The Definitive Guide to Keto

keto diet meal with chicken, greens and avocado

As someone interested in the world of keto, you’ve likely heard about its incredible potential for weight loss, mental sharpness, and more. Sure, there are some overblown or downright baseless claims out there, but by and large, keto deserves the hype it gets. A well-designed ketogenic diet is a highly impactful tool for burning fat for energy, managing your weight and many chronic health conditions, supporting cognitive acuity, and promoting healthy aging. 

Notice, however, that I said a well-designed ketogenic diet. With the exploding popularity of the keto diet, it’s easy to find approaches focusing only on increasing fat consumption or avoiding carbohydrates at all costs, while completely ignoring food quality and non-food factors that influence metabolism. These strategies, in my experience, miss the bigger picture of what keto should be—and what is possible with the keto diet.

In today’s post, I will attempt to provide a comprehensive overview of the science and motivation behind keto and how to do it right by adhering to Primal principles. I’ll also link to a multitude of other posts that provide even deeper dives on these specific topics. Buckle in, there’s a lot of information here. But if you’re going to go keto, let’s  make sure you’re equipped to eke out the greatest possible benefit. 

What Is the Keto Diet?

“Keto” is a loose term to describe a whole host of very low-carb diets. The underlying commonality (and sometimes the only one) among the many keto approaches is low carbohydrate intake—low enough to prompt the liver to make ketones. Ketones, or “ketone bodies,” are a source of energy that most cells of the body, including the brain, can use for fuel. More on this process shortly. 

On a typical high-carb diet like the Standard American Diet, our bodies run on glucose from the carbs we regularly eat throughout the day. When carb intake is restricted, though, the body needs to tap other energy sources. That can include fat and ketones.

A typical keto dieter will need to increase the amount of fat they eat in order to make up for the energy (calories) they are no longer getting from carbs. Especially if you’re escaping the clutches of low-fat diet dogma, your fat intake might increase considerably. That’s why keto a low-carb, high-fat (LCHF) diet. However, the high fat intake isn’t what defines a keto diet; the low carb intake is. And if you have a lot of weight to lose, you won’t be eating a ton of fat because you want to covert fat from your body, not your plate, into ketones. 

Although haters often frame keto as a restrictive “fad” diet, a look into human evolutionary history shows us this would’ve been a common, if not default, arrangement. Depending on their location, our hunter-gatherer ancestors didn’t have regular access to much carb intake beyond seasonal fruits or tubers. They spent much of the time operating in ketosis. Our bodies today fully retain this ability—and there are substantial benefits from a lifestyle that incorporates that full metabolic flexibility.

Ketogenesis: The Science

To understand ketogenic diets, you must understand the conditions that promote ketosis. And to do that, you must understand how our cells beta-oxidize (metabolize) fatty acids for energy.

  1. Fatty acids are broken down into acetyl-CoA.
  2. Acetyl-CoA combines with oxaloacetate.
  3. The acetyl-CoA/oxaloacetate duo starts the Krebs cycle.
  4. The Krebs cycle produces ATP, the body’s energy currency.
  5. Congratulations. You’ve just turned fat into energy.

If the supply of acetyl-CoA exceeds the supply of oxaloacetate, the liver converts any excess acetyl-CoA into ketone bodies via a process called ketogenesis. These ketone bodies act as an “alternative” energy source for the brain and body. 

The main hormonal regulator of ketogenesis is insulin. In order for ketogenesis to occur, insulin must be low. Low insulin also allows for the release of stored fatty acids from adipose tissue, which make their way to the liver for conversion into ketones. 

Given these two facts, you’ll see that anything that provides oxaloacetate to the liver or raises insulin can prevent ketone production or knock you out of ketosis. What is the big offender here? Carbohydrates. (Protein too, but to a much lesser extent. The average keto dieter generally does not need to worry about “too much” protein interfering with ketosis. People doing keto for medical reasons, and who need to strictly maintain high circulating ketone levels, may need to watch their protein intake somewhat. However, recent research suggests that may not be as necessary as once believed.1)

Ketosis occurs in certain instances without any dietary change at all:

  • Extreme physical exertion that depletes liver glycogen and depletes around half of stored muscle glycogen
  • Fasting for significant time period (at least 24 hours for most people)
  • Starvation or significant restriction in total calories for a significant time period

In all of these conditions, there’s a common ketogenic thread: low insulin and liberation of body fat in excess of that which we can beta-oxidize.

