Jenna Jameson lost 57 pounds on the keto diet — a doctor weighs in

Jenna Jameson is on the popular ketogenic diet. She revealed all about her #ketotransformation via Instagram.

Yet another celeb is touting the weight-loss benefits of the ketogenic diet, with former adult film actress Jenna Jameson sharing on Instagram that she dropped 57 pounds, dropping from a 16 to a six in pants size, in less than four months, courtesy of the high-fat, low-carb diet. That's almost 15 pounds a month, which is sorta ridiculous (and not necessarily in a good way).

Fast, dramatic results are a big part of keto's appeal, but weight-loss specialist Charlie Seltzer, M.D., offers this reality check: "For every 100 people who try the ketogenic diet, 99 of them will fail — and by that I mean they'll either be unable to stick to it at all or they'll lose a massive amount of weight, then gain it all back," he says.

That may sound like an exaggeration, but experts tend to agree that sticking to a keto diet long-term isn't realistic: In fact, earlier this year, keto tied for last place in U.S. News and World Report diets ranking. The reason? Experts cited concerns about the diet being "too extreme and rigid" and difficult to sustain.

When it comes to weight loss that lasts, the Centers for Disease Control and Prevention (CDC) concludes that losing weight gradually is the way to go (think one to two pounds a week). "To get rapid weight loss, the lifestyle changes need to be extreme, which is a setup for rebound weight gain," Dr. Seltzer says.

What's more, when you shed more than 10 pounds in the first week or two on any very low-carb diet (in the case of keto, Dr. Seltzer says that means only 5 to 10 percent of your calories come from carbs), you're losing mostly water weight, not fat.

As Dr. Seltzer explains, muscle contains large amounts of glycogen from carbs and water (every gram of glycogen is stored with at least three grams of water). Eliminate carbs from your diet and you'll deplete glycogen stores and the accompanying water.

Still, proponents of the ketogenic diet tout its appetite-suppressing benefits, which can help with weight loss. That was the case for Jameson, who wrote that after the first week of keto, "The cravings subside and your body adjusts."

Although the results of a 2015 study in Frontiers in Psychology support a link between the ketogenic diet and hunger control, more research is needed to understand the relationship. It could, at least in part, be a placebo effect: "If someone convinces himself he won't have cravings, he very well might not," says Dr. Seltzer.

"In our experience, the longer someone's on the diet, the worse the cravings get until they give in," he says. That's particularly easy to do when your weight loss (inevitably) plateaus — which happened to Jameson earlier this month. "Weight-loss update.... I'm stuck at 129," she wrote on Instagram.

In fact, despite the popular claim that you burn way more calories on a keto diet compared to other diets, the authors of a 2016 study from the American Journal of Clinical Nutrition found that while you may burn 100 more calories in the first week of a keto diet, that benefit doesn't last.

Still, Jameson says she's sticking with keto. "I'm no longer really losing fat, I'm tightening," she told her followers in a post. Her focus now? Returning to the gym after a three-year hiatus.

The keto-fitness combo has certainly worked for Halle Berry, though. Dr. Seltzer points out that "anyone can build muscle, even on keto." For most people, he recommends a balanced plan that includes carbs.

Or you could always try a keto-ish diet, ditching just the unhealthy carbs (like chips, crackers and cookies), a la Megan Fox.

Read more: From Cabbage Soup to Keto: The Most Popular Diets Through the Decades

What Do YOU Think?

Have you tried the ketogenic diet or any version of it? If so, did you have trouble sticking to it? Did you lose weight quickly? Do you think it's something you could maintain long-term? Let us know in the comments below.