New England Patriots quarterback Tom Brady and his supermodel wife, Gisele Bündchen, have been making headlines this year because of their strict and health-focused diet. What they eat has been credited with helping Tom stay injury-free (along with winning another Super Bowl) and Gisele stay, well, a supermodel.
What exactly do they eat? Their family eats a mostly plant-based diet rich in whole grains, fruit, vegetables, and legumes—all of which I fully support. They also avoid added sugar and most processed foods—again, I totally agree. But there are, however, some questionable aspects of their diet. One such aspect, is that Tom apparently avoids nightshade vegetables because of the belief that they cause inflammation. This notion—that nightshades cause inflammation—is something I’ve frequently seen on nutrition blogs, or mentioned in popular magazines. Is there any evidence to suggest that nightshades cause inflammation? And what exactly is a nightshade?
Nightshades, or solanaceae, are a family of flowering plants. There are over 2,000 species in the nightshade family. Edible species include: potatoes, tomatoes, eggplant, peppers, tomatillos, okra, sorrel, goji berries, and gooseberries. Although some species are edible, a handful of species are extremely toxic and can be deadly if consumed. These poisonous species have been feared for centuries and their ancient folklore is still used in popular culture. For example, Atropa belladonna, or “deadly nightshade” likely inspired the deadly “nightlock” berries in The Hunger Games books. There’s also the Mandragora officinarum, or “mandrake”, and Datura stramonium, or “devil’s snare”—both of which were featured in the Harry Potter books. Tomatoes were considered “poison apples” in late 18th century Europe after numerous reports that aristocrats were falling ill and dying after consuming them. However, it turned out to be the lead-containing plates that, when in contact with highly acidic tomatoes, leached lead into the food. Those eating tomatoes off plates without lead were fine.
So yes, some nightshade plants are very toxic, and thus, we should avoid eating them. Just like we should also avoid eating off lead plates. But what about the nightshades that humans have been eating safely for centuries? Are these harmful? Do they cause inflammation?
After reviewing the literature on this topic, I found no peer-reviewed, human studies suggesting that edible nightshades cause inflammation or are harmful in any significant way. The most serious side effect I could find was heartburn from eating spicy peppers (1). Some people reported improvement in join pain after eliminating nightshades from their diet, but this is based on anecdotal evidence with no human studies actually putting it to the test. Potatoes are often considered unhealthy, but this a result how we prepare them (fried and covered in salt). When prepared in a soup, boiled, or roasted, potatoes are actually quite healthy. Similarly, all other nightshades vegetables are extremely health-promoting and we should be making an effort to include them in our diet, not exclude them. In fact, some nightshades are rich in unique nutrients that appear especially beneficial to our health.
There is a small amount of evidence showing that capsaicin (the compound that gives peppers their heat) may be capable of slowing cancer cell growth (in a petri dish), may improve vascular function, and appears to improve symptoms in people with irritable bowel syndrome (2-5). Men consuming high amounts of lycopene (the pigment that gives tomatoes their red color) have a lower risk of developing prostate cancer (6-8). And smoking tobacco may reduce one’s risk of developing Parkinson’s disease. Wait, what?
You heard correct. There is strong epidemiological evidence that tobacco smokers have a lower risk of developing Parkinson’s disease compared to non-smokers (9). The theory is that nicotine, found in tobacco leaves, may offer some sort of protection from this disease. Now I’m not saying anyone should start, or continue, smoking tobacco, as the negative consequences far outweigh any potential positive ones. But what if there was another way to ingest nicotine without damaging our health?
It turns out there is! Tobacco just so happens to be part of the nightshade family. And it’s not the only family member that contains nicotine. Tomatoes, potatoes, eggplant, and peppers all contain small amounts of nicotine (although not enough to cause an eggplant addition). In 2013, a study was published that looked at dietary nicotine consumption and Parkinson’s disease (10). They found that nightshade vegetable consumption was inversely associated with Parkinson’s disease (people without the disease tended to eat more nightshades, whereas people diagnosed with Parkinson’s tended to eat fewer). This association was strengthened when they specifically looked at total dietary nicotine consumption.
Now this type of study can’t prove cause and effect, but it supports the hypothesis that nicotine may be protective against Parkinson’s disease. It also aligns with observations of Mediterranean populations that consume a lot of these foods and, maybe not so coincidentally, have low rates of neurodegenerative diseases. Plus, given the lack of evidence that (edible) nightshades cause inflammation, or have any other negative health effect, why not eat more peppers, tomatoes, eggplant, and potatoes, as these foods are good for our overall health.
In the end, Tom Brady is a great quarterback (although not as great as Aaron Rodgers—Go Pack Go!), but his choice to avoid nightshade vegetables is unsubstantiated. There are no peer-reviewed, human studies indicating that nightshade consumption causes inflammation. Until there are studies to prove otherwise, people should continue to include edible nightshades in their diet, as the evidence suggests they promote our health, not undermine it. The same cannot be said for the poisonous species—those ones will kill you.
- The effects of capsaicin on reflux, gastric emptying and dyspepsia.
- Capsaicin, a Spicy Component of Hot Pepper, Induces Apoptosis by Activation of the Peroxisome Proliferator-Activated Receptor γ in HT-29 Human Colon Cancer Cells
- Capsaicin Inhibits in Vitro and in Vivo Angiogenesis
- Influence of capsicum extract and capsaicin on endothelial health.
- Effect of red pepper on symptoms of irritable bowel syndrome: preliminary study.
- Intake of carotenoids and retinol in relation to risk of prostate cancer.
- Lower prostate cancer risk in men with elevated plasma lycopene levels: results of a prospective analysis.
- Inverse associations between plasma lycopene and other carotenoids and prostate cancer.
- A meta-analysis of coffee drinking, cigarette smoking, and the risk of Parkinson’s disease
- Nicotine from edible Solanaceae and risk of Parkinson disease