Current intakes of EPA and DHA in European populations and the potential of animal-derived foods to increase them

The Third Congress of Socie

Franc¸ais de Nutrition with the Nutrition Society was held at Faculte

de Me

decine Henri Warembourg,

le Recherche, Lille, France on 6 and 7 December 2007

Symposium on ‘How can the n-3 content of the diet be improved?’

Current intakes of EPA and DHA in European populations and

the potential of animal-derived foods to increase them

D. Ian Givens

and Rachael A. Gibbs

Nutritional Sciences Research Unit, School of Agriculture, Policy and Development, Faculty of Life Sciences,

University of Reading, Reading RG6 6AR, UK

The beneﬁcial effects of long-chain (C chain ‡ 20) n-3 PUFA are well documented and,

overall, increased intake reduces risk of CVD. Recent evidence also points to a role in reducing

age-related decline in cognitive function. The two key fatty acids are EPA (20:5) and DHA

(22:6), with current UK recommendation for adults being 450 mg EPA + DHA/d. Whilst some

EPA and DHA can be synthesised in vivo from a-linolenic acid, recent data indicate this source

to be very limited, suggesting that EPA and DHA should be classiﬁed as dietary essentials. In

many parts of Europe the daily intake of EPA + DHA by adults and especially young adults

(18–24 years) is < 100 mg/d, since many never eat oily ﬁsh. Poultry meat contributes small but

worthwhile amounts of EPA + DHA. Studies to enrich the EPA + DHA content of animal-

derived foods mainly use ﬁsh oil in the diet of the animal. Recent work has shown that such

enrichment has the potential to provide to the UK adult diet a daily intake of EPA + DHA of

about 230 mg, with poultry meat providing the largest amount (74 mg). There are, however,

concerns that the continued and possibly increased use of ﬁsh oils in animals’ diets is not

sustainable and alternative approaches are being examined, including the genetic modiﬁcation

of certain plants to allow them to synthesise EPA and DHA from shorter-chain precursors.

EPA and DHA intakes: Meat: Milk: Eggs

It was shown in key studies in the 1960s and 1970s that

consumption of ﬁsh is associated with a reduced risk of

CVD in the Greenland Eskimos despite an overall diet

rich in fat

(1,2)

. This work laid the foundation for the con-

cept that the long-chain (C chain length ‡ 20; LC) n-3

PUFA, in particular EPA (20:5) and DHA (22:6) typically

found in marine foods, provide the cardioprotective effects.

Subsequently, the beneﬁcial effects have been well docu-

mented and include anti-atherogenic, anti-thrombotic and

anti-inﬂammatory effects and, overall, increased intakes

lead to reduced risk of CVD (for review, see Scientiﬁc Ad-

visory Committee on Nutrition/Committee on Toxicity

(3)

There is also a high requirement for DHA in the last tri-

mester of pregnancy and the ﬁrst 3 months of life, with the

fetus and neonate being dependant on a maternal supply of

DHA. There is some evidence that increased maternal LC

n-3 PUFA intake during pregnancy may produce beneﬁcial

effects, especially in populations that tend to have a lower

background intake of LC n-3 PUFA

(4)

. Current evidence

suggests that it is unlikely that the fetus can make sufﬁ-

cient DHA to support its brain development. Thus, mater-

nal DHA will compensate for the limited ability of the

fetus to synthesise DHA and therefore it is likely that an

adequate intake of LC n-3 PUFA could impact fetal

development (for example, see Ruxton et al.

(5)

). However,

the question of exactly how important dietary DHA is

during human brain development remains unresolved

(6)

Evidence is also accumulating that the intake of EPA

and DHA may protect against dementia

(7,8)

and in parti-

cular Alzheimer’s disease

(9)

. Less evidence is available in

relation to cognitive function, although recently the ﬁsh

consumption of 210 male participants (aged 70–89 years in

Abbreviations: ALNA, a-linolenic acid; LC, long-chain.

