Picture this: You’re on a new diet, but instead of feeling hangry and deprived, you’re brimming with energy and the weight is melting off. Welcome to the keto diet. It’s a high-fat, low-carb eating plan that Hollywood stars and athletes like Halle Berry, Adriana Lima and Tim Tebow credit for blasting away their fat.
It seems counter-intuitive — eat fat to lose fat? But that’s exactly what happens on keto. Here’s everything you should know about this diet, including tips to reach your weight loss goals and troubleshoot common problems. Before you dive in, check with your doctor before making any dietary changes.
WHAT IS THE KETO DIET?
The keto diet is short for the “ketogenic diet.” It’s a high-fat diet that has the potential to turn your body into a fat-burning machine.
The keto diet changes the way your body converts food into energy. Normally, your body turns carbohydrates (think bread and pasta) into glucose for energy. Eating a lot of fat and very few carbs puts you in ketosis, a metabolic state where your body burns fat instead of carbs for fuel.
WHAT ARE KETONES?
When your body can’t get glucose from your diet, your liver turns body fat and fat from your diet into molecules called ketones, an alternative source of fuel. This puts you into ketosis, aka prime weight loss mode.
According to some metabolic experts, you’re in the state of ketosis when your ketone levels measure 0.5-3.0 millimoles per liter. The keto diet is one way to get your body to make ketones. Other ways to run on ketones include intermittent fasting and using up your glucose reserves by exercising.
BENEFITS OF THE KETO DIET
The keto diet quickly boosts weight loss because your body turns fat from your diet and your internal fat stores into ketones. And unlike glucose, ketones can’t be stored as fat because they aren’t digested the same way.
That’s surprising, right? For decades, you’ve heard that fat makes you fat. Your body is actually built to use fat as an alternative source of fuel. For most of history, people weren’t eating three square meals and snacks throughout the day. Instead, humans would have to hunt and gather their food, and they learned to thrive when there wasn’t any food available, sometimes for days on end. To keep going, their bodies used stored fat for energy. Thanks, evolution.
KETO DIET BENEFITS:
- Burns body fat: When you’re on keto, your body uses stored body fat and fat from your diet as fuel. The result? Weight loss.
- Reduces appetite: Ketones suppress ghrelin — your hunger hormone — and increase cholecystokinin (CCK), which makes you feel full. Reduced appetite means it’s easier to go for longer periods without eating, which encourages your body to dip into its fat stores for energy. More research needs to be done in the area of appetite and ketosis, but it seems a lot of people experience reduced hunger.
- Reduces inflammation: Inflammation is your body’s natural response to an invader it deems harmful. Too much inflammation is bad news because it increases your risk of health problems. A keto diet can reduce inflammation in the body by switching off inflammatory pathways and producing fewer free radicals compared to glucose. 
- Fuels your brain: Ketones are so powerful that they can provide a good portion of your brain’s energy needs, which is way more efficient than the energy you get from glucose. Did you know your brain is made up of more than 60 percent fat? That means it needs a lot of fat to keep the engine humming. The quality fats you eat on a ketogenic diet do more than feeding your day-to-day activities — they also feed your brain.
- Increases energy: When your brain uses ketones for fuel, you don’t experience the same energy slumps as you do when you’re eating a lot of carbs. When your metabolism is in fat-burning mode, your body may tap into its readily available fat stores for energy. That means no more energy crashes or brain fog. Ketosis also helps the brain create more mitochondria, the power generators in your cells. More energy in your cells means more energy to get stuff done.
- Curbs cravings: Fat is a satiating macronutrient. You eat more smart fat on keto, so you feel fuller, longer.
HOW TO LOSE WEIGHT ON KETO
So, how exactly do you lose weight on keto?
When you start eating more fat and cut out the extra carbs (think sugar, bread, and pasta), you tend to experience fewer blood sugar swings and cravings that plague most people on the Standard American Diet. When your body runs on ketones for fuel, it has a steady supply of energy in the form of body fat. When your body relies on glucose, it needs a regular hit of carbs to keep it going.
Ketones may help control your hunger and satiety hormones so you feel satisfied and full, not hangry. That means fewer cravings, more energy, and increased fat-burning.
