The small intestine: Your primary line of defense

November 22, 2025

Healthcaretoday, Dr Kheng Kien Soo, Clinic Dr Kheng, probiotics, Gut Health, microbiome, digestive health, Lactobacillus, bifidobacteria, gut flora, Healthy Gut, digestion, intestinal health, beneficial bacteria, Microbiome Balance, probiotic supplements, health and wellness, gut brain axis, prebiotics,

By Dr Kheng Kien Soo, Family physician,
anti-ageing /aesthetician;
Clinic Dr Kheng,
Kota Kinabalu, Sabah

Your small intestine is not only the area where most food digestion take place, it is also where any harmful bacteria that have survived their travels through the stomach arrive next.

The upper parts of your small intestine, the duodenum and jejunam, are sparsely populated, the transient (travelling) bacteria stay in the gastrointestinal tract for a relatively short time.

However, further down in the ileum there is a varied and permanent population of organisms. The types of bacteria found here include Streptococci, small amounts of Bacteroides, a variety of yeasts and enterobacteria, some of them are harmful; Bifidobacteria, a friendly neighbour that lives primarily in the large intestine, and lactobacilli. Lactobacilli acidophilus is the most important of the friendly bacteria that live in your small intestines.

The Lactobacilli family
Lactobacilli acidophilus, L.bulgaricus, and L.casei are all beneficial members of the Lactobacilli family.

By far, the most important bacterial resident of your small intestine is L.acidophilus. This is colonizers, constitutes your first line of defense against alien invaders, as well as opportunistic organisms like yeast, which can spread when the defense forces are weakened.

In the large intestine
The large intestine is primarily an anaerobic environment, no oxygen is present. This area of your gastrointestinal tract is where the highest concentration of bacteria is found.

When the beneficial friendly bacteria are present in sufficient numbers in the large intestine, very little putrefaction occurs and waste matters passes through in a timely fashion.

However, numerous problems arise when there aren't enough beneficial bacteria. You usually harbour the same total number of bacteria in your large intestine, but ratios of various groups can shift disastrously. Bad bacteria can multiply and attach themselves to the intestine walls, crowding out the defenders. Also, bacterial infection such as ulcerative colitis, become a real possibility when the levels of beneficial bacteria fall.

Bifidobacteria
The friendly Bifidobacteria found in large intestine include Bifidobacteria bifidum, Bifidobacteria longum, and Bifidobacteria infantis.

When Bifidobacteria are present in sufficient strength, they compete ferociously for both nutrients and attachment sites along the intestinal walls.

Another way Bifidobacteria protect themselves is by producing acetic and lactic acids, which create a hostile environment for dangerous microbes that require an alkaline atmosphere. Bifidobacteria also thrive happily without oxygen, so the aerobic bacteria that need to "breathe" cannot survive passage through this area.

In addition, they act against certain harmful bacteria lurking in the region and prevent them from altering nitrates into nitrites, which are known cancer causing agents.

The beneficial bacteria that inhibit your gastrointestinal tract are absolutely essential to your health and well-being. Without strong and viable colonies of both Lactobacillus and Bifidobacteria, your body will lose the all-important services of these first-line defenders.

Probiotics powders or capsules?
Probiotics supplements are available in a number of forms, the two most popular being capsules and freeze-dried powder. As a consumer, there are a few bits of information that can help you to decide which form is best to suit your individual needs.

Freeze-dried powders
All probiotic supplements come in freeze-dried powders, which are generally taken in unchilled filtered water. When purchasing powders, be sure each product contains a single bacteria super strain. In powdered form, the friendly bacteria get into the gastrointestinal system faster than when taken in capsules. In addition to simple personal preference, this form is recommended for children and those who have difficulty swallowing capsule.

As the powders they are especially helpful for treating such problems as nausea, stomach upset, and acid reflux.

Capsules
Certain strains of L.acidophilus and B.bifidum, including the super strains, are sold individually in capsule forms. Generally, capsules are preferred over powders because of their convenience.

Wafers
Convenience L.bulgaricus wafers are great to nibble on at the first sign of nausea, indigestion, or acid reflux. They're also good for curbing appetites. Because of their convenient form, you can slip them easily into a purse or carry them in a briefcase when travelling away from home.

Liquid
As virtually all liquid probiotics lose their potency within two weeks after they are produced, they should be avoided. Overall, liquid probiotics are the most misrepresented products in the market. They provide little, if any, benefits to the consumer. More stringent standards must be maintained and adhered to by manufacturers.

As always, be an educated consumer when choosing probiotic products. Read labels. Choose only high' quality products that include the beneficial supernatant, and avoid those that include FOS (Fructoligosaccharides).

The small intestine: Your primary line of defense

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