*Corresponding author: Professor Ian Givens, fax + 44 118 378, email [email protected]

Proceedings of the Nutrition Society (2008), 67, 273–280 doi:10.1017/S0029665108007167

The Author 2008 First published online 23 May 2008

Proceedings of the Nutrition Society

https://doi.org/10.1017/S0029665108007167 Published online by Cambridge University Press

1990) of the Zutphen Elderly Study was examined, along

with measurements of cognitive function collected in 1990

and 1995

(10)

. A signiﬁcant (P <0

01) linear trend was seen

for the relationship between EPA + DHA intake and cog-

nitive decline, with a mean difference in intake of about

380 mg/d being associated with a 1

1 point difference in

cognitive decline. It was thus concluded that moderate

intakes of EPA + DHA may delay the decline in cognitive

function in elderly men

(10)

Theoretically, the dietary essential a-linolenic acid

(18:3n-3; ALNA) can be desaturated and elongated to

EPA and DHA, but whether the dietary essentiality of

ALNA primarily reﬂects the bioactivity of ALNA itself or

of EPA and DHA synthesised from it has been a matter for

debate for some time. However, a number of recent studies

(for example, see Burdge et al.

(11)

) and a review

(12)

have

concluded that the principal biological role of ALNA is

indeed as precursor for EPA and DHA but, critically,

stable-isotope studies clearly show that the efﬁciency of

conversion of ALNA to EPA is very low, especially in

men, and that further transformation to DHA is often

minimal. The conversion of ALNA to EPA and DHA is

greater in women, possibly as a result of an up-regulatory

effect of oestrogen. Overall, it has been concluded that

ALNA is probably a quite limited source of EPA and DHA

in man

(12)

, leading to the concept that these PUFA should

now be regarded as dietary essentials. This conclusion is

supported by a recent systematic review that has concluded

that increased consumption of n-3 fatty acids from ﬁsh

or ﬁsh oil supplements, but not from ALNA, reduces the

rates of all-cause mortality, cardiac and sudden death and

possibly stroke

(13)

The present paper will review current recommendations

for intake of EPA and DHA, assess current intakes in

various countries and consider how intake may be in-

creased, with emphasis on enriching their concentration

in foods of animal origin.

Recommended intakes of EPA and DHA

In the review of dietary factors affecting CVD the

Department of Health has recommended that in the UK

intake of LC n-3 PUFA should be increased to 200 mg/d

from the estimated, then current, intake of about 100 mg/

(14)

. The subsequent review of the Scientiﬁc Advisory

Committee On Nutrition/Committee On Toxicity has con-

cluded that the dose required for a demonstrable effect on

CVD risk factors such as reductions in plasma TAG con-

centration, blood pressure, platelet aggregation and the

inﬂammatory response is ‡ 1

5 g/d

(3)

. The Scientiﬁc Ad-

visory Committee On Nutrition/Committee On Toxicity

has also cited other data

(3)

, including a study of 240

patients who had suffered a previous myocardial infarction

that has demonstrated a reduction in all-cause mortality

when these patients were supplemented with 2 g LC n-3

PUFA/d

(15)

. The Scientiﬁc Advisory Committee On Nutri-

tion/Committee On Toxicity has concluded, however, that

the population recommendation of the Department of

Health

(14)

should be increased from 200 mg/d to 450 mg/d,

which is consistent with the consumption of two portions

of ﬁsh per week, one of which is oil-rich

(3)

. No consider-

ation was given to the role of EPA and DHA in arresting

cognitive decline because of the paucity of data in this

area.

Table 1 summarises the recommended daily intake of

EPA + DHA from various sources. Current recommend-

ations range from 270 mg/d in the USA

(16)

to approxi-

mately 700 mg/d in Belgium

(17)

. However, both these

intakes are calculated from the original recommendation

expressed as % energy intake assuming an intake of 8

MJ/d, which may be an underestimate for the USA at least.

