Is Keto Bad for Your Heart?

Why Keto may increase the risk of high cholesterol

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The ketogenic, or “keto,” diet is a diet in which energy is obtained primarily from fat, while protein and carbohydrates are limited. The lack of carbohydrates causes the body to go into a state of ketosis, in which energy is derived from the breakdown of fat.

Despite some promising benefits, there are concerns that such high fat intake is not heart healthy. Specifically, fat derived from processed foods and animal products contribute to high cholesterol, which increases the risk of heart attack.

This article discusses the facts and risks of the keto diet.

Keto, ketogenic diet, low carb, high good fat, healthy food
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The keto diet dates back to the 1920s when it was used for treatment of seizure disorder in children. It was also found to be useful in controlling blood sugar in people with diabetes.

Emphasis of dietary guidelines in the past several decades has been on a low-fat diet, but the continued rise of obesity and diabetes has renewed interest in the keto diet for its role in weight loss and blood sugar management.

What Is Ketosis?

Food provides macronutrients, which are compounds that are broken down to provide energy for the body. These macronutrients include fats, protein, and carbohydrates (“carbs”).

Fats are broken down into fatty acids, and proteins are broken down into amino acids. Carbohydrates are broken down into simple sugars like glucose, which is used as the primary energy source in the body. This is particularly true in the brain, since fats cannot cross the blood brain barrier to provide energy there.

When carbohydrates are restricted, such as in the keto diet, several things happen. The body starts a process called ketosis to break down fats to provide energy. This breakdown of fats creates ketone bodies, which can be used for energy throughout the body, including in the brain.

At the same time, another process called gluconeogenesis occurs to create glucose by the breakdown of non-carbohydrate substances, like certain amino acids and triglycerides.

A range of carb-restricting diets exist, but a true ketogenic diet is one that induces a state of ketosis. The exact amount of carbohydrate restriction that will induce ketosis varies between individuals.

In general, ketosis will occur when less than 10% of total intake is from carbohydrates, which comes to approximately 10-50 grams per day, depending on caloric needs.

Macronutrient Breakdown

Carbohydrates, known as carbs, are a macronutrient made of sugar molecules.

  • Simple carbohydrates are made of just one or two sugar molecules. They are more rapidly broken down in the body and used as energy. Examples of foods with simple carbs include candy, cakes, pastries, and sweet beverages like soda and juice.
  • Complex carbohydrates are a chain of multiple sugar molecules. They take longer to break down. Examples of foods with complex carbs include whole grain bread, vegetables, and fruit.

Fat is a macronutrient that is broken down into fatty acids. Most fats in the diet are triglycerides, having a chemical structure with three fatty acid tails attached to glycerol. Fat is transported in the blood as triglycerides in lipoproteins with cholesterol.

  • Unsaturated fat has double bonds in its chemical structure and is typically liquid at room temperature. Unsaturated fat is found in olive oil and other plant oils, nuts, and salmon.
  • Saturated fat has no double bond, is “saturated” with hydrogen bonds, and is often solid at room temperature. It is found in animal meat, dairy products, and coconut oil.
  • Trans fat is mostly formed artificially through a process called hydrogenation. Found in processed foods like packaged snack foods and fried foods, it is known to increase the risk of heart disease.

Cholesterol is a compound needed by the body to make cell membranes and certain hormones. Cholesterol is carried in the blood in lipoproteins. It is both made by the liver and obtained in the diet by eating animal products.

Lipoproteins that carry cholesterol in the body include:

  • High-density lipoprotein (HDL), known as “good” cholesterol
  • Low-density lipoprotein (LDL), known as “bad” cholesterol

Macronutrient Breakdown

In the keto diet, carbohydrates are restricted to no more than 10% of total intake, with fat making up the majority of intake at around 70%-80%, and protein making up the remaining 10%-20%.

Benefits

The ketogenic diet has established success in achieving short-term weight loss. Studies have shown that when on a keto diet, people had higher energy expenditure, which translates to burning more calories. They also reported less hunger, even when total calories remained the same.

When total calories are restricted, the keto diet has been shown to be more effective than a low-fat diet for weight loss. However, the keto diet is difficult to maintain for long periods, and after two years, the benefits for weight loss when compared to a low-fat diet were not different.

The keto diet also has a powerful effect in lowering blood sugar. This diet has been shown in multiple studies to decrease blood sugar as measured by hemoglobin A1C levels and reduces the need for diabetes medication.

However, people taking medication for diabetes should not start this diet without speaking to their healthcare provider first. Medication adjustment may be needed to avoid dangerously low drops in blood sugar.

Studies have also shown beneficial effects on some metabolic markers with the keto diet. The diet lowers triglycerides, a type of fat in the blood that, when present in high levels, increases risk for heart disease, stroke, and pancreatitis.

The keto diet is associated with higher levels of HDL, a lipoprotein known as good cholesterol that is associated with decreased risk of heart disease. Despite these promising effects, the keto diet is also associated with higher levels of LDL or bad cholesterol that increases cardiovascular risk.

The long-term effect of this diet remains unclear.

Popularity of the Ketogenic Diet

The popularity of the ketogenic diet is due in part to its effectiveness in weight loss, appetite control, and lowering blood sugar. The diet has also been found to have some beneficial effects on metabolic risk factors, including triglyceride and HDL levels.

How the Keto Diet Works

Following a keto diet involves replacing carbohydrates with fats. Carbohydrates are restricted to less than 10% of total intake, and fat up to 80% of intake.

