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7 Possible Keto Diet Side Effects

Author: Amanda Cofer, MPH

We all probably know someone who has tried a ketogenic diet. It’s one of the more common diets out there, and requires followers to almost entirely cut out one food group: carbs.

Historically, the ketogenic diet was used in clinical settings for children with severe epilepsy. However, it has made its way into the mainstream due to its weight loss results and the ability to help you drop pounds fairly quickly. A ketogenic diet is not only low-carb but is also a high-fat diet, with most calories coming from fat and protein sources. 

So, what are the side effects for those using an ultra low-carb, high-fat diet approach to weight loss?

1. The ketosis flu

Before diving into this first point, we have to understand a little more about ketosis. Ketosis is the process in our bodies of switching from burning glucose for fuel to burning fat or ketones for fuel. In order to force this switch, the intake of carbs has to be drastically lowered, essentially forcing the body to its next physiological source of energy. This process is also termed keto-adaptation and can last on average 4 weeks. This means for the first few weeks of your ketogenic diet you could experience the following: 

  • Headache
  • Brain fog or slowed thinking and judgement
  • Dizziness or lightheadedness
  • Fatigue
  • Racing heart rate
  • Trouble sleeping
  • Cravings
  • Irritability

If you read that and thought “carb withdrawal,” you wouldn’t be wrong! While some will experience these signs and symptoms at varying levels of severity, we can all agree that they don’t sound fun. In these first few weeks, you may see weight drop quickly as well. When you see the scale drop big numbers in one week, you may feel motivated by this weight loss but also be left questioning where this weight came from. 

2. Dehydration and electrolyte imbalances

If you’ve tried a low-carb diet in the past that sent you reeling into ketosis, you probably felt some of those symptoms and saw that big dip on the scale. This initial drop in weight is mostly due to losing water weight. When your body is in ketosis and is burning fat for fuel, the ketones that are produced have to be eliminated via urination. You may not only find yourself needing to hit the bathroom more often while you’re on a ketogenic diet, but because of this you’ll need to drink more water to stay hydrated as well. 

You may also experience muscle cramps and spasms due to imbalances in your electrolytes caused by wonky hydration needs and limiting fruits and vegetables containing essential nutrients. Our bodies need minerals such as magnesium, sodium, potassium, and calcium to for muscles to contract properly. When these are thrown off due to eating an unbalanced diet, you could find yourself waking up to a charley horse in the middle of the night. #ouch. 

Because some of these nutrients are so vital, your body may steal from itself in extreme cases, which could lead to bone loss and osteoporosis over time. According to Mayo Clinic, if sodium gets too low it could cause even more serious symptoms such as confusion, coma, and seizures.

3. Nutrient deficiencies

Limiting food groups brings us to our next point. Deficiencies when losing weight on a ketogenic diet can result from limiting fruits, certain vegetables, and legumes. These healthy, whole foods are higher in carbs and therefore not generally permitted on a diet like keto. These foods contain fiber, minerals and vitamins, antioxidants, and phytochemicals that keep our bodies healthy and whole. 

Going long periods of time without these nutrients can result in increased risk for chronic disease. You may think your weight loss on keto is making you healthier, and to an extent that may be true. However, your body might also be craving nutrients from the foods you’ve cut out to see results on the scale. 

In fact, a long-term study published in 2018 found that your mom’s sage advice of everything in moderation was pretty spot-on! You may see weight loss results for a time, but removing food groups such as carbs (and the nutrient deficiencies that can bring) could have negative health impacts down the road. 

Of course, we don’t want to go the other extreme and eat carbs in excess, but we want to find the sweet spot that works best for us as individuals. The study above found that those who were taking in 40% or less calories from carbs daily were more likely to experience premature death than those eating in moderation. If that doesn’t make you want to run out and grab a bagel, we don’t know what will.

4. Kidney or heart damage

Along the lines of nutrient deficiencies is another risk: possible kidney and heart damage from eating a ketogenic diet for weight loss. The idea that you need to eat fat to lose fat is largely behind the concept of eating a low-carb diet, such as keto. However, high-fat diets can also lead to increased health risks. 