Current intakes of long-chain n-3 fatty acids

For the UK some estimates of EPA + DHA intake have been

made over the last 15 years but they have produced variable

numbers. An intake of 308 mg/d may be calculated from

Gregory et al.

(18)

, whilst Saunders & Roshanai

(19)

and

Saunders & Reddy

(20)

have reported intakes of 600 mg/d

and 500 mg/d respectively. A much lower value of 100 mg/

d was used by the Department of Health

(14)

. Some of the

variability in estimated mean intake is likely to be the result

of the use of different food consumption surveys that sug-

gest different levels of consumption of the key food types.

Based on the recommendations of the Scientiﬁc Advisory

Committee On Nutrition/Committee On Toxicity

(3)

that

canned tuna should be excluded from the oil-rich ﬁsh food

category, it is also likely that some of these studies have

substantially overestimated EPA + DHA intake.

A recent study has re-evaluated EPA + DHA intake for

UK adults using calculations based on intakes of ﬁsh, meat

and eggs according to the data of the Scientiﬁc Advisory

Committee On Nutrition/Committee On Toxicity

(3)

, the

National Diet and Nutrition Survey

(21)

and the British Egg

Information Service

(22)

respectively

(23)

. This re-evaluation

followed the principle adopted by the Scientiﬁc Advisory

Committee On Nutrition/Committee On Toxicity

(3)

recognising the National Diet and Nutrition Survey data

(21)

as being the most appropriate current estimate of

consumption by adults except where there is strong

Table 1. Recommended daily intakes of EPA + DHA for adults in

various countries

Country

Recommended

intake of

EPA + DHA

(mg/d) Reference

UK 200 Department of Health

(14)

Various 500* World Health Organization/Food

and Agriculture Organization

(58)

UK 450 Scientiﬁc Advisory Committee on

Nutrition/Committee on Toxicity

(3)

Various 500 International Society for the Study of

Fatty Acids and Lipids

(59)

USA 270† Institute of Medicine

(16)

Belgium 680† Belgian Health Council

(17)

*Estimated from recommendation to eat one to two portions of ﬁsh per week.

†Estimated from original recommendation expressed as % energy intake,

assuming an intake of 8

3 MJ/d.

274 D. I. Givens and R. A. Gibbs

Proceedings of the Nutrition Society

https://doi.org/10.1017/S0029665108007167 Published online by Cambridge University Press

evidence that other or adjusted values should be used.

Based on the food intakes as given in Table 2, together

with reported values for the concentrations of LC n-3 fatty

acids in these foods (for details, see Givens & Gibbs

(23)

Table 2 provides mean estimates of the daily intake of LC

n-3 fatty acids for UK adults. It is of concern that the mean

intake is only about 54% of the target of 450 mg/d

(3)

.Of

the total mean intake of 244 mg/d, approximately 54% is

provided by oil-rich ﬁsh, but notably it is poultry meat that

is the major contributor (73%) of all the meats.

However, it is critical to realise that only about 27% of the

adult population consume any oil-rich ﬁsh

(3)

and thus for

the vast majority of the adult population the daily intake

will at best be approximately 100 mg, with almost half this

amount provided by animal-derived foods. The contribu-

tion made by poultry meat may indeed be higher than this

level if the consumption data for poultry meat reported by

the Association of Poultry Processors and Poultry Trade in

the EU Countries

(24)

are a truer reﬂection of reality than

those of the National Diet and Nutrition Survey

(21)

A key assumption in this analysis is, however, that the

LC n-3 fatty acid content of poultry meat purchased by the

public is similar to that observed in research studies. It is

likely that much of the LC n-3 fatty acids found in poultry

meat from birds that did not have ﬁsh oil in their diets is a

result of the diet containing ﬁshmeal, which contains some

residual ﬁsh oil. In 2004 approximately 48 000 t ﬁsh meal

(25% total use) was used in the UK for poultry diets

(25)

although this level of use has probably declined somewhat

subsequently. There are now considerable amounts of

poultry meat imported into the UK both from other EU

Member States and from other parts of the world. Whether

this imported meat will have similar background con-

centrations of LC n-3 fatty acids is not known, but a study

is currently underway in the author’s laboratory to analyse

a range of poultry meat products at retail to obtain new

data.

