In the short term, high-protein, low-carbohydrate ketogenic diets reduce hunger and lower food intake significantly more than do high-protein, medium-carbohydrate nonketogenic diets.
The effect of diet quality on urea production, entry into the gastrointestinal tract (GIT) and subsequent diversion to anabolic or catabolic fates was examined in four sheep (mean live weight 49´5 kg). The animals received, in a crossover design, each of two rations, hay±grass pellets (1:1 HG) and a mixed concentrate±forage (CF N]urea enrichment was at plateau. The latter is derived from hydrolysis of urea to 15 NH 3 in the digestive tract with subsequent absorption and reconversion to urea. The diets were not isonitrogenous (14´3 v. 17´1 g N supplied daily for HG and CF respectively) but showed no difference in N balance. Urea-N production was much greater (16´3 v. 11´1 g/d; P 0´011 for CF compared with HG and more urea-N entered the GIT (9´9 v. 7´7; P 0´07X A larger proportion of GIT entry was returned to ureagenesis (51 v. 42 %; P 0´047 for the CF diet but a smaller fraction was lost in the faeces (3´3 % v. 7´1 %; P 0´013X In consequence, most of the additional urea-N which entered the GIT on the CF diet was returned to the ornithine cycle (probably as NH 3 ) and the absolute amount available for anabolic purposes was similar between the rations (3´9 v. 4´5 g N/d).
PurposeLow fruit and vegetable consumption is linked with an increased risk of death from vascular disease and cancer. The benefit of eating fruits and vegetables is attributed in part to antioxidants, vitamins and phytochemicals. Whether increasing intake impacts on markers of disease remains to be established. This study investigates whether increasing daily intake of fruits, vegetables and juices from low (approx. 3 portions), to high intakes (approx. 8 portions) impacts on nutritional and clinical biomarkers. Barriers to achieving the recommended fruit and vegetable intakes are also investigated.MethodIn a randomised clinical trial, the participants [19 men and 26 women (39–58 years)] with low reported fruit, juice and vegetable intake (<3 portions/day) were randomised to consume either their usual diet or a diet supplemented with an additional 480 g of fruit and vegetables and fruit juice (300 ml) daily for 12 weeks. Nutritional biomarkers (vitamin C, carotenoids, B vitamins), antioxidant capacity and genomic stability were measured pre-intervention, at 4-, 8- and 12 weeks throughout the intervention. Samples were also taken post-intervention after a 6-week washout period. Glucose, homocysteine, lipids, blood pressure, weight and arterial stiffness were also measured. Intake of fruit, fruit juice and vegetables was reassessed 12 months after conducting the study and a questionnaire was developed to identify barriers to healthy eating.ResultsIntake increased significantly in the intervention group compared to controls, achieving 8.4 portions/day after 12 weeks. Plasma vitamin C (35%), folate (15%) and certain carotenoids [α-carotene (50%) and β-carotene (70%) and lutein/zeaxanthin (70%)] were significantly increased (P < 0.05) in the intervention group. There were no significant changes in antioxidant capacity, DNA damage and markers of vascular health. Barriers to achieving recommended intakes of fruits and vegetables measured 12 months after the intervention period were amount, inconvenience and cost.ConclusionWhile increasing fruit, juice and vegetable consumption increases circulating level of beneficial nutrients in healthy subjects, a 12-week intervention was not associated with effects on antioxidant status or lymphocyte DNA damage.Trial registrationThis trial was registered at Controlled-Trials.com; registration ISRCTN71368072.Electronic supplementary materialThe online version of this article (doi:10.1007/s00394-017-1469-0) contains supplementary material, which is available to authorized users.
There are concerns that weight-loss (WL) diets based on very low carbohydrate (LC) intake have a negative impact on antioxidant status and biomarkers of cardiovascular and metabolic health. Obese men (n 16) participated in a randomised, cross-over design diet trial, with food provided daily, at approximately 8·3 MJ/d (approximately 70 % of energy maintenance requirements). They were provided with two high-protein diets (30 % of energy), each for a 4-week period, involving a LC (4 % carbohydrate) and a moderate carbohydrate (MC, 35 % carbohydrate) content. Body weight was measured daily, and weekly blood samples were collected. On average, subjects lost 6·75 and 4·32 kg of weight on the LC and MC diets, respectively (P, 0·001, SED 0·350). Although the LC and MC diets were associated with a small reduction in plasma concentrations of retinol, vitamin E (a-tocopherol) and b-cryptoxanthin (P,0·005), these were still above the values indicative of deficiency. Interestingly, plasma vitamin C concentrations increased on consumption of the LC diet (P,0·05). Plasma markers of insulin resistance (P, 0·001), lipaemia and inflammation (P, 0·05, TNF-a and IL-10) improved similarly on both diets. There was no change in other cardiovascular markers with WL. The present data suggest that a LC WL diet does not impair plasma indices of cardiometabolic health, at least within 4 weeks, in otherwise healthy obese subjects. In general, improvements in metabolic health associated with WL were similar between the LC and MC diets. Antioxidant supplements may be warranted if LC WL diets are consumed for a prolonged period.
It is not known if the ruminant animal gastrointestinal tract (GIT) can oxidise essential amino acids (AA) other than leucine. Therefore, the oxidation of four essential AA (leucine, lysine, methionine and phenylalanine), supplied systemically as labelled 1-13 C forms, was monitored across the mesenteric-drained viscera (MDV; small intestine) and portal-drained viscera (PDV; total GIT), as part of a 4 £ 4 Latin square design, in four wether sheep (35 -45 kg) fed at 1·4 £ maintenance. Oxidation was assessed primarily by appearance of 13 CO 2, corrected for sequestration of [13 C]bicarbonate. The GIT contributed 25 % (P, 0·001) and 10 % (P, 0·05) towards whole-body AA oxidation for leucine and methionine respectively. This reduced net appearance across the PDV by 23 and 11 % respectively. The contribution of MDV metabolism to total PDV oxidation was 40 % for leucine and 60 % for methionine. There was no catabolism of systemic lysine or phenylalanine across the GIT. Production and exchange of secondary metabolites (e.g. 4-methyl-2-oxo-pentanoate, homocysteine, 2-aminoadipate) across the GIT was also limited. Less AA appeared across the PDV than MDV (P, 0·001), indicative of use by tissues such as the forestomach, large intestine, spleen and pancreas. The PDV: MDV net appearance ratios varied (P, 0·001) between AA, e.g. phenylalanine (0·81), lysine (0·71), methionine (0·67), leucine (0·56), histidine (0·71), threonine (0·63) and tryptophan (0·48). These differences probably reflect incomplete re-absorption of endogenous secretions and, together with the varied oxidative losses measured, will alter the pattern of AA net supply to the rest of the animal.
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