Ngala et al. BMC Nutrition (2016) 2:28DOI 10.1186/s40795-016-0053-yRESEARCH ARTICLEOpen AccessEffect of dietary vegetable oil consumptionon blood glucose levels, lipid profile andweight in diabetic mice: an experimentalcase—control studyRobert A. Ngala1*, Isaac Ampong1, Samuel Asamoah Sakyi1,2 and Enoch Odame Anto1AbstractBackground: Free fatty acids have been reported to impair insulin action; Dietary fat composition has beenimplicated in the development of insulin resistance as well as fasting glycaemia and type 2 diabetes mellitus. Thiswork was designed to determine the benefits of consuming vegetable oils on the management of diabetes indiabetic mice.Methods: Forty eight (48) maledb/db diabetic mice were randomly divided into eight groups of six. The first fourgroups were fed on chow (control), 10 % Red palm oil feed, 10 % groundnut oil feed, and 10 % coconut oil feed.The second four groups were fed similar to the first four groups but in addition were administered glibenclamide(2 mg/kg -wt i.p) daily at 8. AM.Results: Plasma glucose in the diabetic mice was significantly reduced after consuming diets fortified with 10 %palm oil, groundnut oil and coconut oil and also in mice additionally treated with glibenclamide. In mice that werenot treated glibenclamide, treatment with groundnut oil reduced total cholesterol and LDL-cholesterol and raisedplasma HDL. Plasma triglycerides were unchanged. Palm oil and coconut oil had no effect on any of the plasmalipids. In mice that were treated glibenclamide, the control and palm oil treatment significantly reduced totalcholesterol (p 0.05). The control, groundnut oil, palm oil and coconut oil significantly (p 0.05) reduced plasmaLDL-cholesterol. HDL-cholesterol was raised in groundnut oil, and coconut oil. Plasma triglycerides were raised inonly on groundnut oil.Conclusion: Ten percent fortified vegetable oil feeds (red palm oil, groundnut oil and coconut oil) significantlyimproved lipid profile and significantly reduced blood glucose in diabetic mice. Groundnut oil raised HDL andlowered LDL even in mice given glibenclamide but it did not lower total cholesterol in mice given glibenclamideKeywords: Palm oil, Groundnut oil, Coconut oil, GlibenclamideBackgroundIncreased plasma free fatty acids reduced insulinstimulated glucose-uptake. The mechanism responsiblefor this inhibition, however, remains unclear. There issufficient evidence suggesting that the defects in glucoseuptake and storage in the presence of free fatty acidsmay be related to abnormal fat metabolism [1, 2]. Most* Correspondence: [email protected] of Molecular Medicine, School of Medical Science, KwameNkrumah University of Science and Technology (KNUST), Kumasi, GhanaFull list of author information is available at the end of the articlepatients with type 2 diabetes are obese and have elevatedplasma free fatty acids concentrations , and these havebeen shown to inhibit insulin-stimulated glucose uptake[4, 5]. The Randle glucose-fatty acid cycle has been usedto explain insulin resistance in skeletal muscle ofpatients with type 2 diabetes or obesity. An alternativehypothesis proposes that muscle insulin resistance results from decreased mitochondrial oxidation of fattyacids [6–9]. The unoxidized fatty acids are re-routed toward the synthesis of diacylglycerol and ceramide, whichin turn stimulate stress-induced protein kinases that 2016 Ngala et al. Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, andreproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link tothe Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication o/1.0/) applies to the data made available in this article, unless otherwise stated.
