Key takeaways

The keto diet is not suitable for everyone, particularly due to its restrictive nature, potential nutritional deficits, and difficulty in maintaining long-term.
It was originally developed for epilepsy treatment in the 1920s and puts the body into ketosis to burn fat, but its effectiveness and safety for weight loss and other claimed benefits lack long-term study.
Certain populations, including people with seizures, may benefit from a keto diet, whereas it is not recommended for individuals with specific health conditions, pregnant or breastfeeding women, children, or those with a history of disordered eating.
Short-term side effects known as “keto flu” can occur, and success on the diet requires a calorie deficit and careful food selection to avoid potential weight gain despite being in ketosis.

If you haven’t heard of the keto diet by now, it’s probably safe to say that keeping up with the latest health trends isn’t really your thing. From wellness websites and doctor’s office magazines to the Twitter feeds of your favorite celebs, the keto diet has been everywhere in recent years. There are an array of diets encompassing the “ketogenic dietary therapies” (KDTs). KDTs include the classic ketogenic diet, the modified Atkins diet, the low glycemic index treatment, and the medium-chain triglyceride diet.

Though the jury is largely still out on the benefits of keto, it’s often touted as the answer to everyone’s weight loss prayers. But does the keto diet work for everyone? Unfortunately, nutrition experts say no. It can be restrictive, tough to sustain, and downright unhealthy for some people.

If you’re thinking of trying it, here’s what you should know.

What is the keto diet?

The classic ketogenic diet is a high-fat, adequate-protein (like 1 gram/kg), low-carbohydrate diet that produces metabolic changes associated with the starvation state. The ketogenic diet was developed in the 1920s as a treatment for epilepsy, according to registered dietitian Lainey Younkin, owner of Lainey Younkin Nutrition. Now, Younkin says, it’s a fad diet based on putting your body into ketosis, a process of burning stored fat cells for energy.

Does keto work?

Proponents of keto say the low-carbohydrate, high-fat approach can lead to significant amounts of weight loss. “People do lose weight,” agrees Younkin. “But can they keep that weight off and can they follow keto long-term? For most people, the answer to those questions is no.” In other words, it’s not necessarily the kind of permanent lifestyle change you’re hoping to achieve.

Many health professionals worry about the extreme nature of the diet, which limits your carb intake to less than 50 net grams per day and may lead to nutritional deficits.

Who should try a keto diet?

So who is a good candidate for keto? In short: people with seizures. While people with seizures should be on medication, the addition of maintaining a keto diet can help decrease their risk of a breakthrough seizure. (For more information on the connection between epilepsy and keto, this 2019 review in Frontiers in Neuroscience breaks down much of the relevant research.)

According to registered dietitian Danielle Schaub, culinary and nutrition manager for Territory Foods, the diet can also help people who are looking to:

improve or reset their insulin sensitivity;
improve some health biomarkers, like blood pressure;
or lose weight or body fat with a sedentary lifestyle.

Who shouldn’t try a keto diet?

On the flip side, there are several groups of people who should not do keto. You should stay away from the keto diet if you are:

Looking to lose weight fast without having a plan on how to maintain the weight loss long-term
Someone with a poor relationship with food and/or disordered eating patterns
An elite athletes
Have pancreatitis, liver failure, kidney disorder, or other fat metabolism disorders
Diabetic and have ever been diagnosed with diabetic ketoacidosis.

Like with most restrictive diets, children and pregnant or breastfeeding women should also avoid keto unless otherwise instructed by their physicians.

Additionally, ketogenic diets should absolutely be avoided if you have a rare genetic condition, such as porphyria, fatty acid beta-oxidation defects, or primary carnitine deficiency. Consult with your primary care provider before beginning any diet.

Keto diet and diabetes

You may have noticed that people looking to improve their insulin sensitivity are often good candidates for the keto diet; typically, this refers to people who have diabetes, though not everyone with diabetes should try keto.

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“Patients with Type 1 diabetes must be very careful with the keto diet because the ketosis process could increase their risk of diabetic ketoacidosis, a very dangerous state which can lead to hospitalization and death,” says Laila Tabatabai, MD, an endocrinologist at Houston Methodist.

