# Does The Digestive System React Badly When A Long-Term Vegan (Years, Decades) Eats Meat? **URL:** \ **Category:** Factual Questions\ **Created:** [February 25, 2019, 7:21pm UTC](https://boards.straightdope.com/t/does-the-digestive-system-react-badly-when-a-long-term-vegan-years-decades-eats-meat/830201 "2019-02-25T19:21:10Z")\ **Posts on this page:** 3\ **Page:** 2
**Author:** ![XT](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/xt/32/456_2.png) [@XT](https://boards.straightdope.com/u/XT)\ **Post date:** [February 28, 2019, 4:43pm UTC](https://boards.straightdope.com/t/does-the-digestive-system-react-badly-when-a-long-term-vegan-years-decades-eats-meat/830201/21 "2019-02-28T16:43:45Z")
Well, according to [this](http://sciencenordic.com/does-meat-make-vegetarians-ill) there is some doubt that there is a scientific basis for this (unlike the anecdotal one that we have all heard and, frankly, I thought was fact): > [@](#): > > People sometimes say that vegetarians get sick if they begin eating meat again. Research doesn’t back them up. > > Most of us who know vegetarians have heard scary stories: A vegetarian accidentally gets a bit of pepperoni on her pizza slice or her soup contains chicken broth and she gets very ill. > > Do our bodies really react so strongly to meat after avoiding it for a while? Or is this just a vegetarian myth? > > We’ve put the question to scientists. > > If our scientists are right, they say there’s no reason to fear a catastrophe if a vegetarian chomps into the wrong pizza. But a vegetarian who decides to start a new life as a carnivore with a huge T-bone steak might risk an upset stomach > [@](#): > > Don’t lose it > Few researchers have studied the consequences when vegetarians fall for temptation or simply make a mistake. However, Professor Birger Svihus of the Norwegian University of Life Sciences (UMB)’s Department of Animal and Aquaculture Sciences can make some educated guesses based on his general knowledge of the human digestive system. > > “There’s no reason to believe we get sick. I can’t conceive of our bodies losing the capability to tackle meat,” he says. > > “The nutrients in meats also have to be digested when we eat other foods. The enzymes that the body produces to break down meat proteins are also used to metabolize plant proteins.” > [@](#): > > Heavy start > Professor Bjørn Skålhegg of the University of Oslo’s Department of Nutrition concurs. Nothing would indicate that the bodies of vegetarians should reject meats. > > “A person might have a little problem if he or she started right out on a huge steak. Their body might not have sufficient levels of the right enzymes. Along the same lines it can be hard to digest any large meal after a long fast or period of starvation,” he says. > > You might also have this problem if you start to eat other kinds of foods that you haven’t eaten in a long time. > > The lonely geek who does nothing but heat up frozen pizzas day in and day out might experience some intestinal discomfort if he suddenly starts eating a lot of fruit and vegetables. > [@](#): > > One-sided diets with large seasonal variations > “We tend to forget human history,” says Svihus. “Just 50 years ago many people [in Norway] had very unbalanced diets from day to day. And there were big variations from season to season.” > > “In the late summer they had vegetables and in the autumn there was a meat surplus. But the last rutabagas stored in their cellar would be consumed by March. In March, April and May they had almost no vegetables. Fresh fruit wasn’t available after Christmas.” > > Human beings are adapted to these kinds of regimes. > [@](#): > > Meat allergies > This means that little in our physiology and our ancestral history should cause vegetarians to have problems if they eat a piece of meat. > > “Despite that, there can be some differences between various types of vegetarians. Some have eaten eggs and milk all along, whereas vegans avoid everything from animals. I don’t believe that a vegetarian who has eaten eggs or dairy products would get sick from chicken broth,” says Skålhegg. > > He says that in that case, the reaction would have to be due to a food allergy. > > A very few – less than one percent of the population – are allergic to meats from common livestock, such as pork and beef. If a vegetarian has this