Tag Archives: immune system

Oyters on Grill |The Paleo Diet

Zinc! It’s the essential mineral that’s praised by many advocates involved in the Paleo community. Most people generally recognize zinc for its reputation as a potent cold and flu virus prevention solution, but its numerous benefits also extend beyond its role as an immunity-boosting mineral.

Ensuring adequate zinc intake in one’s diet is absolutely necessary for achieving long term health goals while following an ancestral eating plan. Zinc is essential for maintaining numerous physiological functions within the human body including tissue and epithelial integrity, immune system regulation, cellular growth, gut health, and inflammation suppression. The current USA government’s recommended daily allowance (RDA) for zinc averages in at approximately 10 mg. The USA RDA for zinc might be adequate for maintaining proper zinc levels for most healthy human beings that do not suffer from a zinc deficiency, but higher short-term dosages are likely needed to correct a deficiency. Physical indications of zinc deficiency include but are not limited to frequent viral infections, white spots or streaks on the fingernails, poor physical growth in childhood, hair loss, impaired vision, diarrhea, acne, dandruff, chronic dry skin, and impaired mental functioning (i.e. depression, anxiety, brain fog). It’s worth noting that all of the listed conditions can also result from the manifestation of other nutrient and mineral imbalances, and ensuring a highly varied nutrient rich ancestral diet that is rich in omega-3’s is crucial to preventing and resolving any of the aforementioned health issues.

Zinc in excess can be equally problematic as zinc deficiency. The daily upper limit threshold for zinc in healthy individuals is about 40 mg for adults over 19 and 25mg for those under 19. Excessive zinc consumption is characterized by severe headaches, nausea, vomiting, and decreased appetite. Over the long term, excessive zinc intake in the absence of copper will result in the gradual depletion of copper from the human body. For this reason it is recommended that those looking to supplement zinc in their diets should avoid zinc dietary supplements and instead opt for “au-naturel” food-based sources of zinc that are inherently proportionately balanced with copper.

Those looking to ensure optimum zinc intake in their diet must decide whether to source their zinc from animal sources or plant sources. Below are two tables demonstrating a handful of the highest ranking sources of zinc from both plants and animals. The zinc content of each source is listed in mg. Note that many of the listed zinc-rich plant foods do not adhere to the Paleo lifestyle.

Zinc Sources Table | The Paleo Diet

When examining the table above, it becomes obvious that ratio of zinc in animal-based foods is significantly higher than the ratio of zinc found in plant-based foods. Additionally, all of the animal-based sources of zinc naturally have appropriate zinc to copper ratios, so you don’t have to worry about creating a mineral imbalance while consuming these foods.

Now you might be wondering if it is still worth considering plant-based sources of zinc in your diet. From the tables above, it is immediately apparent that one would have to consume much higher quantities of zinc-containing plant foods to achieve the same proportion of zinc found in the animal foods listed above. Besides pumpkin seeds and sunflower seeds, all of the other listed plant-based zinc sources are off limits for Paleo followers. Additionally, it is worth mentioning that many of the zinc-rich plant foods such as legumes, seeds, nuts, and grains contain phytates (i.e. phytic acid). Phytates have been demonstrated to bind to zinc and other important dietary minerals such as iron and manganese. The bonding of phytates with zinc and other minerals upon digestion drastically reduces your body’s ability to absorb these key minerals, thus making you more prone to mineral deficiencies. Animal foods do not inhibit the absorption of zinc or other minerals and instead aid in absorption during digestion.

Oysters rank supreme amongst all other zinc containing food sources available for human consumption, and thus are ideal for treating individuals with zinc deficiency, and for those simply looking to incorporate zinc-rich food sources into their diets.

Oysters have long been revered for their rich taste and nutritional qualities across all parts of the globe. Preference for oyster consumption has shown up in historical documentation dating back to the ancient Greeks and Chinese. In fact, in Europe up until the 18th century oysters were considered a “luxury” food only reserved for the highest classes. Within the colonies of North America, oyster consumption was never restricted to the rich and thus most colonists and Native Americans consumed oysters regularly. The 19th century in The United States was marked by the widespread establishment of “oyster bars” that originated on the eastern seaboard and quickly became popular throughout the west. By 1881 there were nearly 379 oyster bars in Philadelphia alone! Zinc deficiency was likely not a major problem for oyster-loving 19th century Americans.

