How long does it take for your intestinal bacteria to be replaced and how to check it

What is intestinal bacterial replacement?

The role and importance of intestinal bacteria

Gut bacteria play a very important role in our bodies. First, they strengthen immune function and increase our defenses against disease. For example, cases where people who are prone to catching colds have shown improvement in their health by consuming yogurt every day indicate that gut bacteria influence immunity. In addition, gut bacteria aid in the digestion and absorption of food, delivering necessary nutrients to the body. They are particularly involved in the production of B vitamins and vitamin K. In addition, improving the intestinal environment facilitates digestion, improves bowel movements, and has a positive effect on skin condition. It is due to these multifaceted functions that gut health is said to be directly linked to overall health.

Types of intestinal bacteria and their characteristics

There are three main types of bacteria in the intestines: good bacteria, bad bacteria, and opportunistic bacteria. They coexist in balance with each other. Good bacteria maintain a healthy intestinal environment, support the immune system, and aid in digestion and absorption. Bad bacteria, if overpopulated, can produce harmful gases and release harmful substances, contributing to poor health. For example, there are cases in which people who suffered from constipation began taking supplements containing lactic acid bacteria and found that their bowel movements improved. This suggests that good bacteria became dominant, leading to a healthy intestinal environment. Specific species of bacteria, such as lactic acid bacteria and bifidobacteria, that regulate the intestinal environment are also important. Opportunistic bacteria have the ability to become either good or bad depending on physical condition and the environment. An imbalance between these bacteria can have a negative impact on the entire body, so it is important to understand the types of intestinal bacteria and their characteristics.

How long does it take for gut bacteria to be replaced?

The replacement cycle of intestinal bacteria

Intestinal bacteria change daily, influenced by diet and lifestyle habits. It is generally believed that major changes in the composition of intestinal bacteria occur in about two weeks. This is because intestinal bacteria are constantly multiplying and dying, and their balance changes depending on the environment. For example, there are reports that people who had been binge eating and drinking changed the smell and shape of their stool two weeks after switching to a diet centered on Japanese food. The intestinal flora is reconstructed depending on which bacteria are favored by factors such as the type of nutrients and amount of dietary fiber.

Intestinal bacteria generally undergo cell division every 20 minutes to several hours, resulting in a relatively rapid generational change. Some bacteria colonize the intestinal mucosa and persist for a long time, while others experience temporary increases and decreases in abundance depending on diet. Factors that influence the intestinal environment include diet, intestinal pH, the condition of the intestinal mucosa, and interactions with the immune system. Research has shown that dietary changes have a particularly sensitive effect on the intestinal environment, with certain changes observed within 2-3 days and the composition settling into a relatively stable state within about 2 weeks.

Factors that influence turnover

The replacement of intestinal bacteria is influenced by various external and internal factors. For example, even within a family with the same diet, there are cases where the father, who is under a lot of stress, tends to suffer from constipation, while the mother, who is relatively relaxed, has good bowel movements. This shows that the intestinal environment is strongly influenced by stress and lifestyle habits.

It is also said that as we age, the number of good bacteria in the intestines decreases, and diversity also declines. The composition of bacteria also varies depending on genetic constitution, the structure of the intestinal mucosa, hormone balance, and the type of medication being taken. For example, people who use antibiotics frequently are more likely to have a decrease in good bacteria, which can lead to an unstable intestinal environment. On the other hand, young people and those who exercise regularly tend to have active intestinal metabolism and a smoother replacement of bacteria. In this way, the period and effectiveness of replacement vary depending on each individual’s background.

A time-based approach to improving your gut health

Changes and realizations in one week

Changes in your intestinal environment can begin to appear in as little as one week by reviewing your daily lifestyle habits. Paying attention to your daily diet and incorporating fermented foods and high-fiber vegetables can support the activity of beneficial bacteria. For example, many people report that eating natto and miso soup every day has improved their bowel movements. In this way, consciously leading a healthy diet will begin to lay the foundation for a healthy intestinal environment. It is also effective to record changes in your diet. Furthermore, by recording your daily bowel movements and abdominal bloating, you can avoid missing subtle changes and find the right improvement measures for you.

Changes in intestinal bacteria over two weeks

The two-week period marks an important milestone in the cycle of intestinal bacterial replacement. Even during this period, consciously consuming fermented foods and soluble dietary fiber can help create an environment favorable to beneficial bacteria. For example, it has been reported that consuming yogurt, kimchi, and amazake (sweet rice drink) for two weeks consistently resulted in clear changes in stool odor and volume. Furthermore, during this period, the types and balance of intestinal bacteria gradually begin to stabilize, making it easier to feel that your intestinal flora is in good condition. By referring to the latest research, you can learn which foods are best for you and expect more effective improvements. It’s a good idea to record any questions you have and use them as hints for the next step.

