A food allergy is serious. This means pretty much instantly what you ate will make your mouth swell up, tongue swell, ears swell, throat gets tight, itching, hives, rashes, watery eyes etc. It can range from mild to fatal depending on how much you eat and how allergic you are. These are foods you want to avoid like the plague because it can make you quite ill. A true allergy is instant and requires the presence of Immunoglobin E (IgE) antibodies against the food, and a food intolerance does not.
A food intolerance is a delayed reaction & takes place in the gut, causing mostly digestion issues, brain fog, inflammation and other body-wide symptoms. The classification of an intolerance is a bit more complex, and it can happen in a few different ways.
1. Intolerance can result from the absence of a specific chemical or enzyme needed to digest a food substance. So when you eat the food (say fructose), when the time comes in digestion to be broke down, it won't be able to. This causes a tough digestion & discomfort/pain. Often this is called a hereditary intolerance.
2. Intolerance can be a result of an abnormality in the body's ability to absorb certain nutrients needed. (Malabsorption)
3. Intolerance can also be a reaction to naturally occurring chemicals in foods which causes the white blood cells to degranulate and release histamine. This can happen to the protein in one specific food such as corn, or a component of it. An example of this is salicylate sensitivity, where all foods containing that chemical will give you a reaction. People with an intolerance or sensitivity to a food component will have to remove a whole variety of foods from their diet to find relief.
An intolerance is delayed. Often times it can happen 1-2 days AFTER you ate the offending food. That's because first it creates inflammation locally in the stomach, but afterwards the autoimmune cascade that happens body-wide can take some time to manifest. Therefore it can be hard to figure out the culprit by looking back at what you ate. Some reactions happen 12 hours later, some 24, some 36. For me personally I have a very sensitive stomach so I will know within a few hours if a food I ate is an intolerance by how it feels in my digestive tract. But the full ramifications of the intolerance (migraines, fatigue, etc) can take a full 24 hours to develop.
Food allergy testing is most commonly done by blood test checking for IgG or IgE antibodies to certain foods. This is important to know if you have a life threatening allergy to anything. You can find an at home test for IgE here, and the test for IgG here.
Food intolerance testing is also done via blood testing, and it is equally important to know what your triggers are in order to reduce inflammation in your body. I have been dealing with food intolerances since 2010 and the best of the best food intolerance test I have found is called MRT. MRT is incredibly sensitive and accurate because instead of looking for specific markers such as IgG, IgE, or IgA (which will not be accurate for an intolerance), it looks at how your white blood cells directly react to foods. The way the test is done in the lab is that they separate out your white blood cells from your whole blood. Once separated they take the protein of many different food items and introduce it to your white blood cells, and then watch for a reaction. If your white blood cells begin to degranulate and release histamine then they know instantly that food is an intolerance, because thats exactly what is happening inside of your body as well each time you eat the food. MRT is very cutting edge and has never failed me in being incredibly accurate. You can get this done via an at home kit (this is what I do), and you can find the MRT test here.
While a food intolerance isn't life threatening it can be painful & really damaging to the stomach & intestines. I REALLY recommend this to those with Lyme or other autoimmune illnesses. Going on a gluten free or paleo diet can help, but until you remove foods not tolerated by your body you won't be able to fully help your immune system to the best of your ability (80% of your immune system is in the gut). And we all know you need the strongest immune system you can get to fight Lyme!
When I first had the MRT testing done in 2010 I had A LOT of foods I ate commonly come up. It made sense because I had a horrible case of leaky gut & candida. Not a good situation in the ole stomach at all! Of course I was stubborn at first, and it took me about 6 months to finally cut those foods out & work on healing my stomach. But since the end of 2011 I have gone on a strict diet, took care of the candida, added in lots of probiotics, began drinking marshmallow root tea & taking DGL licorice daily. And as you can see below (I attached a photo), my intolerance list from 2013 is much smaller. A lot of things have moved off of it & some others moved on. I typically get this test done yearly, because things change in my body and I found that once a year is a perfect timeline.
This came down to me just wanting to better help my stomach out, since its constantly giving me pain & trouble. I also wanted to help take some of the inflammatory burden off of my body. For some reason with Lyme many people develop a lot of different allergies and intolerances.. It's very odd. I have a soy allergy and also developed an apple, pear, kiwi, cherry allergy. My whole mouth swells up & it's actually really scary! A lot of times I will eat something and get an itchy mouth & stop without knowing what did it. So for my safety & to spare myself I get IgE testing as well. I found that a combination of these two testing modalities keep me safe and educated on both my food allergies & also any food intolerances.
This was long but I hope it helped better explain the two!