I recently decided to be vegan. One of my concerns is the impact on health of a sudden change of eating habits.

So, speaking about health, does becoming vegan need a transition?
Do I need to "teach my body" to not have animal-related food anymore to prevent any side effect?

  • Can you please expand upon the last sentence in your question? Do you believe that (or wish to know if) your body can tell the difference between plant and animal nutrients? Are the side effects you're concerned with related to changing your intake of certain nutrients or just the source of the nutrients?
    – user177
    Commented Feb 1, 2017 at 17:19

8 Answers 8


Yes, but because you need to learn what the heck you are going to eat. (And supplement.)

People misunderstand why transition is necessary. Your body can handle new foods just fine. I am more worried about your psychology adjusting, now that "becoming full" might not be telling you what it used to. I wrote this up in a short article which I will share here:

I became a vegetarian in part because I was interested in vegetarianism for a few years. If I ate with one of my vegan friends, I would order what they ordered at most restaurants and sometimes let them take me to a vegan one. I figured out how to assemble a proteinilicious meal using beans and grains long prior to my switch. I knew vitamins B12 and D were the risky ones although regrettably I became deficient in both (tip: take huge doses of each).

I think this is also critically important empathy when working with friends who sort of seem like they might want to become vegan, but don't; though tangential I will share it here:

So as someone who is vegan on ethical grounds it’s tempting to be smug about it. But that misses the tremendous amount of work that went into switching to plant-based food as a step in the process of knowing plant-based food. For people who haven’t done that, it is really hard and they might actually starve themselves.

If you are a vegetarian or vegan and want to promote your diet, the best thing you can do is promote the cuisine and patiently and enthusiastically answer all questions for how you do it. If you are interested in reducing meat consumption, the best thing you can do is dabble in vegetarian cooking and orders at restaurants when you get the chances, then think about going cold tofurkey in about a year.


No need to. I was a teenager when I transitioned and it was cold turkey. Few pieces of advice:

  • Try to change as little as possible. For instance, replace milk with almond milk, meat with soy protein, refined sugar with organic brown sugar.

  • Take B12 supplements. If you don't live in a tropical country, also take D vitamin supplements.

  • Increase your potassium input. Bananas, sweet potatoes, and broccoli are great sources. You'll feel a lot more energetic and improve your blood flow.

  • Start researching now what foods are vegan in places where you and your friends are used to going.

  • 2
    Be careful not to state your opinion as fact without corroboratory sources. Could you explain what you mean by improve your blood flow?
    – dpel
    Commented Mar 22, 2017 at 15:16

You might experience side effects such as gas from too many beans, or a stomach ache from too much fiber, but those can be avoided by eating a varied selection of foods, and might not even be an issue depending on what kind of diet you're transitioning from.

As long as you're able to put together a meal plan that provides the correct nutrients there's no reason your body will have to learn to deal with it. It's much more important to learn how to assemble healthy meals that hit all the things your body needs, but if you're doing that then you don't need an adjustment period for any health reasons.


In my experience of food counselor I've met several people who turned vegan without a transition time, and they were enjoying a plentiful life. So I can definitely say transition time is not necessary, but can be useful to get used to all changes of several kinds that are more related to social lifestyle (e.g learning to cook, how to deal with social meetings in restaurants that have poor veg* options, how to distinguish veg* products in supermarkets, etc.) than to the narrow field of nutrition.


No, I don't think it's necessary.

Many people become vegetarian first and transition to vegan. This is more a developing change and ethics and culture. I've never heard of anyone on a vegan or vegetarian diet not "feeling full". In practice many vegetarians eat vegan for weeks on end anyway, some without meaning to. There are no immediate health risks with abruptly changing. The main health risks of veganism are iron and vitamin deficiencies which manifest long term and can be monitored by your doctor.

It's really as simple as shopping for only items that fit your new diet and figuring out what to cook with them. You'll be vegan before you know it. The hardest part will be training your mind rather than your body. You'll have to get used to cooking entirely new dishes but some people enjoy this aspect. If you stick to home cooked meals with vegan products it will be your new normal in a couple of weeks. Whether you transition or not you will have to get used to this.

