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Our Immune System Uses Plants To Activate Gut Protection

It might seem that our skin is the first line of defense between our insides and the outside world, but our greatest interface with our environment is actually through the lining of our intestines, which covers thousands of square feet. And all that separates our gut from the outer world is a single layer of cells, 50 millionth of a meter thick – less than the thickness of a sheet of paper.

Compare that to our skin. In the video, The Broccoli Receptor: Our First Line of Defense, you can see a layer of skin, dozens of protective cells thick, to keep the outside world outside of our bodies. Why don’t we have multiple layers in our gut wall? Because we need to absorb stuff from food into our body. It’s a good idea for our skin to be waterproof, so we don’t start leaking, but the lining of our gut has to allow for the absorption of fluids and nutrients.

With such a thin, fragile layer between our sterile core and outer chaos, we better have quite a defense system in place. Indeed, that’s where “intraepithelial lymphocytes” come in.

Intraepithelial lymphocytes serve two functions: they condition and repair that thin barrier, and they provide a front-line defense against intestinal pathogens. These critical cells are covered with Ah receptors. Ah receptors are like locks, and for decades researchers have been searching for a natural key to fit in these locks to activate those receptors and sustain our immunity. We recently discovered a key: broccoli.

Cruciferous vegetables—broccoli, kale, cauliflower, cabbage, Brussels sprouts—contain a phytonutrient that is transformed by our stomach acid into the key that fits into the Ah receptor, stimulating our intraepithelial lymphocytes. In other words, broccoli leads to the activation of our immune foot soldiers.

In an editorial about Ah receptors and diet, researcher Lora V. Hooper from the Howard Hughes Medical Institute noted, “From childhood we learn that vegetables are good for us, and most of us eat our veggies without giving much thought to the evidence behind this accepted wisdom or to the mechanisms underlying the purported health-boosting properties of a vegetable-rich diet.” But now we know that “specific dietary compounds found at high levels in cruciferous vegetables such as broccoli, cauliflower, and cabbage are essential for sustaining intestinal immune function.” Green vegetables are in fact required to maintain a large population of those protective intraepithelial lymphocytes.

Maybe that’s why vegetable intake is associated with lower risk of inflammatory bowel diseases such as ulcerative colitis, whereas the more meaty Western diet is associated with higher risk of inflammatory bowel diseases. This may be because the activating receptors on our intestinal immune cells are basically sensors of plant-derived phytochemicals.

This raises a broader question: Why did our immune system evolve this requirement for broccoli and other plant foods? Well, when do we need to boost our intestinal defenses the most? When we eat! That’s when we may be ingesting pathogens. Linking heightened intestinal immune activation to food intake could serve to bolster immunity precisely when it is needed. At the same time, this would allow energy to be conserved in times of food scarcity, since maintaining these defenses takes considerable amounts of energy. Why remain at red alert 24 hours a day when we eat only a couple of times a day? We evolved for millions of years eating mostly weeds—wild plants, dark green leafy vegetables (or as they were known back then, leaves). By using veggies as a signal to upkeep our immune system, our bodies may be bolstering our immune defenses when we most need them. Thus, the old recommendation to “eat your veggies” has a strong molecular basis. (Did we really evolve eating that many plant foods? See my video Paleolithic Lessons).

This discovery has been all exciting for the drug companies who are looking into Ah receptor active pharmaceuticals. “However,” as one research team at Cambridge concluded, “rather than developing additional anti-inflammatory drugs, changing diets which are currently highly processed and low in vegetable content, may be a more cost effective way towards health and well-being.”

As remarkable as this story is, it is just the tip of the cruciferous iceberg! See, for example:

How else can we protect our immune function? Exercise (Preserving Immune Function In Athletes With Nutritional Yeast) and sleep (Sleep & Immunity)!

Given the variety and flexibility of most mammalian diets, a specific dependence on cruciferous vegetables for optimal intestinal immune function would seem overly restrictive, no? I address that in my video, Counteracting the Effects of Dioxins

-Michael Greger, M.D.

PS: If you haven’t yet, you can subscribe to my videos for free by clicking here and watch my full 2012 – 2015 presentations Uprooting the Leading Causes of Death, More than an Apple a Day, From Table to Able, and Food as Medicine.


Michael Greger M.D., FACLM

Michael Greger, M.D. FACLM, is a physician, New York Times bestselling author, and internationally recognized professional speaker on a number of important public health issues. Dr. Greger has lectured at the Conference on World Affairs, the National Institutes of Health, and the International Bird Flu Summit, testified before Congress, appeared on The Dr. Oz Show and The Colbert Report, and was invited as an expert witness in defense of Oprah Winfrey at the infamous "meat defamation" trial.

22 responses to “Our Immune System Uses Plants To Activate Gut Protection

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    1. Savory oatmeal is underrated. Steel-cut oats with beans, salsa, flax meal and cilantro is my favorite breakfast. Never tried cauliflower…..

