15 Things You Need to Know Before Starting the Keto Diet

Updated: Feb. 09, 2023

Eating keto style is about more than just gorging on bacon and butter. Here are expert answers to your most pressing keto diet questions.

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Is the keto diet safe?

To put it simply, yes and no. The ketogenic diet has been around for 90 years. It was first developed to treat patients with epilepsy, who responded well to the way it mimics a fasting state, while still allowing patients to eat and obtain nutrients. The keto diet is highly restrictive, though, cutting out grains and certain fruits and veggies in addition to sugar—which as a short-term diet solution may have some benefits, but long term may be risky. “The ketogenic diet is not a healthy, nutritionally complete diet,” says Diana Lehner-Gulotta, RDN, a ketogenic and neurology dietitian at University of Virginia Health System. “You are completely cutting out large groups of food and eating excessive amounts of fat, which can lead to lipid abnormalities. We also don’t know about the long-term effects of eating such a high-fat diet.” If you’re thinking about following the keto diet for a weight-loss kick start, talk with your doctor first. Here are 13 things doctors want you to know about the keto diet.

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What’s the difference between net carbs and total carbs?

Net carbs are the number of carb grams that remain after dietary fiber and sugar alcohols are subtracted from the total carbohydrates of a meal. Why don’t many keto dieters count fiber in their total carb allotment for the day? The fiber found in many keto-compliant foods, such as broccoli, avocados, and berries, is indigestible once eaten. So, while these foods technically still contain “carbs,” the body can’t use them for energy.

“There’s no right approach between counting ‘net’ and ‘total’ carbohydrates,” says Paul Salter, founder of the Weight Maintenance Channel on YouTube and nutrition editor for Bodybuilding.com. “Using net carbs is a tool to ensure you’re seeking high-fiber carbohydrates, which is essential when following a ketogenic diet.”

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What are your nutrient goals—and how will you track them?

The keto diet is an ultra-low-carb diet. This means you’ll be eating significantly fewer carbohydrates than the average person, even fewer than a person following a classic low-carb diet. Exactly how many carbs you should aim to eat depends on your specific goals, as well as your age, gender, and level of activity, says Salter. Ketogenic diets tend to limit carbohydrate intake to just 20 to 30 net grams per day. On a standard ketogenic diet, fats typically make up 70 to 80 percent of total daily calories, protein about 15 to 20 percent, and carbs just around 5 percent.

Keep track of these important nutrients with nutrition calculators, tracking programs, or smartphone apps like MyFitnessPal and MyPlate. Find out what it’s really like to follow the keto diet.

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How much weight will you lose on the keto diet?

Weight loss is very common with the keto diet, however, the first few pounds you drop will be “water weight”—water that your body would normally store when you eat carbs. What’s happening is just the opposite of what happens to marathon runners when they carb-load. “Carbo-loading, which athletes do, fills muscles with as much glycogen, a storage form of sugar, as possible, which holds more water,” says Melina Jampolis, MD, author of The Doctor on Demand Diet.

During keto, as you reduce carb intake your body dumps its glycogen stores in favor of burning fat. You’ll see the number on the scale go down, which is exciting, but at this point, you’re just dropping water weight, not fat. “Oftentimes, people are discouraged that their rate of weight loss slows down after the first month, but this is healthy,” Lehner-Gulotta says. “In addition to weight loss, many people feel like they have more energy and mental clarity on this diet.”

What else changes? Sugar cravings become non-existent after the first few months, Lehner-Gulotta reports. Her patients tell her that they feel more satisfied after meals, and they’re not hungry all the time. Read more about how the keto diet helped one woman lose 15 pounds in six weeks.

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Will you feel hungry on the keto diet?

Hunger is suppressed on the keto diet. Fat is satiating, so you may find yourself feeling not very hungry some days when you’re on the keto diet. That’s okay. In fact, it’s why many keto dieters eventually begin practicing intermittent fasting (IMF), says Salter. IMF allows you a shorter window of eating, such as only eight to 12 hours each day, then you fast during the remaining time.

Note that fasting is not without medical concerns. “The theory with fasting is that it will help decrease your appetite and cravings over time because it will teach your body to go longer without food,” Lehner-Gulotta says. But it’s not for everyone. In some people “it causes irritability, further nutritional deficiencies, and often leads to loss of lean muscle mass instead of fat.” Talk to your doctor before trying it.

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Will you get the dreaded “keto flu”?

Carbohydrates are your body’s preferred source of fuel, and without them your body turns to a stored source of energy—fat. When your body is adjusting to burning fat (a process called ketosis), you may experience unusual symptoms, such as irritability, brain fog, fatigue, mood swings, or nausea, Lehner-Gulotta says. This is sometimes referred to as the “keto flu.”

Not every person eating keto will experience this, but some will. “It’s important to stay hydrated and push through because if you give in and eat carbs, you’re right back where you started,” Lehner-Gulotta says. The good news is that the symptoms come and go and usually subside altogether within three to five days.

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Does the keto diet have benefits beyond weight loss?

Research suggests the keto diet may deliver health benefits beyond weight loss, such as improved blood sugar levels, insulin sensitivity, and cholesterol numbers, says Grace Derocha, RD, certified diabetes educator, and certified health coach at Blue Cross Blue Shield of Michigan.

Whether it’s the keto diet itself or the accompanying weight loss that is actually responsible for improvements in some health markers, Derocha says, is unclear. “There needs to be more research done regarding the keto diet, its long-term effects on the body, and the impact of the keto diet once someone decides to incorporate a more sustainable meal plan.”

Find out the 15 incredible things that happen to your body when you lose weight.

