High dietary intake of palm oils compromises glucose tolerance whereas high dietary intake of olive oil compromises liver lipid metabolism and integrity.

PURPOSE: Palm (PO) and olive oils (OO) are the two most consumed and/or used oils in the world for food elaboration. These oils should not be confused with the solid palm stearin which is widely used in pastry making. Large number of studies was reported dealing with adverse/beneficial cardiovascular effects of PO and OO, whereas few studies were conducted to compare their potential effects on hepatic steatosis and liver lipid metabolism. The aim of this study was to compare the metabolic effects of high intake of POs (both crude and refined) and virgin OO on surrogate parameters of glucose tolerance, hepatic lipid metabolism and liver integrity. METHODS: Thirty-two young male Wistar rats were divided into four equal groups and fed either control diet (11% energy from fat) or three high-fat diets rich in crude or refined POs or in OO (56% energy from fat), during 12 weeks. Systemic blood and liver biochemical parameters linked to glucose and lipid metabolism as well as hepatic steatosis and liver fatty acid composition were explored. The inflammation and oxidative stress status as well as the expression of several genes/proteins were also analyzed. RESULTS: The major effects of POs intake concerned glucose metabolism and liver fatty acid composition, whereas the major effects of OO intake concerned hepatic TG accumulation, inflammation, and cytolysis. CONCLUSIONS: In conclusion, high dietary intake of PO compromises glucose tolerance whereas high dietary intake of OO compromises hepatic lipid composition and liver integrity. However, adverse hepatic effects of OO observed in this study may not be transposed to human since, (a) the rodent model could lead to different effects than those observed in humans and (b) the average normal OO amounts ingested in the population are lower than those corresponding to a high-fat diet. So, further studies are needed to determine a maximum non-invasive dietary intake of OO.

Impact of Highly Saturated versus Unsaturated Fat Intake on Carbohydrate Metabolism and Vascular Reactivity in Rat.

Palm olein (PO) and lard are considered harmful to health because of their highly saturated fatty acid content. On the contrary, olive oil (OO) with its high level of polyunsaturated fatty acids is considered healthier. This study aims to evaluate the effects of high consumption of these oils on carbohydrate metabolism and vascular function. Male Wistar rats were fed ad libitum for 12 weeks with different high fat diets (HFD) containing 30% of each oil. Systemic glycemia, insulinemia, and lipidemia were assessed by routine methods or by ELISA. GLUT4 muscular expression and hepatic and muscular Akt phosphorylation were analyzed by western blot. Vascular function was evaluated, ex vivo, on aortic rings and on the variations of isometric tensions. The results show that fasting blood glucose was increased with PO and OO diets and decreased with lard. Compared to control diet, this increase was significant only with PO diet. The area under the curve of IPGTT was increased in all HFD groups. Compared to control diet, this increase was significant only with PO. In contrast, stimulation of the pathway with insulin showed a significant decrease in Akt phosphorylation in all HFD compared to control diet. KCl and phenylephrine induced strong, dose-dependent vasoconstriction of rat aortas in all groups, but KCl EC50 values were increased with lard and OO diets. The inhibitory effect of tempol was absent in PO and lard and attenuated in OO. Vascular insulin sensitivity was decreased in all HFD groups. This decreased sensitivity of insulin was more important with PO and lard when compared to OO diet. In conclusion, the results of this study clearly show that high consumption of palm olein, olive oil, and lard can compromise glucose tolerance and thus insulin sensitivity. Furthermore, palm olein and lard have a more deleterious effect than olive oil on the contractile function of the aorta. Excessive consumption of saturated or unsaturated fatty acids is harmful to health, regardless of their vegetable or animal origin.

Peripancreatic Adipose Tissue Remodeling and Inflammation during High Fat Intake of Palm Oils or Lard in Rats.

