ve developed both technological methods and genetic adaptations that enable us to enjoy and benefit from dairy products; other animals don’t have these options, so comparing ourselves to them in this case doesn’t make sense.

All of this being said, there’s no doubt that dairy doesn’t work for everyone. Some people are allergic or intolerant to casein, a protein in dairy, or are highly sensitive to lactose. In these cases, dairy must be strictly avoided or additional steps must be taken to make it tolerable. Since there’s still no gold-standard test for dairy intolerance, I recommend removing it from your diet during the Step 1 Thirty-Day Reset, and reintroducing it in Step 2. See
chapter 11
for guidelines on how to properly reintroduce dairy products.

Notes for this chapter may be found at ChrisKresser.com/ppcnotes/#ch9.

Digestive problems have reached epidemic levels in the United States. Consider the following:

Perhaps by now you’ve been on the Step 1 Reset Diet long enough to note that your gut is feeling better than it ever has, or maybe you’re still tweaking here and there (with further tweaks to come later) and you’re getting there. The point is that our Paleo ancestors—with their
nourishing traditional diets of real foods—probably didn’t walk around with heartburn. In our modern world, however, it’s a different story. Achieving good gut health is a major part of improving your overall health through your Personal Paleo Code, because gut problems don’t affect only the gut.

We now know that the health of the digestive tract is critical to overall health and that an unhealthy gut may contribute to a wide range of diseases, including diabetes, obesity, rheumatoid arthritis, autism spectrum disorder, depression, and chronic fatigue syndrome. The gut has a distinct nervous system of its own; some researchers even refer to the gut as the second brain, because of its size, complexity, and similarity—in terms of neurotransmitters and signaling molecules—to the brain. And recent studies suggest that approximately 70 to 80 percent of the body’s immune cells are in the gut.

Because of this, many researchers and clinicians (myself included) believe that supporting intestinal health will be one of the most important goals of medicine in the twenty-first century. There are two closely related variables that determine gut health: the intestinal microbiota (or gut flora) and the gut barrier. Let’s discuss each of them in turn.

The gut contains over 100,000,000,000,000 (one hundred trillion!) microorganisms from a thousand different species; there are ten times more microbes in the human body than there are human cells, and together, those microbes have one hundred times more genes than the human genome does. It’s not inaccurate, then, to say that at a cellular level, we’re more microbe than human. Indeed, according to Stanford microbiologist Justin Sonnenburg, “Humans can be regarded as elaborate vessels evolved to permit the survival and propagation of microorganisms.” A hundred trillion microorganisms hitching a ride in your gut may sound like something from a creepy science fiction movie, but it turns out that these passengers are crucial to your health. Among other things, the gut microbiota promotes normal gastrointestinal function, provides protection from infection, regulates metabolism, and is home to the majority
of immune cells. And when the gut microbiota is out of balance, you get sick. Changes to the gut microbiota have been linked to diseases ranging from autism and depression to autoimmune conditions like Hashimoto’s, inflammatory bowel disease, and type 1 diabetes.

The colonization of the gut by bacteria begins at birth. While the gut of an unborn baby is exposed to some microbes in the womb (via ingestion of amniotic fluid), the vast majority of an infant’s gut microbiota is acquired when it passes through the birth canal and swallows the mother’s native bacteria. This explains why the method of delivery—vaginal birth or cesarean section—influences how the gut microbiota initially develop. In a vaginal birth, the baby is first exposed to bacteria in the birth canal; in a cesarean, the baby is first exposed to bacteria somewhere in the hospital. Some research suggests that the location of this initial exposure to bacteria affects the composition of the infant’s gut microbiota for months or even years. Other studies indicate that children born via cesarean are at greater risk of asthma, obesity, and type 1 diabetes later in life.

The baby’s diet (and perhaps, to a lesser degree, the mother’s diet) also has a strong influence on the composition of the gut flora. Babies that are exclusively formula-fed have significant differences in gut microbiota when compared to babies that are exclusively, or even partially, breast-fed. This is important, because pioneer bacteria (the first bacteria to colonize the gut) can alter gene expression to create a more favorable environment for themselves and a less favorable environment for later (and perhaps more beneficial) bacteria.

Diet has a major influence on the composition of the gut microbiota later in childhood and into adulthood as well. The amount, type, and balance of proteins, fats, and carbohydrates, as well as the amount and type of fiber, have a large impact on the gut microbiota. For example, foods that are rich in soluble fiber, such as certain fruits, vegetables, and starchy tubers (like sweet potatoes and potatoes) increase levels of lactobacilli, a class of bacteria often used in probiotics because of their
beneficial effects on the gut. (Probiotics are good bacteria that help regulate the balance of gut microbiota.)

Other factors that can negatively influence the gut microbiota at all ages include:

The main functions of the gut microbiota can be broken down into three categories: metabolic, structural, and protective.

The metabolic activity of the gut microbiota is so diverse and important that some researchers refer to it as an organ within an organ. Bacteria in the gut break down dietary compounds that might otherwise cause cancer; they synthesize vitamins like biotin, folate, and vitamin K; they convert nondigestible carbohydrates to short-chain fatty acids, which provide energy and benefit the cells lining the gut; and they help with the absorption of minerals like calcium, magnesium, and iron.

Recent research has revealed a relationship between gut microbes and how we process and store the food we eat. Microbes help us to break down long-chain carbohydrates such as fiber and starch that we can’t absorb on our own. During this process, the microbes produce short-chain fatty acids, including acetate, propionate, and butyrate. As I mentioned earlier, butyrate has several beneficial health effects.

