Update on alpha-linolenic acid

Consumption of omega 3 fatty acids is known to have health benefits. For many years, the importance of the only member of the omega 3 family considered to be essential, alpha-linolenic acid (ALA), has been overlooked. Current research indicates that ALA, along with its longer chain metabolites, may play an important role in many physiological functions. Potential benefits of ALA include cardioprotective effects, modulation of the inflammatory response, and a positive impact on both central nervous system function and behavior. Recommended levels for ALA intake have been set, yet the possible advantages of its consumption are just being revealed.     

The benefits of fish consumption

In 2004, The UK government advice stated that consumers should increase fish consumption to two portions a week, one of which should be oil‐rich fish. However, survey data show that this advice has not been acted upon by most members of the public. In addition, limited data on consumer attitudes highlight barriers to increased fish consumption, such as concerns about buying and cooking fish, perceptions that fish is expensive, and worries that fish meals may not be eaten by all family members. The ‘two‐a‐week’ message is underpinned by strong scientific evidence for heart health, while weaker emerging evidence associates certain nutrients found in fish with a lower risk of immune dysfunction, normal brain development in infants, insulin sensitivity and maintenance of cognitive function in later life. Clearly, further refinement of the two‐a‐week message is needed to ensure that greater numbers of people respond. Ideas include determining appropriate portion sizes for babies and children, increasing awareness of the broad range of fish and shellfish species, highlighting sustainable sources of fish, and reassuring consumers that frozen and prepared fish products count towards the two‐a‐week target. Further work is also needed to address barriers to consumption, particularly among teenagers and younger adults, who have the lowest intakes.     

Chemistry and microbiology of traditional Rihaakuru (fish paste) from the Maldives

Rihaakuru is a traditional Maldivian side dish consumed mainly with rice. It is a thick brown fish paste, made from tuna after prolonged heating. Samples tested were found to have a low water activity (0.55–0.8), slightly acidic pH (5.62–6.18) and moderate salt content (1.4–1.6%). The product was found to be rich in polyunsaturated fatty acids such as omega-3, had high protein content (56–59%) and an energy level of 13.8 kJ/g. The product had a low microbial count (1.54–2.31 log₁₀ cfu/g). The bacteria isolated belonged to the Bacillaceae (Genus Clostridium, and Bacillus), Streptococcaceae (Genus Streptococcus), Micrococcaceae (Genus Staphylococcus), and Corynebacterium. The product appears to be a nutritious and shelf-stable product.     

Use of microencapsulated fish oil as a means of increasing n-3 polyunsaturated fatty acid intake

Background: The successful incorporation of fish oil into foods may provide a means of increasing intakes of n-3 polyunsaturated fatty acids (n-3 PUFA). The aim of the present study was to evaluate the bioavailability of n-3 PUFA in microencapsulatd fish oil compared with a fish oil capsule. Methods: Twenty-eight healthy volunteers were recruited to take part in this randomized controlled trial. Volunteers were supplemented with 0.9 g n-3 PUFA daily for 4 weeks, delivered either as microencapsulated fish oil in a milkshake or as a fish oil capsule. Plasma fatty acid composition and plasma total cholesterol levels were measured at baseline and after supplementation. In addition, volunteers completed a questionnaire on fish consumption, use of supplements and exercise. Results: Responses to the questionnaire indicated that the males who took part in this study took more physical exercise, consumed less fish and were less likely than the females to take supplements. Plasma n-3 PUFA concentrations were raised significantly and by a similar level by both fish oil supplements. Furthermore, no significant difference was observed in plasma n-3 PUFA concentrations following supplementation with either form of fish oil. Plasma total cholesterol levels were not significantly altered by n-3 PUFA supplementation in either group. The results of this study indicated that there was no difference in the bioavailability of n-3 PUFA given as microencapsulated fish oil compared with n-3 PUFA delivered as a fish oil capsule. Fortification of foodstuffs with microencapsulated fish oil therefore offers the potential to increase intakes of n-3 PUFA in line with current recommendations.     

Effects of medium-chain triglycerides, long-chain triglycerides, or 2-monododecanoin on fatty acid composition in the portal vein, intestinal lymph, and systemic circulation in rats.

