Gut Science
The four "R" s have been successfully used in functional medicine for Inflammatory Bowel Disease (Crohn's, Colitis,) IBS, and Small Intestine Bacterial Overgrowth (SIBO.) 
The principles are also used to heal leaky gut, where the lining of the intestine becomes permeable, allowing partially digested food proteins and pathogens to leak into the bloodstream. The body generates an immune response to these foreign invaders, and the antibodies produced often cross react with body tissues, leading to an autoimmune condition.
Many skin conditions (including psoriasis and eczema,) as well as autism, (often considered an autoimmune attack on the brain) are associated with leaky gut. A number of factors can cause leaky gut, including food sensitivities, stress, antibiotic use, and pathogens.
The four "R" s will repair the leaky gut and reverse the autoimmune/disease process:
Remove - Remove all foods that are generating an immune response in the body, as well as all pathogenic bacteria, yeast (candida,) and parasites. Plant derived products, antibiotics, antiparasitic medication, and antifungals may all be utilized in this stage.
Replace - Replace all factors involved in the digestive process that are missing or insufficient, such as bile acids, digestive enzymes, and stomach acid.
Reinoculate - Add back in "good" bacteria in the form of probiotic supplements and fermented foods. Imbalance in intestinal bacteria and an overgrowth of "bad" bacteria, is viewed as a trigger to leaky gut and autoimmunity.
Repair - Once all of the above factors are in an ideal state, products that speed the healing of the GI tract can be incorporated. Research supports the usage of Zinc Carnosine and L-glutamine in increasing the rate of cell turnover and repair of the gut lining. Plant derived products with anti-inflammatory and stomach soothing properties may also be utilized in this stage.
As each case of GI disease or autoimmunity has different causal factors, it is important to choose a qualified practitioner experienced in gut repair from a functional medicine viewpoint, who can evaluate and determine the appropriate course of treatment for the individual case.