kind of allergy, she could have a reaction from just a speck of these meats. I think that any sort of radical change in diet will give anyone gastric distress. I’ve seen this myself…if I suddenly eat a ton of, say, lobster with other rich foods I’ll be in a hell of a lot of distress. I imagine the same goes for someone used to eating Vegan or just vegetarian would have some distress from eating a large steak, since it’s very different than what they are used too. So, I think that the answer to the OP is probably ‘yes’, their digestive systems will react badly and they will probably spend some uncomfortable times on the toilet, but they will adjust fine in a short time…and ‘getting sick’, I’d guess, is probably more a psychological reaction except those who actually have meat based allergies. Getting the shits though…yeah, I think that’s likely. And not just for Vegans or vegetarian types making a change. ---
**Author:** ![doreen](https://avatars.discourse-cdn.com/v4/letter/d/858c86/32.png) [@doreen](https://boards.straightdope.com/u/doreen)\ **Post date:** [February 28, 2019, 6:54pm UTC](https://boards.straightdope.com/t/does-the-digestive-system-react-badly-when-a-long-term-vegan-years-decades-eats-meat/830201/22 "2019-02-28T18:54:58Z")
> [@XT](#): > > I think that any sort of radical change in diet will give anyone gastric distress. I’ve seen this myself…if I suddenly eat a ton of, say, lobster with other rich foods I’ll be in a hell of a lot of distress. I imagine the same goes for someone used to eating Vegan or just vegetarian would have some distress from eating a large steak, since it’s very different than what they are used too. So, I think that the answer to the OP is probably ‘yes’, their digestive systems will react badly and they will probably spend some uncomfortable times on the toilet, but they will adjust fine in a short time…and ‘getting sick’, I’d guess, is probably more a psychological reaction except those who actually have meat based allergies. Getting the shits though…yeah, I think that’s likely. And not just for Vegans or vegetarian types making a change. I agree with this part- whenever I go on vacation I have some sort of gastric issue and I have always attributed it mostly to my diet being different. But this “getting sick” that’s more than a psychological reaction- I’ve only ever heard vegans/vegetarians describe vomiting and/or a case of the runs when consuming animal products. Do people claim that they end up deathly ill or something? ---
**Author:** ![Bill\_Door](https://avatars.discourse-cdn.com/v4/letter/b/50afbb/32.png) [@Bill\_Door](https://boards.straightdope.com/u/Bill_Door)\ **Post date:** [February 28, 2019, 7:55pm UTC](https://boards.straightdope.com/t/does-the-digestive-system-react-badly-when-a-long-term-vegan-years-decades-eats-meat/830201/23 "2019-02-28T19:55:50Z")
I am on an intermittent fasting schedule that has me consuming only water for a 42 hour stretch three times a week. The first 3 or four times I broke my fast after this I experienced GI distress and diarrhea, but since then I have no issues. My theory is that of the more than 1000 individual bacteria that form the gut biome there are some that require feeding more frequently than others. During the first few fasts these bacteria die off and are slowly replaced by ones that are more resistant to periods of fasting. By the time you’ve done this for a week or two natural selection has made your gut biome resistant to fasting. It’s kind of funny, because people on fasting forums will adopt all kinds of special techniques to break their fast, but I’m convinced that time and time alone can eliminate the problem. What happens is they try something, and that doesn’t work, and they try something else, and that doesn’t work, and so on. When natural selection has solved their problem they swear that the cure was the last thing they tried, so you’ll see recommendations for chia seeds, bone broth, nuts, avocados, leafy greens, Greek yogurt, cooked vegetables, etc.; all of which people swear are effective. Vegans may very well have had natural selection alter their gut biome, but in a few days or weeks I’m sure it can evolve to cope with meat. [Previous page](https://boards.straightdope.com/t/does-the-digestive-system-react-badly-when-a-long-term-vegan-years-decades-eats-meat/830201.md?page=1)