      1. KWD: I wanted to thank you for this post! I was pretty skeptical about how much I would like it. I expected to tolerate it at best. But I needed a new breakfast (I tend to get burnt out on food pretty quickly). So, I gave it a try. And to my surprise, I really like it! I ate it all last week and so far this week. And I’ve had fun experimenting with different salsas. That will help keep the interest level up a little longer for me.

        Just an FYI: I find for myself, that the cilantro is optional in terms of enjoying the dish. But I was able to add ground flaxseed with no problems, making me happy that I was getting flaxseed back in my diet again (at least for now). :-) Yeah!!

        Just so you know, your idea has helped someone else.

        1. Thea, sorry I am just seeing this. I’ve been off of disqus for a bit tending to school and some unexpected life issues, but I’m back now! This makes me so happy you tried it and liked it! Many times people will say, “oh, that sounds good” but never actually give it a try.

          Regarding the cilantro – yes, I often don’t have it on hand and it’s tasty without it (sometimes I also add frozen corn or, if I have time, some sauteed onions). It’s a great way to break the fast!

          1. KWD: Thanks for your reply. I’m still enjoying the dish. I keep playing with it. Here’s what I have been doing lately:

            > 1/2 (volume of what I want to eat) cooked steel cut oats
            > 1/2 baked beans – mix it up for interest. I even used Trader Joes’ boxed lentils one week
            > 1-2 T ground flaxseed
            > Generous pinch of amla powder
            > 1/3 or so cups frozen: kale, collards or spinach – whatever I have
            > Salsa to taste

            I am thrilled that I can add the amla powder and not taste it. I hadn’t been eating the amla previously because I had to put in too little in order to not taste it. I just gave up. But I can do a good amount in this dish and because of the salsa’s strong taste, I don’t taste the amla.

            Also note that I found a commercial salsa with a lot of cilantro already in it. This works great, because I had decided that I didn’t like the texture of the dish with the fresh cilantro. So, I add the frozen greens instead, and it’s really working for me. Which is another great plus, because I have never consistently gotten any leafy greens in me for breakfast before. So, this is a big step. :-)

            I can totally see how adding some corn or whatever is on hand would just add more great variety.

            Thanks again!

  1. Do the cruciferous veggies need to be precut and/or have mustard powder added to them (as Dr. G’s advocated in previous videos) in order to create the nutrient that becomes the Ah receptor keys? Or do you get the same benefit from, say, eating frozen greens and the like that have been pre-cooked? I rely on frozen foods, so I’m keenly interested to know if I’m missing out on the benefit of the Ah receptor activation.

            1. So are you saying that if we just cook our veges without letting it sit for the required time we aren’t eating healthy? Dr Greger’s rules about everything just gets too confusing, complicated,to difficult and stressful. Let me just enjoy my whole foods plant based unprocessed way of eating, thank you.

              1. Interesting username, I did not say that. I am talking about sulphorophane specifically. Eat broccoli however way you want as long as its not deep fried or dipped in butter.

              2. Too Many Rules: re: “So are you saying that if we just cook our veges without letting it sit for the required time we aren’t eating healthy?”

                Gosh, no one is saying that at all. Here are Dr. Greger’s overall nutrition recommendations. Note how simple they are:

                “Let me just…” It sounds like your current diet would fit in quite nicely with Dr. Greger’s recommendations.

                What is being discussed here is how to tweak a healthy diet to get even more out of it. Personally, if I’m going to eat broccoli, I want to eat it in a way that will most likely to turn my body into a cancer fighting bio-machine. For some of us, it is interesting and fun to keep making our diets healthier and healthier.

                But if chopping your broccoli and taking a break before eating it is too complicated for you, it’s still healthy to eat the broccoli without the rest break. As Dr. Greger says, the healthiest way to eat your veggies is the one that gets you to eat the most veggies.

                1. Sorry, forgot about the diet tweakers. Should have remembered that since I really like to read the comments. Which are sometimes more interesting than the video or blog. The forgetter or getting sidetracked too easily is what makes 40 minutes difficult.

  2. On a separate subject….Dr Greger, would you write an article on blood pH? I have thought for several years that blood pH does change and that you can keep it ‘normal’ by what you eat and reducing stress, etc. I recently read an article by a supposedly medically knowledgeable person that blood pH does not change, that the body acts to keep it constant, and that testing urine/saliva are not an indication of blood pH. Also that taking potassium bicarbonate does not do anything, because all food that we eat gets neutralized before it enters the intestines, making the pH of food meaningless. Basically this person is saying that the subject of the books “Alkalize or Die” or “The pH Miracle” is bogus. Can you give us the correct facts to sort this out? Thanks!

    1. I would also be interested in Dr. Greger’s take on this. The whole pH thing sounds a little dubious to me, but I’m no doctor.

  3. another plausible theory is that brocolli imitate pathogens so they dont get gobble up.

    when our stomuch mistake them for pathogens , they go on on the defensive and stop absorbing food. A kind of involuntary diet.

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