Very little research was been done that looks at how well the diet works and even less still has been done looking at the reasons that a diet might be effective. However, there are theories about why the diet works, one of which is called the leaky gut theory.
The basic idea in this theory is that a child's intestine is more permeable than it should be and lets all sorts of things into the body that should not be there. One of the things that can get through partially broken down parts of wheat and milk proteins (gluten and casein) and that can lead to a set of problems. But that is a subject for another day.
One of the things that I never fully understood was how or why this condition could develop in the first place - what could cause something like this and why can't the body repair itself.
I ran across a study the other day in Science Daily that might help answer this question. It seems that there is an ingredient in breast milk that helps protect and repair the gut in newborns -
The lining of a newborn's gut is particularly vulnerable to damage as it has never been exposed to food or drink. ...
The researchers found small amounts of PSTI in all the samples of breast milk they tested but it was seven times more concentrated in colostrum samples. The ingredient was not found in formula milk.
The researchers examined the effects of PSTI on human intestinal cells in the lab. When they inflicted damage to the cells they found that PSTI stimulated the cells to move across the damaged area forming a natural protective 'plaster'. They also found that PSTI could prevent further damage by stopping the cells of the intestine from self-destructing. Additional research suggests that PSTI could reduce damage by 75 per cent.So it is possible that breastfeeding can help prevent and repair damage to a newborn's intestinal track which might be able to help prevent something like a leaky gut from getting started. This is obviously not something that "causes" autism but perhaps it can help mitigate some of the damage that autism can cause.
Please note that I am not saying that going the formula route is a terrible thing, after all, we did it with our twin daughters. The twins are on the GFCF diet and have had large improvements because of it.
But the funny thing is that our youngest daughter does not have the same dietary issues that her sisters did. She was breast feed and has never had the bowel issues, or eczema, or abnormalities in her blood work. So maybe there is something to this protect factor.
Just food for thought.