Gl 32k

For glucose and hormones, venous blood samples (7 mL) were collected into ice-chilled ethylenediaminetetraacetic acid-containing tubes. For serum 3-OMG, 3-mL venous samples were collected into untreated tubes and allowed to clot. Plasma and serum were each separated by centrifugation at 3200 rpm for 15 min at 4 °C within 15 min of collection and stored at −80 °C until subsequent analysis.
Plasma glucose concentrations (mmol/L) were quantified by the glucose oxidase method using a glucose analyser (YSI 2300 Stat Plus, Yellow Springs Instruments, Yellow Springs, Ohio, USA). Intra- and inter-assay coefficient variations (CVs) were ≤2%.
Plasma C-peptide concentrations (pmol/L) were measured by ELISA immunoassay (10-1136-01, Mercodia, Uppsala, Sweden). The minimum detectable limit was 15 pmol/L and the inter- and intra-assay CVs were 8.3% and 2.9%, respectively. C-peptide reflects endogenous insulin secretion, since it is not extracted by the liver and its half-life is longer than that of insulin^{23 (link)}.
Plasma glucagon concentrations (pg/mL) were measured by radioimmunoassay (GL-32K, Millipore, Billerica, Massachusetts, USA). The minimum detectable limit was 15 pg/mL, and inter- and intra-assay CVs were 6.9% and 4.2%, respectively.
Serum 3-OMG concentrations (mmol/L) were measured by liquid chromatography and mass spectrometry, with a sensitivity of 0.0103 mmol/L^{24 (link)}.

Study participants received two isocaloric meals (600 kcal), being either a high‐carbohydrate or low‐carbohydrate/high‐fat meal³⁸ (Table 2) in a cross‐over design with at least 1‐ and 2‐month wash‐out period for men and women, respectively. The meals consisted of red meat, potatoes (boiled or French fries), and different vegetables/legumes, depending on meal compositions, and water to drink. The meals were prepared and served at a restaurant located at the Karolinska University Hospital. Study participants were unaware of meal composition and a research nurse oversaw the intake. Approximately 4 hours before the intervention, participants consumed a standardized breakfast at home. The breakfast constituted 400–450 kcal, with 56–66 energy per cent (%E) carbohydrate (8–10 grams of fibre), 21%–24%E protein, and 13–20%E fat. Blood samples were collected 30 and 5 min before the meal intake and then every 30 min from 30 to 240 min after meal intake, enabling sampling over the timeframe incorporating the largest variation in plasma glucose and lipid levels.³⁹ Insulin was measured using ELISA (DAKO, Agilent Technologies), glucagon using RIA (GL‐32K; Millipore), and proinsulin using ELISA (10‐1118‐01, Mercodia).

Blood samples were collected into ice-chilled ethylenediaminetetraacetic acid-coated tubes. Plasma was obtained by centrifugation at 3200× g (1832 × g-force) for 15 min at 4 °C within 15 min of collection and then stored at −80 °C for subsequent analysis.
Plasma glucose (mmol/L) was measured using the glucose oxidase technique (2300 STAT Plus; YSI, Yellow Springs, OH, USA).
Plasma C-peptide concentrations (expressed as pmol/L) were measured by ELISA (10-1113; Mercodia, Uppsala, Sweden). The minimal detectable limit was 15 pmol/L, and intra-assay and inter-assay CVs were 2.4% and 4.9%, respectively.
Plasma glucagon (pg/mL) was measured by radioimmunoassay (GL-32K; Millipore, Billerica, MA, USA). The minimum detectable limit was 15 pg/mL, and intra-assay and inter-assay CVs were 6.9% and 4.2%, respectively.

Venous blood samples (10 mL) were collected into ice-chilled ethylenediaminetetraacetic acid-treated tubes. Plasma was separated by centrifugation at 3200 rpm for 15 min at 4 °C within 15 min of collection and stored at −80 °C until analysed, as described [20 (link)].
Plasma glucose (mmol/L) was measured using a YSI2300 analyser (YSI, Inc., Yellow Springs, OH, USA). Intra- and inter-assay coefficient variations (CVs) were ≤2%.
Plasma insulin (mU/L) was determined by enzyme-linked immunosorbent assay (ELISA, 10-1113, Mercodia, Uppsala, Sweden). Intra- and inter-assay CVs were 2.4% and 9.5%, respectively. The detection limit was 1 mU/L.
Plasma glucagon (pg/mL) was quantified using an RIA (GL-32K, Millipore, Billerica, MA, USA). Intra- and inter-assay CVs were 3.2 and 6.1%, respectively. The detection limit was 20 pg/mL.