What happens when you transition from a plant-based diet to an omnivorous one? We asked a dietitian to find out.
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A piece of steak on a fork in front of a silhouette of person taking a bite
Credit: Getty Images / 4kodiak / Jordi Blasco / EyeEm

I've waffled back and forth between vegetarianism, veganism and an omnivore diet for almost my entire life, but I've definitely spent the majority of my adult life eating a plant-based diet. Whether this decision was influenced by my yoga habit, a lean grocery budget while I lived in New York City, environmental reasons or animal welfare consciousness, I just felt more comfortable eating plant proteins instead of animal products. But for the last six months, I've been slowly reintroducing meat into my diet, and I've noticed some major changes in my body and overall wellness.

I'm definitely not here to tell anyone they should eat one way or another. Nutrition science is so personal, and what feels good in my body may not be right for you. But universally speaking, going from an all-veggie diet to a meat-and-veg routine will have some pretty interesting effects on your body. To help me get to the bottom of why these changes were occurring—and help me support my health throughout the transition—I spoke with Lisa Valente, M.S. RD. If you're considering adding meat into your diet again (or for the first time), here are four considerations you'll definitely want to prepare yourself for!

4 Things That Can Happen to Your Body When You Start Eating Meat

1. Your Digestion May Initially Slow Down

When I first made this change, I ate meat once every couple of weeks; it wasn't enough to notice a difference in my body or digestion. But after dipping my toes into the water, I began eating a moderate portion of meat three to four times a week. Although this frequency feels right for my budget and diet, I noticed one major change: My digestion was much slower than it had been on a plant-based diet! Without going into too much, ahem, detail, I think that most veggie-loving folks will agree that things just flow easier and faster with plenty of plant protein. So what was happening here?

"Meat is high in protein and can be high in fat. It also doesn't have fiber. So all those things can impact your GI tract and can cause constipation or just general changes in ease and frequency when it comes to poops," explains Valente.

This makes sense from a quantifiable science standpoint, and my anecdotal evidence supported the theory: On days that I ate meat, I had been replacing a plant product with that lean ground turkey or seared salmon. To help your body keep up its digestive processes, Valente recommends continuing to prioritize plants in your diet. In other words: Include a small portion of lean meat with your dark leafy greens and roasted sweet potato.

2. You May Pass Less Gas

Nobody wants to be known as a trumpeter, but vegetarians and vegans typically do pass more gas than omnivores. I was used to tooting up a storm on the regular, thanks to my steady diet of lentils, beans and cruciferous vegetables. In addition to being generally hilarious, this kept my stomach pretty flat. I rarely experienced bloating, because I was releasing the excess air in my digestive tract.

Fast-forward to now, and all of a sudden I'm rocking a food baby on the regular. When I started eating meat, my body reduced the amount of gas I passed, which meant it built up in my body. This was a bummer when I reached for my favorite skinny jeans, but more important: It was uncomfortable. I asked Valente if she had any ideas for how to mitigate this problem.

She suggested keeping my fluid intake up, which was easy to do: I make sure to sip on warm water throughout the day. Valente also suggested I snack on fiber-rich foods—like nuts, seeds, fruits and veggies—and make sure that the grains I choose are whole. This means favoring whole-wheat pasta over white pasta, and enjoying things like oatmeal or barley soup.

3. You May Have More Energy

Although I loved how "light" my body felt on a plant-based diet, I experienced energy crashes on the regular. I'd get crazy hangry just an hour or two after a meal, and midafternoon slumps were basically a part of my daily routine. While it's certainly possible to power yourself with adequate amounts of protein on a vegetarian or vegan diet, I found it difficult. After years of living in a catabolic body state, I've been playing catch-up with my protein intake, and now aim for about 80 grams a day. (Note: This number is right for my body, and was arrived at with the help of a dietitian who is well-versed in eating disorder recovery; the ideal amount of protein for you may be more or less. Reach out to an RD if you're curious about finding a plan that's customized for your unique needs.)

Eighty grams of protein from chickpeas is a lot of chickpeas, so most days I didn't hit the mark, and thus experienced that energy crash. Now that I'm incorporating animal protein into my diet, I find it's much easier to give my body the amount of protein it needs to function optimally and allow me the energy to do the things I love. (Here's how to calculate how much protein you need to eat in a day.)

4. You May Gain Muscle Mass

I've always been lean and sinewy—again with that yoga practice! But once I started eating meat, I noticed that I was gaining muscle mass. It's important to note that everybody and every body is different; your body composition may change or remain the same if you undertake a similar dietary journey. It's not necessarily the fact that I was eating animal protein that helped me put on muscle mass, but rather, I was finally eating enough protein, period. Once I got into the groove of giving my body enough of that macronutrient to perform its basic functions, I noticed those changes in my physical appearance.

The two most important considerations when transitioning to an omnivore diet, says Valente, are to go slowly and be mindful of portion control. She reminded me that the serving size of a piece of meat is 3 to 4 ounces—a number that most Americans (myself included) definitely overshoot when piling dinner on our plates. She also suggested varying the type of meat I choose, but keeping processed options (such as bacon and deli meats) to a minimum.

These tips are especially crucial for those who have been vegetarian or vegan for years; you may not see so many dramatic changes if you just took a month off of meat. She also suggests working with a professional, as I did when adjusting my diet: "If there's an underlying health condition that prompted your decision, you may want to work with a dietitian on a healthy plan that's just for you."