Why Do We Need Ketogenesis?

The ability to produce ketones for energy was critical for our ancestors’ survival during periods of little or no food availability. While most of your cells can metabolize fatty acids directly—this is the whole point of becoming fat-adapted—some, particularly the neurons in your brain, rely heavily on glucose… unless ketones are around. Ketones provide an elegant solution for creating quick cellular energy when glucose from carbs is unavailable. 

In one sense, ketosis is a stop-gap solution for situations where you’re burning huge amounts of body fat, like during a famine. Why would you want to mimic abject starvation if there’s all this food around? Grocery stores are an evolutionary aberration. For most of human history, if we wanted carbs, we had to climb a tree and extricate a bee’s nest, spend hours digging tubers, or wait around for the wild fruit to ripen. We are adapted to periods of low food availability, and, especially, low glucose availability. 

Humans are remarkably good at slipping into ketosis. Whereas for most other animals ketosis is difficult to achieve, a human will be mildly ketotic just waking up from a full night’s sleep. Heck, breastfed babies spend much of their time in ketosis despite drinking nutritionally balanced breastmilk. We’re clearly meant to produce and utilize ketones from time to time, and not coincidentally, there are significant health benefits associated with restricting glucose and having ketones floating around.

Let’s go over some of the major ones.

Benefits of Keto

Many of the benefits associated with keto diets can be chalked up to the types of foods that keto diets include (meat, eggs, vegetables, dairy) versus exclude (grains, sugar), but there’s more to it than that.

The ketogenic diet first emerged as a tool for clinicians to treat their patients with epilepsy. It was—and remains—the only tool consistently able to prevent seizures. Most of us aren’t using keto to treat epilepsy, though. Most people are using keto diets as a fat-loss tool. And indeed, keto can be highly effective for shedding extra weight and for preserving precious muscle mass in the process, especially when paired with resistance training

But that’s only one of the many reasons you might want to try keto. The more researchers discover about ketogenic diets and how ketones as signaling molecules, the more promise it seems to have as an (adjunct) treatment for a wide assortment of diseases, including

  • Type 2 diabetes. Diabetes is essentially a condition of carbohydrate intolerance. Removing most carbs from the diet can help regulate blood sugar and improve insulin sensitivity.
  • Certain cancers, potentially including devastating glioblastomas.2
  • Neurodegeneration. The brain thrives on ketones, and ketogenic diets seem to improve focus and memory, including in adults with Alzheimer’s and other types of dementia.3 It may be helpful for patients with diseases like Parkinson’s and MS as well.4
  • Non-alcoholic fatty liver disease.5

And this is just the tip of the iceberg. We know that insulin resistance and chronic inflammation are common comorbidities in just about every chronic disease—whether related causally or by correlation. Ketogenic diets are one of the fastest and most reliable methods of improving insulin sensitivity, and ketones themselves are anti-inflammatory.6 On that basis, keto diets could be useful for all manner of chronic disease. Already, considerable animal evidence and anecdotal human evidence suggests that’s the case, and researchers are hard at work on human trials.

What Is the Keto Reset Diet, and What Makes It Unique?

The Keto Reset Diet

The Keto Reset Diet is what I call the Primal approach to keto. As I explain in detail in The Keto Reset Diet book, there are right ways and wrong ways to do keto. What’s wrong or right is contextual, of course. Even still, there are ways to do keto that are more likely to net you the benefits you want. And there are ways that will technically lead to a state of ketosis but that aren’t exactly what I, or my readers, would consider healthy or ideal. 

The Keto Reset Diet is a particular variation on keto that prioritizes nutrient density and natural, whole-food eating. It’s the Primal diet you already know—based on meat, fish, fowl, eggs, nuts and seeds, produce, optional dairy products, and the occasional sensible indulgence—but with fewer carbs. This is the approach I myself live (and promote) because it’s a sustainable means of achieving and maintaining ketosis without compromising overall nutrition or health. You get all the metabolic advantages of ketosis (lower insulin levels, lower inflammation, more “even” energy and cognitive function, etc.) AND the critical benefits of a nutrient-dense diet. 

