I switched to a ketogenic diet during the middle of my training for my first marathon, not the greatest idea in hindsight. However, it was during this time that I noticed an increase in my active heart rate and wondered why.
An elevated heart rate on keto is often due to low levels of fluids (dehydration) and electrolytes, particularly sodium. As a result, less fluid circulates within the blood, which may cause the heart to pump at an increased rate. Increased caffeine intake may also contribute.
In this article, I'll go over why you may be experiencing an elevated heart rate when switching to a ketogenic diet and what you can do to help bring it back to normal.
As mentioned, I experienced an increase in heart rate when I first switched to a ketogenic diet. It wasn't a small increase either. On average, my heart rate was averaging ten to fifteen beats higher per minute, given the same running pace as previous weeks.
A ten to fifteen beats per minute increase may not seem like much, but it is if you weren't expecting it. An increased heart rate, no matter how low or high, could catch you off guard or leave you worried.
What you eat before a run on keto is vital if performance is of any concern.
When it comes to sports performance, a ten to fifteen beat increase per minute could make a big difference, so what gives?
Why Your Heart Rate is Higher On Keto
You may have noticed that when first starting a ketogenic diet, an increasing frequency in urination. If you're wondering why you probably quadrupled the number of bathroom trips within the first few days on a ketogenic diet, I wrote a little more about it in this article.
Within the first week or two of starting a ketogenic diet, your body begins to expel large amounts of water and electrolytes, most notably sodium. A rapid drop in fluid and sodium, which happens during the beginning stages of a ketogenic or low carb diet, can result in an overall reduction in the fluid circulating the blood. This reduction is what may lead your heart to pump faster than usual or possibly even abnormally.
As your body flushes out water at an increased rate, electrolytes are also rapidly being flushed out. It's like when an athlete finishes a game, or a marathon runner completes a race, they've been sweating and losing electrolytes via their sweat, which they must replace.
We need to be mindful of three electrolytes in particular: sodium, potassium, and magnesium. These electrolytes are involved in many processes of the body, which include muscle contraction, especially of the heart.
Let me explain further…
How Water And Electrolytes Are Lost Rapidly
On average, the typical adult will store 500 grams of carbohydrates in the body that act almost like an energy reserve. Carbohydrates are stored in the body as glycogen within the cells of the liver and skeletal muscle. For every gram of carbohydrate your body stores, approximately three grams of water are stored along for the ride.
When carbohydrates from the diet are restricted, your body must access your glycogen to provide energy to your working muscles and your brain. It's during the first week of a very low carb or ketogenic diet that your body will begin to burn through this stored glycogen.
As a result, water stored with the glycogen is released and expelled through the urine and sweat. Think of each gram of carbohydrate your body stores as a sponge that can soak up three grams of water. When the body uses the sponge (carbohydrate), the water is squeezed out and expelled.
This decrease in both glycogen and water is why you may experience a rapid decline on the scale the first week or two when switching to a ketogenic diet. It's not unheard of for people to drop between five to ten pounds in just the first week of starting a ketogenic diet.
While a significant drop on the scale may lead you to do the happy dance, it doesn't come without its' drawbacks. If you aren't mindful of replacing the lost water and electrolytes, this can potentially lead to some unwanted side effects such as an increased heart rate and the keto flu.
What Is The Keto Flu
A common side-effect of the ketogenic diet people experience when first starting is the dreaded keto flu. It's called the keto flu because many of the keto flu symptoms share similarities to influenza, commonly known as the flu.
Keto flu symptoms include:
- Fatigue
- Headaches
- Increased sweat production
- Runny nose
- Nausea
- Sleeplessness
- Irritability
You may hear people say the keto-flu is a symptom of carb withdrawal, which may be true in some cases. In my experience, most of the keto-flu symptoms are a result of the rapid fluid and electrolytes lost as a result of a low-carb or ketogenic diet.
People will use the keto flu as a scare tactic warning people against a ketogenic diet or reasoning why keto is bad. Anecdotally, many of the symptoms are quickly resolved or avoided altogether by merely being mindful of fluid and sodium intake.
