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Understanding Dietary Phytochemicals

“So let me get this straight. Both of you got poison ivy. Rose went to the doctor last week, started taking meds, and felt better. You didn’t go to the doctor, you didn’t get any meds, and you’re feeling worse.” When Lawton said it like that, I kind of felt like an idiot. Lawton was my brother-in-law and he always seemed to have the voice of reason.

“Yeah…” I muttered sheepishly.

I had been convincing myself of reasons not to go to the doctor. My rash wasn’t as extensive as Rose’s initially, so maybe it wouldn’t get as bad. I started taking regularly scheduled doses of Benadryl and figured that would keep the itching and swelling controlled, but it hadn’t. Most importantly, I didn’t want to spend half a day during our 3 day vacation in a doctor’s office. But the rash kept getting worse, and Lawton’s simplicity made it painfully obvious that I needed to see a doctor.

“Then it sounds like you need to go to urgent care.” Lawton said in a matter-of-fact voice. “Don’t waste any more time. Get going.”

I knew he was right. Rose, my better half, shot me an “I told you so” glare. She had spent half of the morning telling me the same thing.

“Fine, I guess you’re right.” I conceded.

We set down the beach chairs and umbrella we were holding in the front hall of Lawton’s condo rental. “Well, tell LaLa and the kids we’ll be back,” I said as we turned to head out the door. My sister LaLa had taken their kids to the beach to build sandcastles. We’d have to catch up later.

Rose and I walked to the parking spaces underneath the condominium complex and got in the car. She already had the urgent care location pulled up on her phone’s Google maps from earlier that morning.

After a short drive back to the mainland, we checked into the urgent care. There was only one other person there. I was pretty healthy, so the intake paperwork didn’t take long. We completed the paperwork, had my vitals taken and were shown to an exam room.

“The doctor isn’t here right now, so the nurse practitioner will see you,” the technician said as she left us in the room.

“Typical”, I thought. I had no issues with seeing a nurse practitioner. But I suspected the doctor was working at another job right now, and would be ‘available’ to drive over and see a patient if needed. Urgent care practices were a lucrative business, and as a relatively new enterprise at the time they had several legal aspects that were loosely interpreted, including physician oversight.

“Make sure to ask for prednisone.” Rose coached me before the provider came in.

“Rose, I’m sure she’s seen poison ivy before and knows what to do.” I responded.

“Well, I just need you to be feeling better so we can get back out on the beach.”

Knock, knock. The door peeled open and a middle-aged woman stepped in.

“Hi, I’m Judy.” The nurse practitioner said as she walked in the door. “You must be Fill. I heard you have a bad case of poison ivy.”

“Yeah, it doesn’t seem to be getting better.” I said as I pointed to my left ear, which was so swollen it looked like I had cauliflower ear.

“Whoa, that does look bad.” Judy said as she inspected my ear closer. “How long have you had it?”

“It showed up last Monday. So five days now.”

“Were you doing some yardwork last weekend?”

“No. But we went floating and camping with my family.”

“Ah, I see. Did you get poison ivy too?” Judy asked Rose.

“Yeah, it was awful. But I went to the doctor already and got some prednisone a couple days ago. I’m feeling a lot better already.” Rose said, before she turned her head and winked at me.

“Looks like you have some blisters too.” Judy said as she looked at several fluid-filled blisters on my legs. Some of them were 2-3 inches in diameter. “Have any of these popped open?”

“No. I’ve been trying to leave them alone.” I said.

“Have you been out in the sun?” She asked.

“Yes, we’ve been on the beach, but I’ve stayed under the umbrella.”

“Well, no more of that. You have to stay out of the sun altogether.” She said. I saw Rose’s heart sink.

“Are you serious? The whole reason we’re down here is to spend time on the beach.” I asked, almost pleading.

“Yup, no sun for you.” Judy stated in an unforgiving tone.

There was a short pause as Rose and I exchanged glances, deciding what to say next.

“Do you like to drink?” Judy asked, trying to change the subject. Rose and I both nodded. “If you haven’t been to McGuire’s, then you definitely need to go there. It’s a great Irish pub, lots of fun, live music and good food.”

