The keto diet has become the most buzzed about and controversial eating plans out there, with celebrities, dietitians, and even doctors warring over different sides of the fence. While Halle Berry, Vanessa Hudgens, and Al Roker are fans and have said that the diet has helped them improve their health, trainer Jillian Michaels says the high-fat, low-carb diet is "terrible for your health, immunity, longevity, and anti-aging." So what gives? To help you decide whether the diet is right for you, we break down everything you need to know about the keto diet, including some gnarly keto diet side effects and the infamous keto flu.
These celebrities swear by the keto diet. Here's why:
What is the keto diet?
Originally started in the 1920s to help treat people with epilepsy, the keto diet is a high-fat, low-carb eating plan that emphasizes weight loss through burning fat. By eating foods high in fat and limiting carbs, your body can safely hit ketosis, a state in which your body uses fat-in the form of ketones-as fuel instead of carbohydrates. Because your body's preferred fuel source is carbs, it will always turn to those first. But if you eat fewer carbs, your body will burn through them faster and start breaking down fat for energy.
A strict keto diet requires as little as 20 grams of net carbs per day in order to sustain weight loss. If that sounds restrictive, that's because it is. 20 grams is less carbs than what you'd find in one medium-sized apple, for perspective. On the keto diet, 80 percent of the diet is comprised of fat, 15 percent is protein, and a mere 5 percent of calories come from carbohydrates. Other low-carb diets calls for 20 to 60 grams of carbs a day, while the average person's diet is comprised of 55 percent carbohydrates, 30 percent fat, and 15 percent protein.
Does the keto diet work?
The keto diet is known for helping people lose a few pounds very quickly, says Becky Kerkenbush, RD, a clinical dietitian at Watertown Regional Medical Center. Carbs hold on to more water than protein or fat, so when you stop eating them, your body releases all that extra water weight by making you pee more. As a result, the scale might read a few pounds lower, and you may look a bit leaner. And because you're eating high-fat foods, you'll feel fuller longer and curb cravings for sweets.
But what does the science say? Results are mixed. An October 2016 study from The Journal of Clinical Endocrinology & Metabolism followed 20 obese adults, who were put on a low-calorie keto diet, lost an average of 40 pounds over four months. Another small experiment had a similar outcome. In a six-month Experimental & Clinical Cardiology study of 83 obese adults, those on the keto diet lost an average of 33 pounds, while lowering their bad (LDL) cholesterol levels and increasing their good (HDL) cholesterol.
But all those studies were very small, and not all research on the keto diet is as promising. One American Society for Clinical Nutrition May 2006 study of 20 participants found that those on the diet didn’t lose more weight than those on a non-keto diet. But they did have fouler moods and higher levels of inflammation, which has been linked to a variety of conditions, including heart disease and cancer. Another thing to consider is that studies that show the benefits of following low-carb diets don't spell out whether they're as low carb as the keto diet.
What are the downsides of following the keto diet?
As we mentioned, there's not a lot of research and science supporting the weight-loss benefits of following the keto diet. In fact, following a restrictive low-carb diet, like keto, can be detrimental to your health. A February 2019 study from Nutrients suggests that following a low-carb, high-fat diet, similar to keto, can damage blood vessels and increase risk for type 2 diabetes and heart disease.
Moreover, an August 2018 study from The Lancet, which followed more than 15,000 people in the U.S., found that those who limited their carb intake (less than 30 percent of their daily calories from carbs) would live an average of four years less than someone who eats a moderate amount of carbs (5o to 55 percent of their daily calories from carbs). What's more, the keto diet might not be as effective for improving sports performance as many athletes think it can. A February 2017 study in Nutrition & Metabolism, which followed 42 athletes, found that a restrictive ketogenic diet can actually negatively impact physical performance, causing faster exhaustion.
Keto diet results
Some people really do lose weight.
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A post shared by Sugar Free Brie (@sugarfreebrie) on May 8, 2018 at 5:30am PDT
Anecdotally speaking, people do lose weight on the keto diet. Heather Wharton, a 35-year-old business relationship manager from Tampa, Florida, lost 140 pounds since starting the keto diet in January 2016: “I plan on being on the keto diet for the rest of my life,” says Wharton. “My husband and I consider ourselves to be food addicts, and the keto diet is what we use as a form of abstinence from trigger foods that have sugar and other carbohydrates." A typical day of eating for Wharton includes coffee with a protein supplement, a cup of unsweetened cashew milk, cauliflower rice with ground turkey and liquid aminos (a carb-free substitute for soy sauce), spinach, six slices of turkey bacon, six eggs, and a little salsa.
Others consider the keto diet a short-term solution for weight loss. Tyler Drew, a 34-year-old real estate broker from Los Angeles, first read about the diet on Reddit and used it to lose 45 pounds in six months before returning to a traditional diet. While on the keto diet, Drew’s cholesterol levels improved, even though a typical day of eating involved bacon at both breakfast and dinner.
But for others, the keto diet doesn't work.
For some, ketosis can cause more negative than positive side effects. Dorena Rode, a 52-year-old author, and speaker from Occidental, California, tried the diet for a month and experienced heart palpitations and dizziness. Unlike Drew, Rode says her cholesterol increased from 192 to 250 mg/dL after she introduced more fat into her diet. (Less than 200 mg/dL is considered desirable, while anything over 240 mg/dL is considered high.)
How to start the keto diet
Keto dieters eat mostly meat, healthy fats, and and non-starchy vegetables like leafy greens. And...that's pretty much it.