HOW KETONES AFFECT YOUR HUNGER HORMONES
Ketones impact cholecystokinin (CCK), a hormone which makes you feel full, and ghrelin, the “hunger hormone.”
- CCK: Your intestines release CCK after you eat, and it is a powerful regulator of food intake — so much that one study injecting obese men with CCK will cause them to cut their meals short. Ketones increase CCK levels so you actually satisfied after meals.
- Ghrelin: Ghrelin is called “the hunger hormone” because it increases appetite. It’s released from your stomach and intestines, with blood levels reaching their highest point when you fast. When you finally eat a meal, ghrelin drops in response to nutrients circulating in your blood. Ketosis suppresses the increase in ghrelin levels that occur with weight loss. So, when you’re in ketosis, you aren’t constantly thinking about your next meal.
WHY CALORIE COUNTING IS SO INEFFECTIVE
One of the reasons old-fashioned, calorie-restricted diets tend to fail is because these diets make you really hungry and cause food cravings.
Cutting calories to lose excess weight changes your hormones that control hunger and satiety. After you starve yourself enough to lose some weight, your brain and gut start making your hormones work against you.   Your hormones scream, “Eat more and gain that weight back!” So you do. And so begins a lifetime of yo-yo dieting.
But it doesn’t have to be that way. Skip the whole calorie-restriction, hungry-all-the-time thing, and just use ketosis to its full advantage without making yourself hungry. As long as you’re eating a higher percentage of quality fats, moderate protein, and just enough carbs, you’ll feel satisfied and energized — not hangry. No calorie-counting required.
WHAT TO EAT ON KETO
The keto diet is pretty simple: Eat mostly healthy fats (about 75 percent of your daily calories), some protein (about 20 percent) and a very small amount of carbs (about 5 percent). This is the general breakdown that a lot of keto beginners follow, but you may have to adjust your numbers and test your ketones to see what works for you.
Choose lower-carb foods such as meat, fish, eggs, vegetables and quality fats. Check out this detailed keto food list and browse these keto recipes for meal ideas. Most people do best eating somewhere between 30-150 grams of net carbs daily.
“Net carbs” means you can subtract fiber and sugar alcohols (like xylitol) out of your daily carb count — they don’t affect your blood sugar or get stored as glycogen, the storage form of glucose.
TYPES OF KETO DIETS
- Standard keto: Standard keto dieters eat very low carb (less than 50 grams of net carbs a day), every day. Some keto followers eat as few as 20 grams per day.
- Cyclical keto: People who follow a cyclical keto diet eat a high-fat, low-carb (less than 50 grams of net carbs per day) five to six days a week. On day seven, they will have a carb refeed day (approximately 150 grams of net carbs). The Bulletproof Diet falls into this category but tweaks keto for even better performance with intermittent fasting, protein fasting and an emphasis on nutrient-dense, low-inflammation foods.
- Targeted keto: You follow the standard keto diet, but eat extra carbs 30 minutes to an hour before a high-intensity workout. The glucose is meant to boost performance, and you return to ketosis after the workout. If your energy is suffering in the gym during keto, this style of eating might work for you.
- Dirty keto: Dirty keto follows the same ratio of fats, proteins, and carbs as the regular keto diet, but with a twist: It doesn’t matter where those macronutrients come from. Dinner could be a bunless Big Mac with a Diet Pepsi.
- Moderate keto: Eat high fat with 100-150 grams of net carbs every day. Women who experience problems with other forms of keto sometimes do better with this diet — restricting carbs can sometimes mess with hormonal function. Also, some athletes find they burn out with fewer than 100 grams of carbs on workout days.
HOW TO FIND WHICH APPROACH WORKS BEST FOR YOU
- First, check with your doctor before you make any major dietary changes.
- Try different styles of keto for at least a month each.
- Set goals based on fat and carb intake instead of worrying about calories. Eat until you’re full, and listen to your body.
Are you sharpest with a weekly carb refeed, or do you do better on a full ketogenic diet? Do you burn out when you dip below 100 grams of carbs per day? There’s a lot of variation within lower-carb diets, and some people feel their best with different styles of eating. Find a good balance that works best for your personal biology.
