Health Lifestyle

The Keto Diet Explained: What the Science Really Says

9 min read

What exactly is the ketogenic (or keto) diet? Is it effective for weight loss? Does it show other benefits? Is it healthy or safe? Here’s what the science really says.

In 2018, “keto” was the most Googled diet and food category in the world. This way of eating has attracted millions of people looking to lose weight and reap its other purported benefits. So, are they on to a cutting-edge biohack? Or dangerously misguided?

What is the Keto Diet?

There are a few different kinds of keto diets (more on that later). But what they all have in common is a severe reduction in carbohydrate intake. This puts your body into a metabolic state known as ketosis.

Ketosis occurs when your body metabolizes fat, instead of carbohydrates, to produce energy. This process produces ketones — a type of acid — in your blood as a by-product.

It’s actually pretty cool that our bodies can do this. It was once a useful survival tool for our ancestors.

We wouldn’t have made it as a species without our body’s ability to temporarily use fat when we couldn’t find enough carbohydrate-rich foods. When food was scarce, our ancestors got through hard times due to stored fat, which provided a buffer when they went days without eating.

As this process existed as an evolutionary tool, there’s even evidence that challenging the body through fasting-induced ketosis every so often yields health benefits. The fancy term for this phenomenon is “hormesis,” meaning certain stressors in certain doses at certain intervals can actually make us stronger. (Lifting weights to break down muscle fibers is a familiar example of hormesis in action.)

But the modern ketogenic diet movement as we know it doesn’t typically focus on temporary or intermittent fasting as a survival tool. The keto diet seeks to keep the body in a permanent state of ketosis by severely restricting carbohydrates and compensating with loads of fat and protein as an energy source.

So is the keto diet healthy? What exactly do you eat on a ketogenic diet? And what foods do you avoid on keto?

Foods Not Allowed on a Keto Diet

Carbohydrates and refined grains

Carbohydrates are the enemy on a keto diet. Foods not allowed on a ketogenic diet include sugary foods, grains and starches, alcohol, most fruit, beans and legumes, root vegetables and tubers (e.g., sweet potatoes, beets, carrots), low-fat or diet products, and some condiments or sauces. In fact, your entire carbohydrate consumption might be less than you’d derive from a single apple a day.

But a keto diet doesn’t distinguish between “good carbs” like lentils and “bad carbs” like lollipops.

While it’s great that it eliminates refined sugar, white flour, and many processed foods, keto also forbids some of the healthiest foods on the planet.

Avoiding whole, plant-based carbs like fruit, legumes, and grains means that you’re likely to be dangerously deficient in antioxidants, phytochemicals, vitamins, and minerals. And all of these are important for disease prevention and long-term health.

You’ll also likely miss out on adequate fiber, which is no small matter. About 97% of the US population is already deficient in fiber. This puts you at increased risk of heart disease and several digestive cancers, as well as breast cancer.

So What Can You Eat On A Keto Diet?

low-carb keto diet foods

Keto-compliant foods include meats, fatty fish, eggs, butter and cream, nuts and seeds, vegetable oils, avocados, low-carb veggies (e.g., lettuce, zucchini, and peppers), and certain condiments.

Eating plant-based fats from nuts, seeds, and avocados makes good sense. And plenty of studies show us that low-carb vegetables (and actually, pretty much all fruits and veggies) are terrific health boosters. But as you can see, most of the calories of keto eaters typically come from animal products.

Given the overwhelming body of evidence linking consumption of meat and other animal products to cancer, Alzheimer’s and heart disease, the fact that most keto diets rely heavily on animal products seems like a recipe for long-term health problems.

Types of Ketogenic Diets

keto diet food pyramid

There are five main types of keto diets.

  • The standard ketogenic diet is a very low carbohydrate, moderate protein, high fat diet. These macronutrients make up 5%, 20%, and 75% of the diet, respectively. However, you can consume as much as 90% fat.
  • The cyclical ketogenic diet includes higher carbohydrate days to refeed your body. For example, you might follow the standard ketogenic diet for five days, followed by two days of high carbohydrate intake.
  • The targeted ketogenic diet allows you to eat more carbohydrates around exercise to help fuel your workouts.
  • The high protein ketogenic diet is similar to the standard version, but focuses even more on protein intake with a ratio of 35% protein, 60% fat, and 5% carbs.
  • And the plant-based ketogenic diet relies heavily on high-fat plant foods such as nuts, seeds, avocados, coconut, and bottled oils, in addition to relatively low-calorie greens.