BACKGROUND: Fatty acid absorption patterns can have a major impact on the fatty acid composition in the portal, intestinal lymph, and systemic circulation. This study sought to determine the effects of long-chain triglycerides (LCT), medium-chain triglycerides (MCT), and 2-monododecanoin (2mono) on intestinal fatty acid composition during continuous feeding over a brief period. METHODS: The lipid sources were 100% LCT, 100% MCT, a 50:50 mixture of LCT and MCT (LCT/MCT), and a 50:50 mixture of LCT and 2mono (LCT/2mono). A total of 27 rats were randomly given 1 of the 4 diets at 200 kcal/kg/d, with 30% of total calories from lipids over 3 hours. RESULTS: MCT significantly increased each of the medium-chain fatty acids (C6:0, C8:0, and C10:0) as free fatty acids in the portal vein and about 10%/mol of C10:0 as triglycerides in the lymph compared with the other groups. There was significantly less C10:0 in lymphatic triglycerides with LCT/MCT than with MCT, but more than in the LCT and LCT/2mono diets. MCT also significantly increased the contents of C16:0, C18:0, C18:1, and C20:4 in the lymphatic triglycerides compared with all other groups including LCT/MCT. The amount of linoleic acid (C18:2) in lymphatic triglycerides followed the relative amounts of this fatty acid in the diet, with the greatest in LCT followed by LCT/MCT and LCT/2mono and least in MCT. A so-called structured lipid composed of the medium-chain fatty acid dodecanoic acid on the 2 position and long-chain fatty acids on the 1 and 3 positions appeared to be endogenously synthesized in response to the LCT/2mono diet. CONCLUSIONS: The original differences in MCT and LCT content in the diets were preserved in the fatty acid composition in the intestinal free fatty acids and triglycerides during feeding. In addition, the duration of lipid administration can play a role in altering fatty acid composition in the intestine.     

鱼油豆油对大鼠线粒体磷脂脂肪酸组成的影响

方法：大鼠分别饲以低硒和补硒饲料３０天，补加油类之后（５０ｇ／ｋｇ饲料）继续饲养３０天。结果：线粒体膜磷脂中脂肪酸组成可反映大鼠饮食中脂肪酸的组成，磷脂酰胆碱（ＰＣ）和磷脂酰乙醇胺（ＰＥ）中Ｃ２０∶５和Ｃ２２∶６含量鱼油组明显高于豆油组，而且鱼油中Ｃ２２∶６比Ｃ２０∶５优先结合掺入磷脂中。ＰＣ中Ｃ２０∶４豆油组明显高于鱼油组。ω６／ω３比值降低。豆油和鱼油均使线粒体Ｃａ２＋－ＡＴＰａｓｅ活性下降，但对线粒体钙有不同的影响。补硒对脂肪酸组成，Ｃａ２＋－ＡＴＰａｓｅ影响不大，但加速钙的释放。结论：鱼油具有防治心血管疾病的作用，其作用基础可能在于Ｃ２０∶５和Ｃ２２∶６掺入细胞膜磷脂中，影响了脂肪酸组成，并对其功能产生影响     

Specific insulin sensitivity and leptin responses to a nutritional treatment of obesity via a combination of energy restriction and fatty fish intake

Background Nutritional strategies to treat obesity often influence neuroendocrine factors related to body weight control. The present study aimed to investigate whether the inclusion of three fatty fish servings per week within a hypocaloric diet may have specific healthy effects on insulin and leptin functions. Methods Thirty‐two subjects (body mass index = 31.6 ± 3.5 kg m^?2) aged 36 ± 7 years, were assigned to a control or fish‐based energy‐restricted diet over an 8‐week period. Anthropometry, body composition, lipid profile, leptin and insulin values were measured at the start and at the end of the dietary intervention. Results Both experimental diets resulted in a similar mean weight loss (control = 5.3 ± 2.6% versus fish‐based = 5.5 ± 2.5%; P = 0.783). A significant reduction in insulin resistance, as determined by the homeostatic model assessment index (HOMA‐IR = insulin × glucose/22.5), was observed after the fish‐based intervention. The change in circulating leptin was higher in the fish‐based diet compared to the control group. Sixteen percent of the variability in the change of adjusted‐leptin could be explained (P = 0.034) by the HOMA index change and the type of diet. Conclusions Three servings a week of fatty fish included in an energy‐restricted diet appears to be a valid strategy for specifically improving insulin sensitivity and leptin levels in obese subjects, which could involve a better body weight regulation after a nutritional intervention period.     

