You’ve seen and heard about it, and maybe even tried it—the popular Paleo diet. Cavemen, CrossFitters, chronic dieters, and other followers profess the benefits of this fad, claiming it’s the secret to weight loss and muscle gain and may even cure diabetes and other chronic diseases. In my own nutrition practice, I’ve encountered plenty of clients who report great Paleo success, but—here comes the bubble burst—at some point they burned out. Or worse, they start gaining weight for mysterious and unknown reasons!

The promise of a weight loss “quick fix” is all too seductive. When they see a friend shedding weight and eating steak, meat lovers are hooked. They start eating like a caveman, and the sudden shift from the Standard American Diet (SAD) does have dramatic results. At breakfast, bagels, yogurt, and oatmeal are traded for a couple of hard-boiled eggs. For lunch, a sandwich is swapped out for a salad with lean protein, and dinner is typically protein and vegetables. You might allow a little alcohol and snack on a handful of nuts. Sounds healthy, right? The trouble starts once you get bored with this calorie- and variety-deprived diet.

It’s easy to fall into a food rut, eating the same thing every day. If you’re rushing out the door in the morning, Paleo-approved foods need to be quick and easy. Meal planning, food shopping, and cooking become a struggle when the choices are so limited and outright boring. At first, your energy might be up, but over months or even years, you get long-term fatigue. This burnout is common in people who work long hours or travel often. Whether or not they make exercise a priority, their diets take a backseat, as they simply do their best to stick with Paleo foods on the fly.

It’s understandable. On any given hectic day, who focuses on fiber and phytonutrients?! In Paleo followers, I see a lack of fiber, vitamins, and minerals almost across the board. In theory, it’s a balanced diet, but in practice I don’t see that. Without consuming the recommended 7 to 9 servings of fruits and vegetables every day, it’s hard to do. Ironically, I’ve even seen people develop iron-deficiency anemia, despite all of the protein, because they still limit red meat (for known health reasons), and don’t consume enough iron-rich leafy greens and vitamin-C rich fruits and vegetables that increase iron absorption.

When you also remove legumes and grains—both of which are good sources of iron and B vitamins—you simply feel exhausted. That fatigue leads to “carb cravings,” but instead of reaching for quinoa or lentil salad, the sweet treats often sneak back in, in the form of cookies, ice cream, or a caramel macchiato—with pound cake on the side. Unfortunately, those refined carbohydrates that you set out to eliminate in the first place become regulars and repeat diet offenders.

Paleo is a high fat diet—even if they’re “good fats,” such as nuts. If you start sneaking carbs on top of that, you get excess calories, which lead to weight gain. And even if you’re super vigilant, it’s possible to snack too much. What many protein-focused dieters don’t realize is that too many calories, even if from protein, can be stored as fat.

Paleo works for people who are particularly intense about their routines. But if you’re finding it too restrictive, experiencing weight gain, or simply not feeling awesome anymore, it’s time to shift back to a diet that includes additional healthy carbs, or at least make some modifications. Ease up on the restrictions by adding nutrient-rich beans and whole grains like quinoa, oats, brown rice, and farro back to your diet. When you eat these satisfying foods, in combination with lots of fruits and vegetables, you’ll not only feel more energetic, you’ll actually help yourself get and keep the weight off.