You may already be familiar with the ketogenic diet. Keto has been making a big splash in the nutrition world, and we get asked all the time what we think about it.
People are talking about keto for good reason. It can be awesome. But with excitement can also come a lot of misinformation. We’ll help you navigate the ins and outs of a ketogenic diet over the next couple articles. Let’s start with the basic structure of keto, as well as its possible benefits and drawbacks.
What is a keto diet?
In a nutshell, keto is a low-carb, high-fat diet that’s designed to make you burn fat as your main source of energy. Most of the time, your body burns carbohydrates for energy. But if you cut off your body’s supply of carbs, your body begins seeking out fat instead. Eating keto shifts you into a state of ketosis, which is when you stop using carbs (for the most part) and start using fat as your biggest source of fuel.
No surprise, then, that a keto diet cuts out nearly all carbs. Here’s a graph of a typical macronutrient ratio you’d eat on keto, by percentage of calories:
The numbers here are a little flexible: anywhere within 65-80% fat, 5-10% carbs, and 15-30% protein. Some people do better with slightly higher carbs on keto. Others may want more protein. You can try playing with the numbers and seeing what makes you feel best. What’s consistent, though, is that you’re getting your lion’s share of calories from fat. When you’re in ketosis, fat provides abundant and convenient fuel for your body.
Why burn fat for energy?
There are a few possible benefits to going keto. But before we talk about them, a quick disclaimer: the ketogenic diet was created about 100 years ago to treat epilepsy, and while it’s great for that, research on keto for things like inflammation, cognitive benefits, cancer, diabetes, and so on is still in its infancy. A lot of the research on keto has only been going on for the last few years, so take what you read here with a grain of salt.
That said, there’s evidence that keto may be good for a few different things:
To be clear, just because you’re using fat as your main energy source doesn’t mean you’re constantly burning through your stored body fat. You’ll use the fat you eat for energy first, and body fat after that. You won’t be burning stored body fat all the time in keto – that’s a common misconception.
But the cool thing about keto is that you may be able to burn body fat without feeling hungry all the time. A recent well-controlled study found that keto dieters burned about 300 more calories per day than their higher-carb counterparts, without changing anything other than the macronutrients they ate . Researchers haven’t figured out exactly why people burn more calories on keto, but a growing number of rodent studies [4,5,6] suggest it’s thanks to increased thermogenesis – in other words, on keto you may produce more body heat at rest.
Then there’s the psychological value in being able to eat steak and butter all the time. Fat is delicious and keto allows for plenty of it. That can be a refreshing change if you find you struggle with avoiding fat. On the other hand, some people find it exhausting to cut carbs so severely.
Your body’s metabolism is influenced by a number of factors, so ultimately, all this comes down to what works for you. If you’re looking to lose weight, keto may be worth a try.
The other nice thing about keto is that it curbs appetite. Your body likes to maintain homeostasis, which means it tends to protest when you make major changes to it. That includes losing weight – in general, the more weight you lose, the more your body releases ghrelin, a hormone that contributes to hunger, to try to get you to put that weight back on. Keto suppresses ghrelin, which can translate to a less pressing sensation of hunger, and more successful long-term dieting [7,8]. That hunger suppression is also convenient if you’re going a long time without eating. On keto, it can feel easier to skip meals when, for example, you’re traveling.
Again, research on keto and mental performance is pretty new, and there aren’t yet any quality studies using healthy adults. However, keto does dramatically change the way your brain gets its energy. Keto is a well-established way to prevent epileptic seizures — doctors have been using it with epileptic patients since the 1920s — and more recent research suggests that it could help people with Alzheimer’s and Parkinson’s, both of which mess with the brain’s ability to use glucose [9,10].
Anecdotally, many people on keto report more stable energy and mental clarity (a reduction in “brain fog”). We suspect, based on rat studies, that the improved mental function is thanks to a couple different things:
- Keto makes mitochondria (the power plants of your cells) more efficient and more active in rats , which could translate to more available fuel for brain cells.
- Keto also increases antioxidant activity in the brains of rats . Antioxidants keep inflammation and cellular damage low.
- Keto caused brand new mitochondria to grow in rats as well [13,14], further deepening energy stores.
These studies are all in rats. It’s not yet clear whether or not they apply to humans, but enough people report more energy and mental clarity from keto that we figured they’re worth mentioning. Your mileage may vary; you’ll just have to try keto for yourself and see if you notice any benefits.