Nowadays oysters are becoming an increasingly obsolete food source. Oysters can be difficult to source fresh, especially if you are like myself and live thousands of miles inland from the nearest ocean. The best economical solution for inlanders is to purchase canned oysters from your local grocery store. A large majority of the oysters on store shelves are canned in cottonseed oil, which you will definitely want to avoid if you are sticking to a Paleo eating plan. Fortunately, Crown Prince offers a line of smoked oysters that are canned in extra-virgin olive oil. I have seen these oysters available in Sprouts, Whole Foods, and Trader Joe’s for about $2 – $3 per can. If you are not quite adjusted to the “delicious” taste of oysters yet, try topping them with a few drops of Paleo-friendly hot sauce.


1. Berger, Abi. “What does zinc do?.” BMJ 325.7372 (2002): 1062.
2. Hambidge, M. (2000). Human zinc deficiency. The Journal of nutrition,130(5), 1344S-1349S.
3. Lönnerdal, B. O. (2000). Dietary factors influencing zinc absorption. The Journal of nutrition, 130(5), 1378S-1383S.
4. Ma, J., & Betts, N. M. (2000). Zinc and copper intakes and their major food sources for older adults in the 1994–96 continuing survey of food intakes by individuals (CSFII). The Journal of nutrition, 130(11), 2838-2843.
5. Office of Dietary Supplements – Zinc. (n.d.). Retrieved December 28, 2015, from https://ods.od.nih.gov/factsheets/Zinc-HealthProfessional/

The Wheat Series Part 1: Wheat and the Immune System | The Paleo Diet

With a rapidly growing body of nutrition science covering everything from dietary proteins, to microflora composition, to caloric expenditure and cell bioenergetics, it’s surprising that still one of the hardest arguments to counter remains “I’ve always eaten it and I’m fine.” It’s a point my 97 year old grandmother likes to make every time she asks me about my research.

Let me tell you, arguing with a 97 year old about health is not easy.

The epidemiological version of the “I’m fine” argument is an assertion we hear a lot: while evidence exists that people with celiac disease cannot eat wheat, there is no proof that consuming a gluten-free diet will benefit the rest of the population.1, 2

Celiac sufferers can’t eat wheat. We know that. But it certainly appears that most people can have their bagel, get on with their days, and be just fine. Even live to see a century.

The “I’m fine” argument certainly appears to hold up on the surface. The underlying danger, however, is that the term “fine” is so remarkably subjective.

Take the case of tennis player Novak Djokovic. He went gluten-free in 2011 and then proceeded to have the most successful season in tennis history reaching number one in the process. He was certainly fine when he was eating wheat. He was just better without it.

So let’s take the subjectivity out of fine. Since we define a Paleo Diet as eating what we were designed to eat, perhaps a Paleo way of defining “fine” is functioning the way we were designed to function.

Looked at this way, there is in fact a great deal of research showing the various ways in which wheat causes our bodies to function abnormally. A select unfortunate few, such as celiacs and diabetics, may take the brunt of it, but none of us function normally eating wheat. None of us are fine.

This article is the first part in our wheat series summarizing current research on wheat and the immune system. The next few pieces will detail how wheat causes our bodies to stop functioning the way they were designed to function and can, ultimately, lead to disease. But to understand the damage, let’s start by examining what our digestive immune system looks like when it’s functioning just fine.

The Fine-Functioning Gut

Our digestive immune system is one of the most complex and robust systems in our bodies. Some 50×109 immune cells reside in the gut-associated lymphoid tissue (GALT) which makes up the bulk of our immune cells.3

But why are there so many immune cells in the gut? Because, as the image below shows, the gut is an area of constant stress. The digestive tract is continually bombarded by bacteria, food particles, and pathogens.4,5

The Wheat Series Part 1: I’ve Always Eaten It and I’m Fine… Right? | The Paleo Diet

MacDonald, T.T. and G. Monteleone, Immunity, inflammation, and allergy in the gut. Science, 2005. 307(5717): p. 1920-1925.

This image is actually a highly simplified version of what goes on in the GALT. The reality is a complex mix of T Cells, monocytes, cytokines, chemokines, interleukins, adhesion molecules, and intricate processes that would have you running for a book on brain surgery to give yourself some light reading.

Don’t worry, we’re not going to cover all that.

We’re just going to focus on a few key concepts that will hopefully prove to be fascinating. But to do that we need to introduce just a few of the important players in the gut:

First is a row of tightly packed cells that keep the contents of the digestive tract from getting into the body. It is our first line of defense and normally very effective at keeping things out.6,7Leaky gut” is just a term we use for when this barrier breaks down.

