Carbs are out. Fat is in. At least that’s the case if you believe the ketogenic diet. Claims that the keto diet can somehow trigger superhero-level exercise performance and fat-loss have grown so loud that it’s hard to believe the eating approach was originally designed as a way to treat epileptic seizures in children.
But then, taking your body into ketosis — the process by which the body runs on fat because you don’t have enough carbs/glucose — is a rich resource for the seemingly unbelievable. This is, after all, a dieting method that requires you to purchase special test strips to examine your urine in order to confirm if you have “achieved” ketosis. (Yes, seriously.)
So is the keto diet effective? Yes and no.
The claims about keto superiority for fat loss and muscle gain are significantly inflated.
But that doesn’t mean the diet is without value.
To help you determine if the keto diet is the right approach for you, we dig into your biggest keto diet questions—and some you probably hadn’t even thought about asking. In the end, should you decide that going keto is best for you, you’ll at least know how to do it properly (most people don’t), understand what it’s really doing to your body (ditto), and be aware of the risks involved.
What is a ketogenic diet?
In a traditional ketogenic diet, you eat 80 percent of your daily calories from fat. The remaining 20 percent is divvied up between protein and carbohydrates—but most of it protein. Typically, carb intake is capped at 20 grams per day, or less than what you’ll find in a single apple, according to Andy Galpin, Ph.D., C.S.C.S., C.P.T., associate professor of kinesiology and director of the Biochemistry & Molecular Exercise Physiology Lab at California State University, Fullerton.
This number is far lower than what you’ll find with most low-carb diets, which generally max out carb intake at about 45 percent of daily calories, according to a review from Tulane University. For someone following a 2,000-calorie diet, that works out to as much as 225 grams per day.
But, don’t forget the most important part — it’s not the low carbs that surprises most people. After all, keto is known as the low-carb diet. What you need to remember is that the ketogenic diet is also surprisingly low in protein.
Why? As you’ll learn, taking your body into ketosis means having your body run on fat for fuel, and protein can be converted into glucose in your body. That means you need to keep protein levels lower to truly establish a state of ketosis.
Why do ketogenic diets go so low with carbs?
Carbs and glycogen (or carbs stored in the liver and muscles) are the body’s preferred and most efficient energy source. Once you deplete them, your body must find other energy sources.
When you cut carbs so drastically — as one does on a keto diet — you can put the body in a state of ketosis. What does that actually mean? Your liver is forced to convert fat into fatty acids and ketones — compounds the body can use to produce ATP, a.k.a. energy, Galpin explains.
It’s this process that truly separates the ketogenic diet from other low-carb approaches such as Atkins, and why the diet revolves around such a high intake of dietary fat: without it, your body cannot produce the ketones needed to keep you up and running.
To determine whether the body has truly entered a state of ketosis, you’d need to test yourself for high levels of ketones, Galpin notes. That’s why people who go keto have to urinate on at-home test strips.
If your body is not in a state of ketosis, you’re technically just following another low-carb diet.
Which means your body is not running on ketones. And all that carb-depletion isn’t going to work the way you intended.
Through ketosis, your body becomes what many refer to as “fat adapted,” meaning your body adjusts to what you’re giving it and uses fat for energy.
In a world of quick fixes and promises, this usually is not a quick process. Research suggests that it usually takes several weeks to occur, according to ketogenic diet researcher, Antonio Paoli, M.D., director of the Nutrition & Exercise Physiology Lab at the University of Padova in Italy.
What happens in the process of becoming fat adapted? Expect extreme fatigue, brain fog, and sluggish exercise performances. After all, your brain is the primary user of your body’s carbs and glycogen. Without that fuel, your entire central nervous system feels the effects.
In fact, it’s those effects on the neurological system that first popularized the keto diet. According to a 2014 review published in the Journal of Lipid Research, ketosis alters the activity of mitochondria in the brain of those with neurodegenerative conditions, which helps cut down on the frequency and severity of seizures.
Is a keto diet good for fat loss?
For those who are looking to cut their body fat percentage or improve exercise performance, the keto diet comes with mixed results.
In one Nutrients study, male cyclists who followed a keto diet for four weeks decreased their body fat percentages and improved their VO2max levels (the amount of oxygen they could take in and use in a minute), but their max power decreased.
Other studies suggest that following a ketogenic diet can allow the body to burn a larger percentage of calories from fat instead of carbohydrates and glycogen when participating in endurance events such as marathons and triathlons, according to a 2017 review in the Strength and Conditioning Journal.
But some of this is very misleading. According to nutrition researcher Alan Aragon, you’re not actually burning more body fat.
You see, when you eat more fat your body is going to burn more fat. This causes an increase of “fat oxidation,” which can easily be interpreted as an increase in fat loss.
