Does fasting harm your gut microbiome?
Fasting is something I've done since my teens, and recently it's become popularised. Great (as long as you do your research and do it properly).
But what does it do to the health of your gut and microbiome – those healthy flora we need because our cells are only 10% human, and the bacterial cells that live in us and are mainly found in our gut?
The answer is not simple, and we simply haven't done enough research yet.
Certainly, how long and often you fast can impact the health of your microbiome, and everyone's microbiome is unique so it may respond differently.
Two things stand out though
Radical change to your diet is quickly reflected in your gut microbiome. Even a short term diet can alter the composition and population of your gut microbes, so it's thought that fasting likely does too. We know that long-term dietary restriction such as the low FODMAP diet creates low diversity. This could be important as good diversity directly correlates to better health. On the other hand, studies done after Ramadan have found increased levels of some beneficial gut bacteria and butyrate (provides gut immunity and integrity), so fasting could be helpful. Another point, if you’re not needing some microbes e.g. you’re carnivore and you don’t need microbes to break down plant foods, this may not be a problem. Consider the Inuit and other cultures who didn’t have access to plant foods.
We also know that fasting can be gut healing. Just 24 hours of water fasting releases stem cells into your gut. These heal the inner mucosal lining (sitting behind your gut wall), which may have been damaged by antibiotics, birth control and low stomach acid. Fasting can also help heal SIBO (small intestinal bacterial overgrowth), a nasty gut infection, IBS and gut autoimmune conditions.
Of course the health of your microbiome also depends on what you eat when you consume food. Fibrous foods like vegetables and fruits, whole grains and legumes (if you can/do eat them), and healthy fats feed your gut microbiome, while processed foods do not.
These decide whether you have a healthy balance of the two necessary bacterial kingdoms we have in our gut i.e. Firmicutes, which is higher in inflammatory conditions like diabetes and obesity and is common with diets higher in sugar and refined carbs, and Bacteroidites, which grows with a diet that includes healthy proteins and fats.
Either way, don't forget the other benefits of fasting include weight loss, better metabolism (blood sugar and fat burning), increased growth hormone, improved neurotransmitter health, hormone balance and more.
So should you fast?
It could be a powerful tool for you. Listen to your body, and when you're not fasting, give your good gut lots of love!