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How to fast safely

Rachel Lett, RNutr

Chief Care Officer


The quick read :

  • Intermittent fasting is a safe method for improving health.
  • Fasting does not cause hypoglycaemia, starvation, muscle loss or slow down metabolism.
  • A well formulated fasting regime includes, enough protein, enough nutrient dense foods, hydration and electrolytes.
  • Certain people require medical supervision while fasting. This includes, children and adolescents, and those who are underweight, have an eating disorder, breastfeeding, pregnant, type 1 diabetic or type 2 taking blood glucose medication.

Intermittent fasting (IF) is a pattern of fasting and eating over a defined time period ⏰. There are many different types of fasting that you can do to suit your lifestyle and health goals.

In short, yes, intermittent fasting (IF) is a safe and effective lifestyle strategy to improve health and wellbeing. You name it, weight loss, insulin resistance, anxiety, digestive issue, memory loss, IF helps — research has shown it, and millions have tested it.

The societal norm is to eat breakfast, lunch, dinner and snacks, around the clock. Combining these eating habits with a busy, stressful schedule, individuals easily rack up hours of feasting (12-16 hours of non-stop grazing). This type of eating stimulates excessive insulin secretion, which is neither healthy, safe or normal.

Fasting is a strategy that lowers insulin secretion. This is a good thing.

However, there is a right and wrong way to fast, and not everyone should fast. Fasting is a safe method for improving health, but only when it is practised with care.

In this article, we explore common concerns about fasting, important considerations for fasting safely, and individuals who should not fast.

Common Concerns

People are often concerned that IF will cause hypoglycaemia, starvation, muscle loss or slow down metabolism. Neither of these are true, provided you're not taking certain medication (more on this later). The article "stages of fasting' goes into more detail on these common concerns, but here is a quick run through of why you don't need to worry.


The body produces a hormone called glucagon, which maintains blood glucose above 4.0 mmol/l (72mg/dl), during periods of low food availability. If fasting caused hypoglycaemia, then we would need to drip feed ourselves throughout the night.


Starvation is a state of inadequate nourishment, necessarily for normal body functioning. Fasting includes nutrient dense foods during times of eating — it does not starve the body of necessary nutrients.

Muscle wastage

Fasting does not cause muscle wasting. It would be nonsensical for the body to use precious muscle tissue when we have an abundance of stored energy at our disposal — glycogen and fat. A rise in human growth hormone (HGH) during fasting, preserves lean body mass.

Slow metabolism

Fasting increases norepinephrine (adrenalin) levels, which promotes fat liberation and maintains (and increases) metabolic rate. To sum up, fasting does not slow down metabolism.

Here are some important consideration for practising intermittent fasting , safely

Eat enough protein

Intermittent fasting has a natural tendency to put an individual in a calorie deficit and cause weight loss — fat loss is good, but muscle loss is bad.

To prevent muscle wasting, you must meet your protein requirement. This can be challenging when there are less meals, and windows of opportunity to eat protein throughout the day. If you are failing to meet your protein requirement, try supplementing with a low-carb protein powder. Aim for 1.2-1.7g or protein per kg weight, per day.

Eat nutrient dense foods

What you eat, is just as important as when you eat. Remember that intermittent fasting is not a passport to eat poor quality food. Rather, use it to get the most out of your diet and health.

We recommend you stick to high quality, low carbohydrate, high fat and moderate protein meals in-between fasts. This type of diet will nourish your cells, improve body functioning and prevent muscle wastage.

Stay hydrated & replace electrolytes

Electrolyte and water loss is a common and normal response during intermittent fasting. If you don’t replace water and electrolytes, you will experience headaches, fatigue, increased hunger, dry mouth, muscle cramping, nausea and light headedness. In other words, you will feel horrendous .

Fasting does not mean “Nothing can pass my lips. No water. No anything. Ever”. Your body will not do well if you restrict fluids and electrolytes, so make sure you drink plenty and replace essential minerals. Here is a guide on “What to drink while intermittent fasting’ and "Electrolytes" to help you hydrate.

Water requirement is based on your weight and activity level. Check out this website to calculate your personal water requirement and try to aim for this, daily.

People who should not fast

Underweight or have an eating disorders

Intermittent fasting has a natural tendency to promote a calorie deficit and thus weight loss. If  you are underweight (BMI < 18.5), then you should not practice IF. A person with a low weight will not have energy reserves to maintain a fasting regime. This would promote muscle wasting.

Intermittent fasting has been shown to restore balance and a positive relationship with food. However, anyone who has, or had an eating disorders should not fast. The pattern of restriction and eating could trigger a relapse.

People who may need medical supervision while intermittent fasting

Children, Adolescents, Pregnant or Breastfeeding Women

Children, adolescents, pregnant or breastfeeding women require extra nutrients for growth and repair. Nourishing the body with enough protein, fat and micronutrients is essential during these stages of life.

Fasting for too long, or not eating enough during the eating window may lead to under nutrition. This group of people may practice gentle intermittent fasting, provided they are monitored — fasting for longer than 20 hours is not advised.

Diabetes Type 1 and 2

IF is an effective method for reducing insulin and thus reversing insulin resistance for type 2 diabetes. However, if you are taking blood glucose lowering medication like insulin, gliclazide, glimepiride, Farxiga, Jardiance, Invokana then you should practise IF under medical supervision. IF in combination with certain blood glucose lowering medication can increase the risk of hypoglycaemia.

All things considered, fasting is an extremely effective and safe practice, with just a few consideration. This is especially true when we compare it to the western diet, which appears to be nose diving everyone into a cesspool of health issue — it should really come with a health warning, and maybe even a red, flashing beacon for good measure.

If you have any queries on whether or not fasting is for you, hope on over and book a consultation where we are happy to discuss any concerns.

Like what you’re hearing?

Stay tuned for more guides, to help you with your health journey.

If you’re interested in joining Span, download our mobile app on,contact us at , or book a consultation

Take care, 👋

I’m sure you’re curious about the science behind all this 🔬 Here are some recent medical publications about this topic:

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