KETO SIDE EFFECTS (AND WHAT TO DO ABOUT THEM)
Generally, a ketogenic diet is safe for many people — but there are a few side effects to watch out for. Here are some tips to try if you’re experiencing common side effects, however, we recommend you see your doctor if you have any trouble.
DEHYDRATION AND MUSCLE CRAMPS
Carbs require water for storage. Fat does not. On a keto diet, you store less water, and your kidneys actively expel sodium instead of holding onto it. That means it’s easy to get dehydrated eating keto, especially during the first few weeks. With dehydration and low electrolytes, your muscles can start cramping, too.
Do this: Ask your doctor about supplementing with magnesium, sodium and potassium, your body’s three main electrolytes, and make sure you drink extra water. This is particularly important if you work out while on keto. Staying hydrated will also help you avoid symptoms of the keto flu.
DECREASED METABOLIC FLEXIBILITY
A lot of people report struggling to process carbs when they eat a strict keto diet long-term, which makes sense. If you hardly ever eat carbs, you have no need to keep your insulin pathways running. It’s like keeping the lights on during the daytime — a waste of energy.
Do this: Experiment with carb cycling (aka cyclical keto) by eating approximately 150 grams of net carbs one day a week.
There isn’t research on keto and sleep problems, but some people report waking up in the middle of the night on keto. If you find you have trouble sleeping on keto, you may be better off eating some high-quality carbs at night.
These issues are common on strict keto and are a big part of the reason why the Bulletproof Diet includes some quality carbs.
Do this: Take 1 teaspoon of raw honey before bed to provide your body with carbs through the sleep period.
NOT ENOUGH FIBER
If you’re eating fewer than 20 grams of carbs a day, it can be hard to get enough fiber. Fiber intake that’s lower than the recommended amount can contribute to constipation and irritable bowel syndrome (IBS).
- Be sure most of your carbs on a keto diet come from leafy, colorful vegetables.
- Experiment with a cyclical keto diet so you can eat more foods like sweet potatoes and butternut squash.
- Try a keto-friendly prebiotic fiber, which feeds beneficial gut bacteria.
- Salt your food to taste with Himalayan pink salt to make sure you’re retaining enough water to keep your bowels regular.
- Stay hydrated, and load up on magnesium and potassium — vital electrolytes you can find in spinach, avocado, and supplements.
- Keep a food diary. Track what you eat and make a note of what you do and don’t digest well.
- Exercise can help you stay regular and support your digestive tract.
On the opposite end of the spectrum, some people experience diarrhea on keto, especially if they aren’t used to consuming a higher-fat diet.
- Start slowly with MCT oils: MCT oil is a saturated fatty acid that gives your body fast energy in the form of ketones. It helps fuel your body, especially as it adapts to keto. It can take a little bit of time for your digestive system to get used to MCT oils. Start with 1 tsp at a time and work your way up from there.
- Add a digestive enzyme: You may not be properly digesting fats. Try lipase, an enzyme that digests fat in the body, or hydrochloric acid (HCL), which helps increase stomach acid and support digestion.
For a very small number of people who try keto, this diet change can bring on an itchy, red rash on the back, chest, neck or armpit area. Also known as Prurigo pigmentosa, keto rash is not life-threatening or dangerous. The exact causes still aren’t understood, but a small study points to differences in hormones, gut bacteria or exposure to allergens as potential triggers.
Do this: Check with your doctor, and try these tips to deal with keto rash:
- Bring back (some) carbs: You don’t need a full-blown bread-binge, but if a sudden switch to a keto lifestyle brought on a rash, you may want to reintroduce some healthy, high-quality carbs like sweet potatoes, yams, carrots, pumpkin and butternut squash.
- Avoid irritants: Like most rashes, keto rash can worsen with friction, sweat or heat. Avoid aggravating the irritated skin by wearing loose-fitting, breathable clothes, and avoiding perfumes, scented products or sweat-inducing exercise until the skin can heal.
- Support your skin: Supporting your skin with anti-inflammatory foods and supplements can help boost your healing time and calm the rash. Try incorporating foods like this turmeric latte or a DHA omega-3 supplement.
