Leaky gut syndrome is really a nickname for the more formal term increased intestinal permeability, which underlies an enormous variety of illnesses and symptoms. It’s not a disease or an illness itself.

The list of health conditions associated with increased intestinal permeability grows each year as we increase our knowledge of the synergy between digestion and the immune system. If you do a Pubmed search on “intestinal permeability,” you’ll find it linked with nearly five thousand research articles.

A healthy intestinal lining allows only properly digested fats, proteins, and starches to pass through so they can be assimilated. At the same time, it also provides a barrier to keep out bacterial products, foreign substances, and large undigested molecules. This is called the barrier function of the gastrointestinal mucosal lining.

This surface is often called the brush border because under a microscope its villi and microvilli look like bristles on a brush. The intestinal lining lets substances move across this barrier in several ways. The process of diffusion is a simple one: it equalizes the concentrations inside and outside the cells.

Diffusion is the way ions of chloride, magnesium, potassium, sodium, and free fatty acids pass into the cells. Most nutrients are moved through the brush borders via a process called active transport. Carrier molecules, all of low molecular weight, transport nutrients like molecular taxis.

Amino acids, fatty acids, glucose, minerals, and vitamins cross cell membranes through active transport. In between cells are junctions called desmosomes. Normally, desmosomes form tight junctions and do not permit large molecules to pass through.

But when the area is irritated and inflamed, these junctions loosen up, allowing larger molecules to pass through. The substances that pass through the intracellular junctions are seen by our immune system as foreign, stimulating an antibody reaction.

When the intestinal lining is damaged, larger substances of particle size are allowed to pass directly, again triggering an antibody reaction. When the intestinal lining is damaged even more, substances larger than particle size—disease-causing bacteria, potentially toxic molecules, and undigested food particles—are allowed to pass directly through the weakened cell membranes.

They go directly into the bloodstream, activating antibodies and alarm substances called cytokines. The cytokines alert our lymphocytes (white blood cells) to battle the particles. Oxidants are produced in the battle, causing irritation and inflammation far from the digestive system.

That is the basis for a condition called increased intestinal permeability or leaky gut syndrome. Intestinal mucus normally blocks bacteria from moving to other parts of the body. But when the cells are leaking, bacteria passes into the bloodstream and throughout the body.

When intestinal bacteria colonize in other parts of the body, we call it bacterial translocation, and it is often found in people with leaky gut syndrome. For example, Blastocystis hominis, a bacteria that causes GI problems, has been found in the synovial fluid in the knee of an arthritis patient.

Surgery or tube feeding in hospitals can also cause bacterial translocation. Here’s how leaky gut syndrome works. Imagine that your cells need a kernel of corn. They are screaming out, “Hey, send me a kernel of corn.” The bloodstream replies, “I have a can of corn, but I don’t have a can opener.”

So the can goes around and around while the cells starve for corn. Finally, our immune system reacts by making antibodies against the can of corn, treating the corn as if it were a foreign invader. Your immune system has mobilized to finish the job of incomplete digestion, but this puts unneeded stress on it.

The next time you eat corn, your body already has antibodies to react against it, which triggers the immune system, and so on. As time goes on, people with leaky gut syndrome tend to become more and more sensitive to a wider variety of foods and environmental contaminants.

Depending on our own susceptibilities, we may develop a wide variety of signs, symptoms, and health problems. Leaky gut syndrome is associated with the following medical problems: allergies, celiac disease, Crohn’s disease, HIV, and malabsorption syndromes.

It is also linked to autoimmune diseases such as AIDS, ankylosing spondylitis, asthma, atopy, bronchitis, eczema, food and environmental sensitivities, other allergic disorders, psoriasis, Reiter’s syndrome, rheumatoid arthritis, Sjögren’s syndrome, and skin irritations.

The conditions presented in the box on page 84 can arise from a variety of causes, but leaky gut syndrome may underlie more classic diagnoses. If you have any of the common symptoms or disorders associated with leaky gut syndrome, ask your physician to order an intestinal permeability test to see if it is causing your problem.

In addition to clinical conditions, people with leaky gut syndrome display a wide variety of symptoms. Leaky gut syndrome puts an extra burden on the liver. All foods pass directly from the bloodstream through the liver for filtration.

The liver “humanizes” the food and either lets it pass or changes it, breaking down or storing all toxic or foreign substances. Water-soluble toxins are easily excreted, but the break-down of fat-soluble toxins is a two-stage process that requires more energy.

When the liver is bombarded by inflammatory irritants from incomplete digestion, it has less energy to neutralize chemical substances. When overwhelmed, it stores these toxins in fat cells, much the same way that we put boxes in the garage or basement to deal with at a later date.

If the liver has time later, it can deal with the stored toxins, but most commonly it is busy dealing with what is newly coming in and never catches up. These toxins provide a continued source of inflammation to the body. Increased intestinal permeability has been found to be a factor in liver diseases, such as cirrhosis.