Special Issue Information

Dear Colleagues,

Dietary lipids derived from plants and animals are essential for growth and development, and serve as an energy reserve. They encompass fatty acids (saturated, monounsaturated and polyunsaturated, the latter further categorised as omega-3 or omega-6 fatty acids), their derivatives including mono-, di-, and triglycerides and phospholipids, as well as sterols such as cholesterol. Humans have a dietary requirement for essential fatty acids such as linoleic acid (found mostly in vegetable oils) and alpha-linolenic acid (found in some green-leafed plants, seeds, nuts and legumes), because these fatty acids cannot be synthesized from precursors in the diet. Fish oils are a rich source of the longer-chain omega-3 fatty acids eicosapentaenoic acid and docosahexaenoic acid. There is much evidence demonstrating significant health benefits of omega-3 fatty acids in infant development, cardiovascular diseases and some mental illnesses. In contrast, consumption of trans fats which occur naturally in some foods but derive mostly during food processing through partial hydrogenation of unsaturated fats, are a risk factor for cardiovascular disease. Blood lipids are transported as lipoproteins with the liver playing a major role in lipid metabolism. Lipids are essential components of biological membranes, but are also involved in cell signalling and act as substrates for various enzymes leading to the formation of an array of biologically active metabolites known as eicosanoids. The purpose of this special issue of Nutrients is to assemble recent literature on the topic of dietary lipids in humans with particular emphasis on breast feeding, nutrition in childhood and adolescence, omega-3 fatty acids in cardiovascular health and cognitive function, and new findings in their metabolism to bioactive metabolites.

Abstract: Functional innate and acquired immune responses are required to protect the host from pathogenic bacterial infections. Modulation of host immune functions may have beneficial or deleterious effects on disease outcome. Different types of dietary fatty acids have been shown to have variable effects on bacterial clearance and disease outcome through suppression or activation of immune responses. Therefore, we have chosen to review research across experimental models and food sources on the effects of commonly consumed fatty acids on the most common food-borne pathogens, including Salmonella sp., Campylobacter sp., Shiga toxin-producing Escherichia coli, Shigella sp., Listeria monocytogenes, and Staphylococcus aureus. Altogether, the compilation of literature suggests that no single fatty acid is an answer for protection from all food-borne pathogens, and further research is necessary to determine the best approach to improve disease outcomes.

Abstract: In the present study, we used a preclinical model of induced lipolytic enzyme insufficiency, and hypothesized that the use of monoacylglycerols (MAG) will enhance their bioavailability and delivery to the tissues. Experimental diets containing 20% lipids were fed to rats for 21 days with or without Orlistat. The control diet of fish oil (FO), a source of EPA and DHA, was tested against: structured (A) vanillin acetal of sn-2 MAG (Vanil + O) and (B) diacetyl derivative of sn-2 MAG (Acetyl + O) and (C) free MAG (MAG + O). FA profiles with an emphasis on EPA and DHA levels were determined in plasma, red blood cells (RBC), liver, spleen, brain and retina. We observed significant reduction of lipid absorption when rats co-consumed Orlistat. As expected, the FO groups with and without Orlistat showed the biggest difference. The Vanil + O, Acetyl + O and MAG + O groups, demonstrated higher levels of EPA (5.5 ± 1.9, 4.6 ± 1.6 and 5.6 ± 0.6, respectively) in RBC compared with FO + O diets (3.3 ± 0.2, 2.6 ± 0.2). Levels of EPA incorporation, in plasma, were similar to those obtained for RBC, and similar trends were observed for the collected tissues and even with DHA levels. These observations with two MAG derivatives providing the fatty acid esterified in the sn-2 position, show that these molecules are efficient vehicles of EPA in malabsorption conditions which is in line with our hypothesis. Free MAG, characterized as having exclusively sn-1(3) isomers of EPA, demonstrated better absorption efficiencies and accretion to tissues when compared to structured MAG. The study demonstrated that structured and free MAG can be used efficiently as an enteral vehicle to supply bioactive fatty acids such as EPA and DHA in lipid malabsorption where diminished lipolytic activity is the underlying cause.

