Probiotics and Fasting

Written by: Kari Raman, PharmD, RPh
Published July 11, 2023

As a pharmacist, I’ve noticed a surge in questions from patients about the correlation between fasting and probiotics; patients want to know if they can take probiotics while fasting, and if so, when? 

So, like most pharmacists would do, I turned to the medical research to see what the evidence says. Both fasting and probiotics are not like a drug that you’d fill at the pharmacy counter after getting a prescription from your doctor – there is less scientific evidence around diets and supplements. But, thankfully, I was able to dig up some interesting research that should help you understand how the two health strategies can work together. 

Fasting, a dietary practice that has been around for centuries and includes the restriction or complete abstention from food and drink for a set period, is becoming increasingly popular for its potential health benefits. Along with this, probiotics have been making a name for themselves for their role in promoting gut health and overall well-being. As it turns out, your gut microbiome impacts your gut and general health in ways that are profound – and still being understood. 

We need to dive deep into the science of fasting and probiotics to tease out how the two might interact. So, let’s explore this interesting, and somewhat complex, area of research. 

Understanding Fasting and its Health Benefits

Fasting can take different forms: intermittent fasting, time-restricted eating, periodic fasting, and prolonged fasting, among others. Regardless of the type, the goal remains the same: to give the body a break from food intake, allowing it to focus on other processes and sources of energy. For example, Melinda Gong, RD CDCES CSOWM, a registered dietitian at UC Davis Health, says in an article on the University of California at Davis’ website that, “The idea behind intermittent fasting is that by restricting food, our bodies will more quickly and efficiently tap our fat stores for energy. While glucose from carbohydrates is our most direct fuel source, we burn fat for energy when glucose isn’t available.”

There are many potential health benefits talked about in medical research with this diet strategy. These include weight loss, improved metabolic health, enhanced brain function, and even longevity. However, I’m not going to dig into each of these health claims, as it would take an entire website just dedicated to the topic to really tease out which are strongly supported by science and which are less likely. That being said, it does seem like people who are good at following a fasting schedule are able to lose weight. 

The effects of fasting on the gut microbiota – the community of bacteria, viruses, and fungi that reside in your gut – are just beginning to be understood and are a critical piece to the fasting-probiotic relationship.

Probiotics 101

Probiotics are beneficial bacteria, yeasts and fungi that live in your gut, many of which are also found in certain types of food and supplements. They work in numerous ways to boost your health, including aiding digestion, improving nutrient absorption, supporting immune function, and even possibly enhancing mental health.

Not all probiotics are the same, and their effects can depend on the specific strain, dosage, and individual health status. The most commonly recognized, and most researched, probiotics include Lactobacillus and Bifidobacterium species, although many others exist. As with L. acidophilus, these beneficial microbes have varied effects and potential health benefits.

If you are taking these supplements, I recommend taking them at the same time everyday. And, I’ve read up a lot on if you should or should not take them with food; the research isn’t super strong, but seems to indicate that an empty stomach is best because you’ll have the lowest acidic levels, which will help the supplements survive and colonize your gut. 

The Intersection of Fasting and Probiotics

The relationship between fasting and probiotics is a fascinating area of research. Emerging evidence suggests that fasting can modulate the gut microbiota, which could enhance the benefits of probiotics or influence how they work. 

Fasting, Gut Health, and Probiotics

A potential beneficial cycle has been proposed: fasting can induce changes in the gut microbiota, enhancing its diversity and abundance of beneficial bacteria. This altered gut environment may then be more conducive to probiotics, enhancing their colonization and impact on gut health. This study looked at a small group of prediabetic people who were put on a fast and given probiotics; it seems that the two interventions did succeed in changing the participants gut microbiome. 

In turn, a healthier gut microbiota may improve the body’s response to fasting, possibly enhancing its health benefits. However, these findings are preliminary, and more research is needed to establish this potential symbiotic relationship.

Fasting and Probiotic Supplement Timing

More research is required to establish optimal timing and delivery methods for probiotics during fasting. However, I recommend taking probiotics on an empty stomach, often before bed, so this likely works well for most fasting programs. 

Some doctors propose that taking probiotics in the evening might be more beneficial due to the heightened activity of the gut microbiome during this time. Additionally, the likelihood of having a bowel movement at night is lower, reducing the chance of expelling the supplement prematurely before it can exert its beneficial effects. Finally, acidity levels are lower in the evening. 

However, it’s always advisable to adhere to the guidelines given by the supplement manufacturer or your healthcare provider regarding the optimal time and dosage for your probiotic supplement. And asking your doctor is always a good idea. 

Is it Safe to Combine Fasting and Probiotics?

