Fasting can be an incredible tool for improving your health. Many people fast to lose weight, stabilise blood sugar and reverse insulin resistance, and improve focus. For a lot of people, it works very well. 

But fasting is not always a good idea. 

There are certain situations where fasting may actually make your mental and emotional health worse instead of better. This is something that doesn’t get talked about enough, especially in wellness spaces where fasting is often treated like the answer to everything. 

Let’s look at red flags that might suggest fasting is not the right answer for you.

Fasting and the stress response

One thing to understand is that fasting is a stress to the body. It’s a good stress, in that it is very healing, but still a stress. Which means stress hormones like adrenaline and cortisol are triggered. This is normal and temporary. It’s part of what helps the body tap into stored energy (fat) and stay alert while food is unavailable. 

But if your body is already under heavy stress, fasting can add fuel to the fire. 

That’s why people dealing with chronic stress or burnout may struggle with fasting more than expected. If you’re feeling exhausted, emotionally overwhelmed, anxious, or constantly on edge, your body may already be stuck in fight-or-flight mode. Adding more stress through aggressive fasting can push cortisol even higher. 

Sometimes it shows up as poor sleep, irritability, or racing thoughts. Other times it looks like intense cravings, mood swings, or becoming obsessed with food. 

This doesn’t mean fasting is bad. It just means your body may need more support before it needs restriction. 

Anxiety and panic symptoms

Anxiety disorders can also complicate fasting. 

Hunger can naturally cause physical sensations like a faster heartbeat, shakiness, or restlessness, especially if you’re new to fasting. The problem is that these kinds of symptoms can feel almost identical to anxiety and panic attacks. 

For someone with generalised anxiety or panic disorders, fasting can accidentally trigger the brain’s alarm system. The body senses stress, adrenaline rises, and suddenly a person feels panicked without fully understanding why. 

Grief, trauma, and emotional overload

Grief and emotional trauma are another major red flag. When someone is going through loss, heartbreak, or intense emotional stress, the nervous system is already overloaded. During those periods, the body often needs consistency, nourishment, sleep, and emotional safety more than it needs extended fasting windows. 

Trying to force strict fasting during grief can sometimes increase emotional instability rather than improve health. 

On the flip side of that, many people lose their appetite all together during grief and loss. And that’s a normal response. The point is, do what you need to do to take care of yourself during this time. 

Eating disorders and disordered eating

Perhaps one of the biggest red flags involves disordered eating patterns. 

For people with a history of anorexia, bulimia, binge eating disorder, or chronic restriction, fasting can become dangerous very quickly. Even when fasting starts with healthy intentions, it can sometimes reactivate obsessive behaviours around food, body image, or control. Dr Fung, leading fasting expert, advises that if you have been diagnosed with an eating disorder you should not fast. 

If fasting causes constant anxiety, guilt, binge eating, or compulsive behaviours, it may not be helping your health at all. 

This doesn’t mean you can never fast

Let’s be real, many people have anxiety these days. And for some people, fasting does tend to calm the mind. But it’s not the same for everyone, and there’s no shame in acknowledging that fasting is not the healthiest approach for you at this time. 

The goal is to make your life better

Fasting is a tool. It is not a requirement, a personality trait, or a moral achievement. And sometimes, knowing when not to fast is just as important as knowing when to start.