Abstract: Essential fatty acids (EFA) are nutrients that form an amazingly large array of bioactive mediators that act on a large family of selective receptors. Nearly every cell and tissue in the human body expresses at least one of these receptors, allowing EFA-based signaling to influence nearly every aspect of human physiology. In this way, the health consequences of specific gene-environment interactions with these nutrients are more extensive than often recognized. The metabolic transformations have similar competitive dynamics for the n-3 and n-6 homologs when converting dietary EFA from the external environment of foods into the highly unsaturated fatty acid (HUFA) esters that accumulate in the internal environment of cells and tissues. In contrast, the formation and action of bioactive mediators during tissue responses to stimuli tend to selectively create more intense consequences for n-6 than n-3 homologs. Both n-3 and n-6 nutrients have beneficial actions, but many common health disorders are undesired consequences of excessive actions of tissue n-6 HUFA which are preventable. This review considers the possibility of preventing imbalances in dietary n-3 and n-6 nutrients with informed voluntary food choices. That action may prevent the unintended consequences that come from eating imbalanced diets which support excessive chronic actions of n-6 mediators that harm human health. The consequences from preventing n-3 and n-6 nutrient imbalances on a nationwide scale may be very large, and they need careful evaluation and implementation to avoid further harmful consequences for the national economy.

Abstract: The effect of fermented soymilk on rats fed a high cholesterol diet was investigated to clarify the cholesterol-lowering function. Male Sprague-Dawley rats aged 7 weeks were fed a control diet (1% cholesterol, high cholesterol diet), high cholesterol diet containing 11.7% fermented soymilk diet (5% soy protein as final concentration, F-5), or high cholesterol diet containing 23.4% fermented soymilk diet (10% soy protein as final concentration, F-10) for 5 weeks. The liver weight and fat mass were decreased by the ingestion of fermented soymilk. The hepatic triglyceride and cholesterol levels in the F-5 and F-10 groups were significantly lowered compared to those in the control group. The plasma total cholesterol level of the F-10 group was significantly decreased. The expression of SREBP-2, a cholesterol synthesis-related gene, was significantly decreased in liver of the F-5 group, but the expression of CYP7a1, a cholesterol catabolism-related gene, was significantly increased. These results suggest that fermented soymilk can modulate the cholesterol metabolism in rats fed a high cholesterol diet.

Abstract: The present study investigated the effect of a reduced protein diet in combination with different vegetable oils (sunflower seed oil or linseed oil) on carcass traits, meat quality and fatty acid profile in porcine muscle. Forty male Landrace pigs were allocated into four experimental groups (each n = 8) and one control group (n = 8) at a live weight of approximately 60 kg. The pigs were fed ad libitum from 60 kg to 100 kg live weight and restricted to 2.8 kg/day until they reached 120 kg. In contrast to other studies, the intramuscular fat content (IMF) did not increase in animals of groups fed a reduced protein diet and vegetable oils. The IMF ranged between 1.2% and 1.4%. The growth performance and meat quality of the longissimus muscle was not affected by the diet, but the average daily gain (ADG) and drip loss were affected. The muscle fatty acid concentrations were significantly affected by the diet, resulting in higher n-3 FA concentrations up to 113 mg/100 g muscle and lower n-6/n-3 PUFA ratiofor pigs fed linseed oil-containing high- and reduced protein diets, compared to sunflower seed oil-containing diets.

Abstract: The associations between dietary cholesterol and heart disease are highly controversial. While epidemiological studies and clinical interventions have shown the lack of correlation between cholesterol intake and cardiovascular disease (CVD) risk, there is still concern among health practitioners and the general population regarding dietary cholesterol. In this review, several clinical studies utilizing cholesterol challenges are analyzed in terms of changes that occur in lipoprotein metabolism resulting from excess consumption of cholesterol. Dietary cholesterol has been shown to increase both LDL and HDL in those individuals who respond to a cholesterol challenge without altering the LDL cholesterol/HDL cholesterol ratio, a key marker of CVD risk. Further, dietary cholesterol has been shown to increase only HDL with no changes in LDL with average cholesterol consumption and during weight loss interventions. Ingestion of cholesterol has also been shown to increase the size of both LDL and HDL particles with the associated implications of a less atherogenic LDL particle as well as more functional HDL in reverse cholesterol transport. Other changes observed in lipoprotein metabolism are a greater number of large LDL and decreases in small LDL subfractions. All this information put together points to specific roles of dietary cholesterol in substantially altering intravascular processing of lipoproteins as well as reverse cholesterol transport.