What to Eat

Compliant Foods
  • Meat

  • Fatty fish, shellfish

  • Dairy products (eggs, cheese, full-fat yogurt)

  • Plant oils (olive oil, avocado oil, coconut oil)

  • Eggs

  • Low-carb vegetables (spinach, lettuce, asparagus)

  • Avocados

Non-Compliant Foods
  • Sugary foods (baked goods, soda, juices)

  • Grains (breads, pasta, rice)

  • Starchy vegetables (sweet potatoes, squash, parsnips)

  • Legumes (beans, lentils)

  • Fruit

Calories

Ketogenic diets vary in the amount of daily calories allotted. When intended for weight loss in people with elevated body mass index, a hypocaloric diet restricts calories so that calories consumed are less than calories burned.

The number of calories in a hypocaloric diet can range from 800 to 1,500 per day, but it is specific to each individual. A hypocaloric diet should be discussed with a nutritionist or healthcare provider to ensure that the diet provides adequate nutrients.

Duration

Depending on the desired effects of the keto diet, the duration can vary. However, this diet is notoriously difficult to maintain given the strict carbohydrate restriction, and adherence rates for the keto diet are lower than for other diets.

When used for weight loss, a short-term calorie-restricted keto diet can help achieve weight loss goals. When transitioning off of the keto diet, weight gain is common.

The National Lipid Association recommends that, when used for weight loss, it is reasonable for the duration of a very low-carbohydrate diet to be limited to two to six months, with moderate carbohydrate restriction for longer-term weight maintenance.

When used for blood sugar control, following a long-term keto diet can be effective. One study of 262 people with diabetes following a monitored keto diet showed that after two years, they maintained lower blood sugar levels and required less diabetes medication compared to a group of people who were not following a keto diet.

Starting a keto diet can be a first step to overall decreased carbohydrate consumption as a healthy lifestyle change, even if ongoing restriction does not meet ketogenic targets.

Health Considerations

Side Effects

Starting a keto diet can cause several side effects, most of which are temporary, as the body adjusts to using ketones instead of glucose for energy. In the first week, “keto flu” side effects may include:

  • Constipation
  • Nausea and vomiting
  • Fatigue
  • Lightheadedness
  • Decreased exercise tolerance

Effects on Heart Health

As discussed, the keto diet can have positive short-term effects on weight loss, blood sugar control, triglyceride levels, and HDL (good cholesterol) levels. However, there are concerns of negative effects on heart health with the ketogenic diet.

Many studies have shown the association of keto diets with increased LDL (bad cholesterol), but this finding is not consistent in all studies. Keto diets that are high in saturated and trans fats seem to be responsible for the increased LDL levels.

Another study showed higher incidence of atrial fibrillation in people on carbohydrate-restricted diets.

The keto diet has also been associated with increased mortality. This effect was especially true when animal-based fats were substituted for carbohydrates. Substituting plant-based fats for carbohydrates, on the other hand, improved mortality.

To minimize this risk of heart disease while on a ketogenic diet, it is prudent to minimize processed foods high in saturated and trans fats, and instead choose plant-based foods with higher unsaturated fat content.

Whole Grains

The strict carbohydrate restrictions of the keto diet also limit the amount of whole grains that can be consumed. However, whole grains have been recommended for promotion of heart health and prevention of colorectal cancer by organizations like the American Heart Association, as well as in the most recent Dietary Guidelines for Americans, which recommend at least three to five servings of whole grains per day.

Contraindications

People with any of the conditions listed below should not start a keto diet:

  • Severe hypertriglyceridemia
  • Pancreatitis attributed to high triglyceride levels
  • Genetic conditions causing severe hypercholesterolemia
  • Conditions affecting enzymes involved in fat metabolism
  • Liver failure
  • Porphyria
  • People taking SGLT2 inhibitor medication
  • Pregnancy

Summary

The keto diet limits carbohydrates but is high in fat. It has some benefits, like weight loss and lowering blood sugar, but it can have some concerning side effects, particularly on heart health, as it is associated with bad cholesterol.

A Word From Verywell

The keto diet has become a mainstream diet, particularly for weight loss, but its long-term effects on heart health remain unclear. When starting a keto diet, it’s best to speak with a healthcare provider or dietician to ensure nutrition needs are met. Your healthcare provider may recommend monitoring cholesterol levels to ensure LDL levels do not become alarmingly high on a keto diet.

Frequently Asked Questions

  • When does the keto diet become dangerous?

    Strict carb restriction and avoidance of nutrient-rich vegetables can cause deficiency of vitamins and minerals, such as potassium, magnesium, folate, thiamine, and vitamin C, among others. Those on a keto diet can consult a dietician who will recommend keto-appropriate foods and vitamin supplements, if necessary, to ensure appropriate nutrition.

    The keto diet can also be dangerous for people on insulin and other blood sugar-lowering medications, as it can cause dangerously low blood sugar drops. A healthcare provider can help adjust medications in preparation for a keto diet.

  • What are good fats to eat on the keto diet?

    Replacing carbs with unsaturated fats offers the best evidence for heart health. Seafood—like salmon, sardines, trout, and herring—is a great source of omega-3, a type of unsaturated fat. Plant-based sources of unsaturated fats include olive oil, avocado, seeds, and nuts.

  • Do cardiologists recommend the keto diet?

    In 2020, the American College of Cardiology published an expert analysis of the keto diet. While the authors acknowledge that the keto diet may have some beneficial effects on weight loss, blood sugar, and triglycerides, they emphasize that the keto diet may worsen heart health long term. They specifically advise against high intake of animal products.

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9 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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