A cardiologist’s take on the keto diet


by Michael Sills, MD

Nov 3, 2020

Recently, my patients have started coming to me with questions about the keto diet — Is it safe? Is it good for your heart? Do you recommend it? After all, it’s well-established that diet and heart health go hand in hand.

As a cardiologist, here’s what I tell them.

Origins of the keto diet

The ketogenic, or keto, diet is currently trending as a weight loss solution, but you might be surprised to learn that low carb, keto-like diets have been around for a long time. The precursors included liquid protein diets and the Atkins diet, which first became popular in the 1970s when fashion models made rail-thin physiques trendy. 

The theory behind the keto diet was that if a person were to completely fast, the metabolic system, deprived of the glucose necessary for fueling out body, would turn to the muscles, breaking down proteins. There, the liquid protein supplement would intervene, sparing those repositories of protein so that the body burns only fat. This produces ketones, which in manageable levels can help suppress appetite and may improve brain function. This was coupled with significantly decreased carbohydrate consumption, which was believed to help drive fat burning as well. 

However, in circumstances where there is uncontrolled ketosis due to inadequate carbohydrates andprotein supplements, an individual can become very ill. There were a number of deaths reported in the 70s from unmonitored liquid protein diets.

The next iteration of ketogenic diets was popularized by Dr. Arthur Agatston in his book, “The South Beach Diet.” This was also a low carbohydrate diet but it did not rely on protein supplementation and, unlike the Atkins diet, did not emphasize high fat consumption. This concept has remained very popular over the years as a safer approach to keto dieting.

Is the keto diet healthy?

Let’s dive into the different types of keto diets, as well as some potential benefits and risks to keep in mind, based on what science has shown to date about the keto diet.

Today, there are a number of ketogenic diets, each of which focuses on a different way of managing the ratio of carbs, protein and fat in your diet. Here are the basics of how each type works.

  • Standard ketogenic diet (SKD): This is a very low carb, moderate protein and high fat diet. It typically contains 75% fat, 20% protein and only 5% carbs.
  • Cyclical ketogenic diet (CKD): This diet involves periods of higher carb refeeds, such as five ketogenic days followed by two high carb days.
  • Targeted ketogenic diet (TKD): This diet allows you to add carbs around workouts.
  • High-protein ketogenic diet: This is similar to a standard ketogenic diet but includes more protein. The ratio is often 60% fat, 35% protein and 5% carbs.

Of the different types, the standard ketogenic diet has been extensively researched and is most recommended for weight loss. There have been a number of studies comparing ketogenic diets to low fat diets showing superior weight loss with ketogenic diets. 

Keto diet and diabetes

The elevated ketones can help suppress appetite, lower cholesterol and blood sugar, as well as improve insulin sensitivity. This last finding has helped decrease medication requirements for people with Type 2 diabetes, as well as help prevent the progression from pre-diabetes to diabetes in concert with weight loss.

In a study of people with type 2 diabetes, keto diets caused a drop in hemoglobin A1c (HbA1c), which is a marker that reflects your average blood glucose over the past 2-3 months. In addition, over 90% of the individuals in the low carb group managed to reduce or eliminate their need for diabetes medications. However, the difference was small or nonexistent in other studies, potentially because compliance with the study requirements was poor.  

Keto diet and heart health

Ketogenic diets can have a number of potential heart health benefits. There is often an initial drop in LDL (the “bad” cholesterol) but in two studies, this was not maintained over a 12-month period. The “good” cholesterol, or HDL, will often increase somewhat depending on the level of fat consumption. 

Any diet that results in weight loss can help lower blood pressure. In total, ketogenic diets appear to be safe and can potentially help manage the risk factors that drive heart health.

“Keto flu” and other side effects

Ketogenic diets can have side effects, especially initially. Some people will feel very sluggish for the first week or so, often referred to as the “keto flu.” This can manifest as poor energy and mental function, increased hunger, sleep issues, nausea, digestive discomfort and occasionally, decreased exercise performance. 

These side effects can usually be mitigated by gradually lowering your carbohydrate consumption over a few weeks. Increasing water consumption, replenishment of electrolytes and a multivitamin can help as well. Although rare, rapid decrease of carbohydrates can cause severe ketosis with marked fatigue and nausea, as well as impaired mental function.

If you are planning to drastically change your diet, be sure to consult your physician first, especially if you have any underlying health conditions or nutritional concerns.

For people who cannot supplement adequate intake of vegetables, grains and fruit, there is a risk of nutritional deficiencies on the keto diet. People with liver conditions may not metabolize excess fat well and those with kidney insufficiency should not be on a high protein diet. In both of those cases, a ketogenic diet can exacerbate these underlying conditions. Lesser concerns are a risk of constipation, mood swings and clouded thinking from inadequate carbohydrates.

What about intermittent fasting?

There has also been significant recent interest in intermittent fasting, which goes hand in hand with the keto diet for many people. There is considerable evidence that fasting 12-16 hours a day decreases abdominal fat and increases insulin sensitivity. This alone forces the body to break down fat to use for energy production. 

Fasting may also lower blood pressure and resting heart rate. This was an integral part of how humans have eaten up until the last 200 years when food (especially fast food) started to become more plentiful and available.

The verdict

So, like my patients, you’re wondering — as a cardiologist, what do I think about the keto diet? I believe that genetically, humans were meant to eat a lower carbohydrate and higher fat and protein diet, and that intermittent fasting can be beneficial if done safely. 

Related: How to know if the keto diet is right for you

A recent study found that a Mediterranean diet — which is low carb but rich in vegetables, fruits, nuts, seeds, legumes, whole grains and extra-virgin olive oil with fish/seafood and fermented dairy products — engendered the greatest longevity and lowest risk of heart disease. There was speculation in the article that when mixed with intermittent fasting, the results may even be better.

This combination of Mediterranean diet and intermittent fasting is what I personally aim to follow and I would advise the same for people who want to lower their risk of heart disease and maintain the best overall health. There are certain individuals who should not try this diet — which is why you should always consult your doctor before any radical change to your diet.

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About the Author

Michael Sills, MD, is a cardiologist on the medical staff at Baylor Scott & White Heart and Vascular Hospital – Dallas. His clinical interests include diagnostic and preventive cardiology as well as cardiac imaging. He is an avid runner, chef and proud grandfather.

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