Women's diet quality in the UK

Women's diets are of interest as they not only impact on wellbeing and risk of chronic disease in women themselves, but also influence pregnancy outcomes and infant health. UK dietary surveys show that, while some improvements have occurred, intakes of key micronutrients, particularly iron, vitamin D, calcium and folate remain below recommended levels. Women's diets are also too high in saturated fat and salt, and low in fibre, oily fish and fruits and vegetables. Evidence suggests that certain chronic conditions are influenced by dietary components, e.g. inadequate calcium and vitamin D intakes reduce bone density, salt and saturated fat increase cardiovascular disease risk, excessive alcohol intakes increase cancer risk, low intakes of long chain n‐3 fatty acids may adversely affect fetal development and mental health, while adequate folic acid reduces the risk of birth defects. Focused health initiatives are needed to improve diet quality in women, particularly school‐aged girls, women planning a pregnancy, those living in areas of deprivation and elderly women. Vitamin and mineral supplements, and fortified foods may have a role to play alongside dietary improvements in helping women to achieve optimal diet quality.     

Oily fish and fish oil supplements in the prevention of coronary heart disease

Dietary advice for the reduction of coronary heart disease events emphasizes the importance of a low-fat diet and advice on the consumption of oily fish may also be given. This report reviews the evidence linking fish consumption with coronary risk. On the basis of available evidence, a target of two to three portions of oily fish per week (200–400 g, 7–14 oz) is considered reasonable, particularly for secondary prevention. For those who cannot achieve the suggested dietary intake of oily fish, the partial or complete substitution of fish oil supplements may be appropriate. A range of suitable types of fish oil supplements is given, but an awareness of the potential adverse effects of fish oil supplementation is considered important. Further studies are needed to define the role of fish intake in coronary heart disease.     

Oxidation of fish oil supplements in Australia

Fish oils oxidise readily, forming primary and secondary oxidation products, which may be harmful for humans. Some recent studies reported that fish oil supplements in Australasia are oxidised above acceptable international limits, however other studies reported low levels of oxidation. This study employed peroxide and p-anisidine values determination to measure primary and secondary oxidation of fish oils in the Australian market. Of 26 supplements tested, 38% exceeded the limit for primary oxidation, 25% exceeded the limit for secondary oxidation and 33% exceeded the limit for total oxidation, according to international recommendations. Four specially marketed supplements were found to deliver significantly lower amounts of fish oil per capsule (165 vs. 577?mg, p?=?.007), yet cost significantly more on a per gram basis ($2.97 vs $0.39, p?<?.001). However, there were no differences in any oxidative markers between regular supplements and the specially marketed products.     

Docosahexaenoic acid (DHA): an ancient nutrient for the modern human brain

Modern humans have evolved with a staple source of preformed docosahexaenoic acid (DHA) in the diet. An important turning point in human evolution was the discovery of high-quality, easily digested nutrients from coastal seafood and inland freshwater sources. Multi-generational exploitation of seafood by shore-based dwellers coincided with the rapid expansion of grey matter in the cerebral cortex, which characterizes the modern human brain. The DHA molecule has unique structural properties that appear to provide optimal conditions for a wide range of cell membrane functions. This has particular implications for grey matter, which is membrane-rich tissue. An important metabolic role for DHA has recently been identified as the precursor for resolvins and protectins. The rudimentary source of DHA is marine algae; therefore it is found concentrated in fish and marine oils. Unlike the photosynthetic cells in algae and higher plants, mammalian cells lack the specific enzymes required for the de novo synthesis of alpha-linolenic acid (ALA), the precursor for all omega-3 fatty acid syntheses. Endogenous synthesis of DHA from ALA in humans is much lower and more limited than previously assumed. The excessive consumption of omega-6 fatty acids in the modern Western diet further displaces DHA from membrane phospholipids. An emerging body of research is exploring a unique role for DHA in neurodevelopment and the prevention of neuropsychiatric and neurodegenerative disorders. DHA is increasingly being added back into the food supply as fish oil or algal oil supplementation.