The Nightshade family of plants (which includes a variety of fruits and vegetables) contains some of the most aggravating and challenging foods for some individuals’ health. Similarly, scores of people have absolutely no issues whatsoever with consuming Nightshades.
Furthermore, the Nightshade family is expansive, the vegetables and fruits within it numbering in the thousands, so suggesting these plants are troublesome seems (to some) over-prescriptive.
TO NOTE: there is no need for our usual “Hunter-Gatherer Diet Debate” question here – there is absolutely no doubt that the vegetables in this particular plant family would have been eaten whenever they were found by hunter-gatherers. And, in fact, on the Paleo Diet template Nightshade vegetables are perfectly permitted – in fact encouraged. Certain Nightshades contain some compounds which have been found to be beneficial to overall human health – helping to regulate and improve immune health and stimulate healing.
And yet, for those with autoimmune conditions, we must analyse Nightshades from an immunological and inflammation perspective, examining the aggravation potential that the compounds contained within Nightshades may have. Comprehending how Nightshades can stimulate inflammation is fundamental to those following an Autoimmune Protocol. It may also be of interest to anyone who has begun with Paleo and yet found insufficient symptom relief.
Nightshades have been – anecdotally – associated with a variety of inflammation-type symptoms. And yet Nightshades are complex foods which contain many compounds. This makes pinpointing just one compound or molecule as the source of the ‘problems’ with Nightshades challenging, both scientifically and clinically.
This underlines a simple truth about nutritional science. Plants are almost always phenomenally complex. Isolating every individual molecule or compound within them for study has thus far proved relatively impossible. This is why ‘whole food nutrition’ is always deemed better than supplementation with isolated compounds. Basically because the whole plants – with precise, innate ratios and balance – seem to be greater than the sum of their individual parts. For example, we know that eating broccoli sprouts is better for us than supplementing with the compounds we have identified are released when the broccoli seeds actually sprout. Whilst we can postulate as to why, we are not yet able to recreate the plant synergy of ‘broccoli sprouts’ within a laboratory setting (though many supplement companies try).
If this is true for the ‘good side’ of plant nutrition, the same is also true for the ‘dark side’: no single compound in Nightshades has been universally designated as ‘bad’, with studies on certain compounds proving somewhat inconclusive. It could therefore be that it is the whole collection of potentially inflammatory and immune triggering compounds within Nightshades that, when concentrated together in one plant, create issues.
And it must be stressed that these foods DO create issues: there is much anecdotal evidence and case study reporting which attests to the miraculous symptom relief experienced by some individuals after eliminating them (with the immediate return of symptoms when consumption was resumed).
What Are Nightshades
Nightshades belong to the family of Solanaceae plants of the Solanum genus. The common foods included in this family are white potatoes (NOT sweet), tomatoes, peppers – both sweet and hot and all spices derived from these (paprika, pimento, cayenne, chilli etc.) and aubergines. The not-so-commonly known Nightshades are goji berries, ashwagandha and cape gooseberries (physalis).
As you can see, these Nightshades are some of the most polyphenol- and nutrient-rich foodstuffs around, and they are filled with flavonoids and compounds like capsaicin which are linked to a positive impact on overall health. It is perhaps a bit bizarre, therefore, that these foods should be recommended for avoidance in anyone with a health condition. But first, to dispel some myths:
Some have linked Nightshades to a ‘cross-reactive’ issue, suggesting that Nightshades trigger an immune response ‘similar to gluten’. There is little evidence for this in the literature or clinically.
Other suggestions are that glykoalkaloids are to blame (a chemical compound we discussed at length on our All About Potatoes page). In Nightshades, the glykoalkaloid named solanine is purported to have pro-inflammatory properties. This is quite possible, though again the scientific literature does not evidence a direct causation between solanine and inflammation.
Then there’s the “Calcitriol” suggestion – that overconsumption of Nightshades causes us to absorb a ton of calcium from our diet which prevents effective kidney function and causes problems … or deposits calcium in joints etc. which is what causes the joint pain etc… However, yet again this has no evidence to support the claim.
Furthermore, there are suggestions that Nightshades contain not just solanine or calcitriol but other ‘toxic’ alkaloids, all capable of causing inflammation, immune firing and negative health consequences… But again, science (real, hard science which establishes the mechanisms of action) is hard to find.
