If you follow Halle Berry’s Instagram feed and admire her toned physique and youthful appearance at age 52, you may be considering the ketogenic, or keto, diet. The actress shares that this trending diet has helped her manage her type 2 diabetes, slowed down her aging process, improved her skin, controlled her appetite while boosting her energy and strengthened her physical endurance and mental acuity. Wow! And she’s not the only celebrity touting this high-fat, low-carb diet that some say helps folks lose weight—fast.

But before you dive in, note that Berry was following the keto diet long before it gained popularity, and she treats it as a way of life, not a diet; as such, this strict eating plan isn’t for everyone.

So what is the keto diet and how does it work? “The ketogenic diet is the only diet that puts your body into the metabolic state of ketosis,” says chiropractor Josh Axe, DNM, CNS, cofounder of the health and wellness websites DrAxe.com and AncientNutrition.com, “which is what allows you to burn fat for energy [in the form of ketones] rather than glucose [from carbohydrates]. The presence of ketones in your blood actually changes the way your brain and cells work.”

When the consumption of sugar (glucose) from carbohydrates is drastically reduced, the body must use an alternative source of fuel—in this case, fat.

The keto diet is different from other diets in that it’s a very low-carb diet that stresses eating foods high in healthy fats and only moderate amounts of protein.

“This is a key distinction between keto and a diet like the Atkins diet, because consuming too much protein can interfere with ketosis.

“When following the keto diet correctly you consume 75 percent or more of your daily calories from fat, about 20 percent or less from protein and just 5 to 10 percent from carbs,” says Axe, who is a doctor of natural medicine. (His book, the Keto Diet, is scheduled for release in February 2019.)

Getting Started on Keto

To enter a state of ketosis, net carbs—the amount of carbs left after you subtract fiber—must be limited to about 30 grams per day. For some, sticking with this carb count each day won’t be easy. (One small apple contains about 25g of carbs.)

This means cutting out grains—including whole grains— most starchy vegetables, most fruit (you can still have small amounts of berries, avocado and tomatoes; just stick with one cup or less each day to make sure they don’t put you over the limit), legumes and beans, added sugar of any kind, desserts, sweetened dairy products, soda, juices and other sweetened drinks. In addition, limit wine and alcoholic beverages or avoid entirely).

Tips

  • Increase your fat intake—especially from foods such as coconut or olive oil, MCT oil, butter, ghee, eggs, fish and fatty cuts of meat. 
  • Instead of having rice or quinoa, try a low-carb substitute like cauliflower rice.
  • Add plenty of non-starchy vegetables for essential vitamins and minerals, fiber and antioxidants. Green leafy veggies like kale, broccoli, cauliflower, celery and asparagus and fresh herbs like parsley and cilantro are some good choices.
  • Sea vegetables, most nuts and seeds are also beneficial.
  • Eat alkalizing foods, and do not consume too many processed or acidic foods. “When you eat too many acidic foods in proportion to alkalizing foods, the pH of your urine and saliva becomes overly acidic, which can contribute to low-grade acidosis and depletion of essential minerals,” warns Axe.
  • Replace noodles with spiraled zucchini or another veggie.
  • Trade breads made with wheat for those made with almond or coconut flour.

Keto Diet Side Effects

While transitioning into ketosis, it’s common to experience temporary side effects, nicknamed “keto flu,” which usually strike within the first week of starting the diet, “as your body transitions through some major metabolic changes,” says Axe.

“During this time, you’ll be urinating more often [putting you at risk for dehydration] and might feel weak, exhausted or irritable or deal with headaches, body aches, brain fog or constipation,” he continues. “These symptoms should subside within a week or two, so be patient and do your best to stay hydrated and eat nutrient-dense foods. Even when you do enter ketosis, you might feel a bit off for a week or two as your body adjusts.”

Axe stresses that on keto, healthy fats should be the primary source of calories. “Veggies should make an appearance at just about every meal, since they provide electrolytes, such as magnesium and potassium, that can help to fight keto side effects,” he advises.

If you experience constant hunger and cravings on the keto diet, chances are you’ll need to eat more high-quality fat and make sure you’re consuming enough calories.

