A Quick Look at Food Allergies and Intolerances by Lyle McDonald

In recent year, a lot of ideas have become strangely popular on this place that we call the Internets, one of those is concern over various food allergies and intolerances. As I’ll discuss below, not only are true food allergies and intolerance two totally different things, there is a lot of nonsensical information being thrown around about food allergies.

What seems to have happened is that one person stated that certain ideas were true and a bunch of people who didn’t know any better simply started repeating those ideas until they became an accepted ‘truth’. Unfortunately, science says different and that’s what I’m going to look at.

The most common one that seems to be constantly repeated is that if you eat the same food (usually protein since most true food allergies are caused by proteins) continuously, you can give yourself an allergy to that food. This happens to be utterly wrong as I’ll show below.

There are other silly ideas, one of the dumbest I’ve seen of late is that you can cure a food allergy by not eating that food for 6 weeks. This is not only wrong but potentially fatal. True food allergies (again, I’ll discuss what this means in a second) never go away; if someone has a true allergy to a food, they can’t ever eat that food again for all practical purposes.

Actually, that’s not entirely true, one weird study showed that children with peanut allergies could eventually get to where they could eat half a peanut but it took months and months of feeding them like 1/4 peanut to get them to that level. Hooray. For all practical purposes, a true food allergy never goes away and the idea that abstaining from that food will make it go away is simply absurd.

Since most food allergies occur in response to protein foods, I’m actually going to simply be excerpting the section from The Protein Book about food allergies and intolerances. For anybody who’s interested, I’ve included the references cited in this section at the end of the article.

Food Allergies and Intolerances

To finish up this chapter, I want to make a few comments about food allergies and intolerances, which I touched on above in the section on dairy foods. Commonly, the terms food allergy and food intolerance are used interchangeably although they actually represent very different phenomena (40).

Food intolerance, such as lactose intolerance from dairy products, typically occurs due to a lack of appropriate digestive enzymes and this tends to cause upset stomach, gas, bloating or diarrhea. At worst, food intolerances typically cause some discomfort but no real danger.

In contrast, a true food allergy generates an immune reaction in the body. This is potentially much more severe and can cause respiratory, stomach, skin and cardiovascular symptoms; anaphylactic shock and death can also occur in extreme cases (40). True food allergies are typically caused when small amounts of proteins enter the bloodstream. This can occur during childhood when the gut lining isn’t fully developed or later in life due to a compromised stomach barrier. Some allergens can also enter the body through the respiratory system.

While technically any food can cause a true allergic response, protein foods tend to be the most common culprits with milk, egg, peanuts, tree nuts, some fish and shellfish being the most common causes of allergies (41). Gluten, a protein found in grains such as wheat, barley and rye, is also a common source of food allergies (42). Gluten allergies can be especially troublesome for athletes with high caloric and carbohydrate requirements since grains cannot be consumed; increasing commercial availability of gluten free foods can help to ensure adequate calorie and carbohydrate intake.

True food allergies are thought to occur in 3-4% of adults. There are a number of different ways to determine the presence of a true food allergy but, from a practical standpoint, if eating a given protein source causes problems of the sort described above, that tells the athlete all they need to know. For the most part, there is little to no treatment for true food allergies; avoiding the problem food is the best and only option (40).


40. Ortolani C and Pastorello EA. Food allergies and food intolerances. Best Pract Res Clin Gastroenterol. (2006) 20(3):467- 83.
41. Sicherer SH and Sampson HA. 9. Food allergy. J Allergy Clin Immunol. (2006) 117(2 Suppl Mini-Primer):S470-5.
42. Schuppan D et. al. Celiac disease: epidemiology, pathogenesis, diagnosis, and nutritional management. Nutr Clin Care. (2005) 8(2):54-69.

Summing Up: So hopefully the section above helped make the distinction between a food intolerance and a true allergy. True food allergies are rare and can be fatal like any true allergic reaction. Eating that food causes a massive immune response and this can cause people to drop dead.

This is not a joke, children with peanut allergies who are given a food with even trace amounts of peanuts can go into anaphylactic shock, have trouble breathing and can die. Contrast this to when someone has a lactose (milk) intolerance, drinks a glass of milk and gets real gassy. They are not the same thing but people confuse them all the time.

As well, food intolerances are reported at something like ten times their actual rate of occurrence; people eat something and don’t feel good and assume they have an intolerance when they really don’t.

And, as discussed above, true food allergies don’t occur because you eat a given protein source too often. An allergy occurs when a bit of undigested protein gets into the bloodstream and causes the body to mount an allergic reaction to it via the immune system. Since the gut lining is set up to avoid this, the only way that a true food allergy can usually occur is if the gut lining is compromised. Under those conditions, small pieces of undigested proteins can slip through into the bloodstream and that’s when the problems start.

Various disease conditions can cause this to occur (and as noted children with undeveloped gut linings can develop food allergies because of it) but this pre-existing condition has to exist for a true allergy to develop. For example, there is a condition called leaky gut syndrome which is exactly what it sounds like, the gut leaks stuff into the bloodstream; this can cause all kinds of problems.

And once a true food allergy exists, it’s yours forever. The immune system is amazing in this way, remembering how to mount a response to offenders basically forever (this is the basis of immunization of course, give the person a small case of a certain disease so that the immune system ramps up, and then they can fight off that disease in the future). So once you have a true food allergy, you have it for life.

It is certainly not my area of expertise but people who fear that they may have a food allergy can get explicit testing for it done. However, as I noted above, if you eat something and nearly die, you know all you need to know anyhow. This is true at least in the case of severe food allergies. Of course, it seems that it is possible to have mild food allergies (which are probably more like intolerances) and getting tested for those may be useful if someone suspects a problem.

If for no other reason, food intolerances seem to be able to generate a stress response and this appears to cause water retention in some people (in addition to just generally not feeling very good. I have a hunch that the whole idea of ‘eating foods you’re ‘allergic’ to stops weight loss’ is probably due to this mechanism: you start holding water due to a stress response and it masks fat loss.

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