“Help! I’m having trouble fasting, I feel like I can’t concentrate and my energy flags. What can I do?”

Published by cwhealth on

This cry for help came into my inbox this week. And it’s one that I see kinda regularly, and maybe something you’ve come across yourself, so i wanted to take a moment to chat about it.

So many people (including some practitioners) think fasting is this easy breezy thing…

‘It’s just not eating – it’s easy!’ 

‘Everyone can do it’

‘You just have to push through’

But in reality, there are some really important things you need to know BEFORE you try fasting, or if you’re giving it a shot and having trouble getting through your day without crashing and burning.

(If you like to watch rather than read, check out the live video I did on this topic inside The Brain Health Hub)

Here’s are my top 5 fasting troubleshooting tips when you’re struggling to make it through your fast:

Tip #1 : Check for red flags 🚩

Fasting isn’t safe, suitable or easy for everyone. There are some ‘red flags’ which indicate fasting may not be the right thing for you right now. Such as:

  • You have hormonal imbalances or conditions
  • You have low or suboptimal thyroid functioning (this will already make you sluggish and brain foggy and have difficulty producing enough energy to keep you going throughout the day + fasting can worsen this)
  • You’re menopausal or post-menopausal (women in these phases tend to do better on much shorter fasting periods)
  • You have insulin resistance or Type 2 diabetes
  • Your diet quality is poor

Now some people in these categories can fast just fine, but others can’t. Check with a practitioner for personalised guidance if you fall into one of these categories as there may be some steps you need to take first, before trying fasting.

Tip #2: Check your blood sugar and insulin levels 🩸

If you’re having trouble getting through your fasting period without flaking, feeling foggy, turning into a zombie or a hangry monster, it could be a sign you’re not yet metabolically flexible. This means your body doesn’t switch from burning glucose to burning fat easily. This is crucial to provide your body and brain with energy during fasting periods. High insulin levels or insulin resistance will prevent this flexibility and you could have these issues without any major symptoms!
So, get the right blood tests and check your levels to make sure your body is primed and ready to get you through your fast.

Tip #3: Start and proceed slowly 🕰

Lots of people try to dive right into a 16 hour fast. Hold it right there! Your body takes time to adjust and making the shift to longer fasts should happen in small increments. Extend your fast by 30-60 minutes. Do that for a week and if you’re feeling good with it, extend it again the next week. There are no prizes for throwing your body out of balance and feeling like s***t by making a big leap too soon. Take it slow!

Tip #4: What are you doing before and during your fasting window? 🗓

While working out while fasting is totally great and do-able, it’s often not great to try it when you’re new to fasting. Again, the body needs time to adapt and find a new balance in your fasting routine, so throwing a hard HIIT or weights session in at the start or middle of your fast could leave you on the floor. Ideally workout near the end of your fasting window so you can refuel afterwards. And don’t forget to hydrate! Fasting doesn’t mean no water!

Stressful meetings, conversations or mentally taxing tasks can make getting through your fast even trickier. Eventually you’ll be able to take these in your stride, but listen to your body and break your fast when needed if you feel particularly zonked by certain activities.

Tip #5: What are you eating in your feeding window? 🍕 🌭 🥦 🫒

Fasting for 16 hours a day does not cancel out the pizza, soda and candy you eat in the other 8! What you eat when you’re following a fasting routine is even more important because you have less time to get in the nutrients and food you need for your body and brain to run efficiently. Also, if you’re still relying on refined carbs and sugar, the insulin spike will stop you from getting into an effective fasting state and you’ll crash and burn. If your diet isn’t great, work on improving that first, BEFORE starting to fast. Once your body has the right fuel with a low GI diet rich in healthy fats, vegetables and protein, it’ll be more primed to switch into fat-burning mode to have you whiz through your fasting period without a hitch.

Ultimately, fasting can be an incredibly powerful tool in your brain health toolbox.

But it’s not an easy, breezy, one-stop-solution to everyone’s problems!

It’ll suit some of you perfectly and others not so much. You’ll get the most out of your fasting routine if you include it in the right way and at the right time for your needs, while listening to your body and giving it time to adapt to your new routine.

Remember: Your body is a unique, living breathing organism, not a machine!


If you’re not sure if fasting is right for you, or if you’re having trouble incorporating it into your routine then drop me a message on cathy@cathywilliams.co.uk and let’s chat!

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