The keto flu is a natural reaction your body undergoes as it switches from burning sugar to fat for energy. The keto flu, aka carb withdrawal, generally kicks in at the 24- to 48-hour mark. Symptoms include brain fog, headache, insomnia, irritability, muscle soreness, poor focus, and sugar cravings.
Keto flu affects some people more than others. If you ate a diet low in refined sugar and starches before going keto, you’ll likely experience only mild symptoms. A diet high in sugar and carbs may set you up for greater withdrawal symptoms (especially from the sugar).
What causes the keto flu? When you restrict carbohydrates, your body must learn how to burn its backup energy source, and in order to do so, three big changes have to happen:
- Water and sodium flush. When you consume fewer carbs, insulin levels drop, signaling your kidneys to release sodium from the body. This causes a loss of up to about 10 pounds of water weight as water shuttles sodium out of your body. All of this usually occurs in the first five days. The glycogen loss and low insulin levels cause dizziness, nausea, muscle cramping, headaches, and gastrointestinal issues. Do your best to drink plenty of fluids and electrolytes at this point — that’ll alleviate some of these cellular symptoms.
- T3 thyroid hormone levels may decrease. T3 is a hormone produced by the thyroid gland. Dietary carbohydrates and thyroid function are closely connected, so when you cut carbs, T3 levels can fall. In conjunction with T4, another thyroid hormone, these hormones regulate your body’s temperature, metabolism, and heart rate. As your body adjusts to a ketogenic diet, lower hormone levels may leave you with brain fog and fatigue.
- Changes in cortisol levels. The T3 hormonal change is closely connected to a third hormonal change — cortisol levels. If you experience irritability and insomnia, that’s a clue that your cortisol levels have changed. Some people adjust to utilizing fat and ketones as a new fuel source, and cortisol levels fall to their old levels.
Do this: To beat the keto flu, try these remedies.
- Hydrate all day. To determine the minimum amount of water you need, use your current body weight and divide it by two. That’s how many ounces you need. For instance, if you weigh 140 pounds, you should aim for 70 ounces of water a day. Bone broth adds a serving of water to your diet and a dose of electrolytes (sodium and potassium) which will offset some of the discomforts you feel at a cellular level. Get our bone broth recipe here.
- Supplement with electrolytes. Replenishing your electrolytes is a great way to start feeling better fast. Take note of the key players: potassium, magnesium, and sodium. If you aren’t getting enough of them from your diet, which can be difficult to do on lower-carb diets, incorporate them by way of supplements.
- Eat more fat, especially MCTs. Upping your quality fat consumption can speed up your adaptation phase. One caveat: Most fats have to pass through your lymphatic system to your heart, muscles and fat cells before they reach the liver. Only there can they be turned into ketones for the body to use as fuel. MCT oil is different in that it goes straight to the liver after digestion — just like carbs — so it can be used immediately.
- Get a good rest. A sound night’s sleep is a very good thing when it comes to conquering keto flu. It keeps your cortisol levels in check, which will likely lessen your flu symptoms. Aim for 7-9 hours a night.
- Exercise (mildly) and meditate. Note the second word: mild. Yes, mild. The goal here is to reduce cortisol levels (especially initially), so anything that relieves stress will help you. Yoga or gentle walks can do the trick. If exercise isn’t your thing, try meditating. The bottom line, it’s probably best not to go full-on in the gym until you adjust to the keto diet.
- Take an exogenous ketone supplement. Exogenous ketones aid with fatigue and boost energy levels by raising the ketone levels in your blood. Note that they are not a replacement for a proper keto diet, though they may help you take it up a notch — especially on the flu. If you choose to go this route, aim for smaller doses of your supplement spread throughout the day for the first three to five days of the keto flu.
If all else fails, up to your carb intake. For some people, increasing fat simply won’t curb keto flu symptoms. If this is the case — and you tested your limits by adding more fat and are still experiencing flu-like symptoms — you’ll want to up your carb intake just a bit.
KETO FAQ: TROUBLESHOOTING KETO DIET ISSUES AND COMMON QUESTIONS ABOUT THE KETO DIET
Whether you’re thinking about starting keto or you’re five weeks in, here are some tips and tricks for common keto concerns.