Abstract: Eicosapentaenoic and docosahexaenoic acids have been reported to have a variety of beneficial effects on cardiovascular disease risk factors. However, a large inter-individual variability in the plasma lipid response to an omega-3 (n-3) polyunsaturated fatty acid (PUFA) supplementation is observed in different studies. Genetic variations may influence plasma lipid responsiveness. The aim of the present study was to examine the effects of a supplementation with n-3 PUFA on the plasma lipid profile in relation to the presence of single-nucleotide polymorphisms (SNPs) in the fatty acid desaturase (FADS) gene cluster. A total of 208 subjects from Quebec City area were supplemented with 3 g/day of n-3 PUFA, during six weeks. In a statistical model including the effect of the genotype, the supplementation and the genotype by supplementation interaction, SNP rs174546 was significantly associated (p = 0.02) with plasma triglyceride (TG) levels, pre- and post-supplementation. The n-3 supplementation had an independent effect on plasma TG levels and no significant genotype by supplementation interaction effects were observed. In summary, our data support the notion that the FADS gene cluster is a major determinant of plasma TG levels. SNP rs174546 may be an important SNP associated with plasma TG levels and FADS1 gene expression independently of a nutritional intervention with n-3 PUFA.

Abstract: Parenteral nutrition lipid emulsions made from various plant oils contain steroidal compounds, called phytosterols. During parenteral administration of lipid emulsions, phytosterols can reach levels in the blood that are many fold higher than during enteral administration. The elevated phytosterol levels have been associated with the development of liver dysfunction and the rare development of liver failure. There is limited information available in the literature related to phytosterol concentrations in lipid emulsions. The objective of the current study was to validate an assay for steroidal compounds found in lipid emulsions and to compare their concentrations in the most commonly used parenteral nutrition lipid emulsions: Liposyn® II, Liposyn® III, Lipofundin® MCT, Lipofundin® N, Structolipid®, Intralipid®, Ivelip® and ClinOleic®. Our data demonstrates that concentrations of the various steroidal compounds varied greatly between the eight lipid emulsions, with the olive oil-based lipid emulsion containing the lowest levels of phytosterols and cholesterol, and the highest concentration of squalene. The clinical impression of greater incidences of liver dysfunction with soybean versus MCT/LCT and olive/soy lipid emulsions may be reflective of the levels of phytosterols in these emulsions. This information may help guide future studies and clinical care of patients with lipid emulsion-associated liver dysfunction.

Abstract: Scientific literature is increasingly reporting on dietary deficiencies in many populations of some nutrients critical for foetal and infant brain development and function. Purpose: To highlight the potential benefits of maternal supplementation with docosahexaenoic acid (DHA) and other important complimentary nutrients, including vitamin D, folic acid and iodine during pregnancy and/or breast feeding for foetal and/or infant brain development and/or function. Methods: English language systematic reviews, meta-analyses, randomised controlled trials, cohort studies, cross-sectional and case-control studies were obtained through searches on MEDLINE and the Cochrane Register of Controlled Trials from January 2000 through to February 2012 and reference lists of retrieved articles. Reports were selected if they included benefits and harms of maternal supplementation of DHA, vitamin D, folic acid or iodine supplementation during pregnancy and/or lactation. Results: Maternal DHA intake during pregnancy and/or lactation can prolong high risk pregnancies, increase birth weight, head circumference and birth length, and can enhance visual acuity, hand and eye co-ordination, attention, problem solving and information processing. Vitamin D helps maintain pregnancy and promotes normal skeletal and brain development. Folic acid is necessary for normal foetal spine, brain and skull development. Iodine is essential for thyroid hormone production necessary for normal brain and nervous system development during gestation that impacts childhood function. Conclusion: Maternal supplementation within recommended safe intakes in populations with dietary deficiencies may prevent many brain and central nervous system malfunctions and even enhance brain development and function in their offspring.