Effect of a Low Starch Diet in Patients With Ankylosing Spondylitis

The aim of this study is to explore the effect of a low starch diet (reduction of at least 40%) in the gut bacteria modulation, especially Klebsiella pneumoniae, and its relation to disease activity, functional impairment and quality of life in patients with Ankylosing Spondylitis (AS).

Ankylosing spondylitis (AS) is a chronic inflammatory rheumatic disease characterized by axial inflammation and with unknown aetiology. The immune system dysregulation is known, where genetic factors play a key role, in particular, the susceptibility associated to the HLA-B27 allele. The presence of this genetic marker, seems to trigger an abnormal response of the individual, under the action of determine microorganisms, and probably, the combination of these two factors may contribute to the manifestation of the disease, through the induction of an immune and cytolytic response, leading to tissue injury and promoting the inflammation. Intestinal microbiota involvement in spondylarthritis is a controversial issue, however, was observed an increased concentration of Klebsiella pneumoniae bacteria in the faeces of AS patients. It has been suggested that an intervention aiming these bacteria's starving could benefit the reduction of the inflammatory processes and be a part of AS treatment. The bowel microflora depends on dietary intake, like undigested starch, for their growth. Some studies have highlighted the relation between the intake of starch and the disease activity. The modulation of the microbiota, particularly, the reduction of Klebsiella, may be beneficial as a complementary approach to AS therapy.

A sample of 300 patients with AS, followed-up at Portuguese Institute of Rheumatology in Lisbon, will be randomly assigned in two groups. The group A will adopt a balanced diet based on the general recommendations for healthy eating by the World Health Organization, for a period of 6 weeks. In Group B will be implemented an individual balanced low starch diet, which is characterized by the significant reduction of starchy food, of at least 40% of the total daily ingested starch.

The change in biometric data, body composition, intestinal Klebsiella will be related to food intake, disease activity and quality of life assessments. These data will be compared between the 2 groups (diet A versus diet B), obtaining measures on the effect of each diet on the analyzed variables.

Eligibility Criteria:
Inclusion Criteria:

* Age between 18 and 75 years old
* Available to comply with study protocol
* Ability to read and sign the Informed Consent
* Diagnosis of Ankylosing Spondylitis performed by the rheumatologist, according to the ASAS classification criteria, revised in 2016
* Positive HLA-B27allele
* Stable dose therapy within 3 months before selection

Exclusion Criteria:

* Pregnant, breastfeeding or planning to become pregnant within the study period
* Prior or current clinical history of drug or other substances abuse
* Subjects with uncontrolled clinical conditions, like neoplastic diseases, renal failure, liver impairment, uncompensated cardiac disease
* Dietetic restrictions due to religious believes or others incompatible with the study protocol
* Impossibility to attend to the mandatory personal clinical evaluation
* Presence of pacemaker, making impossible to perform the impedance body composition analysis
* Change in therapy during the intervention period