Next in our line of defense are antigen presenting cells (APCs.) They are the macrophages, dendritic, and plasma cells in the image above. These cells “sample” all the food particles, bacteria, and pathogens in the gut and present them to the immune system.

The final players you need to know for this article are T Cells. They are the generals of the immune system. Antigens are presented to the T Cells and then they decide how to respond.

It’s All About Bacteria

Generally when we think about what our immune system deals with, we think about viruses and pathogens and all those nasty things on airplanes and in our kid’s kindergarten classes.

But the truth is, dealing with a pathogen is a rare thing for our digestive immune system. Most of its energy is spent managing our microflora – those beneficial bacteria we pop probiotics and eat yoghurt to encourage. We need them for our health. We just also need them to stay in our gut because they aren’t so beneficial inside our bodies.8,9,10,11

If you’re wondering how big a role these bacteria play, remember there are more cells in our microflora than cells in our own bodies.

They are so important in fact that several researchers proposed that our digestive immune system evolved not because of pathogens but to allow us to live in harmony with our microflora.5,9,11,12

This is a critical distinction!

If a pathogen or even the normally healthy bacteria in our gut gets into our blood, our bodies mount an immediate and strong inflammatory response.13,14 This inflammation is what causes the aches, fever, and chill we associated with being sick.

The response to a bacterial infection in circulation, though damaging, is necessary and keeps us alive. Fortunately, bacteria rarely gets into our blood.

In the gut, on the other hand, the immune system is exposed to bacteria thousands of times each day. An inflammatory response every time would be deadly.5, 15 There’s even a name for this out of control inflammation – sepsis.16

As a result, the digestive immune system takes a very different tact with our beneficial bacteria. It becomes anergic – meaning it actually blocks inflammation.17,18 Special immune cells in the gut called T regulatory (Treg) cells and a unique type of APC cell actively shut down the inflammatory response and then quietly take out the invading bacteria one-by-one.3,15

The Wheat Series Part 1: I’ve Always Eaten It and I’m Fine… Right? | The Paleo Diet

Zeng, H. and H. Chi, Metabolic control of regulatory T cell development and function. Trends in Immunology. 36(1): p. 3-12.

We All Get Inflamed Sometimes

As effective as this system is, bacteria still periodically get the upper hand and an inflammatory response in the gut becomes a necessary evil.

Several things happen. First, gut APCs lose their anergy.20, 21  Second, naturally inflammatory immune cells from the blood are recruited to the gut.5,22 Finally, the Treg cells that are so effective at keeping inflammation down give way to a unique T cell called Th17 cells.

Th17 cells are powerful immune cells believed to have a single purpose – control bacterial infections.8,11,23 They are highly effective at killing bacteria, but they can also be very damaging to our own bodies. It’s the price we pay to manage our microflora, but not one we want to pay often.9,10

Ultimately, the gut remains fine as long as the inflammation ramps up quickly, kills the infection, and then backs down.

The following diagram shows this shift in Treg/Th17 balance during infection:

The Wheat Series Part 1: I’ve Always Eaten It and I’m Fine… Right? | The Paleo Diet

Arrieta, M.-C. and B.B. Finlay, The commensal microbiota drives immune homeostasis. Frontiers in Immunology, 2012. 3

When It Stops Being Fine

Problems arise when the bacterial infestation becomes overwhelming or when the inflammation simply doesn’t go away.5,8

As the inflammation continues, the imbalance between anti-inflammatory Treg cells and inflammatory Th17 cells builds on itself until finally the Tregs can’t control the Th17 cells anymore.24,25,26,27

The Wheat Series Part 1: I’ve Always Eaten It and I’m Fine… Right? | The Paleo Diet

Ohnmacht, C., et al., Intestinal microbiota, evolution of the immune system and the bad reputation of pro-inflammatory immunity. Cell Microbiol, 2011. 13(5): p. 653-9.

No longer protective, Th17 cells can then enter other parts of the bodies and contribute to a variety of chronic diseases.28,29 such as asthma,30 heart disease,31, 32 and most autoimmune conditions28,33 including celiac disease,34,35 type I diabetes,36,37 Crohn’s disease,38,39 rheumatoid arthritis,29,40 and multiple sclerosis.41

The Three Pathways to a Not Fine Gut

This highly pathogenic Th17 imbalance is a result of an abnormally functioning digestive immune system. Three things are known to cause it:

  1. Increased intestinal permeability (leaky gut)
  2. Chronic or two high a bacterial load
  3. Food particles that can hurt immune function

So now that you’ve plowed through all of that only-interesting-to-people-like-me immune function information, here’s the really fascinating point:

Wheat is the only food we’re aware of that causes all three.