Watch the video below to learn more about the Keto Reset approach to ketogenic eating:

Keto Macros

The foundation of any keto diet is the macros, or macronutrients—the level of carbohydrate, fat, and protein intake you target on a typical day. Here, too, the Keto Reset Diet differs somewhat from other versions of keto. 

I recommend starting with

  • 50 grams of carbs, gross (total) not net
  • 0.7 to 1 gram of protein per pound of lean body mass
  • As much fat as you need to get enough calories and feel satisfied

This is a good jumping off point, but there is plenty of nuance here, and you may need to do some tweaking and self-experimentation to find the macros that work best for you. 

With the general suggestion of 50 grams of carbs per day, the Keto Reset Diet offers a generous window to enjoy a flavorful, varied diet every single day. Other keto programs suggest consuming as little as 10 or 20 grams of carbohydrates per day. I find that excessively restrictive for most people. You probably don’t even need to count the carbs from above-ground, non-starchy vegetables and avocados since they contain a lot of fiber and don’t lead to large insulin excursions. However, folks with insulin resistance and type 2 diabetes might have an easier time getting into ketosis at a lower carb threshold around 30 grams per day.7 Conversely, athletes and other highly active folks can probably exceed that limit, sometimes considerably, and still maintain ketosis.

If you’re part of a small group that uses keto to keep seizures at bay, or treat serious neurological diseases, you’ll want to diligently maintain high blood ketone levels. That means sticking to very low-carb and possibly low/moderate protein (though, again, that’s up for debate8). If you’re doing keto for general health or weight loss, you can handle more protein and still remain in ketosis. In fact, many people often don’t eat enough protein while trying a keto diet. The average American, particularly older folks, don’t eat enough protein for their muscle maintenance needs, period. Protein will help stave off muscle loss if you are in a caloric deficit.

When you’re setting your keto macros, carbs and protein are more or less fixed. Fat is the variable you will manipulate to increase or decrease your total caloric intake according to your needs and goals. Carbs and protein both yield roughly 4 calories per gram, while fat is 9 calories per gram. That means you don’t need to eat as much fat as you might think, in grams, to meet your daily energy needs. 

Here’s an important point that a lot of people miss: eating more fat does not make you more ketogenic. The goal is not to eat as many fat bombs and butter coffees as possible. Instead, aim to eat enough to be satisfied and have the energy you need to sustain your activity level. 

What to Eat on a (Primal) Keto Diet

Since keto is defined by carb intake, you technically can follow a ketogenic diet comprising entirely artificial sweeteners, trans fats, and processed meat products. That doesn’t mean you should. Is your goal to make ketones or is it to be healthy, energetic, clear-headed, and long-lived? That’s what I thought.

The bulk of your food intake (in terms of volume) will come from above-ground vegetables like greens, peppers, broccoli, Brussels sprouts, cauliflower, tomatoes, celery, cucumber, kale, cabbage, asparagus, zucchini, mushrooms, etc.—unless, of course, you lean towards a more carnivorous approach. Avocados are a keto staple. You can also include moderate amounts of fruit, but select lower-carb options.

You’re free to enjoy virtually any fish or meat that doesn’t contain added breading or sweeteners. Eggs are also an ideal choice. Bone broth and collagen supplements that don’t contain carb sources like sugars, fillers, or binders are also healthy choices while keto. Organ meats are always encouraged. 

The majority of your calories on a keto diet will come from fat. Choose healthy sources like avocado, avocado oil, extra virgin olive oil, coconut oil, as well as fattier cuts of meat, fatty fish like salmon, and canned small, oily fish. Lots of keto dieters embrace full-fat cheese, butter, cream, and Greek yogurt, but it’s also possible to do keto without dairy.

Nuts and seeds can be eaten in moderation, as they contain healthy fats and a minor amount of protein.

For drinks, coffee and teas without sugar and unsweetened sparkling water and mineral water are ideal choices.

What to Avoid

In short, you’ll want to avoid empty carbs of all kinds. I like to look at healthy eating, and particularly healthy keto, as the optimization of carb sources. Foods and drinks with a high carb count and little nutrient value are obvious choices to avoid: sodas, juices, sweetened nut milks, candy, baked goods, and other sweets and grain-based foods.

