The Impact between Monounsaturated Fatty Acids and Saturated Fatty Acids on Bile when Fasting

The Impact between Monounsaturated Fatty Acids and Saturated Fatty Acids on Bile when Fasting


Too long fasts when in a very high cholesterol situation can lead to gallstones. Switching to a higher carb diet without bringing down cholesterol levels can be even worse, quicker.

Table of contents

Yes, monounsaturated fatty acids (MUFA) and saturated fatty acids (SFA) can affect the bile acid pool size differently, largely due to how they influence cholesterol metabolism and bile acid synthesis. These issues need to be taken into consideration by keto-based eaters and especially by aggressive high-fat dieters like carnivore-based eaters. However, bile flow in general is something that affects every faster, regardless of diet.

Saturated Fats (SFAs) are typically found in animal products like meat, butter, and cheese, as well as some tropical oils such as coconut oil.

Monounsaturated Fats (MUFAs), on the other hand, are primarily found in plant-based oils like olive oil, nuts, and avocados.

Cholesterol Saturation in Bile:

SFA: Saturated fatty acids, commonly found in animal fats and some tropical oils, can increase the concentration of cholesterol in bile. A diet high in saturated fats is associated with an increased risk of gallstone formation due to increased cholesterol secretion into bile, which can lead to supersaturation and potential stone formation.

MUFA: Monounsaturated fats, like those found in olive oil, nuts, and avocados, are generally associated with healthier serum cholesterol levels. Diets high in MUFA are linked to better lipid profiles and may reduce cholesterol saturation in bile. This can result in a more favorable bile composition, potentially reducing the risk of cholesterol gallstone formation.

What does this mean for fasting? Too long fasts when in a very high cholesterol situation can lead to gallstones. Switching to a higher carb diet without bringing down cholesterol levels can be even worse, quicker. Insulin increases cholesterol creation. (See why diabetics usually have messed up high cholesterol?) Fasting is a bile stagnation event, and why liver flushes are recommended before a fast. For someone in a high cholesterol situation, you may benefit most from a quicker return to a regular high-fat diet, but this becomes more and more dangerous the longer you fast (by allowing excess cholesterol to precipitate while bile shuts down). 

Effect on Bile Acid Synthesis

SFA: Saturated fats affect the synthesis of bile acids themselves but the effect increases with dietary cholesterol.

MUFA: Monounsaturated fats encourage bile flow, but don't increase bile pool size as much as saturated fats. This could also help in reducing cholesterol levels in the bile, thereby decreasing the risk of gallstones.

What does this mean for fasting? Monounsaturated fats are preferred when preparing and refeeding early on as you transition to more saturated fats. We want the bile flow to resume first. Kefir and Fish are powerful sources of monounsaturated fats for the early refeed. Kefir also plays the role of a gut bacteria supplement which is critical. The next step would be Coconut fat and cacao butter as you continue the progression towards animal fats. If you come from a vegetarian low-fat-focused diet, your bile pool size is already low, so the impact is not as drastic or something to worry about, but even then bile flow should be something you attempt to correct afterward.

Bile Pool Size and Gallbladder Function

SFA: High intake of saturated fats can lead to larger bile pool sizes due to both increased cholesterol content, but this can also contribute to bile stasis and gallstone formation if the gallbladder does not contract efficiently.

MUFA: By potentially increasing bile acid synthesis and reducing cholesterol content, MUFAs might support a more functional bile pool size and better gallbladder motility, promoting regular emptying and reducing the risk of gallstone formation.

What does this mean for fasting? Returning to a regular diet may be important, especially for keto-based eaters. Bile Pool Size needs to return to a closer representation of pre-fast pool size because this is the current body adaptation. If you want to lower cholesterol it is important to gradually change the diet, instead of drastically, which lowers the risk of liver and gallbladder injuries. Saturated fats increase pool size more effectively than monounsaturated, and one of the best ways to do this while limiting cholesterol is through coconut fat and/or cacao butter. (no cacao for people with chronic illnesses, so you would want to make sure it is pure cacao butter)

is it that saturated fats increase cholesterol, or is it that saturated fats are accompanied by dietary cholesterol?

It's both: saturated fats can independently increase cholesterol levels by stimulating the liver to produce more LDL cholesterol, and they are often found in foods that are also high in dietary cholesterol, contributing further to cholesterol levels. However, effects can vary by type of saturated fat. For instance, coconut oil, which is high in saturated fat but primarily in the form of medium-chain triglycerides (MCTs), may not raise cholesterol levels to the same extent as other saturated fats. This could explain the observed lower incidence of gallstones in diets high in coconut fat, suggesting a more complex relationship between different types of saturated fats and cholesterol metabolism.

What about some people who claim you can jump back in by eating fatty cuts of meat?

We don't have enough information on this, but the possible mechanisms include a different microbiome composition, bile pool size, and body adaptation. It is definitely one of the fastest ways to restart the bile mechanisms, but without good information, the question arises – "At what cost?" Keep in mind that low-carb eaters have impaired glucose metabolism, which means they most likely go hyperinsulinemic very quickly when carbs are introduced, further increasing cholesterol levels. In this case, you'll feel worse refeeding with carbs compared to someone who has a healthier glucose metabolism.

Yannick Wolfe

15 Years of Fasting Experience, Ex-ME/CFS, Ex-Long covid. Tech Consultant, Molecular biologist, Father, Researcher, Experimenter.

Join Our Discord

Discuss All Things Fasting With Other Beginners and Advanced Dry Fasters.

Medical Advice Disclaimer

This website does not provide medical advice. No material on this site is intended to be a substitute for professional medical advice, diagnosis, or treatment. The information, including but not limited to, text, graphics, images and other material contained on this website are for informational purposes only.

Always seek the advice of your physician or another qualified healthcare provider with any questions you may have regarding a medical condition or treatment before undertaking a new healthcare regimen.

Never disregard professional medical advice or delay in seeking it because of something you have read on this website.