1. WHAT FOODS SHOULD I EAT ON THE KETO DIET?
For the best results on keto, stick to these principles:
- An abundance of high-quality fats, like grass-fed butter and ghee, MCT oil, avocado oil, and coconut oil
- Moderate amounts of fatty proteins, like grass-fed meat, pastured eggs, wild-caught fatty fish and collagen protein.
- Lots of nutrient-dense and low-carb vegetables, like organic broccoli, zucchini, avocado, cucumbers, cabbage, and celery.
For a more detailed guide on what to eat on the keto diet, check out this complete keto food list.
2. HOW DO I KNOW IF I’M IN KETOSIS?
It can take anywhere from 2-3 days to a few weeks to enter ketosis, depending on your body’s ability to adapt to burning fat for fuel. Once you enter ketosis, your body will naturally produce ketones — molecules that fuel your brain and body with fat, not carbs.
You can usually tell if you’re in ketosis if you have steady, lasting energy, better focus, and a reduced appetite. For definitive answers, test your blood ketone levels. You’re in ketosis when your ketone levels measure 0.5-3 (that’s millimoles per liter).
You can test your levels using urine sticks, blood sticks or a blood meter. You can also test for acetone levels in your breath using a breath analyzer.
However, just tracking how your body feels is a simple way to know whether you’ve hit that ketosis sweet spot. Here are signs you may be in ketosis:
- Reduced hunger: Ketones suppress your hunger hormones, helping you feel fuller, longer.
- Keto breath: People often experience a metallic taste in their mouth due to raised ketone levels.
- Weight loss: The keto diet burns fat, so if you’re losing weight, you’re likely in ketosis.
- Flu-like symptoms: When you first start out, you may experience symptoms of the keto flu, like headaches, chills, and lightheadedness.
3. DO I NEED TO CALCULATE MACROS, AND HOW DO I COUNT THEM?
Macros, or macronutrients, are the carbs, fats, and proteins that make up your food and help you create energy. It’s not essential to count macros on the keto diet, but it’s a useful way to learn more about your food and understand your body’s needs. Learn more about ideal keto macros, including the benefits (and drawbacks) of counting them.
4. DO I NEED TO CALCULATE NET CARBS?
Even if you don’t calculate macros, you should keep track of net carbs — the carbs your body actually uses for energy. Calculating net carbs can help you stay in ketosis and inform your food choices. Find out how to calculate net carbs on keto and how many net carbs vs. total carbs you need.
5. IS THE KETO DIET HEALTHFUL?
The ketogenic diet is effective and backed by science. When done properly, the keto diet has been shown to support weight loss, create more mitochondria in your brain and reduce inflammation.  
However, any diet can be good or bad for you, depending on what you put on your plate. If you stick to the Bulletproof Diet roadmap, you eliminate keto foods that make you feel weak and don’t belong in a healthy diet — like processed cheese and sugar-free sodas.
6. WHAT ABOUT “DIRTY KETO?”
Dirty keto follows the same high-fat, low-carb structure of the standard keto diet — but it allows processed packaged and fast foods. It’s still possible to enter ketosis and burn fat while you’re on dirty keto, but it has serious drawbacks like inflammation and weight gain.
8. DOES THE KETO DIET CAUSE DIABETES?
No, keto does not cause diabetes. Several studies indicate that ketosis may help manage diabetes by decreasing glucose intolerance and stabilizing blood sugar.  
9. IS THE KETO DIET SUSTAINABLE LONG-TERM?
Yes and no. Some people thrive on the full keto diet without any problems. Other people run into issues from restricting carbs long-term, like insomnia and hormone imbalances. If that’s the case, experiment with keto carb cycling (aka cyclical ketosis), where you eat a moderate amount of carbs one day a week, so your body can cycle in and out of ketosis. It’s an effective modification that helps many people avoid any potential dangers and risks of a keto diet. Here’s how to do a keto carb cycling diet, and whether it’s right for you. It’s always a good idea to revisit your diet with your doctor often.
10. WHAT ARE THE DIFFERENT TYPES OF KETONES?
There are three types of ketone bodies. They are:
- Acetoacetate (AcAc): This is the first type of ketone that your body makes from fatty acids.