For the sake of maintaining ketosis, it’s also important to avoid most legumes (like beans and peas) and starchy vegetables (like potatoes, sweet potatoes, and squashes), as well as dairy items of a higher carb count (like sweetened yogurts and milk).

For more on what to eat and avoid, check out my keto shopping list

How to Get Started with Keto

Ketogenic dieting is a big jump for some people. You’re literally switching over to a new metabolic substrate. That can take some getting used to. Transitioning gradually and smartly can be the difference between feeling fantastic versus suffering from keto flu and generally having a bad experience. 

First, make sure you are well-prepared with a Primal-aligned eating pattern in place. In The Keto Reset Diet, I lay out a protocol for starting with a “Metabolic Reset” in which you dedicate yourself to Primal eating and lifestyle principles for a minimum of three weeks. The purpose is to “re-engage” your cells’ fat-burning capabilities that may be dormant after months or years of high-carb eating.

Once you are ready to go keto, it’s as simple as dropping your carbs and increasing your fat intake proportionately. Here’s what else you should do to have a good experience:

Get plenty of electrolytes. Going keto really flushes out water weight, and tons of electrolytes leave with it. You’ll want lots of sodium, magnesium, and potassium to replenish what’s lost. Failure to get enough electrolytes, especially sodium, is the number one mistake people make and the biggest reason for keto flu symptoms. Aim for 4 to 5 grams of sodium (about 2 teaspoons of fine salt or a little under 3 teaspoons of kosher salt), 300 to 400 mg magnesium, and 1 to 2 grams of potassium each day on top of your normal food. 

Eating extra fat in the first four to seven days can accelerate keto-adaptation by increasing AMPK signaling. Dial it down after, though. Just because a ketogenic diet is a high-fat diet doesn’t mean you should eat ungodly amounts. 

Lift heavy things. A common criticism of ketogenic diets is that they cause loss of lean mass. This isn’t totally unfounded. If you’re on a super-low-protein and/or low-calorie (energy-restricted) ketogenic diet, you might lose muscle. Lifting weights prevents these issues by sending an anabolic signal to your muscles and allowing the consumption of more protein without hampering ketosis. 

Do lots of low-level aerobic activity. Walk, hike, jog, cycle, row. Keep things in the aerobic heart zone (under 180 minus age in beats per minute), and you’ll increase your utilization of body fat, which will speed up ketone production and adaptation.

But don’t overdo the high-demand exercise. It’s pretty common to experience a dip in energy or performance in the gym or on the road during the adaptation phase as your body switches over to new metabolic pathways. If you’re a hard-core strength or endurance athlete, you might notice that it takes a while to feel “normal” again. For that reason, I don’t recommend going keto right before a big race or competition. 

Eat vegetables. The vast majority of vegetables are keto-friendly. They provide important micronutrients and phytonutrients with negligible amounts of carbohydrates. (It is possible to do keto as a vegetarian or vegan, but it’s considerably more difficult.)

Eat berries. Raspberries, blackberries, strawberries, and blueberries are all quite low in glycemic load and extremely high in phytonutrients. While eating a flat of strawberries isn’t very ketogenic, a small bowlful won’t knock you out.

Eat fiber. Many people on ketogenic diets tend to ignore or malign fiber. That’s a mistake. First, fiber doesn’t digest into glucose. It doesn’t “count.” Second, fiber feeds your gut biome, providing fermentable substrate for your gut bacteria to turn into beneficial short-chain fatty acids and to provide support to your immune system

Make a minimum commitment to six weeks of nutritional ketosis. The first three weeks will be the most difficult as you transition to new fuel sources, but then you can expect breakthroughs. Once you get to the six-week mark, the metabolic machinery is in place, and it’s hard to reverse the adaptation. Extra mitochondria don’t just disappear.

Signs You’re in Ketosis

Once you drop your carbs, your liver will start to produce ketones fairly quickly—within a day or so, especially if you do any glycolytic exercise or fasting. You can test your blood, urine (not recommended), or breath ketones to confirm this. There are drawbacks to each, and unless you have a medical condition necessitating a specific level of ketones, obsessive testing may be unnecessary and expensive. 