Rose and Judy ended up discussing several different restaurants we could go to. Meanwhile, Judy sterilized the skin over my blisters, then popped them and applied some bandages. They talked about a wine bar, then they discussed their favorite wines. After Judy found out I was in medical school, which always seemed inevitable around other medical personnel, her treatment plan became somewhat more of a question then a plan. As I laughed to myself, I told her that I didn’t have that much clinical experience, that I just finished my second year. Second year was mainly lectures on physiology and pathology, not much about treatment. I told her that her treatment plan sounded fine to me. Since the medications included prednisone, Rose also approved.

As we gathered our belongings to leave, Judy wrote down the names of several restaurants for us. We thanked her as she led us back to the front desk. We went back to Lawton and LaLa’s beachfront condo, but I stayed inside all that day.

The next day at the beach, as I sat under the umbrella, drinking a cold beer, looking at Rose standing with her feet in the ocean tide, I thought this was pretty relaxing. I glanced down at the towels covering my legs and thought, “Ugh, poison ivy. You almost ruined my vacation. Almost.”


Poison ivy plants and several similar plants in the Toxicodendron genus contain an oil called urushiol. Upon initial exposure to urushiol, the human body produces antibodies against components of the oil, similar to the body’s reaction to vaccines. The next time the body is exposed to urushiol, the antibodies recognize it as a foreign substance, triggering an immune reaction. Even though the urushiol itself isn’t harmful to the body, the body’s immune reaction to urushiol can result in a combination of swelling, pain, itching and blisters, which medical professionals call an allergic contact dermatitis. Most people just call it ‘poison ivy’.

Urushiol is an example of a phytochemical, which is a fancy name for a chemical produced by a plant, or by a bacteria or fungus that lives on a plant. “Phyto” is a prefix which means “of a plant,” so a phytochemical is a “chemical of a plant.”

Although plants produce lots of different chemicals, the term phytochemical only refers to chemicals produced by plants to confer a survival advantage. Think of phytochemicals as “chemical weapons of plant defense”. To distinguish phytochemicals from other plant chemicals, scientists sometimes refer to plant chemicals in two distinct categories, primary metabolites and secondary metabolites.

Plant Chemical Definition
Primary Metabolite Nutrient; essential for sustaining life; like fat, carbohydrate, or protein
Secondary Metabolite (aka Phytochemical) Chemical meant to improve the plant’s chance for survival

Of note, phytochemicals are not nutrients by definition. Thus phytonutrient, a term I used in lieu of phytochemical in prior blog posts, is a misnomer and I won’t be using that term again.

Since urushiol is a phytochemical, it is produced to provide the poison ivy plant a survival advantage. If you’ve ever had painful, itchy blisters resulting from contact with poison ivy, there’s a good chance you may recognize a classic three-pronged poison ivy leaf and avoid it in the future. If so, a phytochemical (urushiol) caused a potential threat (human) to avoid a plant (poison ivy), giving the plant a survival advantage it didn’t otherwise have.

Interestingly, urushiol only affects humans and other primates. A poison ivy plant, like most other plants, will face several other threats to its survival, including temperature shifts, ultraviolet radiation, drought, infection, insects and herbivores. Over millions of years, plants have developed a spectacular array of defense mechanisms against these numerous threats. Although plants may lack the mobility of their animal counterparts, their defense arsenal can be just as dangerous and far more elegant than the typical tooth and claw. Since there are thousands of phytochemicals that exist, and urushiol doesn’t adequately represent the spectrum of phytochemical activity, let me illustrate some more examples with another short story.


Picture a small, hungry ant wandering on a dense forest floor. She breathes a sigh of relief as she reaches the edge of a clearing. A small garden looms ahead, and her antennae perk up as she picks up the scent of a nearby raspberry, food! She races towards the raspberry plant and sinks her teeth into a raspberry. She notices the flavor is intensely bitter. After chewing a few bites, she is overcome with nausea. She spits the food back on the ground and averts her gaze to a large pear on the ground several feet away.

