The AIP diet is an extension of the Paleolithic diet and was developed by Sarah Ballantyne, PhD, who earned her doctorate in medical biophysics.  She authored her AIP diet book in 2014 after experimenting with a Paleolithic diet to improve her own health.
The diet is based on the theory that certain foods could trigger inflammation or cause dysbiosis (an unbalanced gut microbiome), worsening autoimmune disease activity. It is a multiphase elimination diet that encourages the inclusion of bone broth and fermented foods, as well as lifestyle habits such as sleep hygiene, physical activity, and stress management.
The AIP is an elimination diet that initially restricts:
Refined or artificial sweeteners
Non-steroidal anti-inflammatory drugs (NSAIDS)
These are replaced with:
Certain varieties of yam and potato
Minimally processed meat
Minimally processed vegetable oils
Nondairy fermented foods
Protocols vary, and some recommend limiting saturated fats, omega-6 fats, natural sugars, and fruits. The length of the elimination phase depends on how quickly a person notices improvements. During the reintroduction phase, foods are introduced individually, about one week apart. The AIP also encourages health-supporting lifestyle habits such as sleep hygiene, physical activity, and stress management.
Current research on the AIP is limited to open-label (where participants are aware of their treatment), uncontrolled exploratory studies that have examined the effects of the diet on inflammatory bowel disease (IBD) and Hashimoto’s thyroiditis. Improvements in quality of life, IBD disease activity, and markers of inflammation were reported, but randomized controlled trials (RCTs) are needed to confirm these early findings. 
The AIP diet could improve health by encouraging people to increase their physical activity and improve their sleep and stress management habits. It could also increase fruit, vegetable, and fiber intake while reducing the consumption of highly processed foods. Diets high in fiber and polyphenols (beneficial compounds in plants) have been shown to reduce markers of intestinal permeability (or “leaky gut”) and increase quality of life in people with IBD. 
The AIP is a restrictive diet that may be difficult to adhere to and could place people at risk of nutrient deficiencies if they follow the elimination phase for too long.
Research on the AIP is extremely limited, and the current studies don’t provide strong evidence that the diet itself is improving disease activity. The studies experienced high dropout rates; a few of the participants with IBD experienced worsening disease activity; and no markers of thyroid function or thyroid antibodies changed after 10 weeks on the AIP diet in women with Hashimoto’s thyroiditis. Without control groups, it’s impossible to determine whether the observed improvements happened as a result of time, the placebo effect, or other factors. Notably, all three studies on the AIP for IBD relief came from a single experiment done by one research group on the same participants.