A Detailed Guide to the Potential Health Benefits and Risks of the Keto Diet

To say that the keto diet has become one of the most popular diets of recent years is a complete understatement. Case in point: There are more than one million searches on Google every month for the keto diet. It’s unique because the fad diet has captured the interest of people who want to lose weight — and there’s no shortage of reported success stories to be found.

But researchers have taken a greater interest in it as a medical diet, too. In 2015, there were 159 studies listed in the database PubMed (which is run by the U.S. National Library of Medicine and the National Institutes of Health). In 2018, that number doubled, with 322 published studies.

So what is the keto diet?

The diet calls for consuming high amounts of fat, a moderate amount of protein, and a very limited amount of carbs. It’s usually broken down to 75, 20, and 5 percent of your daily calories, respectively, says Pamela Nisevich Bede, RD, a dietitian with Abbott’s EAS Sports Nutrition in Columbus, Ohio. Compare that with the typical American diet — which is usually 50 to 65 percent carbs — and it’s safe to say this is a completely different way of eating, Nisevich Bede says.

After you follow the diet for a few days, your body enters ketosis, which means it has started to use fat for energy. Newbies on the diet find it helpful to track whether they’re in ketosis with a urine ketone strip or a blood-prick meter, but Nisevich Bede says you’ll eventually learn what ketosis feels like and will know whether you’re in it.

The keto diet is all about increasing calories from fat and going very low carb. That means following a restrictive, keto-friendly food list.

Keto-Friendly Foods

Here are some of the foods you may eat on keto:

• Oils (like olive oil, avocado oil, and coconut oil)
• Avocado
• Heavy cream
• Butter
• Cream cheese
• Cheese
• Coconut (unsweetened)
• Nuts (almonds, macadamia) and seeds (chia seeds, flaxseed, sunflower seeds)
• Leafy green vegetables (romaine, spinach, kale, collards)
• Nonstarchy vegetables, including zucchini, asparagus, cucumber, broccoli, cauliflower, and bell peppers
• Meats (chicken, beef, pork, lamb)
• Eggs
• Fish (particularly fatty fish like salmon and sardines)

What You Can’t Eat (or Drink) on the Keto Diet

Foods and drinks that you’ll avoid on the keto diet include many whole fruits (though some fruits are keto-friendly), dried fruits, whole grains, cold cuts, chicken nuggets, milk, ice cream, alcohol, and desserts.

Breakfast Two fried eggs, tomato slices, coffee with heavy cream

Snack Full-fat cottage cheese topped with pine nuts

Lunch Spinach salad with a grass-fed burger on top, cheese and avocado

Snack Roasted, salted almonds

Dinner Grilled salmon with a side of broccoli topped with butter

The keto diet has a massive fan base that has grown at least in part due to the popular Netflix documentary The Magic Pill, which touts a trove of promising keto health benefits. But the fact of the matter is that most of the studies on the keto diet are premature. Meaning: They’re in small populations of humans, or they’re in rats. (And you are very different from a rat.)

The only clear and proven health benefit of the keto diet is reducing epileptic seizures in children. In fact, doctors have been using keto therapeutically for this purpose since the 1920s.

Keto is often suggested for children who suffer from certain disorders (like Lennox-Gastaut syndrome or Rett syndrome) and don’t respond to seizure medication, according to the Epilepsy Foundation. (1) They note that keto can decrease the number of seizures these children have by half, with 10 to 15 percent becoming seizure-free. In other cases, it may also help patients reduce the dose of their medication.

The keto diet may also be beneficial for adults with epilepsy, though the Epilepsy Foundation notes that it’s less frequently recommended for this group because it is so restrictive and difficult to stick with. (1) One study, published in May 2016 in the journal Epilepsy & Behavior, found the diet reduced the frequency of seizures for many study participants, 7 percent of whom were seizure-free at the four-year mark. (2) And though it wasn’t the goal for this study, nearly 20 percent of the participants lost weight while following the diet.

But the No. 1 reason people adopt the keto diet nowadays? Weight loss.

Initially, the weight loss comes from loss of water because you cut down on carbs in your diet and your body uses up the carbohydrates stored in the liver, which hold onto water. The diet results in further weight loss because it encourages you to load up on whole, high-fat foods, Nisevich Bede says.

