What is Keto And How Does it Work?
The big idea: Eating a very high-fat, low-carb diet causes a dramatic metabolic shift in your whole body. That metabolic change has benefits for weight loss and overall health.
Want a few more details? Your metabolism is how you use the energy from food to meet your body’s needs. When your body needs energy to do something (like keep your heart beating, walk the dog, or digest food), it normally uses a mix of carbs and fat. But by changing your diet, you can force your body to stop using carbs or fat and start using other compounds, called ketone bodies for fuel instead.
A ketogenic diet (“keto diet” for short) forces your body to start creating and using ketone bodies.
The shift to burning ketones has some major benefits:
- Reduces hunger: in this study, people on a keto diet voluntarily ate less than people on a moderate-carb, high-protein diet. The authors found that “hunger was significantly lower...and weight loss was significantly greater...with the [ketogenic] diet (6.34 kg) than with the [medium-carb] diet (4.35 kg).”
The very best weight loss diet is one where you just naturally eat less because you’re not hungry for it. But when most people try to lose weight, they start producing more of a hormone called ghrelin, which makes them feel hungrier. Ketosis suppresses ghrelin production and reduces feelings of hunger. Ketosis also increases the release of the hormone cholecystokinin (CCK), which is produced in the gut and makes you feel less hungry. A ketogenic diet might also have effects on other neurotransmitters, like gamma aminobutyric acid (GABA), that reduce hunger even more.
- Improves blood sugar control: one study reported “a significant improvement of glycemia, as measured by the fasting glucose and HbA1c levels in patients with type 2 diabetes. More importantly, this improvement was observed after some antidiabetic medications had been decreased to half in the LCKD group.”
When you eat carbs, your body makes a hormone called insulin to process them. If your blood sugar is really high – or if it’s constantly swinging from really high to really low – that’s a sign that something is wrong with your insulin production and you’re having trouble processing carbs. Diabetes is the most extreme form of this, but even people without diabetes can have insulin resistance or other problems that cause high blood sugar. (Learn more about insulin here and here.)
Eating keto dramatically reduces the need to make insulin. After all, if you’re barely eating any carbs, it doesn’t really matter that you can’t process them very well. Keto basically lets you do an end run around the whole carb/insulin problem and tackle blood sugar spikes at the source.
- Speeds weight loss: according to one study comparing a ketogenic diet to a low-fat diet, “Subjects on the low-carbohydrate diet lost more weight during the six-month study than did those on the low-fat diet.”
Reducing hunger and controlling blood sugar (see above for details) are already two big benefits for weight loss. When you don’t feel hungry all the time, it’s easier to eat less. But wait, there’s more!
- Your brain needs carbs to function: it can’t use fat or ketones. On keto, you don’t eat enough carbs, so your body has to make carbs out of protein. This is hard and burns a lot of calories.
- Eating keto helps you burn fat for fuel more efficiently. Like, say, the fat you want to lose.
Calories still ultimately determine weight gain or loss, but eating keto helps you burn through your stored calories (fat) more quickly.
- Improves blood lipids: blood lipids include cholesterol and triglycerides. Take a look at the effects of a year on a ketogenic diet for obese subjects with high cholesterol (from this study): “The level of total cholesterol, LDL cholesterol, triglycerides and blood glucose level decreased significantly…This study shows the beneficial effects of ketogenic diet following its long term administration in obese subjects with a high level of total cholesterol”
“Blood lipids” are cholesterol (HDL, LDL, and all the different varieties of LDL) and triglycerides. This study explains why keto reduces blood lipids, particularly LDL cholesterol (the “bad” cholesterol) and triglycerides (arguably even more dangerous). One of the simplest ways to reduce triglycerides is fasting, and keto mimics fasting in a lot of ways, so it speeds up the removal of triglycerides without requiring you to actually fast. Eating more fat also has hormonal effects that increase the breakdown of LDL cholesterol.
One of the secrets to the keto magic here is simply the reduction in carbs. Because of the way that the liver converts excess carbs to fat, a high-carb, low-fat diet increases triglyceride and LDL cholesterol levels. Reduce the carbs and you reduce the problem.
But what about all that cholesterol? Eating more dietary cholesterol on keto doesn’t cause any increase in blood cholesterol because dietary cholesterol is actually a very small percentage of total cholesterol. Most of the cholesterol in your blood is made by your own body. Your body can easily respond to changes in dietary cholesterol by just making less cholesterol of its own. Learn more about dietary cholesterol here.