In the remaining articles in this series, I will share with you the surprisingly large number of ways in which wheat breaks down the normal intestinal immune system and leads to damaging Th17 development.42, 43

More importantly, I will show you that it happens in everyone. In other words, a normally healthy gut exposed to wheat isn’t fine in anyone. Stay tuned!

Read The Wheat Series Part 2: Opening the Barrier to Poor Gut Health HERE

Trevor Connor

Trevor Connor | The Paleo DietTrevor Connor is Dr. Cordain’s last mentored graduate student and will complete his M.S. in HES and Nutrition from the Colorado State University this year and later enter the Ph.D. program. Connor was the Principle Investigator in a large case study, approximately 100 subjects, in which he and Dr. Cordain examined autoimmune patients following The Paleo Diet or Paleo-like diets.



[1]Ferch, C.C. and W.D. Chey, Irritable Bowel Syndrome and Gluten Sensitivity Without Celiac Disease: Separating the Wheat From the Chaff. Gastroenterology, 2012. 142(3): p. 664-666.

[2]Gaesser, G.A. and S.S. Angadi, Gluten-Free Diet: Imprudent Dietary Advice for the General Population? Journal of the Academy of Nutrition and Dietetics, 2012. 112(9): p. 1330-1333.

[3]du Pre, M.F. and J.N. Samsom, Adaptive T-cell responses regulating oral tolerance to protein antigen. Allergy, 2011. 66(4): p. 478-90.
[4]MacDonald, T.T. and G. Monteleone, Immunity, inflammation, and allergy in the gut. Science, 2005. 307(5717): p. 1920-1925.

[5]Smith, P.D., et al., Intestinal macrophages and response to microbial encroachment. Mucosal Immunol, 2011. 4(1): p. 31-42.

[6]Visser, J., et al., Tight junctions, intestinal permeability, and autoimmunity: celiac disease and type 1 diabetes paradigms. Ann N Y Acad Sci, 2009. 1165: p. 195-205.

[7]Yu, Q.H. and Q. Yang, Diversity of tight junctions (TJs) between gastrointestinal epithelial cells and their function in maintaining the mucosal barrier. Cell Biol Int, 2009. 33(1): p. 78-82.

[8]Ohnmacht, C., et al., Intestinal microbiota, evolution of the immune system and the bad reputation of pro-inflammatory immunity. Cell Microbiol, 2011. 13(5): p. 653-9.

[9]McFall-Ngai, M., Adaptive immunity: care for the community. Nature, 2007. 445(7124): p. 153.

[10]Ivanov, II, et al., Induction of intestinal Th17 cells by segmented filamentous bacteria. Cell, 2009. 139(3): p. 485-98.

[11]Cao, A.T., et al., Th17 cells upregulate polymeric Ig receptor and intestinal IgA and contribute to intestinal homeostasis. J Immunol, 2012. 189(9): p. 4666-73.

[12]Arrieta, M.-C. and B.B. Finlay, The commensal microbiota drives immune homeostasis. Frontiers in Immunology, 2012. 3.

[13]Koj, A., Initiation of acute phase response and synthesis of cytokines. Biochim Biophys Acta, 1996. 1317(2): p. 84-94.

[14]Ohl, M.E. and S.I. Miller, Salmonella: a model for bacterial pathogenesis. Annu Rev Med, 2001. 52: p. 259-74.

[15]Smythies, L.E., et al., Human intestinal macrophages display profound inflammatory anergy despite avid phagocytic and bacteriocidal activity. J Clin Invest, 2005. 115(1): p. 66-75.

[16]Bone, R.C., et al., DEfinitions for sepsis and organ failure and guidelines for the use of innovative therapies in sepsis. the accp/sccm consensus conference committee. american college of chest physicians/society of critical care medicine. Chest, 1992. 101(6): p. 1644-1655.

[17]Kamada, N., et al., Unique CD14 intestinal macrophages contribute to the pathogenesis of Crohn disease via IL-23/IFN-gamma axis. J Clin Invest, 2008. 118(6): p. 2269-80.

[18]Nagler-Anderson, C., Tolerance and immunity in the intestinal immune system. Critical Reviews in Immunology, 2000. 20(2): p. 103-120.

[19]Zeng, H. and H. Chi, Metabolic control of regulatory T cell development and function. Trends in Immunology. 36(1): p. 3-12.

