Benefits of Fasting

Fasting can be a beneficial way to give your body a reset and clear that backlog of excesses. However, it is nuanced and it is important that you do this safely. Over the holidays, I like to implement slightly longer overnight fasts to keep my blood sugar in check (more below). 

As always, this article is for education only - always check with your own healthcare provider before undertaking a fast. 

There are many different types of fasts: 

  • Intermittent fasting where you eat within a certain time window. And under this umbrella, there are many different types - 5:2, 16.8, overnight. 
  • Juice fasting where you only drink juice and give your digestive system a rest
  • Water fasting where you only consume water - involves a drastic reduction in calories and requires medical supervision. 

In my opinion, most people would benefit from having a window in their day with no food. How long that window is and what time of day this window should occur varies depending on your health status. 


But first - Why is a window without food helpful? 


1) It allows the gut to rest and this activates something called the Migratory Motor Complex which is a fancy way of saying "getting the gut moving" - think of it as the street sweeper that moves our gut along and cleans it out - very important and often impaired in conditions like SIBO (small intestinal bacterial overgrowth).


2) It allows your blood sugar and insulin to return to a normal level - this is beneficial for our metabolic health and can help some people lose weight - particularly if you have insulin resistance, pre-diabetes, leptin resistance (insulin is a fat storage hormone - a constantly high insulin level signals your body to store fat). 


However, here are some caveats to consider:


  • Studies have shown if you consume most of your food earlier on in the day, your blood sugar response is more stable throughout the day vs if you consumed food later in the day. For this reason, I always eat breakfast, and if I was to skip a meal - it'll usually be dinner. There has also been suggestions that skipping breakfast may be associated with a higher risk of gallstones in women. Everyone is different, and this may not apply to you - but this is what the data currently shows.   
  • Anyone with hormone imbalance, particularly thyroid or HPA axis dysfunction (some people like to call it 'adrenal fatigue'), or already has irregular periods (unless overweight), needs to be extra careful with fasting. Essentially, fasting puts stress on the body. It is signaling to the body that food is scarce and to start conserving energy. Depending on your health status, the body may then temporarily turn down thyroid function - so it is possible prolonged fasting can alter thyroid and adrenal function, as well as sex hormones (a recent study showed it lowered DHEA in postmenopausal women - so if you have hormone issues, definitely check with your doctor first as fasting may impact sex hormones) - this is where individuality is so important. Fasting may help some women, but it may not be good for others. 


  • if you are wanting to conceive, are underweight, are pregnant, breast-feeding, or have an eating disorder - fasting is not a good idea. 

What do I do? 


I love Circadian Rhythm Fasting with a 12-hour fasting window. I do this most nights, and over the holidays, if I've overindulged and feel sluggish, I may extend this to 14-15 hours for a day. 

This is when you eat within a 10-12-hour window, and fast for 12-14 hours, but time it with your body clock - i.e. you eat during daylight hours and stop eating when the sun goes down. 


In a small human study conducted by the Salk Institute, participants ate in a 10-hour eating window, with a 14-hour break. After completion, all participants reported better sleep and decreased blood sugar levels, blood pressure, cholesterol, and less body fat. 


An example might be breakfast at around 7AM, lunch around 1PM, and dinner around 5PM. And then there's no food (water and herbal tea without sweetener are ok) - until your breakfast the next day.


This is a lot easier to do for most people, and also leaves plenty of time for your body to digest your food before you sleep, thus improving the quality of your deep sleep - something that plays a key role in satiety and hunger signaling too. 


Gut health


It has been suggested  that our microbiome has a body clock too - i.e. some friendly bugs are active during the day and some at night; they have different functions. Although a lot more research is needed, we know that our gut microbiome is involved with digestion and calorie extraction. This may be one reason why intermittent fasting can aid with weight management and gut health, and why it is better to consume most of your food earlier on during the day when you are more insulin sensitive. 


So… in summary - I think we can all benefit from giving our bodies a break from eating.


If you are feeling the holiday excesses, taking a 12-13 hour food-free break can be beneficial (make sure you stay hydrated). 


Now if you want to dive deeper into the science of fasting - read more below!

Caloric restriction has both been shown to significantly extend lifespan and reduce chronic disease in many organisms from fruit flies to mice. It is proposed that when an organism undergoes calorie restriction, it kicks into survival mode during which it starts to conserve energy, become efficient, and get rid of that which not longer serves its purpose i.e. a process called autophagy.

Autophagy is a process by which the body gets rid of non-functioning or abnormal cells, and in doing so, prevents diseased cells from proliferating out of control. It is not the calorie restriction itself that provides the benefits of fasting, however.

Research is pointing to the fact that it is mainly during the re-feeding phase that the benefits and cellular regeneration occurs e.g. studies have shown for example an increase in peripheral stem cells in the re-feeding phase. You also get processes like mitochondrial biogenesis (new mitochondria being made inside the cells during the re-feeding phase, which can lead to better energy production.

Fasting also gives our overworked digestive tracts a little break. When the gut is busy digesting food, it uses a lot of energy and cannot repair itself. So when you take a break from food, the digestive tract has a chance to now repair itself.

Studies have demonstrated that fasting can increase beneficial bacterial strains like Akkermansia in our gut and improve microbiome diversity and thus gut health. Akkermansia has been shown to be correlated with our metabolic health, and may play a role in preventing obesity. When we fast, our insulin levels drop – this then allows the body to tap into the fat stores and burn fat as energy. It is very difficult for the body to burn fat when insulin levels are high (e.g. in patients with type 2 diabetes).

Also, as discussed above, fasting can improve our gut microbiome diversity and we know that the microbiome plays an important role in how our food is digested and handled, and this may also explain why fasting can improve metabolic health.

Other benefits of fasting may also include lower blood pressure, lower cholesterol, and a reduction in IGF-1 (a hormone in our body that has been correlated with increased risks of certain cancer and diabetes when high). If you want to try fasting, make sure you do so safely – and remember, the food that you nourish the body with after a fast is just as important as the calorie restriction itself. So make sure you follow a fast with a healthy, whole food plant-based diet to gain the maximal benefits.