Short-term comparative study of the influence of fried edible oils intake on the metabolism of essential fatty acids in obese individuals
Highlights
► Effect of fried oils containing antioxidants on obese individuals. ► Changes on concentration of metabolites of arachidonic acid pathway by oil ingestion. ► Difference in effects of fried olive oil versus fried sunflower oil.
Introduction
Dietary fat plays a major nutritional role as a key source of energy despite the concerns about fat intake in developed countries (fat provides 9 kcal/g of metabolizable energy versus an average energy of 4 kcal/g for carbohydrates and proteins). Dietary fat is also the source of essential fatty acids (EFAs) and thus, it must be present in the diet. EFAs derive from two families of fatty acids, namely, n-6 and n-3 unsaturated fatty acids.
Linoleic acid (LA; 18:2 n-6), which accounts for more than 50% of the fatty acids in many vegetable oils (e.g. sunflower oil), is the main n-6 fatty acid in the diet. LA accounts for between 85% and 90% of the n-6 fatty acids in the diet with the balance coming from arachidonic acid (AA; 20:4 n-6) and γ-linolenic acid (18:3 n-6). By contrast, α-linolenic acid (LNA; 18:3 n-3) is a member of the n-3 family of fatty acids. Like LA, α-linolenic acid is the main n-3 fatty acid in the diet, although common vegetable oils contain LNA concentrations below 1%.
Essential fatty acids are important constituents of biological membranes, which surround cells and subcellular particles (McDonald & Eskin, 2006). EFAs also serve as precursors of a variety of biologically active compounds referred to collectively as eicosanoids (e.g. prostaglandins, thromboxanes, and leukotrienes), which are key regulators of a host of physiological reactions, including constriction and dilation of blood vessels, contraction of smooth muscle, platelet aggregation and regulation of immune and inflammatory functions (Wang & DuBois, 2007). Eicosanoids are formed through the action of a set of oxygenase-type enzymes such as cyclooxygenases (COXs), lipoxygenases (LOXs), and cytochrome P450 monooxygenases (CYP450s). Thus, metabolism of C-20 fatty acids by COX enzymes leads to the formation of prostanoids, including prostaglandins (PGs) and thromboxanes (TXs), generating three series of compounds depending on the original fatty acid (Fitzpatrick and Soberman, 2001, Peters-Golden and Brock, 2003, Yang et al., 2006) (Supplementary Fig. 1). Eicosanoids of the 2- and 3-series are of clinical interest because they derive from two competitive pathways (n-3 and n-6), which could justify their opposite functions, as suggested by Schmitz and Ecker (2008). Thus, 2-series eicosanoids produced from arachidonic acid possess pro-inflammatory, pro-aggregating, vasoconstriction action and immunosuppressive properties, as recently reported by Wang and DuBois (2010). On the other hand, eicosanoids of the 3-series produced from eicosapentaenoic acid have anti-inflammatory, anti-aggregating, vasodilatory and anti-arythmic actions and immunomodulating properties (González-Périz and Clària, 2010, Groeger et al., 2010).
Lipoxygenases convert AA, LA and other PUFAs into bioactive metabolites such as leukotrienes (LTs), hydroxyeicosatetraenoic acids (HETEs) and hydroxyoctadecadienoic acids (HODEs). LOX-catalysed products, LTs, HETEs, and HODEs also exert profound biological effects on inflammation processes being involved in the development and progression of specific human cancers such as colorectal or pancreatic cancer (Xian-Zhong, Wei-Gang, & Thomas, 2001).
Deep fat frying is one of the most common processes used worldwide for preparation of cooked food. Complex patterns of oxidative and thermolytic reactions take place in fats and oils during heating and deep-fat frying, including polymerisation, hydrolysis, isomerization, and cyclisation (Dobson et al., 1995, White, 1991, William and Dobson, 2000). Secondary oxidation products are mainly oxidised triglyceride monomers, dimers, and polymers that define the thermal oxidised compounds of the polar material fraction (Dobarganes et al., 2000, Romero et al., 2006). Oxidation modifies the organoleptic properties of oils and affects their shelf life, mainly owing to formation of oxidation products of cholesterol and phytosterols. Degradation results in loss of nutritional value of food as well as changes in its physiological properties (Saguy and Danaa, 2003, Tyagi and Vasishtha, 1996), which cause rejection from the consumers and losses to the target industries, as a result.
The presence of antioxidants, naturally existing in (or added to) oils, exerts beneficial effects by avoiding or delaying oxidation during frying of compounds such as sterols, fatty alcohols, triterpenic dialcohols and unsaturated fatty acids. As happens with other food additives, natural antioxidants such as phenol compounds have demonstrated an antioxidant activity superior to that of synthetic oxidation inhibitors; therefore, there is an increased trend to replace the latter with natural antioxidants. The enrichment of edible oils with phenols protects them, for example, against oxidation that means better oil quality and prevention from the formation of toxic products such as cholesterol oxides (Dobarganes & Márquez-Ruiz, 2006).
The aim of the present research was to evaluate the nutritional impact of the intake of four breakfasts prepared with oils subjected to deep frying on the profile of eicosanoids in human serum. The target metabolites were selected taking into account the direct implication of their metabolism in the inflammatory cascade. Vegetable edible oils with natural or added content of antioxidants were selected for this purpose. Breakfast muffins made with these oils were ingested by 26 obese volunteers who consumed the different muffins throughout eight weeks. Liquid-chromatography coupled to mass detection was used to monitor eicosanoids profile in human serum extracted from all individuals at three different sampling times.
Section snippets
Oils and heating procedure
The edible oils were: (1) extra-virgin olive oil (VOO) as such with a total natural phenols concentration of 400 mg/L, expressed as caffeic acid, 70.5% monounsaturated fatty acids (MUFAs), 11.1% PUFAs, 18.4% saturated fatty acids (SFAs); (2) refined high-oleic sunflower oil enriched with an olive–pomace extract of phenols (ASO) up to 400 mg/L, also expressed as caffeic acid, 76.7% MUFAs, 17.6% PUFAs and 5.8% SFAs; (3) refined high-oleic sunflower oil enriched with 400 mg/L of dimethylsiloxane as a
Characteristics of the cohort selected for the study
There are several events that can turn on inflammatory responses. The most obvious are microbial invasion, injuries and burns. However, it is important to understand how diet can also activate the same inflammatory responses. Obesity is a multifactorial condition resulting from improper balances of hormones and gene expression induced by the diet. It is becoming more evident that inflammation plays an important role in the metabolic consequences of obesity as well as other chronic degenerative
Concluding remarks
The effect of the intake of breakfasts prepared with four edible oils subjected to a simulated deep frying protocol has been assessed in terms of serum levels of well-known biomarkers of the inflammatory cascade. Multivariate analysis has led to discrimination between different breakfasts depending on the content of hydrophilic antioxidants after oils heating. Additionally, the fatty acids profile has been hypothesised as a critical aspect to detect deregulation of the metabolism of EFAs. This
Acknowledgments
The Spanish Ministerio de Ciencia e Innovación (MICINN) and FEDER Program are thanked for financial support through projects CTQ2009-07430 and SAF2007-62005. F.P.-C. is also grateful to the MICINN for a Ramón y Cajal contract (RYC-2009-03921).
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