Unless you’ve been living under a rock the last two years, you probably have a co-worker, family member, or fantasy football buddy who has tried the Whole30 diet—and, no doubt, they rave about it. So it may come as a surprise to know, nutritionists aren’t quite as thrilled about it. Here’s everything you need to know about what the Whole30 is and whether it’s worth your time.

What Is The Whole30?

The Whole30 is exactly what the name suggests: For 30 days, you only eat whole foods—except only those that for sure don’t cause inflammation in your body. The idea is to eliminate all the things that definitely make you feel crappy—processed food, alcohol, sugar—but also foods that might be making you feel bad—beans, legumes (soy, tofu, chickpeas, peas, lentils, peanuts), dairy, and grains. What you can eat: vegetables (including potatoes), fruit (in moderation), unprocessed meat, seafood, eggs, nuts and seeds, olive oil, coconut oil, and coffee (Hallelujah).

The idea of the diet is to detox from foods that are potentially causing low energy, aches and pains, weight retention, skin issues, digestive ailments—the list of side effects goes on. By the end of the month, it also becomes an elimination diet: You can now reintroduce the less dramatic offenders like legumes, dairy, and grains, and see how your body reacts.

What the research says: There is research to suggest that some people may feel better forgoing the offenders because of unknown intolerances. Roughly 65 percent of adults can’t digest the lactose in milk, according to the National Institute of Health, and slight intolerances can cause easily overlooked symptoms like gas and cramping. Meanwhile, people can be sensitive to gluten without actually being allergic to it—meaning the proteins can cause inflammation even if you aren’t full-blown celiac—according to, among other research, a 2017 study analysis in Frontiers in Physiology. (Although there’s a good amount of science to suggest these people are actually FODMAP sensitive, which the Whole30 does not entirely eliminate).

If you’re sensitive to wheat, gluten, or dairy, then yes, going without will help. But research has also shown some grains, like brown rice, and legumes actually help decrease inflammation, and that lactose intolerant folks may be able to tolerate small amounts of cheese and yogurt.

The Benefits Of The Whole30

Obviously, you’re going to feel better cutting back on junk food, sugar, and alcohol, all of which can lead to weight gain, blood sugar spikes, and decreased energy levels, says Natalie Rizzo, RD, author of The No-Brainer Nutrition Guide For Every Runner.

Otherwise, there are three main upsides to following the Whole30 for 30 days, says DJ Blatner, RDN, nutritionist for the Chicago CUBS and author of The Superfood Swap. It helps you start paying attention to what you put in your body and how it makes you feel; you become more savvy about ingredient lists on packaged food; and you start cooking more. These are all cornerstones to making sustainable changes for a better diet, Blatner says.

And chances are, you probably will feel better at the end of the month—pretty much everyone who tries the Whole30 says so. But, more than likely, this isn’t because your body doesn’t like grains and legumes—it’s because your body loves more vegetables and fruit, Blatner points out.

The Cons

Both nutritionists agree, you don’t need to remove dairy, grains, or legumes from your diet—and definitely shouldn’t be doing so longer than 30 days. “All three of these food groups provide plenty of important vitamins and minerals that can enhance your diet,” Rizzo explains. When you look at blue zones—the places in the world where locals live the longest—they all include legumes, healthy grains, and small amounts of dairy, for example.

Blatner adds that giving up healthy carbs in the form of grains, especially, can compromise your ability to work harder and longer on every kind of workout from long runs to heavy lifts. “The Whole30 does allow potatoes, plantains, and fruit, but you’ll likely feel more energized for and recover better from a workout if you can also include oats, brown rice, or quinoa before, during, or after a workout,” she says.

Chances are, if you feel better off grains and dairy, it isn’t because your body can’t tolerate the food—it’s because you were eating way too much of it before, and at the expense of something else. Trading whole wheat bread at every meal for vegetables at two of them will, of course, make you feel more energized, Blatner points out.

Who is the Whole30 Best For?

Both nutritionists agree the Whole30 isn’t a diet that should be followed long term. And you should probably steer clear if you’re in the midst of marathon training, since you need easy access to clean carbs. But if you want to clean up your habits, there’s no real risk in any athlete trying it for 30 days, as long as you’re smart about your carb timing, Blatner says.