- Beta-hydroxybutyric acid (BHB): Acetoacetate converts into beta-hydroxybutyric acid. BHB isn’t really a ketone, based on its chemical structure, but it’s still considered part of the ketone family since it works in a similar way to the others. Fun fact: Brain Octane oil, a purified form of MCT oil, is a precursor of BHB.
- Acetone: A byproduct of acetoacetate, acetone is the least abundant ketone in the blood. It exits the body through the breath or the urine.
You’ll produce more of each type the longer you fast or restrict carbs.
11. HOW DO I KNOW IF I NEED MORE CARBS?
Some people feel fine when they eat very few carbs for extended periods of time. But if you’re dealing with symptoms like dry eyes, insomnia, fatigue and mood swings, your body might be asking for more carbs — especially if you’re a woman, an athlete or dealing with lots of stress (or all of the above).
12. WHY AREN’T AM I LOSING WEIGHT ON KETO?
You might be eating too much, not enough, or the wrong foods altogether. Here are a few reasons you’re not losing weight on keto — and what to do about it.
13. HOW DOES MCT OIL WORK WITH KETO?
MCT oil is a powerful tool on the ketogenic diet because it helps your body produce more ketones and stay in ketosis. However, not all MCT oils are the same, and some are more effective than others.
14. SHOULD I BE TAKING EXOGENOUS KETONES?
Exogenous ketones are synthetic ketones that help raise ketone levels in your blood. They’re popular supplements, but definitely not required — instead, focus on eating enough high-quality fats. Your body will naturally produce all the ketones you need to power through your day. If you want to add a supplement to your keto diet, MCT oil is a great place to start.
15. SHOULD I TRY INTERMITTENT FASTING ON KETO?
Definitely. Intermittent fasting may actually make keto more effective by boosting your fat-burning and weight loss results. Learn more about keto and intermittent fasting.
16. IS KETO THE SAME THING AS THE ATKINS DIET?
No. Whereas the Atkins Diet is extremely high in protein, a keto diet contains moderate amounts of protein. On a keto diet, large amounts of protein can turn into glucose in a process called gluconeogenesis, thus taking you out of ketosis. That’s why fatty cuts of meat are better than, say, chicken breast, which is high in protein and low in fat.
17. TARGETED KETOGENIC DIET VS. STANDARD KETO: WHAT’S THE DIFFERENCE?
With targeted Keto, you time your carb intake around workouts or times of heavy stress to give your body a little extra fuel. A lot of people on a full keto diet report “bonking” during intense workouts: They run out of fuel suddenly and don’t have the energy to keep going. Research suggests that with full keto, you’re likely to run out of energy during anaerobic workouts — any kind of short, intense workout. That includes lifting, CrossFit and high-intensity interval training.
Meanwhile, full keto seems to be good for endurance training like long runs. That said, these are super-athletes who are used to running up to 200 miles at a time. If you don’t fit that bill, you may benefit from doing targeted keto and having some carbs before a longer cardio session.
The other benefit of targeted Keto is metabolic flexibility. People who stay in Ketosis long-term gradually lose their ability to process carbs, and can actually develop insulin resistance. That’s fine as long as you never eat carbs, but if you want to have maximum metabolic flexibility, you’re better off occasionally breaking ketosis with a targeted keto diet or a cyclical keto diet.
The trick with the targeted ketogenic diet is to eat just enough carbs. You want to burn through them during your workout and go back into ketosis a couple of hours post-workout.
This is one of the rare times when you want higher-glycemic carbs. Your goal is to burn through them for quick energy during your workout and have them out of your system by the time you finish. With that in mind, a few good options for carbs are:
- White rice
- Baked sweet potato
- Beets (you’ll get a nitric oxide boost as a bonus, which gives your muscles more oxygen)
- White potato (if you tolerate nightshades)
Note: you don’t want to eat high-fructose carbs on targeted keto. Fructose goes straight to your liver instead of your muscles, so you’ll end up dropping out of ketosis without giving your muscles extra energy. Higher-fructose carbs include fruit, honey, and agave. Steer clear of those for targeted keto.
For the ultimate boost, drizzle Brain Octane MCT oil on your pre-workout carb source, so you have ketones alongside the carbs for maximum energy and metabolic flexibility.