If you’re struggling with cravings for sweets, Axe suggests making smoothies with vanilla or chocolate keto powders, coconut or almond milk, stevia extract, cinnamon, vanilla extract, cocoa powder and chilled coffee or espresso. “All of these can help satisfy cravings and make recipes seem sweeter without adding any actual sugar,” he says.

In addition, drink lots of water. Electrolytes are depleted on a ketogenic diet because the body excretes more water.

“Drinking lots of water, adding extra sea salt to your food and taking a magnesium supplement before bed can also help to offset symptoms like weakness, aches or constipation,” Axe says. “You’ll also want to limit the stress you put on your body by sticking to light to moderate exercise and prioritizing getting enough rest and sleep.”

How Long Should You Stay on Keto?

“The ketogenic diet can be followed short term [for several months] or longer term [for many months or even years] if it’s done in a cyclical pattern,” Axe says. “Most people will likely have the best success if they follow the diet ‘strictly’ for a shorter period initially and then practice cyclical ketosis [alternating periods on and off the diet].”

Warnings

“The keto diet has many benefits to offer, but it’s not a good option for everyone,” Axe says. This means pregnant or nursing women, people who are underweight and those who have trouble digesting fat or have an eating disorder or a history of gallbladder, liver or kidney disease.

“If you’ve had your gallbladder removed or know that fat is difficult for you to digest, don’t start the diet without discussing with your doctor first,” Axe suggests.

“Additionally, due to the effects that the ketogenic diet has on weight loss and hormones, it can mean that diabetes, blood pressure or cholesterol medication dosages need to be adjusted,” he says.

Other drawbacks of the keto diet that some experts cite include diminished athletic performance and a decrease in the consumption of fruits and vegetables.

In addition, not enough is known about the diet’s long-term effects on individuals.

Currently, it’s not yet clear how the keto diet may impact health markers, such as cholesterol or blood glucose, notes Axe.

This is why he recommends that adults stay on the diet for one to six months, depending on the person.

“You might choose to follow the diet for longer if you’re working with a doctor, but don’t attempt to stay in ketosis indefinitely otherwise,” he says.

In addition, avoid nutritional deficiencies by supplementing your diet with a quality food-based multivitamin with minerals and omega-3 fatty acids. “If you feel depleted of energy and like you’re under a lot of stress, adaptogenic herbs, such as ashwagandha can also be helpful,” Axe suggests.

“Exogenous ketones are another option that can help you feel your best on the keto diet by giving you an outside source of ketones that boost your levels of these organic compounds quickly,” he adds.

Don’t jump headfirst into ketosis. Instead, gradually cut back on processed foods and added sugars, then cut back on carbs like grains and starchy veggies, all while simultaneously increasing fat intake, Axe advises.

In addition, it’s easier for beginners to switch to a keto diet if they track their food and note the intake of proteins, carbs and fats. This ensures that the diet is being followed correctly so folks are more likely to enter the fat-burning state of ketosis. Keep a log, and read food labels carefully so you’re always aware of what’s in the food you’re eating too.

Possible Health Benefits of Keto

Illnesses this high-fat, low-carb, moderate-protein diet may target

Diabetes

The burning of fat while on the keto diet is thought to control the release of insulin, which normalizes blood sugar levels and helps reverse insulin resistance, which factors in the development of diabetes.

Heart Disease

The keto diet may help lower cardiovascular risk factors by reducing high cholesterol and decreasing levels of triglycerides and blood glucose.

Cancer

Studies suggest that the keto diet may starve cancer cells by eliminating excess refined sugar and processed carbs.

Neurological Disorders

When glucose is eliminated or drastically reduced, the body makes ketones for fuel. This change might possibly reverse neurological and cognitive impairment. The ketogenic diet was initially used to treat epilepsy. Ketones and decanoic acid (a saturated fatty acid produced by the diet) may help minimize seizures. In addition, the keto diet may defend against Alzheimer’s and Parkinson’s diseases, autism, multiple sclerosis, brain cancer and migraine headaches.

What’s more, the keto diet appears to correct abnormalities in cellular energy usage, a common characteristic found in neurological disorders, one reason why researchers think the diet might help to normalize certain symptoms of schizophrenia.

Stroke

Keto diet supporters believe the use of saturated fat in the regimen provides more protection against this cardiovascular disease because it eliminates processed meats and foods with trans fats that cause the inflammation that can lead to stroke, heart disease and other chronic diseases.