After the nausea subsides, she approaches the pear and begins chewing on the outer skin. Before she can reach the inner fruit, her jaw chomps down on something hard. She spits it out and bites the other side of the pear, but it only takes a few seconds before her teeth grind against another hard substance. Again, she spits it out and continues searching for food.

As she approaches the next plant, she notices firm hair-like projections coming off the stem. She inspects the plant more closely. From past experience, she knows those hairs would break off and stick to her for days, causing an irritating and persistent pain. Not worth the meal…”Keep moving!” she thinks.

Further into the garden, she sees a fellow ant, a young one by the look of it, gourging on a small fruit, juices flowing everywhere. She begins walking toward him, but as she gets closer, her body starts to shudder. She raises her antennae into the air, and a panic quickly ensues. “RUN!” an instinct tells her. She races away toward the opposite end of the garden before looking back or pausing for breath. She frantically glances in every direction to ensure she isn’t being followed.

“Stupid little ant!” she thinks. “You may be enjoying a meal now, but you won’t be alive long.” That scent from the little ant’s juicy meal means one thing and one thing only …spiders are coming!

The hungry ant stands completely still for several minutes, allowing herself to calm down.

“Okay, it should be safe now. Let’s try one more plant,” she thinks.

She scurries to a plant near a small puddle of water. This plant looks new to her, but it appears relatively safe. It has oval shaped leaves with two shades of green, no furs or flowers or bark. She takes a small bite and chews it cautiously… whew! No problems yet! She takes a few more small, slow nibbles, and waits. “Finally, a safe lunch!” she thinks. She opens her mouth wide and chomps down on the leaf…OUCH!!!! Searing pain shoots through her jaw and blood gushes everywhere. She spits out a jagged crystal and notices a few teeth on the ground. Her mouth starts burning and swelling at the same time. As her mind is racing and her heart is pounding, she races back to the forest to find the ant nest, hungry and wounded. She is NEVER going back to that garden again.


The first ant in the story was a victim of several plant defense mechanisms: bitter tannins causing nausea and vomiting, grinding stone cells wearing away at the teeth, stinging nettles causing profuse pain and irritation, volatile organic compounds attracting predators of plant pests, and the mechanical and toxic effects of calcium oxalate crystals. Except for the grinding stone cells, which are a purely structural defense, these mechanisms all contain phytochemicals. By deterring insect feeding through several different mechanisms, all of these phytochemicals provide their plants with a survival advantage.

Tannins, stinging nettles, volatile organic compounds and calcium oxalate can lead to the same side effects in humans as in ants. Some phytochemicals can be even more dangerous, even deadly. For example, the castor bean plant manufactures a phytochemical called ricin that inhibits protein synthesis. This phytochemical is so deadly at low doses that it has been cultivated as a chemical weapon of war.

“Fill, I understand that phytochemicals provide plants a survival advantage, sometimes in pretty cool ways, sometimes in deadly ways. But how do phytochemicals relate to nutrition?”

So far, I’ve only given examples of harmful phytochemicals. But some phytochemicals can be life-saving and are harvested from plants to be used medicinally. For example, the chemotherapy drug paclitaxel is a phytochemical derived from yeast that co-exists on the Pacific Yew tree. Other phytochemicals can be slowly reverse human disease. These are known commonly referred to as antioxidants.

An antioxidant refers to the property of a substance to stabilize reactive oxygen molecules and other harmful molecules that can cause damage to various tissues, including the body. Chemicals with antioxidant properties can be produced by the body, produced by plants or even synthesized in the lab. It turns out that most antioxidants in the diet are actually phytochemicals that have antioxidant properties. Some common examples of phytochemicals with antioxidant properties include resveratrol found in red grapes (and thus red wine), curcumin found in turmeric, and beta carotene found in carrots.