But when protein and calories have been balanced (as in, you’re comparing diets where total calories and protein are the same — but fat or carb intake is difference), there is no difference in fat loss between a keto diet and a non-keto/higher carb diet.
“To lose weight on the diet, you still have to consume fewer calories,” Galpin says. “There are no physiological shortcuts. Calories still matter, and while they aren’t the only thing that matter for fat loss, you still have to maintain a caloric deficit to lose fat.”
Paoli notes that a ketogenic may aid in cutting calories by increasing satiety, but that potential benefit is not yet definitive.
Is a keto diet good for building muscle?
Unfortunately for people who have body-comp goals (think: ditching fat and muscling up), research consistently shows that in order to lose fat without also losing a significant amount of lean muscle, daily protein intake has to be higher than what a traditional ketogenic diet offers.
After all, with only 20 percent of your daily calories coming from carbs and protein combined, there isn’t a lot for muscle-building protein. A 2015 review published in Applied Physiology, Nutrition, and Metabolism showed that, in order to retain muscle mass while cutting calories, protein intake should be set at about 25 percent of total daily calories. And why must protein be so low on a keto diet? It all has to do with preventing side effects (which we’ll get to in the next section).
Just as important, keto research to date seems to indicate no performance benefit among those performing high-intensity activities such as sprinting and weightlifting, according to the review authors. This is due to both a decrease is fast-acting carb availability as well as a recruitment of slow-twitch endurance-based type II fibers over fast-twitch power ones.
It’s worth noting, however, that a lot of the studies on keto done to date have suffered from at least one big design flaw.
“A major problem with the research on the ketogenic diet is that a huge chunk of the it doesn’t establish whether study participants are actually in ketosis,” Galpin says. “Researchers often don’t draw blood to determine a state of ketosis and instead assume that participants were eating few enough carbs and enough fat that they were.”
What about side effects – is a keto diet safe?
When it comes to protein, a keto diet puts people in a sort of “screwed if you do, screwed if you don’t” situation.
While a low protein intakes can cause the body to lose muscle mass, too high of a protein intake can cause the body to spring out of its state of ketosis, Paoli says.
Basically, breaking down protein for energy is easier than producing ketones and using them for energy. So, if that is an option, your body is going to take it.
But a far bigger issue is that eating too much protein during a ketogenic diet can put your body in a state of ketoacidosis, in which keto acids (ketone-containing acids) accumulate and decrease blood pH, Galpin says.
When this occurs, symptoms include nausea, vomiting, excessive thirst and confusion. In very rare cases, “extreme ketoacidosis” can be fatal.
While some may think a keto diet gives them license to go crazy on greasy, processed foods and still lose weight, it’s important to focus on getting dietary fats from whole, natural sources including red meat, eggs, avocado, nuts, olive oil, and dairy (although many forms of dairy have sufficient carbs to kick you out of ketosis, FYI).
It’s worth noting that, since these high-fat foods tend to be low in fiber, a person who does go keto should work with a dietitian to keep their fiber intake at a level that prevents constipation and GI issues such as diverticulitis, Galpin says. He adds that most keto dieters require a fiber supplement to get enough fiber without going overboard on carbs.
Lastly, having a high protein intake can also increase keto-dieters’ already-elevated risk of developing kidney stones. Note that a high protein diet alone is not a precursor to kidney problems like many people believe. But, adding high protein + a keto diet approach can potentially lead to kidney stones.
What else should I know if I want to go keto?
The keto diet has a lot of very interesting research around brain health and fighting autoimmune diseases. For people that struggle with a variety of health problems, the nature of the diet is promising. And for those that don’t mind the fairly rigorous rules, it can be a very effective approach for fat loss — just like several other diet methods.
At the same time, there’s no getting around it: the keto diet is incredibly tough to follow. Researchers have found that to be true even when adults attempt the diet to control their epilepsy. If people who have such a high degree of motivation have trouble following the protocol, you have to ask yourself a simple question: how well do you think you’re going to do following the rules of the diet?
Research has shown over and over again that your success on a diet depends entirely on how consistent you can be.
So if you can’t stick to it for a long period of time, then another option might be a better fit.
After all, nutrients don’t occur in isolation—they are found in whole foods that, generally, contain some mix of the three macros. So it can be difficult to find high-fat foods that don’t put you over your protein or carbohydrate goals. And since fat is an energy dense macro, packing nine calories per gram, it’s also easy to go overboard there and wind up gaining weight, rather than losing it.
If you choose the ketogenic diet, keep a cheat sheet of ways to stay on track. Reminders like “overdoing it on protein can snap you out of ketosis” will help make sure that your efforts pay off. Or how even one carb “cheat” on the ketogenic diet can cancel out any purported benefits of the eating plan. If you’re going to see success with the ketogenic diet, you have to do it to a T — and it’s best to do so under the supervision of a physician or registered dietitian, according to Paoli.