I prefer to go by symptoms and signs. Since you’re trying to divine what works best for you, relying on the subjective signs and symptoms you experience is perfectly legitimate. These include:

  • Reduced urge to snack
  • Fewer sugar cravings
  • Lower appetite
  • Steady energy, no afternoon crash
  • Mental clarity, absence of brain fog
  • Improved focus
  • Better mood
  • Reduction in physical symptoms like joint pain

Variations on a Traditional Keto Diet

So, are carbs out forever? What if you want to incorporate carbs for high-intensity performance while maintaining the benefits of ketosis?

First of all, it may not make much of a difference if you’re just strength training. Carbs likely will help certain populations, namely CrossFitters, sprinters, and anyone else engaged in intense glycolytic work. But even then, being keto-adapted reduces the amount of glycogen you’ll use for a given intensity, so err on the side of fewer carbs, and time them to coincide with exercise. This strategy is sometimes referred to as the targeted keto diet, or TKD. Try 15 to 30 grams of relatively fast-absorbing, simple carbs just before or after a workout.  

For everyone, not just athletes, you always have the option of loosening the reins a bit once you’re keto-adapted, which you can reasonably assume you are once you’ve devoted at least six weeks to keto. One way to do this is by practicing “lazy keto,” where you loosely track carbs but no other macros. Another is cyclical keto, or CKD, you spend the majority of the week in ketosis but eat more carbs a day or two each week. These approaches can work well for people who don’t like to be overly regimented with their diets, but it’s also possible to get too loosey-goosey and start regaining lost weight and generally lose progress. Consider the pros and cons and decide what’s best for you.


Mainstream media seems to delight in disparaging keto. Keto diets are unequivocally safe for the majority of adults when done correctly, but they’re not for everyone. Young kids, teens, pregnant or nursing individuals, and the very elderly should only do keto under the supervision of a doctor.

Despite what you might have heard, keto is not bad for women; in fact, many women of all ages do quite well on keto

People with cancer should absolutely talk to their doctors first, as should anyone who is taking medication that affects blood sugar or blood pressure. Keto can rapidly lower blood sugar and blood pressure, within a couple weeks of starting the diet, so your doctor may need to adjust your dose to keep you in safe ranges. 

I’ve written extensively about specific concerns you might have. Check out these posts if you’re worried about keto causing:

Final Thoughts

These are the basics that work for most people. If you have specific medical or dietary concerns, you’ll want to tweak accordingly.

It should be apparent that I’m a fan of keto. More than that, I think everyone should do stints of keto periodically throughout the year to foster the all-important metabolic flexibility that is the cornerstone of metabolic health and healthy aging. 

That said, not everyone needs to be on a ketogenic diet, and certainly not all the time. I’ll even admit to being a bit leery of long-term, protracted ketosis in people who aren’t treating a medical condition. It just doesn’t seem necessary. After all, while humans are unique in our ability to slip into ketosis, and there are clear evolutionary precedents for being in ketosis, Grok wasn’t starving all the time. Most of the time, he probably had enough to eat.

By all means, try it for a few or (even better) six weeks, build and install some new mitochondria, remain long enough to get really good at burning free fatty acids in your muscles. Then cycle back to a more moderate-carb Primal eating pattern for a while. Pop back into a ketogenic state on a regular basis to keep your capacities topped up.

That’s it for me today. Have you recently tried keto, or are you hoping to? Maybe you’ve done it for a while. I’d love to hear your tips and questions. Thanks for stopping by, and have a great week, everyone.

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About the Author

Mark Sisson is the founder of Mark’s Daily Apple, godfather to the Primal food and lifestyle movement, and the New York Times bestselling author of The Keto Reset Diet. His latest book is Keto for Life, where he discusses how he combines the keto diet with a Primal lifestyle for optimal health and longevity. Mark is the author of numerous other books as well, including The Primal Blueprint, which was credited with turbocharging the growth of the primal/paleo movement back in 2009. After spending three decades researching and educating folks on why food is the key component to achieving and maintaining optimal wellness, Mark launched Primal Kitchen, a real-food company that creates Primal/paleo, keto, and Whole30-friendly kitchen staples.

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