When it comes to fat intake, quality matters. Ketogenic diets have potential to increase your intake of saturated fats, which can lead to increased cholesterol, increased risk of heart attack and stroke, and increased blood pressure. These chronic ailments make it hard for keto to be sustainable in the long term (we’ll dive into this more soon) and even ketogenic diet experts say that you should only eat a high-fat, low-carb diet temporarily. The change in electrolytes can also lead to heart palpitations and arrhythmias in the long term. 

The same factors that put strain on the heart also put strain on the kidneys. When fluids and electrolytes and not in balance, we are at a higher risk of kidney stones and eventually kidney injury or failure. Know that these risks are a bit higher if a keto diet is approached in a high-protein way instead of a high-fat way, in most cases. 

5. Change in menstrual cycles

Ketogenic diets have potential to lead to rapid weight loss, which can cause hormonal disruptions impacting the menstrual cycle. To understand why this happens we first need to understand a bit more about hormones and what controls them in the body. 

There are three glands in the body whose main functions are hormone related: the hypothalamus and pituitary glands in the brain, and the adrenal glands located on top of the kidneys. This is otherwise known as the HPA-axis. (Remember, Noom nerd love their acronyms.) These glands are incredibly sensitive to things like stress, exercise, calorie intake, and (you guessed it) carb intake. If too few carbs are going into the body, the hypothalamus will not release enough of the hormone needed to start the menstrual cycle, which then creates a cascade of keto diet side effects. This will cause hormones such as estrogen and progesterone to also take a nosedive.

Eventually, if this cycle continues over a long period of time, periods may stop all together. While this side effect can be a bit more rare, amenorrhea (the loss of a menstrual cycle for 3 months or more) can set in. It’s also important to note that this may be more likely for women who are already at a healthy weight and body fat percentage when they begin eating a ketogenic diet. 

6. Changes in bowel movements

While bathroom talk isn’t the prettiest conversation topic, it is an important one. Ketogenic diets can create the perfect storm for irregular bowel movements and constipation. This not-so-cute keto diet side effect is a result of taking in less fiber-rich foods (which are typically higher in carbs than what ketosis would allow). This, plus the dehydration effect of keto, means you may see yourself go a few days without this kind of trip to the bathroom. 

Another contributing factor to this constipation is changes in your gut bacteria. While more research on these effects is certainly needed, some research has shown that the unfavorable gut changes brought on by a high-fat diet can lead to increased inflammation and, in the longer term, changes in immune health, digestion, and mental health. 

On the other extreme of irregularity is loose stool and diarrhea. Without much fiber in the digestive system, you may experience this other unpleasant bowel side effect. Eating foods higher in fat content can lead to greasy stool and frequent trips to the bathroom. Our bodies can have a hard time breaking down and absorbing dietary fats, and over time this can put strain on other digestive organs like the gallbladder and liver.

7. Yo-yo dieting

Last but not least on our list of possible keto diet side effects is the likelihood of finding yourself in a cycle of yo-yo dieting. 

Ketogenic diets for weight loss are particularly tough to stick to, and are generally meant to be temporary. The long-term side effects of eating a low-carb diet will eventually start to take their toll on your body and mindset, and the restrictive nature of things could send you reeling in the other direction. The weight loss you saw yourself achieve might all be undone, leaving you at square one to start your ketogenic diet all over again. 

If you’re someone who needs to keep an eye on their carb intake for the sake of their blood sugar levels, make sure you’re finding a mix of healthy carbs that feels doable for you long term. This might include something that resembles keto or it might not. The goal is to make sure you’re finding a balance that works for you and gives you long term results for your health and weight loss. 

Breaking this ketogenic diet cycle is where Noom comes in. The key idea behind changing your eating habits is making sure that they will be sustainable and healthy for the rest of your life. As we’ve learned here, keto diets for weight loss are really only meant to be temporary and not a lasting “fix.” The high-fat, low-carb diet approach can sometimes be harder on your body than you’d expect and be restrictive. Give Noom a try today and experience what true balance and weight loss success (without the crazy limitations) could look like for you!