Stable energy and blood sugar regulation
Carbs – particularly refined carbs – increase your blood sugar and trigger insulin release. Some people do fine with carbs. Others feel a yo-yo effect: a spike in energy after a higher-carb meal, followed by hunger and fatigue a couple hours later. Your blood sugar goes up, and then it goes down, as shown by this handy graph, adapted from this study:
You can see that the more sugar there is in a meal, the greater blood sugar spikes and crashes. The less sugar, the more the blood glucose stays stable.
So if you feel sleepy or you crash after a higher-carb meal, the first step would be to cut out sugar. But some people are particularly sensitive to carbs and feel that spike and crash even with complex carbs.
If you’re one of them, keto may help. It’s an elegant way to skirt the entire blood sugar issue. With no carbs to burn, blood sugar tends to decrease, and then remain stable. Cutting carbs to ketogenic levels may be particularly valuable for people with diabetes , although you should definitely talk to your doctor about that before making any changes. We are not doctors, nor do we play them on TV.
Keto can also be good for endurance training. Ultra-endurance runners performed as well on keto as their fellow runners did on a high-carb diet, without running out of energy and falling apart from exhaustion (colloquially called “bonking”) .
Most of us are not ultra-marathoners, so that study may not apply. Fortunately, normal cyclists see the same results from a keto diet . On a practical level, the benefit here is that you wouldn’t need to carbo-load before an endurance event.
Some scientists have proposed a theory (based on rat studies and conjecture so far) that you actually become more efficient at using oxygen when you’re in keto, and that it may offer advantages over carbs for endurance training. The theorized mechanism is beyond the scope of this article, but if you’re curious and want to get into some deep biochemistry, Dr. Peter Attia breaks it down step-by-step here.
Keto may help decrease inflammation, too. Again, a lot of people report improvements in inflammatory issues like arthritis after they go keto, but there aren’t too many good human studies backing it up yet. There are plenty of rodent and human cell studies, though.
- Keto decreases free radical damage and central nervous system inflammation in rats [18,19]
- Two small studies of humans with fatty liver disease found eating keto significantly decreased liver inflammation [20,21]
- Mice fed a ketogenic diet had higher pain tolerance and decreased inflammation after their paws were injected with a toxin 
- Beta-hydroxybutyrate (BHB), one of the things you turn fat into while on keto, is anti-inflammatory in both rats and human cell cultures 
Who may keto NOT be good for?
Keto may not be for everyone.
- Non-endurance athletes can struggle with keto. While keto seems to be good for aerobic (oxygen-based) exercise, it can fall short for brief, intense exercise, probably because brief, intense exercise taps your glycogen (sugar) stores for fuel, and on keto you store significantly less sugar in your cells. A lot of people report bonking when they try things like powerlifting or CrossFit while on traditional keto. There are ways to tweak keto to accommodate heavy lifting or HIIT workouts, but it takes a little more personal experimenting. We’ll get into those solutions in another post.
- Pregnant women should probably avoid keto, too. Glucose is the main energy source that fuels fetal development . Eat your high-quality carbs if you’re pregnant.
- Children may want to avoid keto, too. It may be fine for them, but it isn’t well-studied, and youngsters have very different nutritional needs than adults do. Probably better not to take a chance on keto with your kids.
- People with hormone imbalances should talk to a doctor before going keto. Typically, keto causes increased cortisol (the stress hormone) during your first week or two on it, because your body isn’t used to burning fat and is demanding more carbs. The cortisol spike can screw with your sleep and stress your body while you adapt. Most people are good after that first couple weeks, but if you’re already dealing with, say, adrenal fatigue or chronic stress in your life, adding another stressor may not be a good idea. Keto may also affect thyroid function, so talk to your doctor before going keto if you have an imbalance in your thyroid hormones.
- Kidney disease may not pair well with ketosis. Kidneys indirectly regulate fat metabolism, so if your kidneys aren’t running at their best, you may struggle to break down lots of fat . Keto also increases uric acid in the blood for the first few weeks you’re on keto. Uric acid can contribute to kidney stones, especially if you’re already prone to them. If you have kidney issues, you should probably talk to your doctor before trying keto.
- Gallbladder removal can make it tough for the enzymes in your small intestine to digest fat. If you’ve had your gallbladder taken out, you may want to avoid keto.
Outside of a few specific cases, though, many people find keto is an excellent way to eat. Let’s recap keto’s potential benefits:
- Weight loss
- Hunger suppression
- Mental clarity
- Stable energy and blood sugar
- Increased endurance
- Decreased inflammation
- Delicious food
Keto may work wonders for you, or it may not. The only way to know is to give it a shot.
Planning on trying keto? Stay tuned. Our next article will get into the biochemistry of ketosis, and the one after that will give you a practical guide to eating keto, day-by-day. In the meantime, leave any questions or comments below. Thanks for reading!