However, counter to common belief, these phytochemicals aren’t always beneficial. Most phytochemicals in nutrition can be either beneficial or harmful depending on the dose. As a rule of thumb, dietary phytochemicals are beneficial at low doses and harmful or fatal at high doses. For example, caffeine is a phytochemical. In its natural form, caffeine is fatal for some insects and fungi, and this is one survival advantage it provides for coffee plants, the cocoa tree, and various plants used for teas. Caffeine can also be fatal to humans, with an estimated average lethal dose of 10grams. At high, but non-fatal doses, caffeine can cause symptoms such as vomiting, diarrhea, gastritis, tremors, insomnia, headache, hallucinations, high blood pressure, increased intraocular pressure, and more. Yet, at low doses, this phytochemical can have several beneficial effects, the most well-known of which includes short-term stimulation of the central nervous system, leading to enhanced mental and physical performance. In addition, chronic low dose use may have a protective effect against Parkinson disease.

How is it possible that the same phytochemical can be both beneficial to the human body at low doses and harmful to the human body at high doses?

The answer is hormesis. Hormesis refers to the ability of an organism to adapt to stress. If you’d like a well-written scientific description of this phenomenon as it pertains to phytochemicals, search for the following article, “Adaptive cellular stress pathways as therapeutic targets of dietary phytochemicals: focus on the nervous system” (Lee, et al 2014). Otherwise, I’ll try to explain this phenomenon briefly using an example of hormesis that everyone has heard of, exercise. Exercise is a form of stress that the body can adapt to. It can be both beneficial at low doses and harmful at high doses.

Exercise stresses the body by breaking down muscle tissue for fuel, accumulating lactic acid due to lack of oxygen, increasing the heart rate and blood pressure to deliver more blood to muscle, and even increasing stress hormones in the body. If you were to take someone who hasn’t exercised in years and expose them to intense prolonged exercise, this could lead to severe damage to the body, like rhabdomyolysis. However, if we limit the amount of exercise and allow the body time to recover in between periods of exercise, the body becomes stronger. During recovery after exercise, the body develops more connections between nerves and muscles. Muscle fibers also grow bigger and become more efficient with oxygen and glucose utilization, resulting in increased strength, power and/or endurance. In short, the body adapts (becomes stronger) to a stress (exercise). But the benefits of exercise go far beyond increased muscle strength. Exercise boosts immune function, lowers blood pressure, improves cholesterol, reduces glucose levels, improves mental health and lots of other benefits.

Similarly, dietary phytochemicals stress the body. They may cause pain, nausea, vomiting, paralysis, or a long list of other side effects, even death. But if we consume low doses of phytochemicals intermittently, and allow our body to recover, this actually stimulates the body to adapt to stress. Just like exercise, this adaptation leads to an incredible number of benefits for the body.

Now that we know why low doses of phytochemicals are beneficial, let’s review why high doses of the same phytochemical can be harmful.

Remember that phytochemicals were developed by plants as chemical weapons, so by nature phytochemicals were intended to be toxic to predators. This may explain why many foods rich in phytochemicals taste bitter, a signal to our brain to avoid these foods. However, many foods that contain phytochemicals also contain essential nutrients for the body. So over thousands of years, the human body has developed means to slowly detoxify the phytochemicals, so that we can continue eating those foods for the nutrients they contain, without significant side effects. But the body, especially the liver, can only detoxify so much phytochemical at a time. Just like too much exercise in an untrained body can lead to rhabdomyolysis, excess doses of phytochemical can lead to a whole spectrum of toxic symptoms for the body, even death.

Overall, the body detoxifies low doses of phytochemicals quickly, so the phytochemical stimulates the body’s stress response systems without causing any harm. But the body detoxifies high doses of phytochemicals much slower, allowing them to accumulate in the body and cause much more harm than benefit.

“Fill, I like the comparison to exercise. But what if I’m not exposed to that much stress?  Why should I care about phytochemicals?”

Everyone’s body is exposed to an enormous amount of stress. Even if we avoid external stress like cigarettes, unhealthy food and radiation, the body produces internal stress like free radicals, misfolded proteins, and inflammatory cytokines every second, even in a healthy person. If the body didn’t have a way to repair the damage of these stresses, it wouldn’t survive very long.