By cutting carbs, you’ll also cut sugar and simple, refined carbohydrates, which means a steadier supply of energy. (No more sugar highs and crashes!) Once their bodies are used to the diet, “The first thing people report is, ‘Oh my gosh, I have this steady energy and I don’t have the need to snack at 3 p.m. because my energy is waning,’” Nisevich Bede says. Research published in January 2015 in the journal Obesity Review showed that the keto diet may lead to fewer hunger pangs and a lower desire to eat. (3)

You lose weight temporarily because “if you’re not hungry every five minutes and can work on your willpower,” you won’t eat as much, Nisevich Bede says. But while some research is promising — one study published in October 2013 in the British Journal of Nutrition found that the keto diet led to greater weight loss than a low-fat diet, for example (4) — there is a lack of long-term research (greater than two years) that suggests a highly restrictive diet like keto is superior for weight loss than others, and it’s certainly not right for everyone.

In the 2019 U.S. News & World Report Best Diets rankings, keto lands at number 38 of 41 diets profiled. (5) That’s because while it may lead to a short-term weight loss, experts flag how difficult it is to follow, the lack of nutrition, and potential health risks from cutting major food groups and eating more saturated fat.

Besides weight loss, the keto diet may play a role in treatment or prevention of diseases other than epilepsy, including:

• Metabolic Syndrome Limited research, including a study published in November 2017 in the journal Diabetes & Metabolic Syndrome: Clinical Research & Reviews, has suggested that adults with metabolic disease following keto shed more weight and body fat compared with those on a standard American diet, which is heavy in processed food and added sugars. (6)
• Type 2 Diabetes Research published in September 2016 in the Journal of Obesity & Eating Disorders suggested the diet could help people with type 2 diabetes and can lead to improvements in HbA1c levels (though be warned, it can also lead to hypoglycemia — that’s low blood sugar levels — if you take medication to lower your blood sugar). (7)

• Bipolar Disorder In people with type 2 bipolar disorder, keto may be a mood stabilizer, and one early study, published in October 2012 in the journal Neurocase, suggested the plan may be even more effective than medication. (8)
• Obesity Compared with those on a typical low-calorie diet, obese individuals on a very-low-calorie ketogenic diet lost more weight and inflammatory visceral (belly) fat in one study, published in December 2016 in the journal Endocrine. (9) It may also help preserve lean body mass during weight loss, according to an article published in February 2018 in the journal Nutrition & Metabolism. (10)
• Dementia and Alzheimer’s Disease A small study published in February 2013 in the journal Neurobiology of Aging found that older higher-risk adults on a keto diet experienced better memory functioning after just six weeks. (11) Some experts, like Richard Isaacson, MD, director of the Alzheimer’s Prevention Clinic at Weill Cornell Medicine and NewYork–Presbyterian in New York City, support low-carb diets for patients as one way to delay brain aging and possibly Alzheimer’s disease, the most common form of dementia.
• Parkinson’s Disease Because these patients are at a higher risk for dementia, researchers like Robert Krikorian, PhD, professor of clinical psychiatry and the director of the division of psychology at the University of Cincinnati College of Medicine in Ohio, are studying how inducing nutritional ketosis may be used to preserve cognitive functioning.
• Certain Cancers Keto may be used in combination with chemotherapy and radiation, some studies have suggested, including one published in November 2018 in the journal Oncology. (12) But ultimately more studies are needed to determine if keto can play a role in cancer therapy, and patients should not use it as a stand-alone treatment or without a doctor’s consent.
• Polycystic Ovary Syndrome (PCOS) Because women with the infertility condition PCOS are at a greater risk for diabetes and obesity, some clinicians recommend the keto diet, says Taylor Moree, RD, LD, of Balance Fitness and Nutrition in Atlanta. But PCOS is no different from most health conditions mentioned here: Long-term research on the safety is needed.

