What Are the Cons of Drinking Kefir? Your Guide to Potential Side Effects

December 15, 2025 •

4 min read

While often celebrated for its probiotic benefits, a study in the Journal of the American College of Nutrition highlighted concerns about kefir's insulinemic index. This highlights that despite its reputation, it is important to understand what the cons of drinking kefir can be for some people.

Quick Summary

Investigate the downsides of kefir, from temporary digestive issues like bloating and gas to significant health risks for immunocompromised individuals and those with specific sensitivities.

Key Points

Digestive Adjustment: Many people experience temporary bloating, gas, or cramps when first adding kefir to their diet.
Immunosuppressant Risk: Live cultures in kefir can pose an infection risk for individuals with compromised immune systems.
Hidden Sugars: Many flavored commercial kefirs contain high levels of added sugar, counteracting health benefits and affecting blood sugar.
Trace Alcohol: Kefir fermentation produces a small amount of alcohol, making it unsuitable for children, those sensitive to alcohol, or people in recovery.
Lactose and Allergy Issues: Kefir is not lactose-free and should be avoided by those with severe intolerance or dairy allergies, though lower lactose levels are tolerated by some.
Medication Interference: Kefir's live cultures can interact with certain medications, such as immunosuppressants.

Kefir has gained widespread popularity as a potent source of probiotics, offering numerous potential health benefits from improved digestion to enhanced immunity. However, the tangy, fermented beverage is not without its drawbacks, and it's essential for consumers to be aware of the potential cons, side effects, and risks associated with drinking kefir. What may be a health-boosting food for one person could cause significant discomfort or pose a health risk for another.

Initial Digestive Discomfort

One of the most common issues reported by those new to kefir is an adjustment period marked by digestive problems. The sudden introduction of a high number of live bacteria and yeast into the gut microbiome can overwhelm the system, especially if a person doesn't regularly consume fermented foods.

Common Gastrointestinal Symptoms

During this initial phase, people may experience a range of uncomfortable symptoms:

Bloating and gas: The fermentation of gut bacteria can produce excess gas.
Stomach cramps: Abdominal discomfort is a frequent complaint.
Diarrhea or constipation: Bowel changes are a reported side effect as the gut adjusts.
Nausea: Some individuals may experience temporary feelings of nausea.

These symptoms typically subside after a few days or weeks as the body adjusts. Health experts often recommend starting with a small amount of kefir and gradually increasing the intake to minimize these effects.

Risks for Vulnerable Populations

For the majority of healthy adults, kefir is considered safe, but certain individuals should approach it with caution or avoid it entirely. The live, active cultures that make kefir beneficial also carry risks for specific populations.

Immunocompromised Individuals

People with weakened immune systems, such as those undergoing chemotherapy, living with HIV/AIDS, or organ transplant recipients, are at an increased risk of infection from the live microorganisms in kefir. In very rare cases, probiotics have been linked to serious infections like sepsis. It is crucial for these individuals to consult a healthcare provider before consuming probiotic-rich foods like kefir.

Medication Interactions

Kefir can interact with certain medications. For example, the live bacteria and yeast can increase the chances of getting sick for those taking immunosuppressants. The trace alcohol content produced during fermentation also means that those taking medications like Disulfiram (Antabuse), used for treating alcohol dependence, should avoid it due to potentially unpleasant side effects.

Hidden Sugar and Alcohol Content

While plain, unsweetened kefir is relatively low in sugar, many commercial varieties come loaded with added sugars to improve palatability. This can negate many of the health benefits and pose a risk for certain individuals.

Concerns About Sugar and Alcohol

Diabetes: Those with diabetes must carefully read labels, as high added sugar content can negatively affect blood sugar levels.
Alcohol Content: Fermentation naturally produces a small amount of alcohol, typically between 0.5% and 2%. This is a consideration for children, pregnant women, recovering alcoholics, and people with alcohol sensitivity.

Comparison of Kefir Types


Feature	Plain Kefir	Flavored Kefir	Water Kefir
Sugar Content	Low, primarily natural milk sugars	High, with added sugars and flavorings	Can be low if unsweetened, but flavored versions can contain high added sugar
Alcohol Content	Minimal trace amounts	Minimal trace amounts, but can vary by fermentation	Minimal trace amounts, up to 2%
Lactose Content	Low due to fermentation	Low due to fermentation	Lactose-free, dairy-free
Primary Con	Initial digestive adjustment	High added sugar, insulinemic concerns	Possible high added sugar, slight alcohol content

Allergy and Intolerance Issues

Despite the fermentation process reducing lactose, kefir is not completely lactose-free and is not suitable for those with severe lactose intolerance or a milk protein allergy. Non-dairy alternatives, such as water or coconut kefir, are available but contain different probiotic profiles and may have their own downsides, like high added sugar.

The “Die-Off” Effect and Raw Milk Risks

For some, especially those with gut imbalances, introducing kefir can trigger a Jarisch-Herxheimer or “die-off” reaction. This is caused by a rapid clearing of harmful microbes, releasing toxins faster than the body can process them, leading to temporary flu-like symptoms. Additionally, homemade kefir made with raw, unpasteurized milk carries a risk of foodborne illness from harmful bacteria like Salmonella or E. coli. The U.S. FDA warns against unpasteurized milk for this reason.

Conclusion

While kefir is a nutrient-dense and probiotic-rich fermented food with many potential benefits, it is not a universally perfect product. The cons of drinking kefir include potential initial digestive distress, risks for immunocompromised individuals, unwanted sugar and alcohol content in commercial varieties, and allergy concerns. Being aware of these potential downsides, starting with small amounts, and choosing unsweetened options can help most people enjoy kefir safely. As always, those with pre-existing health conditions or concerns should consult a healthcare professional before making significant dietary changes. For further information on probiotics, the Mayo Clinic offers resources to help you decide if they are right for you.

Frequently Asked Questions

Yes, it is common to experience bloating, gas, and other digestive discomfort when first introducing kefir due to the high concentration of new probiotics in the gut. These symptoms usually subside as your body adjusts.

People with weakened immune systems, those with milk protein allergies, and individuals taking certain medications like immunosuppressants should avoid kefir or consult a doctor first. People with severe lactose intolerance should also be cautious with dairy-based kefir.

Yes, due to the natural fermentation process, kefir can contain a small amount of alcohol, typically between 0.5% and 2%. This is a consideration for children and those who avoid alcohol.

While fermentation reduces the lactose content, kefir is not completely lactose-free. People with mild lactose intolerance may tolerate it better than milk, but those with severe intolerance or dairy allergies should stick to non-dairy versions or avoid it entirely.

Many commercially flavored kefirs contain high levels of added sugar to mask the natural tartness. For diabetics or anyone monitoring their sugar intake, it's best to choose plain, unsweetened kefir.

The "die-off" effect, or Jarisch-Herxheimer reaction, is a temporary worsening of symptoms like fatigue, headaches, or flu-like feelings when harmful gut bacteria die off rapidly due to the introduction of probiotics.

Homemade kefir made from unpasteurized (raw) milk carries a risk of foodborne illness from harmful bacteria. It is important to use pasteurized milk and maintain high hygiene standards to ensure safety.

For most people, limiting intake to around one to three cups per day is recommended. Excessive consumption can increase the risk of digestive side effects. It's best to start with a small amount and monitor your body's reaction.