When we stimulate the body’s adaptive stress response in an intermittent, controlled manner, like by phytochemical stress in foods or by exercise, the body is able to more efficiently decrease the negative impact generated by ALL INTERNAL AND EXTERNAL STRESS. Since most chronic diseases are initiated by these internal and external stresses, LOW DOSES OF PHYTOCHEMICALS CAN DECREASE THE INCIDENCE OF CANCER, AUTOIMMUNE DISEASES, HEART DISEASE, STROKE, AND MANY OTHER DISEASES!!

“Wow Fill, that’s incredible! What foods have low levels of phytochemicals?”

Good question. The quick answer is ALL PLANT FOODS. By definition, a phytochemical is a chemical “of a plant”, meaning that animal products like meat, eggs, and dairy have no phytochemicals. This is one of the reasons why plant foods like fruits, vegetables, whole grains, legumes, nuts, and spices are the healthiest foods for human consumption.

That said, there are a few examples of plant foods whose phytochemical level may be above tolerance for the human body and can cause some undesired effects, such as:

Plant Phytochemical
Rhubarb Oxalic acid
Raw elderberry Cyanide
Raw red kidney bean Phytohemagglutinin
Raw potato Solenin
Habanero pepper Capsaicin

In addition, there are multitudes of plants not sold as food that can contain dangerous phytochemical levels for humans. For example, the pontic or honeysuckle azalea can be found as a household shrub. The nectar of this plant, sometimes called mad honey, contains a phytochemical called the grayanotoxin which can cause bradycardia, hypotension, cardiac arrhythmias and even death. For this reason, extreme caution should be taken before consuming any plants found outside of a grocery store, restaurant or a food garden.

“Yikes Fill. It’s scary to think that some plants can be so dangerous and others can be so helpful. It sounds like I need to eat more plant foods, but what if I don’t like the taste of them? Can I just get my phytochemical or antioxidant benefits from supplements?”

Many supplements and neutraceuticals are actually phytochemicals isolated from their original food (or made synthetically) and sold in much higher doses than in their food counterparts. So you may be tempted to take a beta carotene supplement instead of eating carrots, or a vitamin C supplement instead of eating oranges. In theory, these amplified phytochemicals should be good for the body because they contain more levels of antioxidants. But as we learned about from the concept of hormesis, high levels of a phytochemical can be toxic or deadly! For example, several studies have shown that beta carotene and vitamin A supplements increased the incidence of lung cancer and lung cancer death! Unfortunately, recent evidence shows that other supplements may also be associated with higher rates of disease or death. So although carrots are healthy, beta carotene extracted from a carrot and turned into a supplement is not healthy. Most supplements don’t have any health value compared to the foods that they come from. Perhaps it is time for the Food and Drug Administration to start regulating the safety and efficacy of supplements, as they currently provide almost no oversight or regulation.

“Okay Fill. Somehow I always knew that most supplements and neutraceuticals were a waste of money. Now I know why plant foods are the best source of these phytochemicals. But what about processed plant foods? Do they contain phytochemicals?”

Actually, yes! It is possible for processed plant foods to have phytochemicals. In fact, sometimes processing a food will increase the ability of the body to absorb its phytochemicals. For instance, chopping garlic or heating and canning tomatoes increases their level of absorbable phytochemicals. Crazy, isn’t it? The level of absorbable phytochemicals is dependent on several other factors as well, such as whether the food has been genetically modified, whether the food is eaten with other plant foods, how the food is cooked, and whether the food is fresh. But in general, processed foods have a fraction of the phytochemicals of whole foods. Any processing that removes the outer skin of the food will remove a large portion of the phytochemicals. Since the outer layer of the food is the portion that is most exposed to insects, sunlight, microorganisms, and other threats, this is where the food needs the most protection. So it concentrates the highest level of phytochemicals in the outer layer. This is part of the reason foods like berries are so healthy, because the skins are eaten. This is why I recommend eating as many foods as possible with the skin still on, as long as the skin is easily digestible (like potatoes, apples and whole grains).