The possible benefits of the diet are impressive, but there are a few potential downsides to note. One is it’s tough to stick to. In fact, in a review of 11 studies involving adults on the keto diet, which was published in January 2015 in the Journal of Clinical Neurology, researchers calculated a 45 percent compliance rate among participants following the approach with the aim of controlling epilepsy. (13) “The diet is pretty hard to follow because it’s a complete shift from what you’re used to,” Nisevich Bede says. Slashing your intake of carbs can also make you feel hungrier than usual — a feeling that can last until you’re three weeks in.

It’s also common for people starting the diet to experience flu-like symptoms, such as headaches and fatigue. This side effect is so common that there’s a name for it: the keto flu. “You shed a ton of water weight at first, which can lead to dehydration,” Nisevich Bede explains. This can worsen the symptoms of the keto flu. To counter it, she recommends staying hydrated and loading up on electrolytes through electrolyte tablets.

Other potential risks include kidney stones, several vitamin and mineral deficiencies, decreased bone mineral density, and gastrointestinal distress. (7) Here’s why: When you’re eliminating certain food groups (like fruits, legumes, and whole grains) and severely limiting others (like many vegetables), it’s not uncommon to experience nutritional deficiencies. A lack of fiber, for instance, can make it more likely you’ll experience constipation.

In order to avoid some of these risks, the diet needs to be well planned to ensure you’re hitting all of your nutritional bases. Unfortunately, a restrictive diet makes this planning a challenge, especially if you’re not working with a registered dietitian who is knowledgeable in keto.

And while some fats can be healthy, there’s a risk that in following a high-fat diet, you’ll increase your intake of unhealthy trans and saturated fats. These “bad” fats are found in things like red meat, poultry skin, cheese, and butter, and can lead to an increase in LDL, or “bad” cholesterol and increased risk of heart disease. (14) This is a controversial issue, as some experts do recommend adopting a low-carbohydrate diet to lower heart disease risk. If you’re at risk or have heart disease, it’s important to speak with your doctor first about your health needs.

Bottom line, the hype around this diet is tempered by the fact that researchers just don’t know about the long-term safety of following a high-fat diet (particularly one that may be high in saturated fat).

Despite claims that the keto diet can help the following groups, experts say the plan may be risky for them:

People With Type 1 Diabetes These individuals are insulin-dependent, and a keto diet could lower their blood sugar to dangerous levels, says Moree.

People With a History of Eating Disorders Going on a strict diet that eliminates food groups could trigger a relapse if you have a personal history of having an eating disorder. And while there’s a growing popularity in treating binge eating disorder (BED) with keto, experts strongly advise against it. Treatment of BED requires regular, adequate food intake without restriction, says Sumner Brooks, MPH, RDN, a certified eating disorder dietitian in Portland, Oregon.

People Who Have Had Their Gallbladder Removed A gallbladder holds bile, which aids in fat digestion. Without this organ, you will not feel your best on a high-fat diet.

People With Thyroid Disease A a keto diet may suppress levels of thyroid hormones, says Audrey Fleck, RDN, an integrative and functional nutritionist and certified diabetes educator in Perkasie, Pennsylvania. That means the diet has been touted as a treatment for hyperthyroidism; nonetheless, the approach is controversial.

People With Multiple Sclerosis (MS) The National Multiple Sclerosis Society raises questions about the long-term safety of the diet for MS, and cautions about the possible side effects, like fatigue and constipation. (15)

Considering these risks, people who have kidney damage (including those with type 2 diabetes), plus individuals with or at risk for heart disease, and pregnant or breastfeeding women, shouldn’t try the keto diet. Also, people with type 1 diabetes shouldn’t follow the plan because of the risk for hypoglycemia (low blood sugar), and anyone who has had their gallbladder removed should avoid it because the diet is so high in fat.

If you’re looking to lose weight, keep in mind that the diet likely requires a complete overhaul to the way you normally eat. But it may be worth it if you’re looking to lose weight or have one of the health conditions it’s been shown to help with.

To be on the safe side, be sure to discuss with your doctor whether the keto diet is right for you before you drastically change your eating habits. While the diet has roots in medicine, its widespread use is still new, and not every doctor understands the keto diet. For more information, you can look to national programs that are gaining steam. Two examples: Virta Health, where they are studying the diet’s role in prediabetes and type 2 diabetes treatment, and the Cleveland Clinic’s Functional Ketogenics Program.

Additional reporting by Moira Lawler.