This Calcitriol suggestion is incredibly far-fetched because most people who stop eating Nightshades notice almost immediate symptom improvement. This means that their problems with Nightshades simply CANNOT emerge from the formulation of calcium deposits because these would take far, far longer to ‘clear’ than a few days not eating the offending plants.
The other suggestions are more plausible, and despite the lack of scientific, mechanistic data to support the claims, there are literally millions of personal stories which support the fact that removal of Nightshades from the diet is associated with overall improvement in health outcomes. And yes, we know that the plural of anecdote is not data. But we are also aware that nutrition is a field in which evidence is building every day. Just because a mechanism has not been identified yet in no way means that it won’t be.
(Sidebar here – fantastic sounding claims in articles like this make the evidence against Nightshades sound overwhelming… skip down to the linked studies and you will see evidence only on Potatoes, a few drugs – and the beneficial use of certain alkaloid compounds in medicines… This type of article and site is one of the main reasons why our site exists… because nonsense like this scares people about food – and fear should never form part of the way we view the nutrition we consume).
Potential Truth: Nightshades and the Plant Protection Principle
The non-scientific way of explaining what it is about Nightshades that makes them so challenging to humans is that packaged alongside all of the ‘goodness’ of these fruits and vegetables is the plants’ protection mechanisms designed to prevent their consumption by animals (which includes humans).
The plant protection mechanisms aren’t just alkaloids (above), but a complex array of compounds – any one of which may prove problematic for any number of reasons.
Some of the chemical compounds in Nightshades which may cause ‘issues’ are as follows:
Lectins – detailed extensively on our All About Gluten page but about which we recap below
Saponins – one of which is the glycoalkaloid solanine, and glycoalkaloids are described fully on our All About Potatoes page but further implications of which are detailed below
To briefly recap Lectins – these are getting a lot of heat at the moment because there are serious concerns about the capacity of the human digestive system to break down certain lectins (though by no means all lectins). These lectins are believed to be a fundamental part of the plant protection systems because they are essentially ‘binding’ proteins which keep the ‘goodness’ in the plant locked away and protected from being broken down.
Known as ‘toxic lectins’, those lectins with high proline content are more difficult to digest. For various reasons and via several mechanisms (again, more in-depth details are on our All About Gluten page) these undigested lectins have the ability to create Intestinal Permeability. This so-called ‘leaky gut’ has been identified as a key underlying factor in the development and progression of autoimmune conditions, contributing to systemic inflammation and a heightened/up-regulated immune response due to the localised immune/inflammatory response and the translocation of compounds across the gut wall.
The issue with Nightshade lectins is that there is a diverse range of quantities within each different plant, within species of the same plant – and in the case of tomatoes, the lectin quantity varies from tomato to tomato (even on the same vine). Tomato lectin is known to cross into the bloodstream relatively quickly (this has been established in laboratory testing) but this isn’t true of all Nightshades.
And yet, when the gut integrity is already compromised (as is always believed to be the case in anyone with an autoimmune condition), the presence of lectins in the diet can exacerbate the situation. Once these lectins are in the digestive tract and the intestines are permeable there is a high correlation with inflammatory conditions which affect the joints (rheumatoid arthritis is commonly associated with Nightshades) and the brain (‘brain fog’ is often reported with Nightshade consumption).
Intestinal permeability is never a good thing for the body as a whole – and the presence of toxic lectins in the diet of those with already compromised gastrointestinal tracts can be incredibly problematic.
Saponins, on the other hand, are believed to have a directly aggravating effect on the immune system. In fact, certain vaccines (all of which must contain ‘irritants’ in order to elicit an immune response and the creation of an immune ‘memory’) use a saponin as the adjuvant (aggravator). Anyone with autoimmunity already has an up-regulated and dysregulated immune response. In autoimmunity the immune system is so heightened that ‘self’ tissue has become a target and the immune response is proving difficult for the body’s own immuno-regulatory systems to turn off. Adding in adjuvants is almost like adding fuel to a fire – and the inflammation that is already systemic can be exacerbated by the consumption of saponin containing foods – i.e Nightshades.