[20]Williamson, E., G.M. Westrich, and J.L. Viney, Modulating dendritic cells to optimize mucosal immunization protocols. J Immunol, 1999. 163(7): p. 3668-75.

[21]Burcelin, R., L. Garidou, and C. Pomie, Immuno-microbiota cross and talk: the new paradigm of metabolic diseases. Semin Immunol, 2012. 24(1): p. 67-74.

[22]Yamazaki, K., J.A. Murray, and H. Kita, Innate immunomodulatory effects of cereal grains through induction of IL-10. J Allergy Clin Immunol, 2008. 121(1): p. 172-178 e3.

[23]Reynolds, J.M., et al., Cutting edge: regulation of intestinal inflammation and barrier function by IL-17C. J Immunol, 2012. 189(9): p. 4226-30.

[24]Zhou, X., et al., Instability of the transcription factor Foxp3 leads to the generation of pathogenic memory T cells in vivo. Nat Immunol, 2009. 10(9): p. 1000-7.

[25]Scalapino, K.J. and D.I. Daikh, CTLA-4: a key regulatory point in the control of autoimmune disease. Immunol Rev, 2008. 223: p. 143-55.

[26]Ejsing-Duun, M., et al., Dietary gluten reduces the number of intestinal regulatory T cells in mice. Scand J Immunol, 2008. 67(6): p. 553-9.

[27]Lochner, M., et al., In vivo equilibrium of proinflammatory IL-17+ and regulatory IL-10+ Foxp3+ RORgamma t+ T cells. J Exp Med, 2008. 205(6): p. 1381-93.

[28]Kamada, N., et al., Role of the gut microbiota in immunity and inflammatory disease. Nat Rev Immunol, 2013. 13(5): p. 321-35.

[29]Tesmer, L.A., et al., Th17 cells in human disease. Immunological Reviews, 2008. 223: p. 87-113.

[30]Cosmi, L., et al., Th17 cells: new players in asthma pathogenesis. Allergy, 2011. 66(8): p. 989-98.

[31]Taleb, S., A. Tedgui, and Z. Mallat, IL-17 and Th17 cells in atherosclerosis: subtle and contextual roles. Arterioscler Thromb Vasc Biol, 2015. 35(2): p. 258-64.

[32]van Bruggen, N. and W. Ouyang, Th17 cells at the crossroads of autoimmunity, inflammation, and atherosclerosis. Immunity, 2014. 40(1): p. 10-2.

[33]Singh, R.P., et al., Th17 cells in inflammation and autoimmunity. Autoimmun Rev, 2014. 13(12): p. 1174-81.

[34]Monteleone, I., et al., Characterization of IL-17A-producing cells in celiac disease mucosa. J Immunol, 2010. 184(4): p. 2211-8.

[35]Castellanos-Rubio, A., et al., TH17 (and TH1) signatures of intestinal biopsies of CD patients in response to gliadin. Autoimmunity, 2009. 42(1): p. 69-73.

[36]Kumar, P. and G. Subramaniyam, Molecular underpinnings of Th17 immune-regulation and their implications in autoimmune diabetes. Cytokine, 2015. 71(2): p. 366-76.

[37]Shao, S., et al., Th17 cells in type 1 diabetes. Cell Immunol, 2012. 280(1): p. 16-21.

[38]Elson, C.O., et al., Monoclonal anti-interleukin 23 reverses active colitis in a T cell-mediated model in mice. Gastroenterology, 2007. 132(7): p. 2359-70.

[39]Brand, S., Crohn’s disease: Th1, Th17 or both? The change of a paradigm: new immunological and genetic insights implicate Th17 cells in the pathogenesis of Crohn’s disease. Gut, 2009. 58(8): p. 1152-67.

[40]Hirota, K., et al., Preferential recruitment of CCR6-expressing Th17 cells to inflamed joints via CCL20 in rheumatoid arthritis and its animal model. J Exp Med, 2007. 204(12): p. 2803-12.

[41]Du, C., et al., MicroRNA miR-326 regulates TH-17 differentiation and is associated with the pathogenesis of multiple sclerosis. Nat Immunol, 2009. 10(12): p. 1252-9.

[42]Antvorskov, J.C., et al., Dietary gluten alters the balance of pro-inflammatory and anti-inflammatory cytokines in T cells of BALB/c mice. Immunology, 2013. 138(1): p. 23-33.

[43]Antvorskov, J.C., et al., Impact of dietary gluten on regulatory T cells and Th17 cells in BALB/c mice. PLoS One, 2012. 7(3): p. e33315.

