I've been catching up on some of Robb Wolf's older podcasts, and yesterday came across an interesting mention. I've often heard that some long-time vegetarians/vegans who later try to eat meat again get very sick, and as a result, believe they have to avoid meat entirely because it's "poisonous" to them. Yet, other vegetarians/vegans can make the transition back to meat without a problem.
Robb Wolf seems to believe that the issue is a psychosomatic one for those who get sick after reintroducing meat to their diets. Once they get over their mental guilt/concern over eating meat, the sickness symptoms go away.
If this is true, then can't we also say that some people who introduce, say, milk, back into their diets after going paleo, may not actually be lactose intolerant or have other real, physical maladies (though possible), but that they have mental blocks/guilt about milk being acceptable in their diet? Can the same be said of other foods?
(Mind you, I don't mean to imply that grains/legumes fall under this psychosomatic phenomenon.)
I've been reading a lot recently on the placebo and nocebo effects... fascinating stuff. I also participated last year in a rigorously controlled double-blind medication study on inflammation and mood, which sort of triggered my interest in Paleo when I came across it. Okay, so, how is this related to your question? This way - the mind is a powerful, powerful thing, when you look at how our thoughts and beliefs are able to affect healing and disease in the body. I'm not so far out that I think one can wish away cancer, but when it comes to illness symptoms like digestion, I absolutely believe you can think your self ill by accident. This is why I'm not a huge fan of the n=1 philosophy; it's just too easy to let your expectations and beliefs influence the outcome. In vivo studies for the win! ;)
Some places to find info:
Check out Ben Goldacre's book Bad Science for a great chapter on placebo and nocebo.
Here's a video of Ben Goldacre talking about the placebo effect:
It's possible that you would stop producing (or produce much less of) certain digestive enzymes such as elastase as a result of going without meat for an extended period of time. The sudden reintroduction might catch your guts unawares. This could occur with lactase etc.
That being said, I experienced no such trouble after adding meat, eggs and cheese back in after 8 years of a vegan diet.
I would think it could be psychosomatic. Another possibility is that since the body produces the enzymes it needs to digest the kinds of foods the person eats, and shuts down production of those the person doesnt' need, perhaps the people who have a hard time re-adjusting to a paleo diet are those who take a longer time for their bodies to start producing the proper enzymes after going a long time without eating certain foods. Or maybe even a combination of the two factors...psychosomatic and enzymatic?
It certainly seems possible that foods can cause nocebo reactions if people believe those foods cause problems.
BACKGROUND: Diagnosis of lactose intolerance is based on a "positive" H(2) breath test associated with abdominal symptoms. The present study established to what extent the occurrence of symptoms during a "negative" H(2) breath test may result from a "nocebo effect" instead of lack of sensitivity of the procedure.
RESULTS: Twelve out of 27 patients (44.4%), and unexpectedly also 14 (25.9%) controls presented abdominal symptoms during the sham test. The difference between the two groups was not significant (P<0.15) OR 2.28; C.I. 0.77-6.78.
CONCLUSION: In most instances, symptoms reported by patients during a negative lactose H(2)BT cannot be attributed to a false-negative test. Instead, a non-organic component, resulting from negative expectations ("nocebo effect") is likely implicated. Moreover, also in patients diagnosed as lactose intolerant, the need for restricting the primary source of dietary calcium should be critically reconsidered.
From the results section of the paper:
Of the 27 patients reporting symptoms, despite a negative test, 12 (4 male, 8 female) (44.4%), presented with symptoms also during the sham test. As expected, no increase in the excretion of H2 or CH4 was recorded in any patient during the sham test. Symptoms consisted of abdominal pain (seven patients), bloating and gaseousness (eight patients), and were, in all instances, the same as those reported during the first test. As occurred during the standard lactose tolerance test, more than one symptom was reported by some patients. Interestingly, no patient had diarrhoea or bowel movements during the sham test or the 4 h thereafter.
No increase in H2 or CH4 excretion was observed in the 54 control patients. Nonetheless, 14 patients (25.9%) in this group also reported symptoms during the sham test, consisting of abdominal pain (nine patients), bloating and gaseousness (11 patients), while the remaining 40 patients (74.1%) did not complain of any symptom. Again, no cases of diarrhoea or bowel movements were reported.
So if you know that lactose can cause certain symptoms it might just cause those symptoms if you think you are eating lactose, even if there is actually no lactose in what you are eating. Even people who were really lactose intolerant reported symptoms in the sham test. I find it interesting that real symptoms of abdominal pain, bloating and gaseousness can appear to be caused by the expectation that they will occur.
How many people here strongly believe that wheat, gluten, sugar or fructose etc are toxic and know that they can cause certain negative effects? I do wonder what effect this knowledge and beliefs have on personal responses to food.
None of this means lactose intolerance or any other food reactions are not real for many people.
I think a lot depends on people's mind sets about foods and eating. If they have strong emotional components to their food choices and food belief systems, I think absolutely that alone can cause physiological side effects. However, if one doesn't really have a pony in the race emotionally, and observes with open minded curiosity, this is probably less of a danger.
But I also agree with Helen that sudden changes in types of food consumption are well known to cause temporary system upset all by themselves, regardless of if the new food is healthier or not. Some people are better adapted to sudden change than others, but this kind of thing is one reason I often suggest a bit of a gradual change over to new eating styles, especially for those who are already ill of health.
I think those symptoms could be entirely real. Digesting different types of foods takes different flora and fauna in our gut. That flora and fauna can change to accomodate what we're eating, but that adjustment takes time. Switching from one food type to another quickly can cause very real problems.
Historian Stephen Ambrose wrote about explorers Lewis and Clark learning this the hard way. As they turned the Great Bend of the Missouri River in North Dakota, their diet went quickly from eating several pounds of meat per day to eating nearly all plant roots. The Indians warned them to change their diets slowly to let their stomachs adjust, but the men were famished and made the switch overnight. The results were disastrous, and the men were utterly incapacitated for days and deathly ill. Ambrose wrote that, at one point, a small child with a pocket knife could have wiped out the entire exploring party!