Just keep in mind that the skin is also the location with the highest level of pesticides. Pesticides are basically synthetic or genetically modified and amplified phytochemicals which contain a much higher phytochemical dose than what is found in the natural food, hence the harmful effects on human health. Since organic produce has much less pesticide on the skin, this provides one incentive to purchase organic produce.

By now you may be realizing that nutrition can be very complicated. But that doesn’t mean that eating has to be complicated. Stick to the basics. Eat whole foods that contain beneficial phytochemicals. These are all the healthiest foods that you probably already know of: fruits, vegetables, whole grains, legumes, nuts, seeds, and even herbs and spices. They are all plants, and they are all whole foods, which are all the healthiest foods for you. Now you know why!

If you’re instantly motivated to change your eating habits, I encourage a “Whole Food Plant-Based Diet.” This diet usually leads to healthy weight loss, but it’s also the only diet that I know of that can consistently reverse medical conditions such as high blood pressure, diabetes, high cholesterol and even heart disease, independent of weight loss. However, since it is more strict than a vegan diet, most people aren’t motivated to attempt this way of eating unless they have accumulated enough diseases and medicines to make their life miserable.

If you’re like the majority of individuals who can’t realistically make instant dietary changes, this is my advice. Use any means necessary to eat more plant based foods. If you need to smother celery or apples in peanut butter to eat them, then do it. If you can’t stop eating pizza, keep eating pizza but add some veggies as toppings. If most beans make you gassy, then try less gassy beans like edamame or lentils. Find a way, be creative.

A healthy recipe should be defined by what percentage of the ingredients are whole plant foods. Try to keep this percentage as high as possible. Use other, less healthy ingredients to make the recipe taste good. And when you’re ready to exclude less healthy foods from your diet, do it.

Remember, as long as you eat healthier 3 months from now than you’re eating today, you’re heading in the right direction. No change is too small.

Photo by Annie Spratt on Unsplash

Freeman, B.C. and G.A. Beattie. 2008. An Overview of Plant Defenses against Pathogens and Herbivores. The Plant Health Instructor. DOI: 10.1094/PHI-I-2008-0226-01

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Murugaiyah V, Mattson MP. Neurohormetic phytochemicals: An evolutionary-bioenergetic perspective. Neurochem Int. 2015 Oct;89:271-80. doi: 10.1016/j.neuint.2015.03.009. Epub 2015 Apr 7. Review. PubMed PMID: 25861940; PubMed Central PMCID: PMC4586293.

Colin-Benoit E, Friolet R, Rusca M, Teta D, Gobin N. [Combination of hemodialysis and hemofiltration in severe caffeine intoxication]. Nephrol Ther. 2017 May;13(3):183-187. doi: 10.1016/j.nephro.2016.10.005. Epub 2017 Apr 25. French. PubMed PMID: 28455110.

Omenn GS, Goodman GE, Thornquist MD, Balmes J, Cullen MR, Glass A, Keogh JP, Meyskens FL, Valanis B, Williams JH, Barnhart S, Hammar S. Effects of a combination of beta carotene and vitamin A on lung cancer and cardiovascular disease. N Engl J Med. 1996 May 2;334(18):1150-5. PubMed PMID: 8602180.

Goodman GE, Thornquist MD, Balmes J, Cullen MR, Meyskens FL Jr, Omenn GS, Valanis B, Williams JH Jr. The Beta-Carotene and Retinol Efficacy Trial: incidence of lung cancer and cardiovascular disease mortality during 6-year follow-up after stopping beta-carotene and retinol supplements. J Natl Cancer Inst. 2004 Dec 1;96(23):1743-50. PubMed PMID: 15572756.

Sahand Rahnama-Moghadam, et al, Richard A. Lange. Heart and Toxins, 2015

https://www.aad.org/public/diseases/itchy-skin/poison-ivy-oak-and-sumac#causes

https://toxnet.nlm.nih.gov/cgi-bin/sis/search/a?dbs+hsdb:@term+@DOCNO+7485

http://lpi.oregonstate.edu/mic/dietary-factors/phytochemicals/

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