Give Your Immune System a "Paleo-Boost!" | The Paleo Diet

The darker, shorter and colder days of winter are upon us and with it comes an increase in colds and flu. The first wave of patients with sore throats and congestion has already passed through my office, so now is a great time to think about how you can support your immune system. There are several key deficiencies that commonly rear their ugly heads over the fall and winter months and contribute to increased frequency and severity of colds and flu. Nothing will slow your productivity at work, in the gym, or family time at home quicker than sick days.

If you are working long hours, exercising intensely, or have kids in daycare or school, then you’ll likely be more exposed to bacteria and viruses that can leave you stuck at home in bed. The research tells us that as your cortisol stress levels increase (from busy days, meeting deadlines, or getting up early with the kids) your first-line of immune defense or innate immune system function decreases.1This leaves your immune defense team short-handed.

Staying active is a great way to enhance your immunity but the more intensely you train, the quicker you deplete critical ‘immune soldiers’ called natural killer cells (NK).2 Studies show your immune system can be depressed for 24-72 hours after intense training, which means you need to provide the right support to reduce your risk of colds and flu.3

What can you do to boost your immunity this winter? (The answer is on your dinner plate!)


If you live in a northern climate with a true fall and winter season, obtaining the right amount of vitamin D is critical for keeping your immune system firing on all cylinders. Vitamin D deficiency is associated with decreased innate immunity and increased risk for infections.4

The best part of a Paleo dietary approach is that it provides you with the most nutrient dense choices for foods. To keep your vitamin D levels from plummeting over the winter months, increase your intake with these 5 vitamin D rich foods:

  • Cod Liver Oil – 1,400 IU per tbsp. (your grandma knew best!)
  • Cold-Water Fatty Fish – trout (645 IU per 3 ounce), salmon, or mackerel
  • Medicinal Mushrooms – Portobello (375 IU per mushroom) or maitake
  • Pork – 78 IU per 3 oz. serving
  • Eggs – 44IU per egg

The Vitamin D Society recommends maintaining your vitamin D levels between 100-150 (nmol/l), so if you struggle with colds and flu, or low mood over the winter, then getting your levels tested would be beneficial.5


If you are low in Vitamin A, it will significantly impair your mucosal immunity and leave you more prone to upper respiratory tract infections (URTI).6 If you work in an office, have kids in daycare or school, or train intensely than you’ll be a much greater risk of URTI, especially through the winter months.

A Paleo Diet is loaded with nutrient dense meats that are the richest source of preformed vitamin A. You can also get significant beta-caretene (which converts to vitamin A) from fruits and veggies.

Try these 5 Paleo rich vitamin A foods to keep your immune system robust:

  • Turkey and Beef Liver – 17,000 IU and 6,400 IU per 2.6 oz., respectively.
  • Cod Liver Oil – 4,150 IU per tbsp.
  • Sweet potatoes – 1,100 IU per medium size
  • Pumpkin -1,000 IU per ½ cup
  • Carrots – 700 IU per ½ cup


Vitamin C and zinc is a powerful combo for ramping up your immune army and fighting off bacteria and viruses. Vitamin C improves the response of neutrophils and lymphocytes, important immune cells that are the ‘front-line soldiers’ of your innate immune system.7,8 Zinc is essential for optimal function of your thymus gland, responsible for developing the ‘special forces’ immune cells of your adaptive immune system.9 This is the seek and destroy arm of your immunity, crucial for knocking out foreign invaders once they’ve breached your first-line of defense.

A Paleo Diet rich in animal protein is the best dietary source of zinc, while a mix of fruit and veggies are key for boosting your vitamin C intake (some sources may surprise you!). To ensure you’re meeting your body’s increased demands throughout the fall/winter months, be sure to include the following foods:

Vitamin C

  • Yellow Bell Peppers – 345mg per large pepper
  • Broccoli – 92mg per cup (chopped)
  • Kale – 80mg per cup (chopped)
  • Orange – 70mg per fruit (medium)
  • Kiwis – 64mg per fruit

  • Oysters – 33mg per 6 oysters
  • Beef – 14mg per fillet (4.5oz.)
  • Lamb – 7mg per 3oz.
  • Pork – 4.3mg per 3oz.
  • Pumpkin seeds – 2.9mg per oz.


There is inherent ‘cross-talk’ between your gut and immune system, therefore ensuring the right balance of healthy microbiota in your intestinal tract will go a long way to fighting off colds and flus.10,11 Common fermented foods and Paleo staples like kombucha tea, sauerkraut, and kimchi, are great options for increasing ‘good’ gut bacteria. In addition, the polyphenols found in green tea also promote the growth of beneficial gut bacteria. If you struggle with frequent or persistent colds or flu, you may want to add a probiotic supplement to add further immune support.