For most healthy individuals, combining fasting and probiotics should be safe and potentially beneficial. This is one of the main questions I get on combining these two health strategies. However, as fasting is a significant dietary modification, it should be undertaken with care and under the supervision of a doctor or medical professional, not a pharmacist blogger on the internet. 

Potential side effects could include fatigue, dizziness, or nutrient deficiencies, particularly with more extended periods of fasting or for those with specific health conditions. Probiotic side effects are generally mild and can include gas, bloating, and changes in bowel habits.

As always, it’s crucial to consult with a healthcare professional before starting any new dietary practices, including fasting and probiotic supplementation, especially for those with underlying health conditions or those on medication.

Ultimately, the connection between fasting and probiotics is a vibrant, emerging area of research. There seems to be a potential synergistic relationship, but more research is needed to fully understand the effects and benefits.

I encourage my patients to remain curious, ask questions, and keep up to date with new research. Always prioritize a balanced diet and healthy lifestyle, and consult your doctor before making significant dietary changes. 

Other questions

Does taking a probiotic break fasting?

The concept of “breaking a fast” primarily pertains to the consumption of food or beverages that contain calories, which would prompt the body to exit the fasting state and begin the digestive process. The primary objective of fasting, such as intermittent fasting, is to give the digestive system a break and trigger specific metabolic pathways.

Probiotic supplements, on the other hand, are typically calorie-free and don’t usually contain macronutrients like proteins, carbohydrates, or fats that the body could use for energy. Therefore, in the strictest sense, taking a probiotic supplement wouldn’t technically “break” a fast in the way that eating food or drinking a caloric beverage would.

Can I take probiotics while fasting?

Yes, you can take probiotics while fasting. 

Probiotics are generally considered safe to consume during a fasting period. They are typically low to no calories and don’t significantly stimulate metabolic processes or digestion, which means they won’t disrupt your fasting state. It’s generally safe and potentially beneficial to take probiotics during a fast, individual responses can vary, and it’s always a good idea to consult with your healthcare provider or a registered dietitian to figure out the best regimen for you.

Remember, whether fasting or not, consistency is key with probiotics, so find a routine that fits best with your lifestyle and stick to it. And keep in mind, every individual’s gut microbiome is unique, so what works best for one person may not work as well for another. 

Does fasting hurt the microbiome?

Research is still emerging, but suggests that fasting does not hurt a person’s microbiome. In fact, some studies have found an increase in healthy bacteria during a fast. Intermittent fasting, for instance, has been found in some studies to positively affect the gut microbiota. This type of fasting, which involves cycles of eating and fasting within certain time frames, can lead to increased diversity of gut bacteria – generally considered a sign of a healthy gut. Additionally, some research suggests that intermittent fasting might increase the abundance of beneficial bacteria, which can enhance gut barrier function, improve metabolic health, and reduce inflammation. This research is still emerging, but it doesn’t seem that you are going to hurt your gut, if you are otherwise healthy.

Some of my other gut health articles

I’ve written a lot about gut health and the microbiome, and how supplements can help. Read up on some of my other articles:

Constipation: One of the most common digestive issues many patients at the pharmacy face is constipation. It can be caused by a variety of factors ranging from diet to stress. Dive into my comprehensive guide on constipation to get a better grasp on its causes, symptoms, and potential solutions.

Diarrhea: Diarrhea, on the other hand, is another challenge that can disrupt daily activities. Whether it’s due to an infection, certain medications, or other underlying conditions, it’s vital to address the issue promptly. Our in-depth article on diarrhea provides a thorough look into its causes and offers advice on restoring balance to your digestive system. And I’ve reviewed two of the most commonly used probiotics when you are taking antibiotics to try to prevent diarrhea, Florastor and Culturelle.

How to take them: So, you’d be surprised at the conflicting advice out there on when it the best time to take a bacterial supplement. I dug into the research and wrote my article on the best time of day to take them, and also wrote up an article on how long they take to work. And, sometimes you forget to take your supplement for a few days – or you don’t like how they are making you feel. So I get asked how long they stay in your system. Or I also get asked how many you can take or if you can combine them.

Pharmacist Kari Raman

I’m Kari Raman PharmD, RPh, and I am a licensed, practicing pharmacist. I hold a Doctorate in Pharmacy from The University of the Pacific, and I’ve served patients in retail, compounding and hospital pharmacies.

Probiotics are confusing!

One of the most common questions I get asked by patients is about probiotics. And the truth is, probiotics are not as well understood by the healthcare community as they should be.

So I’ve been reading a lot of probiotic clinical trials, and sharing what I’m learning here.

I hope Pharmacist Probiotics helps you find out if there is a type of probiotic that works for you!