Good Gut Bacteria and the Body’s Immune Defence
I’m often asked what’s the best thing I can do for myself to ward off infection during the cold and flu season. While supporting a healthy gut microbiome is often part of my answer, the question assumes a simplistic reply. In reality, there are several fronts to pay attention to when reducing infection risk and supporting immune function.
Rarely do people want the full set of possibilities for protection. So, rather than overwhelm someone with a long response, I generally explain the body’s main lines of immune defence and the practical ways to support them.
The Body’s Defences
Our bodies have multiple layers of defence. In simple terms, infection risk depends on exposure plus the strength of your barriers and immune response. This helps explain why one person in a household can be sick while others exposed to the same “bug” may not develop symptoms.
First defence: skin barrier
Your skin is a major physical barrier. Basic hygiene still matters, especially hand washing, because it reduces the chance that microbes reach your nose, mouth, eyes, or food. This remains one of the simplest, highest-impact habits to reduce infection spread.
Second defence: gut microbiome
If microbes enter through the mouth or nose and make their way into the body, they interact with the digestive tract and its immune tissues. The gut is home to trillions of microorganisms (bacteria, viruses, and fungi) that live alongside us. This community helps with digestion and also interacts with immune signalling and the gut lining.
In early life, Bifidobacterium species are often prominent. In adulthood, many species can be common, and the overall balance varies widely between individuals. Rather than thinking in terms of a single “good” strain, it is more accurate to think in terms of an ecosystem that can be supported through diet, lifestyle, and (in some situations) targeted supplementation.
Bacterial Flora in the Gut
The gut microbiome is highly active. Different organisms tend to be more common in different parts of the digestive tract, and the large intestine generally contains the greatest density and diversity. Some probiotics used in supplements and fermented foods include strains from the Lactobacillus and Bifidobacterium groups, but “which strain helps” depends on the goal and the person.
These organisms may support health by:
- supporting digestion and nutrient processing, including lactose digestion for some people
- supporting the gut lining and normal immune signalling in the digestive tract
- producing or helping the body access certain vitamins (including some B vitamins) in some contexts
- supporting bowel regularity for some people
When the balance in the gut shifts (for example after illness, major dietary changes, or antibiotic use), some people notice digestive symptoms such as bloating, altered bowel habits, or discomfort. These symptoms can have many causes, so persistent or severe symptoms should be assessed rather than assumed to be a “probiotic deficiency.”
Probiotics are live microorganisms intended to have health benefits, but effects vary by strain and condition. They are not risk-free, and rare serious infections have been reported in vulnerable populations.
Replenishing Good Bacteria
It can be helpful to support beneficial gut microbes while discouraging overgrowth of less helpful organisms. In most people, the foundation is diet and routine. Probiotics are sometimes used as an adjunct, particularly after antibiotics or during specific digestive complaints, but the evidence is mixed and depends on the exact strain and purpose.
As seasons change, people often look for simple immune-support strategies. If you choose to use probiotics, treat them as one possible tool rather than a stand-alone shield against infection.
Some germs in the environment are antibiotic-resistant, and modern stress, poor sleep, and highly processed diets can coincide with digestive issues. That does not mean probiotics are required for everyone. If you are immunocompromised, have a serious underlying illness, or are caring for a premature infant, seek medical guidance before using probiotic supplements.
Probiotic products often list the strain(s) (not just the species), a viable count, and storage instructions. The following are examples people ask about, but they are not a substitute for medical advice or an individualized recommendation: UltraFlora Plus (Metagenics), Culturelle, Trenev’s Trio (Natren).
People often ask why they cannot just eat yogurt. You can. Fermented foods may be a practical option for many people. The key limitation is consistency and strain specificity. Some yogurts contain live cultures; others contain very low amounts by the time you eat them, and the strains may not match the outcomes people are seeking.
For overall health, basic hygiene, hydration, sleep quality, and diet quality usually deliver more reliable benefits than any single supplement. If you want the “most bang for the buck” approach, start there, then treat gut support as an additional layer rather than the entire strategy.