Intermittent Fasting and Gut Health

What is intermittent fasting?

Intermittent fasting (IF) is an eating pattern that cycles between periods of fasting and eating.  It doesn’t specify which foods you should eat but rather when you should eat them.  A common intermittent fasting method involves daily 16-hour fasts.  The 16/8 method involves restricting your eating to certain times of the day such as 12pm-8pm or 1pm-9pm.

What happens to your body when you are fasting?

When you fast, several things happen to your body.  When we fast, the body does not have its usual access to glucose, forcing the cells to resort to other materials to produce energy. As a result, the body begins gluconeogenesis, a natural process of producing its own sugar. The liver helps by converting non-carbohydrate materials like lactate, amino acids, and fats into glucose energy. Because our bodies conserve energy during fasting, our basal metabolic rate becomes more efficient. 

Benefits of Intermittent Fasting:

There have been many studies done on IF in both animals and humans.  Studies have shown that it can have powerful benefits for the health of your body.  Studies show these are some of the benefits of intermittent fasting:

  • Weight loss: IF has shown to help with weight loss without having to consciously restrict calories.
  • Insulin resistance: IF can reduce insulin resistance, lower blood sugar, and fasting insulin levels which can protect against type 2 diabetes.
  • Inflammation: Studies show reductions in markers of inflammation.  Inflammation is a key driver of many chronic diseases.
  • Heart health: IF may reduce risks of heart disease by lowering LDL cholesterol and triglycerides.
  • Cancer: Animal studies suggest that IF may prevent cancer.
  • GI function: IF can change the makeup of your microbiome.  IF promotes white adipose browning and decreases obesity by changing the gut microbiota.

Intermittent Fasting and GI Health

We are just starting to understand how intermittent fasting may impact gut health and microbiomes, and how this may in turn explain some of the health benefits of going without calories for extended periods of time on a regular basis. Scientific research, mostly in animals, is showing that intermittent fasting may restore microbe diversity in the gut and increase tolerance against “bad” gut microbes.

IF has a large impact on gut diversity.  IF leads to increased diversity in the microbiome with a higher percentage of good bacteria.  These good bacteria release fermentation byproducts like lactate and acetate.  Lactate and acetate increase fat metabolism and muscle mass and reduce glucose intolerance in the liver.  They are short chain fatty acids produced by fermentation in the gut of complex carbohydrates.  Intermittent fasting could further promote the health impacts of a diet high in fiber and complex carbohydrates by preparing our gut microbes to ferment these products into fat browning signals.

In terms of the gut, it’s less about where your calories come from and more about giving your digestive system a break.  We are hosts to bacteria, fungi, protists, etc. in our gut.  Our daily habits affect their living environment, and like all living things, your gut needs rest too!  Some early research studies indicate that an extended fasting period can let our guts rest and restore the integrity of our intestinal walls.  This may be especially important to protect us against a “leaky gut.”

Our bodies operate on a 24-hour cycle that affects sleep, hormones, body temperature, and other functions.  Our bodies switch from metabolizing sugars during waking hour to fats overnight while we are sleeping.  Those who maintain time-restricted feeding that aligns with their circadian rhythm are more resilient to metabolic diseases mostly because of a change in microbiome composition.  

More research is needed on the interplay of calorie intake, meal frequency and timing, nutrient modifications and the microbiome on human biomarkers of health. But so far, there’s reason to believe that meal timing, diet and the microbes in our guts will play an important role in gut health.  

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