Changes in physical condition after one month

After one month of improving your intestinal environment, you can expect to see a variety of positive effects both inside and outside your body. Many people, in particular, experience improvements in their skin condition and sleep quality. For example, one case involved a person who had previously been prone to facial breakouts, who, after modifying their diet and continuing the practice for a month, saw their skin stabilize. The intestines and skin are so closely connected that they are sometimes referred to as the “gut-skin relationship,” and healthy intestinal flora improves skin health. It’s also important to review your lifestyle habits during this time, and paying attention not only to diet but also to exercise and sleep can further improve your intestinal environment. Seeking a doctor’s opinion can help you find a more accurate and personalized approach.

Sustained improvement after 3 months

By continuing to improve your intestinal environment for more than three months, the effects will be sustained and stable. By this time, the composition of your intestinal bacteria will be well established and less susceptible to changes in lifestyle. For example, there are cases where a person who suffered from chronic diarrhea and constipation found that after consuming fermented foods and dietary fiber for three consecutive months, their toilet visits stabilized and their daily life became significantly easier. While sustained effort requires skill, finding habits that work for you will make it easy to continue. Here, it’s important to look back at the improvements you’ve tried so far and identify which ones were effective. Doing so will help you see the path to maintaining a good intestinal environment in the future.

How to promote gut bacteria replacement

The relationship between dietary improvement and intestinal bacteria

Improving your diet is the most effective approach to promoting healthy replacement of intestinal bacteria. Fermented foods such as yogurt, natto, miso, and kimchi support the growth of beneficial bacteria and help balance the intestinal flora. For example, there are testimonials from people who have experienced relief from constipation after a month of eating a diet that combines yogurt and fruit for breakfast with natto and miso soup for dinner. Also important are foods rich in dietary fiber, such as vegetables and seaweed. These act as prebiotics, feeding beneficial bacteria and stimulating their activity. Furthermore, avoiding unbalanced diets and excessive animal fat intake and creating a nutritionally balanced menu can help improve and maintain your intestinal environment.

The relationship between exercise and intestinal environment

Moderate exercise has also been shown to have a positive effect on the activity of intestinal bacteria. Exercise stimulates intestinal peristalsis, helping to regulate bowel movements. For example, there are cases in which people who previously led desk-bound lives started walking in the morning a few times a week, and by the time the seasons changed, their bowel movements became more regular. Active intestinal movement also stimulates bacterial metabolism, regulating the rhythm of the intestinal environment. Combining diet and exercise can help stabilize the bacterial balance in the intestines more quickly. Even 30 minutes of light stretching three to four times a week is effective enough. Continuing to a reasonable extent is essential for intestinal health.

Stress management and gut bacteria

Stress has a significant impact on the intestinal environment. Long-term stress can disrupt the balance of the autonomic nervous system, reducing intestinal motility and potentially allowing bad bacteria to dominate. For example, some people who suffered from repeated constipation and diarrhea during periods of prolonged work stress found that their intestinal health stabilized after leaving work early just once a week to attend yoga classes, or, when they couldn’t attend, consciously incorporating relaxation techniques such as deep breathing while at work. Mental relaxation is closely related to the balance of intestinal bacteria, and combining it with fermented foods and ingredients containing oligosaccharides can be expected to produce even more effective improvements. Hobbies, exposure to nature, and good quality sleep are also effective ways to reduce stress.

Points to check for replacement of intestinal bacteria

Intestinal environment as seen from stool condition

Stool is like a mirror of the intestinal environment, and it most clearly reflects daily changes. The color, shape, and odor of stool reflect the balance of intestinal bacteria. For example, when good bacteria predominate, stool is yellow to light brown in color and has a mild odor. On the other hand, when bad bacteria increase, stool may become dark, hard, and have a strong odor. Frequent constipation or diarrhea are also signs of an unhealthy intestinal environment. Observing and recording the condition of your stool is important to ensure you don’t miss these changes. By keeping a record of your daily bowel movements and noting any unusual changes, you can easily understand the progress of your intestinal bacterial replacement. Observing your toilet habits is a simple yet highly effective self-check method.

Observe changes in your physical condition

Changes in the intestinal environment are reflected not only in the condition of your stool but also in your overall physical condition. In particular, skin problems, fatigue, and moodiness may be caused by imbalances in your intestinal bacteria. For example, one woman who began efforts to improve her intestinal environment about a month later reported feeling less irritable and waking up refreshed in the morning. The intestines are so closely connected to the nervous system that they are sometimes called the “second brain,” and their function affects mental health and concentration. When monitoring your physical condition, it is important to take a comprehensive look at your mood, skin condition, appetite, sleep, and other factors. If possible, keeping a record in a health management app or diary can help you identify trends. Getting medical tests, if necessary, can also lead to early intervention.

Frequently asked questions about gut bacteria turnover

The replacement of intestinal bacteria occurs in everyone

The replacement of intestinal bacteria is a natural phenomenon that occurs in basically everyone. However, the speed and degree of impact vary from person to person. Various factors, such as lifestyle, diet, age, genetics, and even contact with family members living together, affect the intestinal environment. For example, even family members who eat the same diet may exhibit differences in bowel movements and physical condition. This is because each person’s intestinal bacterial composition, intestinal mucosal condition, and immune response are different. Furthermore, an environment with a high concentration of bad bacteria can make it difficult to reconstitute the intestinal flora. By consciously incorporating good bacteria into your daily life, you can support natural replacement.

