7 Things Nutritionists Want You to Know About the Keto Diet

Here's a surprising fact about the ketogenic (or keto) diet: Even though it seems like ​everyone ​is trying it, many nutrition experts have some concerns about the trend.

That doesn't necessarily mean you need to steer clear altogether, though. A few small studies have shown that eating keto can lead to weight loss, at least in the short term. One of the most promising, published February 2017 in the ​Journal of Clinical Endocrinology and Metabolism​, followed 20 people with obeisty over four months and found that a very-low-calorie ketogenic diet helped them lose a substantial amount of fat while preserving their muscle and strength.

But if you're new to a keto diet plan, there are definitely some concerns that are worth keeping in mind.

Here's what five registered dietitians want beginners to know about ultra-low-carb eating plans and keto diet foods. Plus, the one thing you ​must​ do if you're thinking about giving keto a try.

The goal of the ketogenic diet is to achieve and maintain a state of ketosis. According to Harvard Health Publishing, ketosis occurs when there is a lack of sugar (from carbohydrate-rich foods) circulating in the blood, prompting your body to break down its stored fat for energy.

"But most people don't actually limit their carbs enough to reach ketosis, or they jump in and out of ketosis so quickly that they're not truly following a ketogenic diet," explains Amanda Kostro Miller, a Chicago-based registered and licensed dietitian-nutritionist.

In order to reach ketosis and stay there, most experts agree you need to consume just 5 to 10 percent of your calories from carbs.

​Read more:​ Signs That You Are in Low-Carb Ketosis

There's no shortage of keto diet fans on social media, and many of them love sharing nutrition advice. "That large and enthusiastic group can be helpful, but it can also be a hotbed of misinformation and unhealthy ideas," explains Annie Kay, MS, RDN, a holistic dietitian based in the Berkshire Hills of Massachusetts.

Of course, it's totally fine to pick up keto-friendly recipes and tips online. But when it comes to answering the bigger nutritional questions (like how to get enough fiber, or how much water you should be drinking), you should talk with a pro. "The key is getting support from a registered dietitian to make sure you're following a keto diet in the healthiest way possible," Kay says.

The human body has evolved to use carbohydrates as its main source of energy, so it'll do everything it can to get itself out of a state of ketosis, Miller explains. With that in mind, you shouldn't be surprised if you find yourself with an intense craving for a bagel or a cookie. "You're really fighting against nature," Miller says.

It's frustrating, but true: Because of their genes, some people simply don't do as well on a low-carb, high-fat diet. "The ACSL1 gene controls your ability to burn fat as an energy source and the ApoA2 gene is the overeating gene. If there are mutations on those genes, the body won't break down fats in the same way," says Jennifer Smith, a registered dietitian in the Detroit area.

That's not to say you should undergo genetic testing before trying the keto diet. But you should keep in mind that if you follow the diet perfectly and still aren't losing weight, your body might simply be better suited to a different type of eating plan.

​Read more:​ How Long Does It Take for the Ketosis Diet to Work?

Most Americans struggle to get enough fiber — in fact, the majority of us only get about half the recommended 25 to 30 grams per day, according to the University of California San Francisco Medical Center (UCSF).

Adopting a keto-style diet tends to slash fiber intake further. Which can be bad news, since fiber is important for a healthy digestive system and has been linked to other health benefits, according to UCSF.

"In the short term, too little fiber can lead to constipation. And in the long term, poor fiber intake can increase the risk for diverticular disease and cause a decrease in beneficial gut bacteria," explains Erin Judge, a Nashville-based registered dietitian-nutritionist who specializes in irritable bowel syndrome and digestive health disorders.

The good news? Most experts agree that it's possible to get enough fiber on a keto diet, but it takes some careful planning. A registered dietitian can offer suggestions for working more low-carb, high-fiber foods into your diet, like nonstarchy veggies, nuts and avocado. You'll stay more regular, but that's not all. "Over time, a fiber-rich diet can boost beneficial gut bacteria and lower your risk for health problems like heart disease, diabetes, hemorrhoids and some cancers," Judge says.

​Read more:​ 8 Keto-Friendly Snacks Anyone Going Low-Carb Should Try

Fat- and protein-rich foods are super satisfying. That's a good thing, since staying full means you're less tempted to snack mindlessly. But it can also make you forget to drink enough water. That can put you at risk for dehydration, and potentially make it harder for your kidneys to flush out nitrogen-containing byproducts from protein that could lead to kidney damage, explains Kay.

How much water ​should​ you be drinking? Well, according to the Mayo Clinic, men should aim for about 15 cups of fluid each day (including from water, other beverages and food), while women should get just over 11 cups.

But there are no specific recommendations for keto-dieters, which is another reason it's so important to work with a registered dietitian. He or she can help you figure out how much water you need based on your size and activity level — and the best ways to get it every day.

The keto diet comes with a long list of foods that are off limits. High-fat and protein-based foods tend to be considered "good," while anything containing more than a few grams of carbs is essentially "bad."

But labeling foods this way can set people up to believe that ​they're​ being "good" or "bad" based on whatever they're eating, says Shana Spence, MS, a registered and certified dietitian-nutritionist based in Brooklyn. So if you give in to a high-carb craving or eat something that's not on your list of prescribed foods, you might end up feeling like you lack willpower or that you'll never be able to lose the weight.

The key is foregoing the "good" and "bad" labels, and instead accepting that some foods are simply healthier or less healthy. "Yes, you had a piece of cake that wasn't the healthiest, but that doesn't mean ​you​ are 'bad' or that you'll never lose weight," Spence says.

​Read more:​ 6 Keto Diet Mistakes to Avoid