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Do you need specialty keto products to do this diet?

If you spend any time researching the keto diet, you’ll likely run across websites, social media posts, and ads promoting a variety of keto-compliant foods, from oils that you can add to your coffee to low-carb chocolate syrup. If that feels overwhelming, ignore these products and save your money, Lehner-Gulotta says. “You can get into ketosis by altering the way you eat; you don’t need exogenous ketones,” she says.

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Is the Atkins diet is a type of keto diet?

The Atkins has been a popular low-carb diet for several decades. If you’ve tried Atkins in the past, you might recognize many of the same guidelines in the keto diet. But the keto diet is lower in carbs than Atkins.

“The main difference is that the keto diet encourages 75 to 90 percent of one’s calories come from fat and less than five percent to come from carbohydrates,” says Colette Heimowitz, vice president of nutrition and education at Atkins Nutritionals. “The Atkins program encourages a daily intake of 55 to 70 percent of calories coming from fat and allows for 5 to 15 percent of daily calories to come from high-fiber carbohydrates.”

A key dietary difference between the two, Heimowitz says, is the vegetable allowance. “Eating too many veggies, especially starchy ones such as corn and potatoes, can undermine your weight-loss and weight-maintenance efforts, which is why they are prohibited on the keto diet,” Heimowitz says. “On Atkins, however, we encourage individuals to spend their carbohydrate grams wisely by choosing vegetables that provide the most antioxidant protection in combination with the fewest grams of carbs.”

Learn the truth behind the low-carb diet myths that could be wrecking your health.

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Will I be eating a lot of fat?

You’ll be focused on eating healthy fats. “Not all fats are created equal,” says Adam Splaver, MD, a cardiologist in South Florida. Dr. Splaver says good fats, like the kinds found in avocados and nuts—”anything which comes from nature”—should be the focus of your fat intake on any keto diet plan. “All hydrogenated oils, such as margarine or Crisco are problematic for your cardiovascular health,” he adds. These 10 keto diet recipes will make you forget you’re on a diet.

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Will I experience side effects such as cramps and constipation?

“The process of changing body fuel from carbohydrates to fat can cause decreased serum sodium, leg cramps, constipation, decreased energy, and headaches,” Dr. Splaver says. Because you’re eating fewer sources of fiber—fruits and vegetables, for example—you may have fewer bowel movements. Bowel changes are very common with the keto diet, and you may experience periods of constipation as your body adjusts to the new diet. Learn about the 11 hidden dangers of the keto diet.

Likewise, without stores of carbohydrates in your body to hold water, you run the risk of dehydration as you will urinate more frequently, explains Carolyn Dean, MD, ND, and author. “The keto diet flushes out water by reducing inflammation and glycogen levels,” Dr. Dean says. Drink half your body weight in ounces of water, she suggests.

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Do I need to take supplements?

People on a keto diet may develop nutrient deficiencies. Dr. Salter says that sodium and magnesium deficiencies are possible with a keto diet because many carb-rich foods are the highest sources of these nutrients.

“Vitamin D, calcium, B-complex, in particular, may be beneficial,” says Adrienne Youdim, MD, an associate clinical professor of medicine at UCLA David Geffen School of Medicine says. “Fiber supplementation may also help digestive health.”

You may want to get a blood workup and supplement only the vitamins you actually need. Learn why nearly half of all multivitamins don’t do what they say.

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Do I need a meal plan?

Making a formal meal plan is a great way to set yourself up for success. Plan for variety in your keto diet, so you don’t get bored. Keto meals are very high in fat, moderate in protein, and low in carbohydrates.

“This diet is great for carnivores and people who like lots of fatty foods,” says Keith-Thomas Ayoob, RD, associate clinical professor emeritus at the Albert Einstein College of Medicine. “The focus is on fat, however, not protein, because high fat is what keeps your body ‘ketotic.'”

What’s not allowed? Experts agree that you’ll want to avoid processed foods and most packaged foods, sugary desserts, and plain starches. And you’ll want to watch your carbs. Healthy sources of carbs include non-starchy vegetables, like broccoli, leafy greens, cauliflower, asparagus, and cucumber, Dr. Slater says. “The bulk of your diet includes red meat, poultry, fish, seafood, eggs, avocado, coconut oil, bacon, butter, and cheese,” Derocha says.

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Is the keto diet hard to sustain?

The weight-loss results may come quickly, but other physical changes—constipation, stomach issues, depression, mood swings, fatigue—can accompany the shrinking waistline, warns Dr. Youdim. These unfortunate side effects may test your endurance on the keto diet.

That’s not to mention the lack of “wiggle room” in your day-to-day food choices. Extremely restrictive diets like keto may be too unrealistic for some people because it requires strict compliance. Want to enjoy cake for your co-worker’s birthday? One small slice is more carbs than you should eat in two days.

Smart strategies, including meal planning, however, can help you navigate social situations that test your will to stick to the keto diet.

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How do I transition off the keto diet?

Transitioning off the keto diet requires thought and planning. If you begin eating carbs but still have a taste for high fat, you may experience a dramatic weight rebound, and you may even harm your metabolism, too, Dr. Youdim says. A healthy transition back to carbs should focus on gradually adding whole-food sources of carbs, such as sweet potatoes, fruits, and whole grains. As you increase your carbs, decrease your fat intake, too. You’ll still see a few pounds adding up on the scale. (Remember water weight?) That’s expected as your body rebuilds its glycogen stores. However, if you maintain a low-carb diet, you may be able to sustain the weight-loss results longer.

Read on for the weight loss tips from people who lost 50+ pounds—and kept it off.