Excessive fat consumption leads to the development of ectopic adipose tissues, affecting the organs they surround. Peripancreatic adipose tissue is implicated in glucose homeostasis regulation and can be impaired in obesity. High palm oil consumption's effects on health are still debated. We hypothesised that crude and refined palm oil high-fat feeding may have contrasting effects on peripancreatic adipocyte hypertrophy, inflammation and lipid oxidation compound production in obese rats. In Wistar rats, morphological changes, inflammation and isoprostanoid production following oxidative stress were assessed in peripancreatic adipose tissue after 12 weeks of diets enriched in crude or refined palm oil or lard (56% energy from fat in each case) versus a standard chow diet (11% energy from fat). Epididymal white and periaortic brown adipose tissues were also included in the study. A refined palm oil diet disturbed glucose homeostasis and promoted lipid deposition in periaortic locations, as well as adipocyte hypertrophy, macrophage infiltration and isoprostanoid (5-F2c-isoprostane and 7(RS)-ST-Δ8-11-dihomo-isofuran) production in peripancreatic adipose tissue. Crude palm oil induced a lower impact on adipose deposits than its refined form and lard. Our results show that the antioxidant composition of crude palm oil may have a protective effect on ectopic adipose tissues under the condition of excessive fat intake.

Effects of high-fat diets on inflammation and antioxidant status in rats : comparison between palm olein and olive oil.

Palm olein (PO) and olive oil (OO) are widely consumed in the world. PO is considered harmful to health, whereas OO is considered healthy. The aim of the study was to compare the effects of consumption of these oils on antioxidant status and inflammation in rats. This was an experimental study in male wistar rats fed a diet containing 30% of each oil. Rats had free access to food and water. After being fed for 12 weeks, animals were sacrificed and liver and aortic blood were collected. Plasma was used for the determination of interleukin-6 (IL-6) and oxidative stress parameters (Superoxide dismutase -SOD; Gluthation peroxidase - GPx; Thiobarbituric acid reactive substances - TBARS; Thiol groups and isoprostane). The inflammation and oxidative stress status as well as the expression of several genes/proteins were also analyzed in liver homogenate. No significant differences were observed between PO and OO in plasma and liver levels of the studied inflammation and oxidative stress parameters. This study showed that the consumption of PO induces an antioxidant status superimposable to that of OO.   Key words : Palm olein - Olive oil - Oxidative stress - Inflammation - High fat diet.

Impact of diets rich in olive oil, palm oil or lard on myokine expression in rats.

It has recently emerged that myokines may be an important skeletal muscle adaptive response to obesogenic diets in sedentary subjects (who do not exercise). This study aimed to assess the influence of various high fat (HF) diets rich in either crude palm oil (cPO), refined palm oil (rPO), olive oil (OO) or lard on the modulation of myokine gene expression in the gastrocnemius. Five groups of 8 rats were each fed HF or control diet for 12 weeks. Systemic parameters concerning glucose, insulin, inflammation, cholesterol, triglycerides (TG) and transaminases were assessed by routine methods or ELISA. Akt and ACC phosphorylation were analyzed by WB in the soleus. Mitochondrial density, inflammation, and the gene expression of 17 myokines and the apelin receptor (Apj) were assessed by qPCR in the gastrocnemius. We found that HF diet-fed rats were insulin resistant and Akt phosphorylation decreased in the soleus muscle, but without any change in Glut4 gene expression. Systemic (IL-6) and muscle inflammation (NFκB and IκB) were not affected by the HF diets as well as TBARS, and ASAT level was enhanced with OO diet. Soleus pACC phosphorylation and gastrocnemius mitochondrial density were not significantly altered. The gene expression of some myokines was respectively increased (myostatin and Il-15) and decreased (Fndc5 and apelin) with the HF diets, whatever the type of fat used. The gene expression of two myokines with anti-inflammatory properties, Il-10 and myonectin, was dependent on the type of fat used and was most increased respectively with cPO or both rPO and OO diets. In conclusion, high-fat diets can differentially modulate the expression of some myokines, either in a dependent manner or independently of their composition.