Standard & high protein ketogenic diets are the most common; cyclical and targeted are mainly used by athletes.

While a plant-based keto diet may sound nice to folks who are grossed out by the notion of basing their diet around animal products, it often derives a surprising amount of calories from fish or other meats. Vegan keto eaters tend to eat large amounts of nuts, oils, avocados, and coconut. And they may still be deficient in any number of antioxidants, phytochemicals, fiber, and other nutrients that are important for long-term health.

What are the Risks of a Ketogenic Diet?

“Keto Flu”

When beginning a ketogenic diet, some people may experience a set of symptoms dubbed the “keto flu.”

These symptoms can include, but are not limited to:

  • Nausea
  • Vomiting
  • Constipation
  • Diarrhea
  • Headache
  • Weakness
  • Fatigue

Symptoms usually last for around a week or so as the body adjusts to the lack of carbohydrates.

Due to possible symptoms of keto flu, such as diarrhea and vomiting, along with the fact that most of the initial weight loss on a keto diet is water weight, hydration (with electrolytes) is especially important.

Nutrient Deficiencies

Animal products have zero fiber, so we need to rely on plants to get our fiber. But since the keto diet relies so heavily on fat and restricts all carbs, including fruits and vegetables, it can be a recipe for developing nutrient deficiencies.

Fiber itself is an essential nutrient — particularly prebiotic fiber. Prebiotic fiber feeds the good bacteria in your gut. And it also helps your body absorb nutrients from food and eliminate waste and toxins.

Fruits and vegetables contain high amounts of fiber, vitamins, minerals, antioxidants, and phytochemicals. And you won’t find many of these nutrients in animal products or high-fat foods.

High-carb foods like beans, bananas, and oats also contribute to your body’s electrolyte stores. These are more easily lost on the keto diet from excess water extraction. And a lack of these and other nutrients has been shown to contribute to a variety of chronic diseases such as heart disease, osteoporosis, cancer, and mental health disorders.

Disease Complications or Death

Not to scare you, but the ketogenic diet has been shown to increase the risk of disease complications, and even (for some people) premature death.

People with diabetes can have a more severe type of ketosis called ketoacidosis if they don’t have enough insulin. Ketones build up and change the chemical balance of their blood. The combination of acidity in the blood and dehydration from fluid loss can cause organ damage, coma, or death.

In 2018, the European Society of Cardiology found that people who followed a low-carb diet had the highest risk of overall cardiovascular, cerebrovascular (like stroke), and cancer death.

The ketogenic diet is also not recommended for patients with pancreatitis, liver failure, disorders of fat metabolism, or kidney disease because of certain long-term recorded effects such as fatty liver disease, kidney stones, and dehydration related symptoms, which may complicate these diseases.

Positive Uses of the Keto Diet


The keto diet has been successfully used to treat intractable epilepsy in children since the 1920s. But the original ketogenic diet fell out of use after World War II with the development of more effective anti-epileptic drugs. Then, interest was revitalized again in the 1990s thanks to an epileptic boy named Charlie Abrahams.

Charlie had up to 100 seizures a day with no relief from medication until his parents learned about the diet in a medical textbook. His seizures stopped almost immediately, and he remained on the diet for five years.

In 1994, Charlie’s family created The Charlie Foundation for Ketogenic Therapies. The foundation helped spread awareness about the diet and assist other children with epilepsy.

Although the ketogenic diet has been used to treat children with epilepsy, and shows some promise, it’s rarely recommended because of how strict it is. It’s generally only prescribed in severe cases of epilepsy and only under the care of both a medical doctor and dietician.

Weight Loss

Nearly 70% of all Americans are overweight or obese. Obesity is correlated with a higher risk of nearly every major chronic disease of our times.

The #1 thing that people go on a keto diet for is rapid weight loss. And research tells us that keto diets can be effective at helping people lose weight — at least in the short run.

In fact, when you compare to those on a more traditional low-fat or Mediterranean diet, studies show faster weight loss when people go on a keto diet. However, that difference in weight loss seems to disappear over time. After two years, the dietary approaches yield similar weight loss results.