Limiting the growth of ‘bad’ or dysbiotic gut bacteria is crucial to maintaining optimal intestinal microflora and therefore immunity. Short-chain saturated fats like butyric acid and lauric acid, found in butter and coconut oil, exert potent antmicrobial effects that help to keep bad bacteria in check.12,13

Don’t let the cold, dark months slow you down. Enhance your Paleo Diet by incorporating the foods richest in the key immune boosting nutrients – vitamin D, A, C, zinc, and probiotics – to increase your resiliency this cold and flu season.

Enjoy a healthy winter!


[1]Nieman DC et al. Influence of carbohydrate on the immune response to intensive, prolonged exercise. Exerc Immunol Rev 1998;4:64-76.

[2] Nieman DC, Pedersen BK. Exercise and immune function. Recent developments. Sports Med 1999;27(2):73-80.

[3] Walsh PH et al. Position statement. Part one: Immune function & exercise. Exerc Immunol Rev.2011;17:6-63.

[4] Youssef D et al. Vitamin D’s potential to reduce the risk of hospital-acquired infections. Dermatoendocrinol. 2012 Apr 1;4(2):167-75

[5] Heaney R, Bggerly C, Sorenson M, Vieth R. Toronto Vitamin D Disease Prevention Symposium. November 6th, 2013. Toronto, ON

[6] Semba RD. The role of vitamin A and related retinoids in immune function. Nutr Rev. 1998;56(1 Pt 2):S38-48

[7] Douglas RM et al. Vitamin C for preventing and treating the common cold. Cochrane Database Systematic Review. 2004 Oct 18;(4):CD000980.

[8] Peters EM, Goetzche JM, Grobbelaar B, Noakes TD. Vitamin C supplementation reduces the incidence of post race symptoms of upper-respiratory-tract infection in ultra marathon runners. Am J Clin Nutr 1993 Feb;57(2):170-4.

[9] Mangini S et al. A combination of high-dose vitamin C plus zinc for the common cold. J Int Med Res. 2012;40(1):28-42.

[10] Rask C et al. Differential effect on cell-mediated immunity in human volunteers after intake of different lactobacilli. Clin Exp Immunol 2013 May;172(2):321-32.

[11] Madden J.A.J. et al. Effect of probiotics on preventing disruption of the intestinal microflora following antibiotic therapy: A double-blind, placebo-controlled pilot study. Int Immunophar 2005: 5: 1091-1097.

[12] Mortesen FV, Nielsen H, Aalkjaer C, et al. Short chain fatty acids relax isolated resistance arteries from the human ileum by a mechanism dependent on anion-exchange. Pharmacol Toxicoli 1994;75(3-4):181-5. 6.

[13] Mortesen FV, Nielsen H, Mulvaney MJ, et al. Short chain fatty acids dilate isolated human colonic reistance arteries. Gut 1990;31(12):1391-4.

Mackerel Tartare: A Paleo Recipe for Common Cold Prevention

The common cold is a viral infection of the upper respiratory tract caused by some 200 different viruses, the most common of which are rhinoviruses. While there are not scientifically vetted cures for common colds, there are many proactive strategies both for preventing them and dampening the severity of their symptoms.

One effective strategy is maintaining adequate vitamin D levels. Emerging research, including both interventional and epidemiological studies, suggests that vitamin D plays a major role in regulating the immune system, including theorized direct anti-viral effects.1, 2 Research published in the British Journal of Nutrition shows vitamin D status to have a linear association with respiratory infections, though further research is needed to establish the underlying mechanisms.3

More than possibly preventing common colds, vitamin D may also accelerate your recovery once a rhinovirus infection takes hold. Rhinoviruses induce inflammatory responses in the airway epithelium by increasing pro-inflammatory cytokines.4 Research shows vitamin D can reduce this inflammation, though further research is again, required.5

While daily sun exposure is an ideal, it is not always feasible to maintain adequate vitamin D levels. Luckily, many Paleo foods are rich in vitamin D, particularly fatty fish. Mackerel, salmon, halibut, and herring are all potent sources of vitamin D. Just 3.5 oz. of mackerel has 360 IU vitamin D, or 90% of the USDA’s recommended daily value.6

With this recipe, you’ll also be getting a healthy dose of vitamin C from juiced limes. Vitamin C also boosts the immune system and may also protect against viral infections. Whether vitamin C reduces the incidence, duration, or severity of common colds has been a controversial, yet enduring hypothesis for over 70 years.7 Nevertheless, based on its low cost and low risks, many researchers recommend increased vitamin C consumption, whether from supplements or high-vitamin-C foods, for common cold prevention.8

With winter just around the corner, now is a great time to start increasing your consumption of vitamin D- and vitamin C-rich foods. Our delicious Mackerel Tartare will whet your appetite and amp up your immune system.


