Sulfur amino acid restriction, energy metabolism and obesity: a study protocol of an 8-week randomized controlled dietary intervention with whole foods and amino acid supplements

Table 1 Primary and secondary outcomes

Primary outcome	Measured by
• Body weight	• DXA

Secondary outcomes	Measured by
• Resting energy expenditure, respiratory quotient, substrate oxidation	• WRIC
• Changes in body composition including body fat compartments and lean mass	• DXA • Waist circumference • Hip circumference • Waist-hip-ratio
• Plasma and urine concentrations of SAA and related intermediates and compounds (sulfurome)	• LC–MS/MS
• Plasma lipoprotein profile, total fatty acid profile, and glucose, c-peptide and insulin changes	• LC–MS/MS, GC–MS/MS, ELISA, colorimetric and/or enzymatic methods
• Adipokines and satiety hormones	• ELISA
• mRNA expression of enzymes involved in SAA, lipid and energy metabolism in adipose tissue and white blood cells	• qPCR and untargeted analysis (mRNA sequencing)
• Vitamin status, including plasma folate and B12 and methylmalonic acid	• LC–MS/MS
• 24 h-urine urea nitrogen for nitrogen balance	• Modified Kjelldahl method • BUN-assay
• Changes in plasma biomarkers	• Untargeted analysis (metabolomics)
• Serum changes in FGF21	• ELISA
• Changes in markers of liver status: ALAT, ASAT, ɤ-GT, LD, ALP, CK and bilirubin	• Colorimetric and/or enzymatic methods
• Changes in gut microbiota	• Sequencing of fecal samples

BUN blood urea nitrogen, DXA dual-energy x-ray absorptiometry, FGF21 fibroblast growth factor 2, WRIC whole-room indirect calorimetry, qPCR quantitative polymerase chain reaction, ELISA enzyme-linked immunosorbent assay, MS, LC–MS/MS liquid chromatography–mass spectrometry-tandem, MS, GC–MS/MS gas chromatography/mass spectrometry-tandem, ALAT alanine aminotransferase, ASAT aspartate aminotransferase, ɤ-GT gamma-glutamyltransferase, LD lactate dehydrogenase, ALP Alkaline phosphatase ALP, CK creatine kinase

ISSN: 1479-5876