Diet, Carbohydrate-Restricted

Participants completed a validated food frequency questionnaire (FFQ) [19 (link)]. Baseline dietary intake data which was taken from food composition tables, was used to recognize CQI according to the four criteria: the GI, the ratio of carbohydrates of whole grains to carbohydrates of total grains, the proportion of solid carbohydrates to total carbohydrates, and total dietary fiber intake. Liquid carbohydrates such as fruit juice and sugar-sweetened beverage consumption, while solid carbohydrates were matched to the carbohydrate content of the rest of the meal with each carbohydrate content. The total score range was between 4 and 20 (higher amounts mean better quality of carbohydrates) [7 (link), 20 ].
For calculating the LCDS, all participants were divided into 11 strata for carbohydrate, refined grains, monounsaturated fatty acid (MUFA), vegetable protein intake, fiber (g/1000 kcal), GL, and polyunsaturated fatty acid (PUFA)(n3/n6) [14 (link)]. For MUFA, n3/n6 PUFA, fiber, and vegetable protein, participants in the highest stratum got 10 points and lowest stratum got 0 points. For refined grains, GL and carbohydrates, the intake of the lowest carbohydrate got 10 points and the intake of the highest carbohydrate got 0 points. Finally, the overall diet score was between 0 (the lowest intake of protein and fat and the highest intake of carbohydrates) and 70 (the highest intake of protein and fat and the lowest carbohydrates). So the higher the score, the higher the low-carbohydrate diet pattern named “LCDS”.
GI was calculated from this formula: (GI × available carbohydrate)/total available carbohydrate. Available carbohydrate means total carbohydrate minus fiber [21 (link)]. The United States Department of Agriculture food composition table was used for total carbohydrate and fiber content. Iranian GI table was just used for 6 out of 85 foods [21 (link)]. For 62 other foods, international tables were used [21 (link)], and for 17 foods, we used similar foods because the GI of these foods was not accessible. The GL was calculated from this formula: (total GI × total available carbohydrate/100).
II refers to the increase in insulin level under the curve during 2 h in reaction to 1000 kJ of test food divided by the area under the curve after consumption of 1000 kJ of reference food. Previous studies were used to obtain the II. II of similar foods was used for some items that were not in the list of foods based on the relationship between carbohydrate, fiber, protein, fat, and energy content. For example, raisins were used for dates. To assess IL for each person, IL was calculated (II of the food × energy of one gram of that food × amount of the food eaten) then the IL of each food was summed and then II was calculated (IL/total energy intake) [22 (link)–25 (link)].

This study was approved by the Ethical Committee of the Faculty of Veterinary Medicine, Ghent University, Belgium (EC 2011/056). Twelve healthy Beagles with a mean age of 6.0 years old were included in this study. Six Beagles (one spayed and three intact females; two intact males) were lean, with a body condition score of 4–5/9, and six Beagles (two intact females and two intact males) were obese, with a body condition score of 8–9/9. Obesity was induced ∼1 year before the present study by feeding the dogs a high-fat commercial diet as described by Van de Velde et al. (2013 (link)). Before the study, dogs were deemed healthy (apart from obesity in four dogs), based on physical exams, complete blood counts, and serum biochemistry.
Two isocaloric experimental diets, a high-protein/low-carbohydrate (HPLC) diet consisting of 50.0 g crude protein, 12.2 g ether extract, and 32.2 g nitrogen-free extract on 100 g dry matter basis, and a low-protein/high-carbohydrate (LPHC) diet consisting of 17.8 g crude protein, 13.6 g ether extract, and 62.3 g nitrogen-free extract on 100 g dry matter basis were formulated with the same ingredients (Co. NV Versele-Laga, Deinze, Belgium). Full details of the ingredients and dietary composition were described previously (Xu et al. 2017 (link)), and the main ingredients are presented in Supplementary Table S1. Both diets met the minimal requirement for adult dogs according to the National Research Council (2006 ). The initial amount of feed offered was calculated based on individual maintenance energy requirements according to individual history and adjusted to maintain a stable body weight throughout the study. Dogs were fed twice daily and had free access to water.
The study was designed as a crossover with two 4-week periods. The first 3 weeks consisted of an adaptation period and samples were taken in the fourth week (on day 27). In the first period, three lean and obese dogs were randomly selected and assigned to the LPHC diet first, whilst the other three lean and obese dogs received the HPLC diet. In the second period, diets were switched. Each dog was therefore assigned to one of four groups (group 1: lean dogs received the LPHC diet first; group 2 lean dogs received the HPLC diet first; group 3 obese dogs received the LPHC diet first; group 4 obese dogs received the HPLC diet first). On day 27 of each period, fresh faecal samples were collected within 10 min after spontaneous voiding. An aliquot of ±2 g was placed into a sterile plastic tube, frozen immediately on dry ice, lyophilized as soon as possible, and stored at −80 °C in preparation for metabolomics analysis. Two obese dogs were excluded from the metabolomics analysis due to an insufficient amount of faecal samples, and as such, each group ended up containing three lean and two obese dogs.

The preparation, acquisition, and evaluation of [¹⁸F]FDG PET/CT were all performed in accordance with the European Association of Nuclear Medicine (EANM) guidelines [11 (link)].
A 24 h high-fat, low-carbohydrate diet and 6 h fasting time prior to the scan were used in all patients. Additionally, if there were no contra-indications against its use, an intravenous heparin injection of 50 IU/kg was given 15 min prior to the scan to further suppress physiological [¹⁸F]FDG uptake. All scans were acquired on the Biograph Vision digital PET/CT system (Siemens Healthineers, Knoxville, TN, USA). Gating was performed using co-registration of an ECG, both for regular gating (single gate) and CardioFreeze^TM, and in which the sequences were performed in a single-bed position for 10 min, immediately after the regular non-gated [¹⁸F]FDG PET/CT scan had been completed.