The Breadth & Variation of Nightshade Sensitivity
To us here at Paleo in the UK, it is the Nightshades which exemplify the whole Autoimmune Paleo approach. These plants contain perfectly tolerable compounds when the body is healthy. And yet these compounds are also proven to be immune triggering, inflammatory and disruptive to the intestinal barrier. Therefore, in those with compromised health to begin with it is perfectly possible that the added burden that is placed on the body by the glycoalkaloids (saponins) and lectins found in Nightshades can prove to be one stress too many in an already inflamed body.
We have observed that very few people are equally sensitive to all Nightshades. Those with very impaired immunity tend to have obvious and clear reactions to these vegetables. Those with immune-based reactivities tend to react more to certain plants, those with gut-centred inflammation and autoimmunity often reacting to different plants. It is common to tolerate potatoes and not tomatoes – and vice versa.
It is also relatively common that once a degree of healing has taken place Nightshades can often re-enter the diet. This is often not all Nightshades, with some continuing to create reactions even years after AIP has been trialled (certain seed spices, chilli/peppers and tomatoes are common long-term aggravators for some, though many reintroduce all Nightshades without issue). Nightshades, Eggs and Nuts & Seeds are all substances that really should be brought back into the diet as soon as possible if tolerated. These are incredibly rich sources of nutrition and, speaking honestly, it really should be possible to regulate the immune system enough to allow such potent nutritional powerhouses back into the diet. Of course, there will always be exceptions – and successful reintroduction will depend on precisely what was being reacted to in the Nightshade.
Is It Really the “NIGHTSHADE” Part…
There are two further considerations we would like to expand upon when it comes to Nightshades. The first is to question the cause of intestinal permeability and hence where the real issue is with Nightshades. Often blamed as the ‘culprit’ for issues, it is very possible that the saponin content of the Nightshade is only problematic because it is in the wrong place in the body. The translocation across the gut barrier of compounds that do not belong in the bloodstream is a major factor in autoimmunity and multiple sensitivity syndromes. In cases such as this, the Nightshade (and the compounds within) really are not to ‘blame’ – they are simply escapees which cause immune aggravation, though the real cause for the intestinal permeability is elsewhere (gluten, for example, or even excess stress, excess alcohol, highly refined-sugar diets, diets too full of damaged fats… all of which are capable of creating intestinal permeability which will allow the Nightshades to get into the wrong place).
The second consideration is that beyond lectins and saponins, other plant compounds have been suggested to cause inflammatory issues in susceptible individuals (i.e. those with existing health conditions, existing intestinal permeability and/or ever-present stresses which are weakening the immune system etc.). The most well known of these are salicylates and oxalates.
Again, the prospect that salicylates and oxalates could be problematic for individuals is regularly dismissed by the conventional medical model. And yet, these are organic salts inherent in many plant foods which are now being reported to cause issues. There are overlapping concerns, however – because many of the foods high in oxalate are also high in salicylates and oxalates. Some Nightshades contain all of these salts, many of them contain none of these…
You see – plants are complex.
In truth, a full discussion of the science behind Salicylates, Oxalates, Histamine etc. will probably crop up on our Blog and our Deeper Science page in the future… But behind all of these perfectly natural plant compounds lies one essential truth:
When it comes to Paleo principles, we focus on foods that our human digestive systems were evolved to eat. In this approach, Nightshade vegetables are not only acceptable – they are positive encouraged.
When we are discussing the limitations of digestion and ‘processing’ within autoimmunity, this has little to do with human evolution and everything to do with the impaired functioning of the individuals in question. Each of the plant compounds mentioned above are either well tolerated or easily processed/eliminated in healthy individuals. If you are finding strong reactivity and pain associated with the consumption of Nightshades (or Oxalates, Salicylates, Histamine etc.) we would first recommend working with a practitioner to help you gain dietary clarity.
But secondly, we would encourage you to remember that the goal is never to construct an overly restrictive, obsessive diet which eliminates every food that you have ever reacted to. Instead, the goal is to heal your body, improve your own ‘defence mechanisms’ and re-regulate your immune health and digestive tolerance in order to expand your nutritional landscape to incorporate these foods – including the Nightshades – which are, ultimately, rich sources of nutrients ON TOP of any potentially aggravating compounds.