Table 1 Overview of the selected studies on green-leafy vegetables
From: Food intake biomarkers for green leafy vegetables, bulb vegetables, and stem vegetables: a review
Dietary factor | Intervention | Dose of intervention | Study design | n | Analytical method | Sample type | Candidate biomarkers of food intake | Primary reference |
|---|---|---|---|---|---|---|---|---|
Spinach | ||||||||
Just-boiled fresh spinach | 1.2 kg | Acute single dose | 8 | HPLC-UV | Plasma (after 3 h) | Chlorophyll-related compounds (CRCs) (pheophytin (Phe) and pheophorbide (Pho)) | [46] | |
Vegetable together with fried rice | 200 g | First study: acute single doses (4 distinct treatments: spinach, celery, onion, no vegetables) Second/third studies confirmation: singles doses or combinations | 10 (and 3 for secondand third) | LC−MS (UPLC and Q-TOF MS) (untargeted metabolomics) | Urine (up to 7 h) | 4-guanidino-butanoic acid with an Isoprene modification (tentative identification) | [47] | |
Spinach-containing diet–frozen spinach thawed and cooked | 453 g spinach/day | 2-arm cross-over intervention (2 × 3 weeks) | 7 | Atomic absorption spectrophotometry (Faecal, urinary, and dietary calcium and zinc levels) kits for oxalate and hydroxyproline-assays | Urine | Hydroxyproline | [48] | |
Freeze-dried 13C-labeled spinach | 5 g (providing 160 μmol methoxyflavonols, including 70 μmol TMM4’-glucuronide) | Acute single dose | 5 | UHPLC-MSn | Plasma (up to 24 h) | 13C17TMM-glucuronide 13C17TMM-sulfate 13C16Patuletin-glucuronidesulfate-methyl 12C113C16Spinacetinglucuronide-sulfate 13C17Spinacetinglucuronide-sulfate | [49] | |
Lettuce | ||||||||
Fresh lettuce | 250 g | Acute single dose | 11 | HPLC-Coularray | Plasma (up to 6 h) | ρ-coumaric acid Caffeic acid | [50] | |
Endive | ||||||||
Endive soup (300 g) with a slice of white bread | 150 g (precooked mass) of endive = 9 mg kaempferol | Acute single dose | 8 | LC/MS | plasma and urine (up to 24 h) | Kaempferol-3-glucoside Kaempferol-3-glucuronide | [51] | |