- Keto may also have benefits for brain health (like in this study where a ketogenic diet improved memory in older people with cognitive impairment) and as an addition to normal treatment for cancer (read a research paper on keto and cancer here). But these benefits are still very experimental and mostly studied in animals so far, so it’s not totally clear how well they translate to humans.
How the Diet Works
The trick to the ketone magic is a diet high in fat, low in carbs, and moderate in protein. Keto isn’t a high-meat diet or a high-protein diet. It’s a high-fat diet.
The exact amount of protein, carbs, and fat can vary a little bit. For example, some people can eat a little less fat and a little more protein. Another popular strategy is to not worry about ratios at all - just keep carbs very low, under 50 grams or so, and eat as much protein and fat as you want. But the basic idea is high-fat, adequate-protein, low-carb.
After eating this type of diet for a few days to a week, you’ll end up in ketosis - burning ketones for energy instead of carbs or fat - and that’s how the magic happens.
Keto & Paleo: What's The Difference?
Keto and Paleo aren’t the same thing, but they are related.
Paleo is all about eating foods that humans evolved to thrive on. And as it turns out, humans can thrive on a huge variety of different diets, including both high-carb and low-carb diets. One good guide to Paleo nutrition is the way that modern hunter-gatherer tribes still eat today. When one group of researchers studied hunter-gatherer diets, they found some groups that ate just 3% of energy as carbs and other groups who ate up to 50% of energy as carbs. This suggests that carb consumption in the Paleolithic probably varied a lot, and people can probably do well on a huge range of diets. Paleo is about cutting out inflammatory and unhealthful foods (like grains), not about specifying any particular carb level.
But keto diets do restrict carbs, because keto isn't about imitating hunter-gatherers in general; it's about achieving a specific metabolic adaptation. Keto diets are all about restricting carbs (and protein), not because that’s the One True Healthy Way for People to Eat, but because (for some people) it has specific metabolic benefits on top of a regular Paleo diet.
Paleo doesn’t have to be low-carb, but keto always is. For some people, plain Paleo works great. But other people get better results by combining Paleo and keto: get all the anti-inflammatory, gut-healing benefits of Paleo, plus the metabolic magic of keto.
Paleo Guidelines, Keto-ified:
- Avoid gut-irritating foods like grains and legumes.
- Avoid industrially processed oils, like soybean oil, “vegetable oil,” canola oil, and corn oil.
- Avoid processed sugar, high-fructose corn syrup, and other industrial sweeteners.
- At every meal, eat high-quality animal protein like pastured meat, free-range eggs, and wild-caught fish.
- At every meal, eat a big pile of fresh vegetables. Eat fruit too if you like it, but eat more vegetables than fruit. (Some wiggle room in this for people with severe digestive problems who don’t tolerate fiber-rich foods well)
→ on keto, make sure to eat low-carb vegetables and limit fruit.
- At every meal, eat at least some healthy fat (olive oil, fatty meat like pork belly, avocados…)
→ this is especially crucial for keto!
- Eat nuts, seeds, dried fruit, cocoa, and other Paleo treats occasionally, as treats. (Or not at all, if that works better for you).
- Carb-dense Paleo foods include potatoes, sweet potatoes, chestnuts, bananas, and honey. These foods are Paleo-friendly, but they have too many carbs to fit into a keto diet.
Caveats & Potential Speedbumps
There’s solid experimental evidence at this point (see here or here) that a moderate-carb, non-keto Paleo diet is effective for weight loss. Keto is an optional tweak that works for some people but it’s not necessary for weight loss and better health.
Keto isn’t right for everyone! People with some kidney diseases are at higher risk from eating keto diets. Also, kids often have serious side effects from eating keto (this has been studied a lot, since keto is used as a treatment for epilepsy in children). Keto hasn’t been established as a safe diet for pregnant women yet (one of the very first studies just came out this year).
Don’t risk your health for a weight-loss diet: talk to your doctor if you have any doubts about keto or if you experience any serious issues.
With that said, even if keto is the best diet for you, it doesn’t always go off without a hitch: take a look at some common problems and issues you may run into and how to manage them.
Potential Speedbumps: The First Few Weeks
Low-Carb Flu: for the first two weeks or so, while your body adapts to keto, you may feel tired, cranky, brain-foggy, or just out of gas.
