What are the Side Effects of a Low-Carb Diet?

Are you thinking of making the switch to a low-carb diet? If so, there are some side effects you need to be aware of before you start. The good news is that these side effects are almost always temporary.

Low-carb diets have become increasingly common in recent years – and many people have had success using them to lose some serious weight.

What many people don’t realise is that such a big change to your diet can be a shock to your system. Aside from the mental struggle of restricting the foods you eat, there are physical changes that can cause a variety of temporary side effects (this is also why low-carb hybrids, such as the Half Day Diet, are becoming popular). If you’re going to stick to a low carb diet in the long run, you need to be aware of these side effects so you can counteract them.

It’s important to point out that any big dietary change can cause side effects. If you want to stick to a diet beyond the first few days, however, it’s vital you know what you’re up against.

That’s why we’ve put together this post of the most common side effects of a low-carb diet. Most are temporary and go away after a couple of weeks, but if you notice long-term symptoms it’s always important to speak to your doctor.

A woman holding her head with induction flu

The “Low-Carb Flu” Side Effects

When you first start a low-carb diet, you may experience symptoms that mimic the flu. These can be unpleasant (to say the least) and are one of the main reasons why people give up before they start seeing results.

Most people start to experience these symptoms after 2-4 days of eating a low-carb diet. They usually disappear within the first week, so hang in there!

Low-Carb Flu Side Effect #1 – Headaches

Headaches are probably the most common side effect of a low carb diet. You may also feel lightheaded.

These headaches can sometimes be minimised by adding a small amount of salt to a glass of water. If you notice symptoms improving over the next half an hour, repeat the tactic daily until it’s no longer needed.

If you’ve tried the salt trick and your headaches aren’t going away after a few days, you may need to slightly increase your carb intake.

Low-Carb Flu Side Effect #2 – Brain Fog

One of the strangest side effects is a sense of “fogginess” in the brain – almost like you’re slightly drunk. You may find yourself unable to concentrate or being completely unproductive.

According to BodyBuilding.com, this happens because your brain starts to burn ketones when you switch to a low-carb diet. This only happens when your body has used all its supply of glycogen though. Until then, you’ll probably feel a little spaced out.

Fortunately, this usually clears up within the first week – although it can take up to 14 days to fully disappear.

Low-Carb Flu Side Effect #3 – Fatigue

When you go on a low-carb diet you’ll urinate more often. This is because your body is burning glycogen which releases water.

A side effect is that your body also loses vital minerals. A lack of magnesium, salt and potassium can cause a range of symptoms, including fatigue.

As you’ve probably guessed, replacing these minerals is an easy way to prevent fatigue (at least for most people).

A low-carb diet can impair athletic performance

Other Side Effects

While induction flu symptoms are probably the most common for people starting a low-carb diet, they are far from the only ones. Here are some other side effects to watch out for.


Do you feel like everyone is even more annoying than usual after starting a low carb diet? If so, it’s probably you and not them!

When you cut out carbs from your diet – or make any dietary change – it can temporarily affect your mood. This is partly because you’re struggling to avoid the foods you previously enjoyed.

So if you find yourself becoming more irritable than usual, try to remember it’s a temporary feeling.


We already saw how insufficient salt can cause induction flu. The same problem can also result in leg cramps.

The easiest way to prevent cramps is to drink more water and increase your salt intake. You may also need to supplement magnesium, although talk with your doctor before you do this.


Like any dietary change, switching to a low carb diet can cause constipation. This is because your gut needs time to adapt to your new diet.

Constipation usually passes, but it can take a few weeks for your digestive system to fully adapt. Make sure you eat plenty of vegetables and stay hydrated. If constipation is too uncomfortable, visit your doctor to see whether a laxative may be required.

Hair Loss

When you make a big dietary change, you may experience hair loss. This can be a frightening experience but is nearly always temporary. It’s also usually only a thinning of the hair, so it’s unlikely other people will notice.

Hair loss often starts after a few months on a low-carb diet. It can last for several months, but once the hair follicles have regrown your hair will be back to normal. For people with long hair this can take a long time though.

Temporary hair loss is one of the more uncommon side effects of a low carb diet. While there is debate over why it happens, you may be able to decrease the risk by reducing stress, getting plenty of sleep and avoiding restricting calories. It’s also probably best to avoid starting a high-intensity exercise routine at the same time as switching to low-carb.

Bad Breath

Some people find that switching to a low-carb diet causes their breath to smell “fruity.” This smell is sometimes compared to nail polish remover.

In the low-carb world, this can signal that your body is burning more fat. That’s because the smell is caused by acetone, which shows that your body is burning fats and converting them into ketones.

The good news is that only some people notice this symptom. It also usually goes away in a couple of weeks. If you find that it doesn’t go away, however, you may need to drink more water, improve your dental hygiene or use a breath freshener.

Reduced Performance and Strength

If you’ve assumed that all the extra protein from switching to a low carb diet will improve your performance in the gym, you may be mistaken! At least in the short term.

While many people don’t notice any difference to their athletic performance, some find that their numbers have dropped soon after making the switch. This is usually temporary, but people on a heavy weight lifting routine may need to adjust their diet or include more carbohydrates as fuel.

Mineral or Vitamin Deficiencies (rare)

When you change your diet, it’s important make sure you’re getting all the required nutrients. Most people on a low-carb diet find the variety and nutritional value of their foods increases, but it’s possible to make mistakes. In the long run, this can lead to deficiencies.


The potential side effects of a low-carb are many and varied. The ones listed in this article are amongst the most common, but low-carb diets have been known to cause others such as gout, rashes, gallstone issues and even elevated cholesterol.

Fortunately, side effects of a low-carb diet are nearly always temporary. If you’re really struggling, however, you may need to increase your carb intake. Many side effects can also be reduced by making sure you’re staying hydrated, getting enough salt (especially in the first week) and eating a nutritionally complete diet.

0 0 vote
Article Rating

Information or content on this website is not meant to replace the advice of a doctor or other healthcare professional. It is not to be used to cure, treat, diagnose or prevent any disease, illness or condition. It should not be used as medical advice. Always consult your doctor before taking any supplements or starting a diet or exercise program.

Content on this website is written based on internet research and our own opinions. We do our best to make sure all articles are up-to-date and accurate, but we cannot guarantee the safety, effectiveness or accuracy of any content. If you find any inaccuracies, please contact us and we will investigate.

Affiliate Disclosure: Links on this website may be affiliate links. If you purchase a product or service after clicking these links, we will receive a commission. This does not affect how much you pay. Read our full disclosure.

Notify of
Inline Feedbacks
View all comments
Would love your thoughts, please comment.x