Although fat is the centerpiece of any keto diet, that doesn't mean you should be subsisting on butter-topped steaks, says Kristen Mancinelli, RD, author of The Ketogenic Diet. “A big misconception is that you should just put meat at the center of your plate and add more fat on top,” she says. You also shouldn't be relying on fatty meats to hit your fat quota, she adds.
Keto diet foods list
Best keto foods
Fats: Olive oil, coconut oil, butter, avocado oil, MCT oil, avocados
Proteins: Beef, poultry, eggs, fish
Non-starchy veggies: Leafy greens, cruciferous veggies (broccoli, cabbage, cauliflower, Brussels sprouts), cucumbers
Keto foods to eat sparingly
Full-fat dairy: Milk, cheese, yogurt
Medium-starchy veggies: Carrots, beets, parsnips, peas, artichokes, potatoes
Legumes: Beans, chickpeas, lentils, peanuts
Nuts and seeds: Almonds, cashews, walnuts, pumpkin seeds, sunflower seeds
Fruits: Berries, bananas, melons
Keto foods to avoid
All types of sugar: Including honey, agave, maple syrup
Grains: Wheat, oats, all types of rice, corn
All foods made with flour: Breads, pastas
Processed foods: Anything that comes in a bag or a box
Despite how limiting the keto diet is, diet experts say that with careful planning, you can still fit in all of your vital vitamins and minerals. However, to play it safe, you should work with a dietitian to come up with a well-rounded keto meal plan to avoid nutrition deficiencies.
Keto diet side effects you should know about
Cutting down on carbs (way down) can really mess with your body-at least at first. Here are all the potential keto side effects that could happen:
Carbs hold fluids in your body (think of how bread soaks up water compared to a chicken breast), so when you cut back on the nutrient, extra water is excreted in your urine. This makes it vital for those on the keto diet to stay hydrated.
Increased risk of kidney stones
This is due to dehydration and acidic urine that's high in calcium.
Depending on how you choose your fats, the keto diet can contain an abundance of saturated fat, which raises levels of dangerous LDL cholesterol and causes atherosclerosis, the buildup of fats and cholesterol in the arteries. If you decide to go keto, have a doctor monitor your cholesterol levels monthly to ensure you remain within a healthy range.
As we mentioned earlier, when your body enters ketosis, it starts to store fat in the form of ketones. This includes acetone, the same chemical in nail polish remover, which can cause "keto breath," a nasty, metallic taste in your mouth. Don't worry, though, it's a side effect that will pass as you adjust to the diet.
Because you're limiting your carb intake significantly, that means you're eating less vegetables, fruits, whole grains, and beans. Pair that with the fact that you lose more water weight, and you've got the recipe for constipation. But you can improve your digestion by eating more fiber-rich, keto-approved foods like avocados, nuts, and non-starchy veggies.
In the same vein, whenever you drastically change your diet, it can cause some digestive distress. Filling your plate with mostly fat can cause diarrhea. Moreover, some keto-friendly snacks use artificial sweeteners and sugar alcohols that can upset your stomach, so be sure to avoid those if you're sensitive to them.
The "keto flu"
A cluster of symptoms called the keto flu typically kicks in a day or two after starting the keto diet, says Mancinelli, and come on as your body goes through carb withdrawal.
Is the keto diet safe?
Experts are split on whether the keto diet is a good idea. On the one hand, Lori Chang, registered dietitian and a supervisor at the Center for Healthy Living at Kaiser Permanente West Los Angeles, says using a “cleaner” source of energy-ketones rather than quick-burning carbohydrates-can improve mood and energy levels. When you eat refined carbohydrates or just too many carbs in general, the blood is flooded with excess insulin, Chang says. "This can lead to a blood sugar rollercoaster that stresses the body and negatively impacts energy levels and mood. When you’re in a state of ketosis, however, ketone bodies don’t require insulin to cross the blood-brain barrier, which wards off unfavorable blood sugar levels."
Other experts say the long-term accumulation of ketones could be harmful. “Those ketones are emergency fuel sources, and we’re not meant to run on them long-term,” says Kristen Kizer, a registered dietitian at Houston Methodist Hospital. “Ketones are negatively-charged molecules, which means they’re acidic. When you build up ketone bodies in your system, you’re building up acid. One of the ways your body buffers acid is by pulling calcium from your bones.” Kizer also notes that the diet isn't very balanced and involves a very high intake of animal products, which generally do not protect against cancer, diabetes, or other diseases.
If you do try the diet outside of medical supervision, Kizer says it’s important to test your urine with urinalysis ketone test strips to ensure your ketone levels don’t become dangerously high. Ketone urine test strips are also used by people with diabetes to determine if they’re at risk for ketoacidosis (DKA), a life-threatening complication that occurs when an individual doesn’t have enough insulin in their body. (Healthy ketosis is considered 0.5 to 3.0 mM blood ketones.)
Bottom line: Talk to your doctor to make sure the keto diet is right for you
You’ve heard this line before, but really: Check with a doctor before trying the keto diet. The keto diet is an extreme eating regimen that could be harmful to certain people. It may not be right for those with heart disease, or metabolic diseases like type 1 diabetes or type 2 diabetes not controlled by insulin.
Although experts like Kizer have concerns about the keto diet, if you’re set on trying it, a doctor can help you determine if it is right for you and provide you with tools and information for accurately tracking your ketosis status.
If ultimately you decide that the keto diet isn’t for you, including a blend of healthy fats in your diet can still protect your brain, raise good (LDL) cholesterol, lower risk of heart disease, and help you stay satiated throughout the day.
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