Solution: drink plenty of water but also make sure to get lots of salt: eating keto increases your body’s need for salt, and too little salt can make you feel really crummy. Drinking bouillon or adding bouillon cubes to soups and stews is a good way to get a lot of salt in without really trying. Get gentle exercise and make sure you’re eating enough food overall, even if you’re reducing carbs. Learn more about the low-carb flu here.
Constipation: a common complaint for keto beginners.
Solution: make sure you’re still eating some vegetables, not just meat and fat. Alternately, if you’re keeping carbs very low, a psyllium supplement might be helpful. If your stools are very hard and dry, a magnesium supplement might be useful (magnesium draws water into the colon, so it can make stools softer and easier to pass). Probiotics might also help.
Nausea/vomiting/diarrhea: this may be part of the low-carb flu, but it can also be a separate problem.
Solution: try eliminating coconut oil if you eat it (the fat in coconuts can cause diarrhea in some people). If the problem keeps up, try a probiotic supplement; the evidence suggests that lactobacilli are particularly good for diarrhea.
Physical fatigue: for the first few weeks, you might struggle with energy during workouts.
Solution: just take it easy for a few weeks. There’s been a lot of research on keto diets and exercise, and in most studies (like this one), there’s an adaptation period where performance goes down, but after that, performance returns to normal.
Potential Speedbumps: The Long Term
Muscle cramps: painful muscle cramps that may or may not happen during exercise.
Solution: muscle cramps are often caused by electrolyte deficiency and/or dehydration. Try drinking more water, eating more salt, and getting more foods rich in potassium and magnesium (or taking supplements).
Plateaus: weight loss slows or stops
Solution: check your diet for creeping carb sources (it may help to track for a while). Alternately, consider that maybe your body has changed since you started keto. Keto might not be right for you now, even if it was at the beginning of your weight loss. (Learn more about plateaus and busting them)
Nutrient deficiencies: If you eat an extremely low-carb version of keto, you might not get enough of nutrients like vitamin C, which are mostly found in plant foods.
Solution: essentially, just be aware that it is a risk. After you’ve settled into a solid routine, plug a day or two of your normal food into a nutrient tracker. If you’re constantly coming up short on something, add more food sources or consider a supplement.
Another note: keto doesn’t have to be forever.
Some people get excellent results by starting with a ketogenic diet and then slowly adding carbs to end up at a more moderate-carb Paleo style diet for the long term. If you’re into studies, here’s one where a slow shift into a moderate-carb approach (120 grams of carbs per day) had good results. This can make social events easier and give you more variety – it’s also easier to get a nutritionally complete diet if you aren’t limiting carbs quite so much.
3 Ways to Keto
In general, keto is a low-carb diet. But there are some variations that allow you to add carbs at specific times for specific purposes.
Take a look at low-carb days (in orange) and high-carb days (in teal) on three different variations of keto.
Standard ketogenic diet (SKD)
All low-carb, all the time!
Best for: most beginners - it’s consistent and not confusing.
Probably not ideal for: athletes who do a lot of cardio exercise (e.g. running) and struggle with performance on a low-carb diet.
Cyclic ketogenic diet (CKD)
1-2 days of higher carb intake every week or so. During the high-carb day, your diet will be almost all carbs with very little fat. This helps restore glycogen (the fuel that your muscles use during exercise) and gives you a chance to eat high-carb foods that would otherwise be off the plan.
Best for: endurance athletes and people who stick to a diet better if they get a break every week.
Probably not ideal for: people who don’t work out much and people who tend to turn one “cheat day” into a “cheat week” or a “cheat month.” For some people, it’s easier to just get into the rhythm of all keto, all the time.
Targeted ketogenic diet (TKD)
Carbs only around workouts. The exact amount depends on the intensity of your workouts, but around 50 grams of carbs pre-workout and another 50 grams post-workout is a good starting place to experiment with what works for you.
Best for: People who do a lot of very intense workouts and want to maximize their athletic performance.
Probably not ideal for: people who don’t work out much.
Other ways to carb up
Some people use a TKD or a CKD as a structured way to add occasional carbs to a ketogenic diet. But you can also use other kinds of carb re-feeds (also called carb ups). Learn more about the science of re-feeds here.
Time for the practical stuff! Check out the world’s simplest keto meal plan:
Most of your calories will come from fat, but the biggest volume of food on your plate should be from vegetables. Fat is very calorie-dense, so you don’t need a big physical amount of fat to get most of your calories from it.
Other encouraged foods include all kinds of spices, spice blends (just make sure they don’t have sugar added), herbs, vinegar, and salt.