Ngala et al. BMC Nutrition (2016) 2:28inhibit insulin signalling [8, 9]. This hypothesis is supported by measurement of the concentrations of lipidsin mitochondrial oxidative capacity, and the phosphorylation state of several components of the insulinsignalling pathway in hearts perfused with palmitate inpathological samples from type 2 diabetic patients .Increasing evidence implicates dietary fat composition in the development of insulin resistance, including impaired fasting glycaemia and Type 2 diabetesmellitus [11, 12]. Several cross-sectional studies haveshown an association between dietary saturated fatcontent and hyperinsulinaemia  impaired glucosetolerance [14, 15] and overt diabetes . Groundnutoil contains 46 and 32% of mono unsaturated fattyacids (MUFA) and polyunsaturated fatty acids (PUFA),respectively Palm oil contains approximately 50 % ofsaturated and 50 % unsaturated fatty acids , whilstcoconut oil is, a saturated fat which contains predominantly medium-chain saturated fatty acids with highantioxidant properties [18–20].Several management strategies of diabetes such asdietary modification, exercise, oral hypoglycaemicagents, and insulin have been in used for decades. However, these regimen have not adequately proven to be effective in curbing the complications associated withdiabetes mellitus . Vegetable oils have also beenfound to be useful in the management of diabetes .These oils contains different fractions of fat and othercomponent such as tocotrienols, tocopherols, oryzanol,phytosterols which have varying effect on insulin resistance and metabolic control . Many vegetable oils including groundnut oil, red palm oil, coconut oil andpalm kennel oil are widely used in many developingcountries as part of their dietary preparations. Afavourable glucose response was also induced by fish oilfeeding and this was mediated through body weight loss. Noninsulin diabetic model mice fed on palm oilhad improved glycaemic control despite their markedobesity . However, public perception that intake ofthese edible oils contributes to dyslipidaemia andincrease cardiovascular risk has reduced their consumption. It is against this background that this study wasaimed at determining the metabolic effect of some vegetable oil consumption in the management of diabetes indiabetic mice.MethodsAll procedures and techniques used in this study were inaccordance with the National Institute of Health Guidelines for the care of Laboratory Animals (NIH). Departmentof Health Service Publication No 83-23, revised 1985). Theprotocol for the study was approved by the Health ServiceEthics committee, School of Medical Sciences, KwamePage 2 of 8Nkrumah University of Science and Technology KumasiGhana.Forty eight (48) male diabetic mice (BKS.Cg-m / Leprdb/BomTac) strain each weighing between 25and 40 g and a mean weight of 35 g and approximately8 weeks old were obtained from the Department ofAnimal Experimentation, Nuguchi Memorial Institutefor Medical Research, University of Ghana. The micewere transported in specialized cages and brought to theAnimal house of the pharmacology Department, KwameNkrumah University of Science and Technology(KNUST)-Ghana where the study was carried out. Themice were housed in groups of two at 25–30 C with12 h daylight. The mice were fed ad libitum with normalrodent chow (composed of 21 % protein, 5 % fat and34 % carbohydrate, made from fish meal, maize, rice andwheat bran) was bought from the Nuguchi MemorialInstitute for Medical Research laboratories (Departmentof Animal Experimentation) Accra – Ghana.Diet preparationThe test diets were prepared by mixing 10 g vegetableoils with 90 g normal commercial rodent chow to obtaina 10 % by weight of the vegetable oils. Three different10 % fat diets were prepared by adding red palm oil (extracted from the pulp of African oil palm (Elaeisguineensis), groundnut oil (extracted from the nuts ofArachishypogaea) and coconut oil (extracted from thekennel of Cocosnucifera) and pure chow as control dietand kept in a refrigerator until use. The supplementationin vegetable oils is in addition to the 5 % fats that are inthe 90 % of the chow. The vegetable oils were boughtfrom the Ghana Food Distribution Corporation. The redpalm oil is composed of 51 % saturated fatty acid, 39 %monounsaturated fatty acids and 10 % polyunsaturatedfatty acids. The groundnut oil is composed of 18 % saturated fatty acid, 48 % monounsaturated fatty acids and34 % polyunsaturated fatty acids, whilst the coconut oilis composed of 92 % saturated fatty acid, 6 % monounsaturated fatty acids and 2 % polyunsaturated fatty acids.Experimental designAfter one week of acclimatization, during which periodmice were fed on normal chow ad libi tum, overnightfasting glucose levels were determined. Only mice whosefasting glucose was 11.0 mmol/L were selected for theexperiment.The selected animals were randomly divided into eightgroups of six animals each:Groups I–IV were on diet treatment only and groupV–VIII, were additionally treated glibenclamide(2 mg/kg body-wt, i.p) daily at 8.00 AM, for the4 week period as follows)
