The integrity of the gut lining relies on structures called tight junctions. These act as selective barriers, normally allowing only very small, digested food particles to pass into the bloodstream. However, factors like stress and other causes can compromise these tight junctions, leading to increased permeability of the gut lining. This increased permeability can allow partially digested food, bacteria and toxins such as pesticides, to leak from the gut into the bloodstream.

The conditions Dr. Campbell-McBride lists, are in several broad categories of health issues, including:

Neurological and Psychiatric Disorders:

* Autism Spectrum Disorders (ASD)
* Attention Deficit Hyperactivity Disorder (ADHD)
* Attention Deficit Disorder (ADD)
* Dyslexia
* Dyspraxia
* Schizophrenia
* Depression
* Obsessive-Compulsive Disorder (OCD)
* Bipolar Disorder
* Anxiety disorders
* Eating disorders
* Epilepsy
* Learning disabilities
* Speech delays
* Sensory processing issues

Digestive Disorders:
* Irritable Bowel Syndrome (IBS)
* Inflammatory Bowel Disease (IBD) (Crohn’s disease, Ulcerative colitis)
* Celiac disease
* Food allergies and intolerances
* Constipation
* Diarrhea
* Bloating
* Acid reflux

Autoimmune Disorders:
* Type 1 diabetes
* Rheumatoid arthritis
* Multiple sclerosis
* Systemic lupus erythematosus (SLE)
* Hashimoto’s thyroiditis
* Ankylosing spondylitis
Other Physical Conditions:
* Asthma
* Eczema
* Psoriasis
* Allergies (respiratory and skin)
* Chronic fatigue syndrome
* Fibromyalgia
* Arthritis
* Migraines
* Hormonal imbalances
* Skin problems
* Frequent infections
* Failure to thrive (in children)

Intestinal permeability plays a significant role in the development and progression of a wide spectrum of health problems across different systems of the body.