I'd also advise against substitutes, they're quite expensive and many vegetarians and vegans reserve these for social occasions (such as taking to a barbecue). It's these sort of events and eating out at restaurants that can take longer to adjust to, many places are improving but many still have few vegan options.

  • This might be a bit rich coming from a long-term vegie but I've recently had to make similarly abrupt dietary changes to low FODMAP on the advice on my doctor. I've based this answer mainly on these recent experiences with a very strict diet (vege, wheat-free, lactose-free, fructose-free).
    – Tom Kelly
    Commented Feb 1, 2017 at 12:40

The best arguments for or against a transition period have to do with habits. We need approximately 30 days to form a new habit.

If we really want to go vegetarian or vegan, we can do so right away, but in order to follow through, we might need to have some contingency plans in place.

New vegans are still going to announce, spontaneously “Let’s eat lunch at our favourite steak house!” out of habit before realizing that, oh, I didn’t want to go there anymore. Being on a transition period – phasing out the restaurants, phasing out one type of meat could help with success in the long run, if each is slowly replaced by vegan alternatives. Someone who knows nothing beyond SAD (Standard American Diet) might be totally overwhelmed by the idea of a vegan barbecue. It isn’t difficult, but one needs to take the time to think through a plan. That might be the case for every event, since one needs to decide on the right approach to ask grandma to make her Christmas kale without the sausages or how to act gracefully when friends invite you to a non-vegan meal.

Gradually upping the amount of vegetarian dishes in one’s everyday life starts with realizing which staple dishes are already vegan (maybe your favorite spaghetti with tomato sauce) and finding alternatives at our favorite restaurants.

Why is it good to have contingency plans in place?

Well, when we feel like we fail, it’s much more probable that we’d say “well, veganism isn’t for me, it’s too hard” and just give up on it. Be compassionate with yourself and find a strategy that works for you. If you feel prepared, why not go cold tofurkey right away? If you don’t feel prepared, start with a Meatless Monday a week and identify which dishes you love that are already meat- and cruelty-free.


I've never heard of transition times for any diet. You could need a transition in case you have been a long time without eating (you need to grow again intestinal bacteria), also if you are trying to lose weight it is better to transition gradually mostly for a psycological factor (you will starve less).

If you are becoming vegan for ethical reasons, I see no point in continuing eating meat and stopping gradually. As Always, ask for opinion of a nutritionist before taking any diet.


As with many things in life, it depends. For a lot of people, if you have a guide, someone who can tell you what's what about the diet you're going to, no.

But different people are different. I think it's important to note that even if you have a guide on your transition, such as an exciting new romantic partner, it's probably useful to try out each new sort of food you'll be eating, because if you just suddenly flip your diet and have a problem with something, you won't know what that something is. The more your diet will be changing, the more this might matter.

A couple years ago, I met a new friend who was interested in going vegan. However, it wasn't her top priority, and she'd not yet actually started doing any research on it. My ex and I are old-school vegans - no meat, dairy, or eggs, and the three of us got along very well, so she just started eating meals with us, attempting a change that had taken us years with virtually no transition.

It didn't work; something in our diet is very problematic for her. We're not sure exactly what it was, but she's stubborn enough she tried really hard to adapt to the new diet, and when she finally gave up, she basically gave up almost completely. She's now really reluctant to even try a slow transition that would help her identify exactly what was problematic about the diet, because of how intensely unpleasant the trying really hard in the face of her GJ system telling her no.

I'm not attempting to claim that she should necessarily try to transition, because I don't know what her issues are. I've seen what she went through, and I wouldn't want to put anyone through that. But she continues to make comments indicating she's unhappy with her diet. I would like to think that having a more gradual transition would have either helped us better identify exactly what dietary change caused her issue, or give her body enough time to adapt to it.

Just to clarify, there was nothing in our diet that was completely foreign to her. The closest to that was seitan, but she certainly had wheat before. But the amount of gluten, soy, and various veggies went way up.

Most of the people I've heard making sudden transitions to vegetarian or vegan diets didn't have these sorts of issues. But different people are different. My friend isn't the only person who I've met who's had an issue with a no transition plan transition. She's just the only one I've actually witnessed going through this.

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