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Everything You Should Know About the Keto Diet

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By now, you know fat isn't as bad as everyone once thought. But we're guessing you still think twice before cooking with butter and indulging in a little cheese. Sound about right? Then the ketogenic diet will blow your mind. Simply called "keto" by its army of devoted followers, the plan revolves around eating lots of fats and not a lot of carbs. It's closely related to the Atkins diet but differs in that it limits your protein intake and calls for sticking to very low amounts of carbs the whole time you're on the diet, versus just during the introductory phase.

What is the ketogenic diet?

Following a traditional Western diet means the body sources its fuel from glucose found in carbohydrates. The ketogenic diet takes an entirely different approach. "You're taking carbohydrates out of the equation, and the body kind of pauses and says, 'Okay, I don't have any sugar. What am I supposed to run off of?'" says Pamela Nisevich Bede, R.D., a dietitian with EAS Sports Nutrition.

The answer? Fat. Or, more specifically, ketone bodies, which are substances the body produces when it sources energy from fat rather than glucose. The keto diet is high in fat, low in carbs, and includes only a moderate amount of protein (because the body ends up converting excess protein to carbohydrates, Bede says).

When we say high in fat, we mean it. The diet calls for sourcing 75 percent of your calories from fat, with 20 percent from protein, and 5 percent from carbohydrates. Exactly how many grams you should get depends on your energy needs (online calculators can help you figure it out), but most people will want to take in no more than 50 grams of carbs, Bede says.

To put things into perspective, one sweet potato has about 26 grams of carbs. "Usually 50 to 65 percent of our calories come from carbohydrates, so it's a complete shift," Bede says.

How do I know when I'm in ketosis?

Follow the diet for a few days and your body will enter ketosis, which means it'll start to burn fat rather than glucose. You can measure your ketone levels with a blood-prick meter or urine ketone strips, both of which are easy to find on Amazon. Bede notes that while you might find your body has reached ketosis within three days, it'll take between three and five weeks to fully adapt.

Most people only track their ketone levels in the beginning of the diet. After that, you'll likely get used to what it feels like. "This is one of those diets that if you cheat, you absolutely know it, you absolutely feel the ill effects," Bede says. Cheating on the diet can make you feel tired, almost like you're hungover from too many carbs. "Nutrition experts speculate that there could be a hyperinsulinemic response to the carbohydrate influx," Bede says. "That is, when reintroducing a huge influx of carbs into the system, you experience a huge spike and then sugar crash."

What does a day on the diet look like?

You don't necessarily need to put a strict limit on the number of calories you take in, but you do want to make sure no more than 5 percent of them come from carbs and that 75 percent come from fat. Bede suggests using an app like Lose It! to keep track.

A day on the diet could include Bulletproof coffee for breakfast; a taco bowl made up of ground beef, sour cream, coconut oil, cheese, salsa, olives, and a bell pepper for lunch; and steak topped with onions, mushrooms, and spinach sautéed in butter and coconut oil for dinner.

What are the benefits?

Carbs attract water, so drastically cutting back on carbs makes you shed loads of water weight initially, Bede says. That weight loss will continue, mostly because you'll be less hungry thanks to satiating fats and because you'll reach for whole foods rather than unhealthy snacks that aren't keto approved.

Following the diet can help your gym efforts, too. One study published in the journal Nutrition & Metabolism found women on a ketogenic diet while resistance training lost more body fat than those who ate normally. Bede says the diet can be especially helpful for endurance athletes with sensitive stomachs who have trouble digesting sugary gels and sports drinks.

It's also been shown to have health benefits outside of fitness and weight loss. One study published in the journal Neurocase found maintaining ketosis for a few years helped stabilize the mood of patients with bipolar disorder, even more effectively than medication. Another study published in the journal Epilepsy & Behavior found the diet can help adults with epilepsy, though the researchers noted the study participants had trouble sticking to it.

Any health concerns to be aware of?

The initial loss of water weight can lead to dehydration, which leads to what's known as the keto flu. "That's when the headaches come. That's when the fatigue comes. That's where that loss of concentration comes," Bede says. To counter it, Bede recommends making sure you're hydrated and loading up on electrolytes via beef broth, chicken broth, electrolyte tablets, or Pedialyte.

You also may be unusually hangry when you first commit to this way of eating. A study published in the International Journal of Obesity found the hungry feelings can last for the first three weeks on the diet. Feeling tired and hungry as you're adjusting may also make your workouts feel a little bit harder, Bede warns.

There are also some suggestions the diet could harm your kidneys if you follow it long term, says Taylor C. Wallace, Ph.D., CFS, FACN, a food scientist and nutrition expert. Most of the long-term studies have been done on epileptic kids. While following the diet drastically reduces the number of seizures they have, many end up developing kidney stones because of the added stress the diet puts on the kidneys, Wallace says. Research suggests that happens because high levels of ketones can lead to dehydration and urine that's high in calcium, low in citrate, and with a low pH, all of which contribute to kidney stones. Still, Wallace adds that it could be worth the risk for someone who is morbidly obese and already experiencing loads of added stress on their organs.

Finally, the diet's fat-heavy aspect can have negative health consequences if dieters load up on too many trans and saturated fats. Wallace says it's easy to do. "People will go to McDonald's and get a triple cheeseburger, take the bun off, and eat that," he says. "[The diet] drives more unhealthy fat intake versus healthy fat just by the limited number of options of food you have." Taking in too many bad fats can increase LDL cholesterol levels, which could lead to atherosclerosis (the buildup of fats and cholesterol in the arteries), says Sean P. Heffron M.D., M.S., M.Sc., an instructor of medicine at NYU Langone Medical Center.

Should you do it?

If you're a planner and willing to take the time to meal prep, it could be worthwhile. "I can't iterate enough that you've got to have a plan," Bede says. "You can't wake up Monday morning and say, 'Today's the day.' I would really research it ahead of time."

Wallace says there's no reason to be overly concerned about the potential health risks if you'll only be on the diet for a number of weeks. "You can lose a lot of weight fast on it if you adhere to it for two weeks," he says. "I don't recommend doing it for long term, like six months, but I think doing it short term is perfectly fine." Ease yourself off the diet by gradually adding carbs back in so you can avoid that carb crash as your body adjusts.

Final thoughts...

Research and anecdotal evidence suggest the diet can be an effective way to shed fat and positively impact your health, but it hasn't been studied long term yet. "We don't quite know what will happen if you follow keto for 20 years," Bede says.

There's also no getting around the rigidness. "The diet is pretty hard to follow because it's a complete shift from what you're used to," Bede says. It's difficult both for practical reasons (such as finding something to eat while out for dinner or at the airport) and psychological reasons (coming to terms with the idea that an extra serving of cheese is A-OK).

Bede also says the diet's not for the instant gratification seeker. "You have to give your body time to find the alternate fuel source and adapt," she says. "Don't give it a week and give up."

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