The effectiveness of supplements to promote cell turnover

Supplements can be used as a supplementary measure to improve the intestinal environment and help replace intestinal bacteria. Supplements containing probiotics and prebiotics are expected to promote the establishment of beneficial bacteria and restore intestinal balance. For example, one study reported that a person who suffered from constipation began to experience regular bowel movements after taking a supplement containing lactic acid bacteria for two weeks. However, the effectiveness of supplements varies greatly from person to person, depending on factors such as constitution, diet, and timing of administration. When using supplements, it is important to choose products from reliable manufacturers and verify scientifically based information. Furthermore, greater effectiveness can be expected by combining supplements with a balanced diet, exercise, and stress management rather than relying solely on supplements.

Summary

The replacement of intestinal bacteria is a natural cycle that is deeply connected to our health. Influenced by daily diet, lifestyle habits, and stress levels, bacteria constantly replace themselves in the intestines, maintaining a balance. The intestinal environment is something we “nurture.” Starting today, gradually adopting a diet and lifestyle that suits you will likely see changes in your physical condition and mood. Discover how to best interact with your intestinal bacteria and aim for daily health.

The Gut Flora Transplantation Clinical Research Group has already performed over 690 cases of “gut flora transplantation,” a new procedure that does not require antibiotics and places less strain on patients. We also offer intestinal flora testing to determine your own intestinal flora. If you are interested in the current state of your intestinal flora or in improving your intestinal environment, please feel free to contact your nearest clinic.

References

Liao W, Su M, Zhang D. A study on the effect of symbiotic fermented milk products on human gastrointestinal health: double-blind randomized controlled clinical trial. Food Sci Nutr. 2022;10(9):2947-2955. doi:10.1002/fsn3.2890
Wastyk HC, Fragiadakis GK, Perelman D, et al. Gut-microbiota-targeted diets modulate human immune status. Cell. 2021;184(16):4137-4153.e14. doi:10.1016/j.cell.2021.06.019
Oliphant K, Cruz Ayala W, Ilyumzhinova R, et al. Microbiome function and neurodevelopment in Black infants: vitamin B12 emerges as a key factor. Gut Microbes. 2024;16(1):2298697. doi:10.1080/19490976.2023.2298697
Zhang Y, Liu L, Wei C, et al. Vitamin K2 supplementation improves impaired glycemic homeostasis and insulin sensitivity for type 2 diabetes through gut microbiome and fecal metabolites. BMC Med. 2023;21:174. doi:10.1186/s12916-023-02880-0
Gu Y, Zhang W, Zhao W, Zeng X. Investigating causal relationships between the gut microbiota and inflammatory skin diseases: a Mendelian randomization study. Australas J Dermatol. 2024;65(4):319-327. doi:10.1111/ajd.14231
Zhang C, Zhang Y, Ma K, et al. Lactobacillus plantarum Lp3a improves functional constipation: evidence from a human randomized clinical trial and animal model. Ann Transl Med. 2022;10(6):316. doi:10.21037/atm-22-458
Bourdeau-Julien I, Castonguay-Paradis S, Rochefort G, et al. The diet rapidly and differentially affects the gut microbiota and host lipid mediators in a healthy population. Microbiome. 2023;11(1):26. doi:10.1186/s40168-023-01469-2
David LA, Maurice CF, Carmody RN, et al. Diet rapidly and reproducibly alters the human gut microbiome. Nature. 2014;505:559-563. doi:10.1038/nature12820
Ma L, Yan Y, Webb RJ, et al. Psychological stress and gut microbiota composition: a systematic review of human studies. Neuropsychobiology. 2023;82(5):247-262. doi:10.1159/000533131
Schwartz DJ, Langdon A, Sun X, et al. Effect of amoxicillin on the gut microbiome of children with severe acute malnutrition: a placebo-controlled trial. Lancet Microbe. 2023;4(11):e931-e942. doi:10.1016/S2666-5247(23)00213-6
Li J, Wu Y, Yang Y, et al. Metagenomics reveals an increased proportion of an Escherichia coli-dominated enterotype in elderly Chinese people. J Zhejiang Univ Sci B. 2025;26(5):477-492. doi:10.1631/jzus.B2400341
Couvert A, Goumy L, Maillard F, et al. Effects of a cycling versus running HIIT program on fat-mass loss and gut microbiota composition in men with overweight/obesity. Med Sci Sports Exerc. 2024;56(5):839-850. doi:10.1249/MSS.0000000000003376
Casertano M, Dekker M, Valentino V, et al. GABA-producing lactobacilli boost cognitive reactivity to negative mood: a double-blind placebo-controlled cross-over study. Brain Behav Immun. 2024;122:256-265. doi:10.1016/j.bbi.2024.08.029
Vaughn BP, Fischer M, Kelly CR, et al. Effectiveness and safety of colonic and capsule fecal microbiota transplantation for recurrent Clostridioides difficile infection: a multicenter cohort study. Clin Gastroenterol Hepatol. 2023;21(5):1330-1337.e2. doi:10.1016/j.cgh.2022.09.008