The 6 Signs of Keto Flu – And Quick Tricks to Help You Beat Them

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Helen Foster
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Using keto to lose weight has its positives like rapid weight loss and no hunger pangs, but it does come with a few issues as well – not least side effects that many people refer to as keto flu. Here we explain why it happens, what to expect and how you can handle some of the most common side effects of going keto.

Keto foods including salmon, avocado, oils and nuts

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Why Do You Get Side Effects on a Keto Diet?

When you cut out carbohydrates from your diet and eating high levels of fat your body enters a state called ketosis where it burns fat for fuel. When you do this, you produce substances called ketones. And these can trigger some side effects.

Swapping to a keto diet which has no sugars and very few carbs of any kind can also trigger a form of sugar withdrawal which can impact the body leading to mood swings and cravings.

If you’re suffering low energy for other reasons and usually use sugar as a crutch to give yourself a buzz – say mid-afternoon – you might also find yourself more tired simply because you’ve taken away your normal energy lift.

If you do suffer low energy, then have a look at our guide on ways to increase vitality. Some of them work within minutes.

Eating the high levels of fat on a keto diet can also cause a few symptoms – it might leaving you feeling a bit queasy for example.

Also, one of the reason fat is so satisfying is what’s known as mouthfeel – the creamy taste you get on your tongue when you eat it. While this feels like a treat when you eat fat now and again, when you’re eating a diet very high in fat it can start to feel more unpleasant than tasty.

How to Handle the Side Effects of Eating Keto

The good news is that many of the symptoms of keto flu pass after a few days once your body gets used to using ketones for fuel – it normally takes me about five days for this to happen but when it does everything changes and my energy soars.

But until that happens, here’s how to tackle some of the most common side effects of keto eating.

None of the above replaces advice from your doctor and you should always speak to your GP about any symptoms that last longer than a few days or that make you feel really ill.

Also never go on a keto diet without medical advice if you have any long-term health condition like heart disease or Type 2 diabetes.

You might have to search around a bit for a doctor, dietician, nutrition specialist who works with keto but they are out there.

Low Energy and Dizziness

These can occur in the first few days of a keto diet as you start to run out the sugar stores in your muscles and liver but before your body realises it should be burning fat for fuel. Because it can’t find sugar your body acts as if it’s being starved causing a drop in energy.

Depending on how strict a keto diet you are on, simply swapping in a red vegetable might be enough to stop this slump, however if you’re on a very strict keto diet like The High Fat Diet (that I stick to when I do it), anything other than green and white veggies are banned, but you can add a little lemon juice to sparkling water or black tea can help give enough of a tiny blood sugar jolt that changes things without spoiling the plan.

Personally, I just use the time to have a rest – it only lasts a few days before things turn again.


If you go straight into eating a high-fat diet from one normally packed with carbs and sugar you can find you feel a bit sick while your blood sugar stabilises, this will pass but if you need to, use the lemon juice tip above.  

If you start to feel queasy later in the diet, then it might be because the food is too rich, swapping to lighter -tasting fats like avocado rather than heavy butters, creams or cheeses can also help until your body gets more used to things.

Grumpiness and Irritability

These are a side effect of sugar withdrawal and may occur during a few days into a keto diet.

Resist the urge to give in, this will only last for 1-2 days eating something sweet will kick you out of ketosis and you’ll only have to start this process again. The issues will pass.

Just make sure you’re keeping your fluids up as dehydration can make things worse – remember, your urine should be a pale yellow colour. If it’s darker you need to drink a bit more.

Okay, so they might not all work to handle the keto grumps, but, you might be able to cheer yourself up a bit with our list of fun mood boosters here.


These can also occur because of sugar withdrawal or dehydration if you’re not drinking enough.

Try to avoid using painkillers if you can – a lot of them contain sugar which, if you’re very sensitive to insulin swings can reduce your results.

A great natural way to fight a headache is Tiger Balm – just apply it to your forehead and it starts to tingle. This interrupts the pain signals and distracts your brain reducing the pain you feel. 

Bowel Changes

Most keto diets are low in fibre and as such you’re likely to need to go to the bathroom less than normal and when you do go you’ll pass less than you are used to. That’s okay, so long as you are not straining to go to the loo, just go with it.  

However, sometimes going keto can bind you up.

If this happens, make sure you’re drinking enough water which helps keep stools softer and easier to pass. Also, look at what you’re eating, eggs and foods containing calcium can be the culprit so switch the diet around a bit if you’re relying on these too heavily.

Or alternatively, soak one teaspoon of chia seeds in a glass of water for five minutes then drink – chia seeds are rich in fibre but low GI and so don’t upset the keto process. Buy them and have them delivered ASAP here.

Constipation can contribute to bloating as, the longer contents hang around the gut, the longer the bacteria in the bowel have to feast on them – which produces gas. Admittedly, the low fibre count of the keto diet does make this less likely, but if you are suffering from bloating on keto, have a look at our top tips for reducing gas here.

Bad Breath

Going into ketosis can trigger bad breath. Drinking a plain peppermint tea can help freshen things up. If the problem is not so much odour as a stale taste in your mouth, fizzy water is your friend. It really does help dilute the taste.

If you’re giving keto a try, here’s a few things you might want to buy to make the process easier…

Your Keto Shopping List

The High Fat Diet by erm, me – and the brilliant Zana Morris. Meeting Zana got me into keto – and I admit when I first tried it I couldn’t believe it could work. But it does – I will lose 10lb in 10 days without fail on this diet – and so, I asked Zana if we could write a book about it – and this is it!

Oh and yes, if I’m sensible that 10lb stays off – or course, most of you who read this blog regularly will know I’m very good at not being sensible!

A good keto cookbook – if I had one of these I probably would find it a lot easier to stay sensible!

While I love the results on the High Fat Diet it is a VERY strict keto diet which is why I can’t stay on it long term – the recipes in this book are a bit more relaxed and easier to incorporate in day to day eating particularly as they all take 30 minutes or less to prepare.

Keto Strips – I never normally bother measuring whether I’m actually in ketosis on The High Fat diet as I know Zana has tested it to ensure that it gets you there.

But if you are in on a plan that allows coloured vegetables and lower fat nuts then you might want to check everything is going to plan with some ketosis sticks. Basically, you pee on them and the colour of the strip them tells you whether you’re in ketosis or not.

What to Read Next

If you’re doing keto you might be wondering how you get all the nutrients you need. Have a look at our post on how to get your micronutrients on keto to find out.

Wondering about MCT oil and using it to extend fasting periods on plans like intermittent fasting, find out whether MCT breaks a fast here.

Need some ideas on how to replace carbs on a low carb or keto plan. We’ve got 33 suggestions.

Who is The Wellness Nerd?

My name is Helen Foster, and I’m a health journalist and wellness author. Publications I’ve written for include Women’s Health, Reader’s Digest, Body and Soul, Good Health at the Daily Mail, and more. I have also written 16 books on health and nutrition.

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