The short-chain fatty acids produced by fermentation (the breaking down of a substance by bacteria or other microorganisms—in this case, by gut microbiota) of carbohydrates have other important effects. For example, they stimulate the growth and differentiation of epithelial cells
(the cells that form the inner lining of the colon). Butyrate also inhibits cell proliferation in the colon, which can lead to colon cancer.

The gut is first and foremost a barrier designed to keep certain things (like pathogens and toxins) out, and let other things (like beneficial nutrients) in. The mucosal lining of the intestine is the primary interface between the external environment and our immune system. Some might assume that the skin plays a more important role in this respect, given its continual exposure to the environment. But the surface area of the gut is approximately one hundred times larger than that of the skin, and the gut contains around 70 to 80 percent of the immune cells in the body. These immune cells form a layer of tissue called the gut-associated lymphoid tissue, or GALT.

Studies have shown that the microbial composition of the gut affects the composition and function of the GALT. It’s also true that bacteria in the gut form a crucial line of resistance to invasion by pathogenic microbes. Germ-free mice that have been bred to have sterile guts (with no microbes at all) are highly susceptible to infection, and antibiotics can disrupt the delicate balance of gut microbes and allow overgrowth of pathogenic species like
Clostridium difficile
.

Think of the gut as a hollow tube that passes from the mouth to the anus. Anything that goes into the mouth and is not absorbed into the bloodstream will be eliminated as waste and will never enter the body. The gut barrier thus serves as a gatekeeper that decides what gets into our body and what stays out.

Normally, this process works very well. However, when the intestinal barrier becomes permeable (that is, leaky), substances that should not escape the gut—such as large, undigested protein molecules and bacterial toxins—pass into the bloodstream. This triggers an immune reaction, since these particles are viewed as foreign invaders by the body. And
we now know that this immune reaction, resulting from intestinal permeability, contributes to everything from autoimmune disease to depression to obesity to skin disease. In fact, some researchers, such as Dr. Alessio Fasano (a pioneer in the study of celiac disease and gluten intolerance), now believe that intestinal permeability is a
precondition
to developing autoimmunity. In other words, it may not even be possible to develop an autoimmune disease unless you have a leaky gut first.

The term
leaky gut
used to be consigned to the outer fringes of medicine, and conventional researchers and doctors originally scoffed at the concept. Yet today it’s one of the hottest topics in the scientific literature. Researchers have identified a protein called zonulin that increases intestinal permeability in humans and other animals. Many, if not most, autoimmune diseases—including celiac disease, type 1 diabetes, multiple sclerosis, rheumatoid arthritis, and inflammatory bowel disease—are characterized by abnormally high levels of zonulin and a permeable gut barrier. In fact, researchers have found that they can induce type 1 diabetes almost immediately in an animal by exposing it to zonulin. It develops a leaky gut and begins producing antibodies to islet cells, which are responsible for making insulin.

As you can see, a leaky gut causes an immune reaction that affects not only the gut but also other organs and tissues, including the skeletal system, the pancreas, the kidney, the liver, and the brain. This explains why a person who has a leaky gut doesn’t always have gut symptoms, and why the range of symptoms people experience are so diverse. These include (but are not limited to):

Here are several factors that can damage gut-barrier integrity and make it permeable.

Gliadin is a protein found in wheat that’s responsible for the intestinal damage observed in celiac disease. In people with celiac disease (and perhaps in those without it), gliadin activates zonulin signaling, which in turn reduces intestinal barrier integrity and permits the passage of gliadin through the gut barrier. In these cases, wheat and other gluten-containing foods directly contribute to intestinal permeability. This is one reason I recommend that most people do not regularly consume wheat, even if they don’t have gluten intolerance or celiac disease.

Diet can also have an indirect effect on gut-barrier integrity via its impact on the gut microbiota. The standard American diet—which is high in refined flours and sugars and industrial seed oils and low in whole fruits, vegetables, and soluble fiber—has been shown to cause undesirable changes in the gut microbiota. These changes to the microbiota make the gut barrier permeable and may increase the risk of autoimmune disease and other problems associated with a leaky gut. By contrast, traditional diets rich in fruits, vegetables, and soluble fibers and with very little processed, modern food cause beneficial changes in the gut microbiota that preserve barrier integrity and improve overall health.

Small intestinal bacterial overgrowth, or SIBO, is a condition involving inappropriate growth of bacteria in the small intestine. The large
majority of the bacteria in the gut should inhabit the colon. However, chronic stress, poor diet, infection, antibiotic use, and other factors can cause bacteria to migrate from the colon into the small intestine. This causes malabsorption of proteins, fats, B vitamins, and other micronutrients. It also causes intestinal permeability.

Chronic stress has been shown to reduce gut-barrier integrity in both human and animal studies.

Infection with bacteria (such as
H. pylori,
the bacteria that causes stomach ulcers), viruses (such as HIV), or parasites (such as
Giardia lamblia
) have all been shown to disrupt intestinal-barrier integrity.

Excess alcohol can promote the growth of certain types of bacteria in the gut that in turn increase intestinal permeability.

NSAIDs, aspirin, proton-pump inhibitors (PPIs, prescribed for acid reflux), and several other medications increase gut-barrier permeability. Antibiotics may indirectly disrupt gut-barrier function via their adverse effects on the gut microbiota.