Furthermore, there has been very little study conducted on keto diets over the long-term. If you want to see the effects of diet on disease, you need to study people over decades because most health problems take years to develop.


People with type 2 diabetes who go on ketogenic diets often show improvements in glucose levels and biomarkers for blood sugar stability. But in these studies, subjects are essentially starved of food, sometimes only ingesting 650 kcal/day.

And there’s a profound difference between managing biomarkers and addressing the underlying metabolic dysfunction that exists in diabetes. Cut out all starchy foods — grains, legumes, fruits, starchy veggies — and the biomarkers that can get out of whack in response to stimulation from these foods may look fabulous. However, the diabetes still exists — it’s just not showing up in the biomarker numbers because you’re not eating the foods that would show the insulin resistance.

This is a bit like taking a bad driver off the road. They won’t get any speeding tickets, but that doesn’t make them a safer driver. It just means they’re no longer “in the game.” The same is true with carbs. If you don’t eat carbs, your blood glucose levels will drop. But the real measure of insulin sensitivity is being able to eat carbs and process them healthfully. And there’s nothing about the keto diet that helps that to happen.

In fact, to the contrary, a growing body of research shows us that a diet high in animal products, as most keto diets are, leads to higher rates of type 2 diabetes. And a keto diet might even cause type 2 diabetes, according to some recent research.

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Keto for Cancer?

There’s a popular theory fueled by the controversial research of Dr. Thomas N. Seyfried and the book, Keto for Cancer, that the keto diet can help fight cancer.

Dr. Seyfried’s theory is that cancer is a metabolic disease and therefore a low-carb, low-calorie diet will starve cancer cells of their supposed fuel. He states “Nutritional ketosis induces metabolic stress on tumor tissue that is selectively vulnerable to glucose deprivation.”

While nutrition does influence cancer growth, cancer cells don’t just eat sugar. A 2016 study published in the journal Nature, showed that high-fat diets, especially from animal products and processed oils, actually fed cancer tumors and initiated their spread throughout the body.

Additionally, cancer can actually feed on ketones, causing tumors to grow and metastasize. A 2012 study concluded doctors should design ketone inhibitors to treat cancer patients, especially those with repeated cancer growth and metastasis.

Keto Diet and Life Expectancy

There is not now, nor do we have a record of there ever having been, a human population anywhere in the world eating a keto diet and experiencing long lifespans. To the contrary, in a 2018 study published in The Lancet, researchers concluded that people who eat low-carb diets have shorter lifespans (by an average of four years). The authors write:

“Low carbohydrate dietary patterns favouring animal-derived protein and fat sources, from sources such as lamb, beef, pork, and chicken, were associated with higher mortality, whereas those that favoured plant-derived protein and fat intake, from sources such as vegetables, nuts, peanut butter, and whole-grain breads, were associated with lower mortality…”

And in another 2018 study published by the European Society of Cardiology (which we also referenced in the Disease Complications or Death section of this article), researchers found that people who ate low-carb diets had a 32% increased risk of death from all causes when compared to those eating the highest amount of carbs. The researchers also learned that low-carb eaters suffered from a 51% higher risk of dying from heart disease and a 35% higher risk of dying from cancer.

The Verdict on Ketogenic Diets

The ketogenic diet originated as, and still is, a medical diet that may be helpful for epilepsy. And it can lead to rapid weight loss in the short-term. However, starvation and illness can cause drops in weight — but that doesn’t make them healthy ways to do so.

There are currently no studies showing a ketogenic diet to be beneficial to long-term health. In fact, multiple studies show that such low-carb, high-fat diets can actually lead to shorter life expectancy and higher rates of disease.

Ditching processed foods, refined carbs, and added sugars can do wonders for your health —and the keto approach gets that right. But you can do all of that without basing your diet around animal products and high-fat foods.

After all, a whole foods, plant-based diet with lots of delicious fruits, vegetables, legumes, nuts, seeds, and whole grains can also lead to weight loss. And in the process, it will also help your body fight and prevent cancer, heart disease, obesity, Alzheimer’s, type 2 diabetes, and virtually every other major chronic illness of our times.

Tell us in the comments below:

  • Are you on the keto diet or are you considering it?
  • What do you think about the ketogenic diet?

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