Is Leaky Gut Syndrome a real phenomenon?
To assess this hypothesis let’s first take a look at the anatomy of the gut and its role in health.
Lining our gut are cells called Epithelia, the role of these cells is to form a barrier that separates the internal environment from external influences. In addition to this role they also function to provide a controlled passageway to ions and molecules from and into the internal environment. In between each epithelial cell are complexes called Tight Junctions, Adherens Junctions, Desmonsomes and Gap Junctions. For the purpose of this article we will focus on Tight Junctions.
Tight Junctions perform two roles:
Firstly they play a role in the formation of barriers via cellular proliferation which is the growth and production of cells by multiplication, cell differentiation which is the process by which a cell becomes specialized in order to perform a specific function, and polarization which in cells, refers to the asymmetric organization of different aspects of the cell including the cell surface, intracellular organelles, and the cytoskeleton.
Secondly their role is to regulate the entry of nutrients, ions and water while restricting pathogen entry and thus regulating the barrier function of the epithelium .
Now we need to look at pathophysiological influences on Tight Junctions, of note are the bacterial, viral and dietary influences.
Although human cells have incorporated epithelial barriers to block organisms that covet access to deeper cell layers within tissues, certain pathogens have evolved to exploit, and thus control, tight junctions to alter this barrier . Some pathogens use tight junction proteins as receptors for their attachment and subsequent internalization. Others destroy the junctions thereby providing a gateway to the underlying tissue . Different bacteria’s such as Escherichia coli, Salmonella, Helicobacter pylori, and Clostridium perfringens have all been implicated, as have different viruses such as Hepatitis C virus (HCV), Reovirus, and Adenovirus. 
The effects of dietary components have also been implicated. Interactions between the dietary components and the microbiota are crucial in the regulation of barrier integrity . For most autoimmune diseases there is little or no knowledge about the causing agent or genetic makeup underlying the disease . Celiac disease represents a unique autoimmune disorder because the environmental trigger is known, the gliadin fraction of gluten containing grains.  Interestingly, recent data also suggest that gliadin is also involved in the pathogenesis of Type 1 Diabetes.
It is hypothesised that since tight junctions allow this interaction, new therapeutic strategies aimed at re-establishing the intestinal barrier function offer innovative, unexplored approaches for the treatment of these devastating diseases. 
I will be posting information aimed at helping people to support their gut function but in the meantime the best resource I know of is the GAPS diet by Natasha Campbell-McBride. 
REFERENCES http://www.bio.davidson.edu/people/kabernd/berndcv/lab/epithelialinfoweb/polarity.html  http://www.biomedcentral.com/1471-230X/11/109  http://www.sciencedirect.com/science/article/pii/S0005273608003477  http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2886850/ http://www.doctor-natasha.com/