Omega-3 Fatty Acid Composition of Habitual Diets in Australia Neil J Mann Department of Food Science Melbourne Australia
Background Generally agreed amongst lipid researchers that the western diet has: High n-6 : n-3 PUFA intake Low total n-3 PUFA intake This leads to an over emphasis of arachidonic acid (20:4 n-6) derived eicosanoids (TXA2 PGE2 LTB4 etc) with subsequent increased risk of vascular disease and inflammatory conditions.
Recommended dietary intakes for n-6 and n-3 PUFA Workshop on the essentiality of / and recommended dietary intakes for n-6 and n-3 fatty acids. (NIH Bethesda Maryland USA, April 1999). Adequate intakes (AI) for adults Fatty acid Grams/day % Energy (2000 kcal diet) Linoleic acid 4.44 2.0 (Upper limit) 6.67 3.0 a-linolenic acid 2.22 1.0 EPA (min) 0.22 0.1 DHA (min) 0.22 0.1 EPA + DHA 0.65 0.3
Determination of n-3 PUFA intake • To make public health recommendations we need to know what amounts of fatty acids are being consumed by different dietary groups. • In many tables of fatty acid content of foods, information is reported as g fatty acid/100g food (to one decimal place). • Except in certain foods, such as fish, LC PUFA are present in only trace amounts. • Most fatty acid databases cannot be used to estimate long chain PUFA intake (AA EPA DHA etc). Because the trace levels disappear ! But these small (ignored) contributions can accumulate to significant levels of biological importance in the context of a total diet.
Determination of n-3 PUFA intake (contd) Due to the low levels of LC PUFA present in foods, composition tables can round them down to zero when reported to a single decimal place (g/100g food). For example 100g lamb chops contain: (130mg LA, 52mg AA, 44mg EPA, 36mg DPA and 10mg DHA) This would appear in a composition table as shown:
Aims • Create a fatty acid database of current food supply to two decimal places in g/100g • Determine the consumption level of fatty acids in specific dietary groups • Investigate the main dietary sources of LC n-3 PUFA in the diets
1. The fatty acid database • The database consists of 1077 foods with full fatty acid analysis (at present) • The reported analytical data contains 11 sat fatty acids, 7 MUFA, 10 PUFA (6 n-6, 4 n-3) and 3 trans fatty acids • The database concentrates on foods with greater than 1% total fat by weight
The dietary study Healthy male subjects were recruited from 4 habitual diet groups.
2. The dietary study Characteristics of subjects in the dietary groups (mean + s.d) Values on the same line with different superscripts are significantly different at (p<0.05).
2. The dietary study Daily intake of selected items by the 4 dietary groups (mean + s.d)
2. The dietary study LC fatty acid intake (mg/day) for the 4 habitual diet groups.
2. The dietary study Combining the two meat eating groups into one “omnivore group” we see the following mean daily intake patterns: Group 18:2n-6 18:3n-3 LC n-3 n-6:n-3 Omnivores (n=71) 14.2 g 1.5 g 190 mg 9.5 : 1 Ovolacto (n=42) 18.4 g 1.4 g 10 mg 12.9 : 1 Vegan (n=18) 21.6 g 1.2 g 0 mg 18.7 : 1 Recommended < 6.7 g > 2.2 g > 650 mg
2. The dietary study The results for omnivores closely approximate those reported in an evaluation of the Australian population based on the National Nutrition Survey (1995) and use of this fatty acid database. (Meyer, Mann, Howe, Lewis & Sinclair. Lipids 38, 2003) Australian adult mean daily intakes Total n-6 Total n-3 n-6 : n-3 LC n-6 LC n-3 11.3 g 1.4 g 8.1 : 1 100 mg 188 mg
2. The dietary study USA n-6 : n-3 intake ratio approximately 11 : 1 (Production and consumption data; Hunter, Am J Clin Nutr, 1990) “Natural” human diets as represented by modeling of paleolithic diets and current hunter-gatherers give very different results: 18:2 n-6 18:3 n-3 18:2 : 18:3 LC n-6 LC n-3 n-6 : n-3 8.8 g 12.6 g 0.7 : 1 1.8 g 1.1 g 0.9 : 1 (Eaton, Eaton, Mann, Cordain, Sinclair, World Rev Nutr Diet, 83, 1998)
2. The dietary study Plasma PL fatty acid concentrations (mg/100ml) 18:2 18:3 20:4 20:5 22:5 22:6 Total n6:n3 n-6 n-3 n-6 n-3 n-3 n-3 LC n-3 H. Meat 24.5 0.3 12.9a 1.4a 1.5a 3.9a 6.9a 6.0:1a M. Meat 26.9 0.2 12.7a 1.2a 1.5a 3.9a 6.6a 6.5:1a Ovolacto 27.0 0.3 9.8b 0.7b 1.1b 2.2b 4.0b 9.6:1b Vegan 25.4 0.3 10.1b 0.6b 1.1b 2.0b 3.7b 9.9:1b
2. The dietary study Correlation of dietary intake of fatty acids and plasma status Significant correlation No correlation 18:0 18:2 n-6 18:1 18:3 n-3 20:4 n-6 20:5 n-3 22:5 n-3 18:2 n-6 with 20:4 n-6 22:6 n-3 18:3 n-3 with 20:5 n-3
3. Dietary sources of LC n-3 PUFA • Australians are not big fish eaters (approx 26 g/day). • Australians are moderate to high red meat eaters (approx 170 g/day). • Australian sheep / cattle are almost entirely pasture fed, hence accumulate 18:3 n-3 from grass and produce appreciable levels of EPA and DPA. • Grain fed animals tend to accumulate 18:2 n-6 and and have very low levels of LC n-3 PUFA.
3. Dietary sources of LC n-3 PUFA Selected fatty acid levels in beef rump (mg/100g lean meat) Total 18:2 18:3 20:5 22:5 22:6 fat n-6 n-3 n-3 n-3 n-3 Grass fed 2800 a 190 a 49 a 40 a 58 a 7.7 Grain fed* 4800 b 255 b 21 b 21 b 48 b 6.5 USDA 4900 200 17 0 0 0 * Pasture then 200 days grain fed a,b data in columns with differing superscripts significantly different (p<0.05)
Concluding Comments • A comprehensive, accurate fatty acid composition database is needed to assess dietary LC n-3 intake. • Non-meat/fish eaters consume virtually no LC n-3 PUFA • Omnivores are consuming 190 mg LC n-3 PUFA per day • This is well below the recommended 650 mg/day • Omnivores have higher plasma PL n-3 PUFA levels than vegetarians and a lower n-6 : n-3 plasma ratio • Red meat from pasture fed animals is a major contributor to LC n-3 PUFA intake in Australia