Increased Heart Rate May Affect Certain Individuals More Than Others
While an increased heart rate can affect just about anyone switching to a low carb or ketogenic diet, specific individuals may experience an increase more than others, such as individuals who typically have low blood pressure.
The following individuals should also be aware of possible conflicts. Consult with your doctor before switching to a low carb or ketogenic diet should any of the following apply to you.
Diabetics
By nature, low carb or ketogenic diets may reduce the need for medicine that's taken to lower blood sugar. If you're prescribed a dosage based on a diet moderate to high in carbohydrates and switch to a very low carb or ketogenic diet, this can result in your blood sugar dropping too low.
Low blood sugar can lead to both a rapid or abnormal heart rate. It's best to consult with your doctor before undertaking a low carb or ketogenic diet if you are on any medication.
Those with high blood pressure
A low carb or ketogenic diet has the potential to improve blood pressure, taking a dose prescribed based on your previous diet may prove to be too strong.
Similar to individuals with diabetes taking medication to lower blood sugar, if you're taking medication to reduce high blood pressure, please consult with a doctor before undergoing a drastic change to your diet.
Athletes
As mentioned in the beginning, I experienced this increase in heart rate when transitioning to a ketogenic diet. The increase in heart rate was mainly due to dehydration, a lack of sodium, and my body adjusting to burning fat instead of carbohydrates as its primary fuel source.
Something as simple as taking half to a full teaspoon of salt and a glass of water before a run was enough to bring my heart rate to pre keto levels. While I still take a little sodium before my workouts, my body has naturally adjusted to burning fat and ketones for fuel.
However, if you are just getting started on your ketogenic journey and do perform regular physical activity, it may take time for your body to adjust and become keto-adapted.
On average, it takes most individuals at least three weeks and sometimes even longer before their exercise performance gets back to baseline.
Wondering how to best fuel your run while on keto? What to eat before a run on keto.
Three Ways To Solve Heart Palpitations While Following A Ketogenic Diet
So now that you know why you may be experiencing an increased heart rate on a low carb or ketogenic diet, what do you do?
Increase your fluid and sodium intake
Sodium is mostly responsible for maintaining the body's fluid balance. To help offset the electrolytes and fluids flushed from your body due to a reduction in carbohydrates, you should increase your sodium and water intake.
Many individuals find themselves switching from sodium-filled pre-packaged foods to more whole foods after adopting a healthy ketogenic lifestyle. While eating a healthy and whole foods-based diet is probably best. Changing from pre-packed to whole foods leads many to become sodium deficient if not used to salting their foods previously.
To make sure you're getting enough sodium, you can easily accomplish this by salting your food liberally and to taste. If you're an athlete or sweat excessively, you may find that you need to supplement a little extra sodium to help with performance and replenish any electrolytes lost through sweat.
Additionally, staying hydrated is essential. Make sure you're drinking water throughout the day and even more if you're very active. How much water should you drink on keto? While there's no need to carry a little water jug wherever you go, make sure you are drinking to thirst.
Exercise patience
If you've already increased your sodium and fluid intake, it may simply be a matter of time. It can take a few weeks and sometimes months for your body to become keto-adapted.
When you become keto-adapted, your body switches from using sugar to fat as its primary fuel source. Any side-effects, such as an increased heart rate, may take time. Exercising while your body is undergoing this transition may help your body adapt faster and become more efficient at using fat and ketones.
Increase carbohydrate intake
If you've increased your sodium and fluid intake, given your body enough time to adapt, and the problem doesn't stop, try increasing your carb intake slightly.
Increasing carbohydrates isn't an excuse to revert to junk food and eating copious amounts of sugar, but upping your carbohydrate intake from low or ketogenic numbers to more moderate levels may be required if any of the side-effects do not subside.
The Takeaway
A ketogenic or low carb diet may increase heart rate in specific individuals due to a rapid loss of fluid and electrolytes. Make sure you stay hydrated by drinking to thirst and increasing your salt intake by salting your foods to taste.