Serves 2

  • 2 whole mackerel, scaled and cleaned
  • 1 bunch fresh cilantro
  • 2 limes, juiced
  • 1 small purple onion, finely chopped
  • 1 mild red chili, seeded and finely chopped
  • 3 tbsp olive oil
  • Freshly milled black pepper


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Christopher James Clark, B.B.A.
Nutritional Grail

Christopher James Clark | The Paleo Diet TeamChristopher James Clark, B.B.A. is an award-winning writer, consultant, and chef with specialized knowledge in nutritional science and healing cuisine. He has a Business Administration degree from the University of Michigan and formerly worked as a revenue management analyst for a Fortune 100 company. For the past decade-plus, he has been designing menus, recipes, and food concepts for restaurants and spas, coaching private clients, teaching cooking workshops worldwide, and managing the kitchen for a renowned Greek yoga resort. Clark is the author of the critically acclaimed, award-winning book, Nutritional Grail.

See more recipes!


1. Grant, DB, et al. (December 2010). Ample evidence exists from human studies that vitamin D reduces the risk of selected bacterial and viral infections. Experimental Biology and Medicine, 235(12). Retrieved from http://www.ncbi.nlm.nih.gov/pubmed/21171208

2. Beard, JA, et al. (March 2011). Vitamin D and the anti-viral state. Journal of Clinical Virology, 50(3). Retrieved from http://www.ncbi.nlm.nih.gov/pubmed/21242105

3. Berry, DJ, et al. (November 2011). Vitamin D status has a linear association with seasonal infections and lung function in British adults. British Journal of Nutrition, 106(9). Retrieved from http://www.ncbi.nlm.nih.gov/pubmed/21736791

4. Chu, WC, et at. (2013). Vitamin D Reduces Inflammatory Response To Rhinovirus In Human Airway Epithelium. American Journal of Respiratory and Critical Care Medicine, 1(87). Retrieved from http://www.atsjournals.org/doi/abs/10.1164/ajrccm-conference.2013.187.1_MeetingAbstracts.A5968

5. Ibid.

6. Nutrition Data. Retrieved from http://nutritiondata.self.com/facts/finfish-and-shellfish-products/4072/2

7. Hemilä, H, et al. (January 2013). Vitamin C for preventing and treating the common cold. The Cochrane Database of Systematic Reviews, 1(CD000980). Retrieved from http://www.ncbi.nlm.nih.gov/pubmed/23440782

8. Ibid.

Race | The Paleo Diet

Dear Dr. Cordain,

Should The Paleo Diet produce the same results across different races and populations?

I am curious as to how different groups of people react and are expected to react to The Paleo Diet. For instance, since Central Asian people followed a nomadic lifestyle for centuries past. Over time, their diets changed to include milk and meat, but few vegetables and fruit. Consequently, these peoples’ digestive systems adapted in such a way to better digest these foods and extract the nutrients from them. While these people could more efficiently digest milk, other people, like those in East Asia, are often lactose intolerant since their diets were not heavily dairy-based.

The logic behind The Paleo Diet is very convincing. Yet, I am always wary when I hear there’s a diet that is universally beneficial-that is, all groups of people will benefit. Perhaps, there need to be variations within The Paleo Diet to target specific populations by taking into account the nutritional history of each populations’ ancestors. Could you comment on this thought and does any existing literature address this question?



Dr. Cordain’s Response:


Good question. Unfortunately, there is currently no hard data (randomized controlled trials) or even epidemiological data to support or deny these conjectures. However, there is some theoretical evidence to suggest that various HLA (human leukocyte antigen) sub-populations across the planet possess immune system characteristics that may interact with diet. Moreover, some worldwide populations maintain gut enzymes like lactase and sucrose, which seem to have evolved specific to diet, primarily post-agriculture. I have written extensively on this concept in the scientific paper “Malaria and Rickets Represent Selective Forces for the Convergent Evolution of Adult Lactase Persistence.”


Loren Cordain, Ph.D., Professor Emeritus

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