Vegetable Carb Counts
- Lettuce (1 gram carbs [0.5 fiber] per cup of raw green leaf lettuce)
- Spinach (1.1 gram carbs [0.7 fiber] per cup of raw spinach)
- Celery (1.5 grams carbs [0.8 fiber] per half cup of raw celery)
- Bok choy (pak choi, Chinese cabbage) (1.5 grams carbs [0.8 fiber] per half cup of cooked bok choy)
- Cucumber (1.9 grams carbs [0.3 fiber] per half cup of raw cucumber)
- Radishes (2 grams carbs [0.9 fiber] per half cup of sliced radishes)
- Green peppers (2.1 grams carbs [0.8 fiber] per half cup of sliced green pepper)
- Zucchini (2.4 grams carbs [0.9 fiber] per half cup of cooked zucchini)
- Cauliflower (2.5 grams carbs [1.4 fiber] per half cup of cooked cauliflower)
- Tomatoes (2.9 grams carbs [0.9 fiber] per half cup of cherry tomatoes)
- Swiss chard (3.6 grams carbs [1.8 fiber] per half cup of cooked chard)
- Kale (3.7 grams carbs [1.3 fiber] per half cup of cooked kale)
- Asparagus (3.7 grams carbs [1.8g fiber] per half cup of cooked asparagus)
- Turnips (4 grams carbs [1.6 fiber] per half cup of cooked turnips)
- Mushrooms (4.1 grams carbs [1.7 fiber] per half cup of cooked mushrooms)
- Spaghetti squash (5 grams carbs [1.1 fiber] per half cup of cooked squash)
- Brussels sprouts (5.5 grams carbs [2.0 fiber] per half cup of cooked Brussels sprouts)
- Broccoli (5.6 grams carbs [2.6 fiber] per half cup of cooked broccoli)
- Carrots (6.1 grams carbs [1.8 fiber] per half cup of chopped carrots)
- Beets (8.47 grams carbs [1.7 fiber] per half cup of sliced cooked beets)
- Onion (10 grams carbs [1.5 fiber] per half cup of cooked onion)
- Acorn squash (15 grams carbs [4.5 fiber] per half cup of cooked squash)
- Sweet potatoes (23.6 grams of carbs [3.8 fiber] per 1 medium sweet potato)
Good Protein Sources: Focus on Fatty Meats
Keto isn’t a high-protein diet. It’s moderate in protein, but protein is less important than fat. Keto is basically a high-fat diet with enough protein to meet your needs.
Most meat is quite high in protein and quite low in fat, which isn’t ideal for keto. Meats like canned tuna and chicken breast have almost no fat! If you eat those foods, make sure to add some healthy fats to your plate. Another option is to focus on fatty meats like…
- Pork belly
- Fatty steak (e.g. ribeye steak)
- Bone marrow
Good Fats to Know
You can still eat leaner cuts of meat, like chicken and turkey, on keto - just make sure to add plenty of good fats. Take a look at three great options:
- Butter or ghee (if you do dairy): high in saturated fat and conjugated linoleic acid (a fat that helps with weight loss). If dairy doesn’t tend to sit well with you, you might still be able to do ghee: it’s butter with most of the dairy proteins rendered out. Dairy is optional on keto, but it can be a tasty way to get a lot of healthy fat in.
- Coconut oil: high in medium-chain triglycerides (MCTs). MCTs promote ketone production, so they’re really good for ketogenic diets. Learn more about coconut oil here.
- Extra virgin olive oil: rich in monounsaturated fat and anti-inflammatory antioxidants. Olive oil has all kinds of great health benefits that you can read about here.
- Other healthy plant fats: avocado oil, macadamia oil, and palm oil can all be good choices and add some variety to your salad dressing and cooking. Learn more about healthy plant fats here.
Should I Count Grams of Protein, Carbs, and Fat?
For some people, tracking their food is an easy way to stay with the program. This is especially true for people who haven’t tried low-carb before and might not be familiar with the carb counts of different foods. Tracking can be an easy way to stay on the plan and avoid any unpleasant food surprises.
On the other hand, some people hate food tracking. It drives them crazy. If that’s you, a good compromise might be to follow the easy keto meal plan (fatty meat + low-carb vegetables) and just look up the carb counts of some foods that you buy regularly to make sure you don’t get any unpleasant surprises. Some foods, like nuts, can have more carbs than you might think!