Ketones are produced by the liver as an alternative fuel when there’s not enough sugar to be converted to energy. Both the keto diet and uncontrolled Type 1 diabetes can result in high ketone levels. For people without diabetes, ketones aren’t usually dangerous. However, a buildup of ketones can be very dangerous for people with Type 1 diabetes, which can result in dehydration, acidic blood, coma, and even death.

Patients with Type 2 diabetes, though, could benefit more readily from the keto diet. Dr. Tabatabai says that the reduction in carbs and overall weight loss on keto means your body requires less insulin, which in turn helps stabilize blood glucose levels.

But that still doesn’t mean you should start keto ASAP if you have Type 2 diabetes. “Studies have shown that short-term use of the keto diet can help patients with Type 2 diabetes lose weight [but we] do not yet have long-term data on its safety and efficacy,” emphasizes Dr. Tabatabai.

A 2019 review of the recent research into Type 2 diabetes and low-carb diets published in Nutrients shows that most of the studies performed lasted several months (one, published in the American Journal of Clinical Nutrition, lasted 52 weeks). Though the results are positive in the short-term, all diabetes patients—whether Type 1 or Type 2—should talk to their doctors before starting the keto diet.

Keto side effects

The long-term effects of the keto diet are still unknown; however, there are several common short-term side effects to be aware of.

Nausea
Hypoglycemia
Vomiting
Headache
Fatigue
Dizziness
Insomnia
Lower exercise tolerance
Constipation
Kidney stones

These side effects are also called the “keto flu” and it can take a few days to a few weeks for symptoms to resolve.

What to eat on keto

Eating keto means choosing foods that are low in carbs and high in fat…but that’s not always as easy as it sounds. Carbs aren’t just lurking in refined pastas and breads; many healthy foods, such as fruits and veggies, contain carbs (along with dozens of necessary vitamins and minerals).

Here’s an example of some popular keto-friendly foods:

Meat and poultry
Eggs
Dairy products like cheese, Greek yogurt, cottage cheese, and whipping cream
Low-carb vegetables like spinach, cauliflower, and mushrooms
Avocados
Nut butter
Bacon, jerky, and sausage
Nuts, seeds, and monounsaturated oils like olive oil

Keto is very popular, so there’s no shortage of recipes and eating plans catered to the diet’s specifications. Eating keto does require careful planning and preparation.

I’m in ketosis but not losing weight

As a reminder, the goal with keto is to put your body into a state of fat-burning ketosis by eliminating most carbs. Schaub says some people will reach ketosis after about one week, while others may take a little longer.

“Once you are in ketosis, if you are consuming fewer calories than you are expending, you will burn body fat and lose weight,” she explains.

However, it’s possible to be in a state of ketosis and not lose weight. Schaub says that if you enter ketosis but continue eating enough food to cover your energy needs, your body won’t start burning fat cells as a source of energy because it simply isn’t necessary. You still need a calorie deficit to lose weight, ketosis or not.

There’s also another reason why you could find yourself not losing weight on keto or, worse, gaining weight: eating too many fatty foods. Since the keto diet is high in fat and fat is very calorie-dense, Schaub says you will gain weight if you are in an overall calorie excess regardless of where those calories come from. (In other words, keto is not a free pass to chow down on fast-food burgers all day.)

There isn’t a daily calorie limit for the keto diet, but most sources suggest 70% to 80% of total daily calories should come from fat, 10% to 20% from protein, and 5% to 10% from carbohydrates.

The bottom line: keto doesn’t work for everyone

Keto can work for some people, and there are benefits to being in ketosis even if you’re not dropping pounds; Schaub says it can improve insulin sensitivity and lower blood pressure. The short-term weight loss could be beneficial for preventing chronic conditions like obesity, diabetes, and heart disease, but there’s not a lot of research about keto yet to prove its claims. “We don’t know the effects of following keto long-term since most of the studies on the diet are short-term in the setting of treating epilepsy,” explains Younkin.

Diet wisely. Keto diet can be difficult to maintain and most dietitians prefer that people adopt eating habits they can commit to long-term for optimal health benefits.