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Ketogenic Diet Side Effects: 7 Signs That You’re In Ketosis


How do you know when you’re in ketosis?

It’s a question a lot of people ask when they first start a ketogenic diet. 

When you begin eating keto, your body shifts to burning fat as its primary fuel source instead of carbohydrates. 

That’s a big metabolic change, and it comes with quite a few side effects — both good and bad. 

Not everyone experiences side effects when starting a ketogenic diet, and thankfully, the negative side effects of keto are usually temporary. In the vast majority of cases, they go away within the first week or two of you starting the diet. 

Here’s a look at seven of the most common side effects and health benefits of ketosis. 

1. Weight Loss

Normally, your body runs on glucose (sugar) as its main fuel source. But when you start a low-carbohydrate diet, your metabolism begins to switch over to burning fat for fuel. 

Before your body makes the switch into ketosis, it has to burn through the glucose stored in your liver and muscles. You typically work through your carb stores within the first week of starting a ketogenic diet. 

Carbs require a lot of water for storage, so as your carb stores deplete, you lose a lot of water weight. One sign of ketosis is rapid weight loss shortly after you start a keto diet. Before you get too excited, most of the first bit of weight you lose is probably water, not body fat. 

But if you’re doing keto for weight loss, don’t worry — keto diets are an excellent way to lose weight long-term, outperforming low-fat diets by a significant margin[*][*]. After the first week or so of keto, once you’ve lost water weight and gotten into a state of ketosis, fat loss comes quickly and easily. 

In the meantime, make sure you drink plenty of water and replenish your electrolytes so you don’t get dehydrated. 

2. Frequent Urination

Again, you’re losing a lot of water weight when you first start a low-carb, high-fat diet like keto. Keto dieters often experience frequent urination for the first week or two.

As long as you’re drinking water, this side effect isn’t a big deal. It’ll go away once your metabolism switches over to burning fat for fuel. 

3. Keto Flu

Keto flu is the most common side effect of a ketogenic diet. Fortunately, keto flu is temporary, and should go away within 7-10 days after you start keto. 

When you cut out carbs, your metabolism goes through a period where it’s not sure how to efficiently burn fat yet, but it doesn’t have access to sugar from your diet. 

As a result, you may experience keto flu — a collection of flu-like symptoms that includes headaches, fatigue, low energy, diarrhea, dry mouth, sugar cravings, and brain fog. 

Keto flu usually passes pretty quickly, and you may be able to avoid it altogether. Here’s how to get rid of keto flu.

4. Muscle Cramps

When you’re on a low-carb diet, your insulin levels stay stable and low most of the time, because you aren’t eating carbs that spike your blood sugar levels.  

Decreased insulin release makes your kidneys actively expel sodium[*]. You also lose other electrolytes, including magnesium. 

Low sodium and magnesium can cause muscle cramps, so it’s important to replenish your electrolyte stores — again, especially during the first couple weeks of keto, when your body is still learning how to transition into fat-burning mode. 

So, contrary to standard medical advice, you don’t want to limit your salt intake when you’re on a keto diet. 

Make sure you salt your food generously, and consider taking 400 mg of magnesium a day or using an electrolyte supplement when you first start keto, especially if you get muscle cramps. 

5. Appetite Suppression

 One reason keto is so good for fat loss is that ketones — the fat-based fuel that your body burns when you’re in ketosis — are great at suppressing hunger. 

High ketone levels inhibit ghrelin, your body’s main hunger hormone[*]. The result is significant appetite suppression, meaning you feel full on less food. 

As an interesting aside, you also burn, on average, about 300 more calories a day when you’re in a state of ketosis[*]. 

That means you feel full while eating less, and you’re burning extra calories on keto. That’s a great recipe for weight loss. 

6. Increased Energy Levels and Mental Clarity

Once you’ve transitioned into ketosis, you may experience a significant increase in your energy levels. Ketones are a superb fuel source for your mitochondria, the powerhouses of your cells. Your brain in particular thrives on ketones[*]. 

A lot of people who switch to keto report better mental clarity and more even, sustained energy throughout the day. 

7. Temporary Bad Breath

You may have heard of “keto breath” — a short-term change in the way your breath smells when you start keto. 

Keto breath happens thanks to acetone, a ketone body that you produce when you burn fat. Acetone has a fruity smell reminiscent of nail polish remover. 

When you first start producing ketones, your body doesn’t know how to use them efficiently, and you end up excreting a lot of them. Acetone comes out through your breath, and a small percentage of people release enough acetone to make their breath smell like nail polish remover. 

Keto breath is rare, and it only lasts until your body gets more efficient at using ketones.  

How To Avoid Negative Ketosis Side Effects

Ketosis Side Effects

You may notice that most of the negative side effects  of the ketogenic diet happen during your initial transition into ketosis. Changing into a new metabolic state is a big shift for your body. 

The first week or two of keto can be difficult for some people. Fortunately, the downsides are temporary — virtually all of them go away once your metabolism comfortably switches over to burning fat for fuel. 

Additionally, most of the common ketosis side effects can be helped or eliminated by:

  • Drinking more water
  • Increasing your salt intake
  • Making sure you’re eating enough fat

If you’re still experiencing side effects after your switch into ketosis, a keto diet may not be a good fit for you. Consider increasing your carbohydrate intake with an alternate meal plan, like the cyclical keto diet or the targeted keto diet

The negative side effects of keto are usually minimal and temporary. Most people find they pass after a few days — a fair trade-off for the many benefits of a ketogenic diet.  

Want to give keto a try? Our complete beginner’s guide to keto has everything you need to start a keto diet today.


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