Ngala et al. BMC Nutrition (2016) 2:28Page 3 of 8Group I: chow (control)Group II: groundnut oil dietGroup III: palm oil dietGroup IV: coconut oil dietGroup V: Chow glibenclamide (2 mg/kg b-wt)Group VI: groundnut oil diet glibenclamide (2 mg/kgb-wt)Group VII: palm oil diet glibenclamide (2 mg/kg b-wt)Group VIII: coconut oil diet glibenclamides(2 mg/kg b-wt)Biochemical assayAfter 28 days of treatment, the 12 h-fasted animalswere killed by cervical decapitation between 8 AM.and 9 AM. About 2.0 ml of blood sample was takenfrom each mouse, of which 1.5 ml was dispensed intoa plain tube to clot whiles 0.5 ml of the blood wasput into separate EDTA tubes. The tubes were thenplaced in a centrifuge and spun at 3000 x g for10 min to obtain the plasma and sera. Plasma glucosewas measured immediately and the serum for themeasurement of other biochemical variables wasstored at 80 C until analysis.Biochemical assays including glucose, Total cholesterol, LDL-cholesterol, HDL-cholesterol, triglycerides,were analysed using the automated analyser, MindrayChemistry Analser (BS 120) (China) with reagent kitsmanufactured by the (ELITech Clinical System SAS 2.161500 SEES- FRANCE 2014-2010) compatible with theauto analyser, and according to the reagent kit manufacturer’s protocol.Statistical analysisThe data analysis was done using Graph Pad Prism version 5.00 for windows (GraphPad Software, San DiegoCalifornia, USA). Baseline characteristics were expressedas mean standard error of means (SEM). One-way analysis of variance (ANOVA) with Dunnett’s test was usedfor multiple comparisons between metabolic groups. Pvalue 0.05 was considered significant.Results and discussionThe management of type 2 diabetes mellitus includesthe use of diet, exercise, oral hypoglycemic agents, andinsulin. However, these remedies do not effectively prevent the complications of diabetes mellitus . Extractsof many local medicinal plants have been successfullyused in the management of diabetes . Some dietaryfats have also been reported to be effective in loweringblood glucose . However, dietary fat may also have anegative effect on the lipid profile  which may negatethe gains of glucose lowering.Dietary fats differ in chain length and degree of unsaturation and this affects plasma lipoprotein constitution. Serum cholesterol level increases when dietarycarbohydrates are replaced by saturated fatty acids anddecreases when carbohydrates are replaced by polyunsaturated fatty acids containing omega 3 . Studies havesuggested that the cholesterol-decreasing effect of polyunsaturated fatty acids affects both LDL and HDL cholesterol [28, 29]. However, the mechanism by which thesefats affect serum lipoproteins concentration is unclear.Plasma total cholesterol, and LDL (Table 1) were significantly (p 0.05) reduced and HDL-cholesterol was increased in diabetic mice fed on the groundnut oil diet,whilst the palm oil and coconut oils diets did not haveany significant effects. None of the diets significantly affected the plasma triglycerides level. This means that theconsumption of these vegetable oils does not pose cardiovascular risk. This is supported by the low cardiovascular risk index (HDL-cholesterol/Total cholesterol)Tables 1 and 2.Humans and animal studies have shown that, saturated fat intake increases both LDL and high-densitylipoprotein (HDL) cholesterol levels [30, 31]. Theincreased LDL is due to the inhibiting of LDL receptor activity and thus enhancing apolipoprotein (apo)B-containing lipoprotein production . In contrast,intake of polyunsaturated fatty acids had a modestbut significant LDL cholesterol-lowering effect .The lowering of LDL cholesterol in mice fed withTable 1 The effect of vegetable oil consumption on plasma lipid profile in diabetic MiceVegetable oil without Glibenclimide treatmentParametersControl (C)Palm (PO)Groundnut (GO)aCoconut (CO)bp-valueTC (mmol/l)3.72 0.103.51 0 .043.18 0 .024.06 0 .180.0010LDL (mmol/l)2.57 0 .102.37 0 .061.67 0.04ba2.90 0 .200.0187HDL (mmol/l)0.45 0 .040.45 0.040.72 0 .06ba0.42 0 .040.0252TG (mmol/l)1.52 0 .051.50 0 .041.70 0 .051.60 0.110.8973HDL/TC ratio0.12 0 .0010.13 0 .0010.23 0 .001ba0.10 0.0010.0137Mean effect of vegetable oils on the lipid profile of diabetic mice. Mean value are expressed as mean SEM. N 6 in each group. TC total cholesterol, LDL lowdensity lipoprotein, HDL high density lipoprotein, TG triglycerides. aindicate significant difference compared to controls, p 0.05, bindicate significant differencecompared to other vegetable oils. Total cholesterol, LDL, and LDL were significantly reduced in mice fed on groundnut oil diet only (p 0.05), while HDL wassignificantly increased
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