A number of studies have taken place recently to esti-

mate EPA + DHA intake in various countries. A summary

of these studies is given in Table 3. A large variation in

mean intake is apparent between studies and countries but

many values are considerably below the recommended

target intakes. Some of the variation may be a result of the

different methods for the collection of food consumption

data, with some (for example, see Howe et al.

(26)

) being

based on 24 h recall and some (for example, see Givens &

Gibbs

(23)

) being based on 7 d weighed intakes. Two other

points should be noted. First, in agreement with the study

in UK adults, that with Belgian women shows that the

majority of the population consume considerably less than

the mean value

(27)

. The lack of normality in the distribu-

tion of EPA + DHA intake across many populations has

recently been highlighted

(28)

, indicating the dangers of

interpreting mean values derived from non-normally-

distributed population data. Second, intakes of EPA + DHA

appear to be generally lower in young adults (18–24 years)

and children. It has been shown that in the UK at least

there is a trend towards increased consumption of oily ﬁsh

with increasing age, rendering young adults particularly

vulnerable to suboptimal intakes of LC n-3 PUFA

(29)

. The

data for Belgian children

(30)

support this view. Low intakes

Table 2. Estimated mean intakes of EPA and DHA by adults in the

UK (from Givens & Gibbs

(23)

)

Food

Intake

(g/week)*

Intake

EPA + DHA

(mg/d)

Fish

White ﬁsh 104 38

Shellﬁsh 27 14

Oil-rich ﬁsh 50 131

Other ﬁsh 36 14

Total ﬁsh 217 199

Meat

Beef and veal 249 4

Sheep meat 51 2

Pork 63 1

Bacon and ham 105 1

Poultry 374 26

Sausages 68 0

Other products 216 1

Total meat 1126 37

Eggs 194 8

Total intake 244

*Intake of ﬁsh, meat and eggs based on data from Scientiﬁc Advisory

Committee on Nutrition/Committee on Toxicity

(3)

, the National Diet and

Nutrition Survey

(21)

and British Egg Information Service

(22)

respectively.

Table 3. Recent estimated daily intakes of EPA + DHA in various countries

Country Details

Intake of EPA +

DHA (mg/d) Reference

UK Adults, 19–64 years, mean 244 Givens & Gibbs

(23)

UK Females, 19–24 years, mean 109 Gibbs et al.

(29)

Belgium Females, 18–39 years, mean 209 Sioen et al.

(27)

Belgium Females, 18–39 years, median 50 Sioen et al.

(27)

Belgium Children, 4–6

5 years, mean 75 Sioen et al.

(30)

France Women, 45–63 years 344 Astorg et al.

(31)

Australia Adults 143 Howe et al.

(26)

North America Adults 200 Vermunt & Zock

(60)

Mid-Europe Adults 250 Vermunt & Zock

(60)

Northern Europe Adults 590 Vermunt & Zock

(60)

Japan Adults 950 Vermunt & Zock

(60)

How can the diet n-3 content be improved? 275

Proceedings of the Nutrition Society

https://doi.org/10.1017/S0029665108007167 Published online by Cambridge University Press

of EPA + DHA in the young are a result of low or zero con-

sumption of oil-rich ﬁsh, a habit that young adults may

carry forward into middle and later life. It is interesting to

note that in young women (19–24 years) the intake of

canned tuna has been reported to be considerable

(29)

, pos-

sibly in the belief that this product is a good source of ﬁsh

oils.

In most studies the primary source of EPA and DHA is

ﬁsh and seafood and thus variation in intake is a function

of variation in consumption of these foods. Two studies

have reported that meat, poultry and eggs contribute

substantially to the intake of docosapentaenoic acid

(22:5n-3)

(26,31)

, with docosapentaenoic acid contributing

29% total LC n-3 fatty acids consumed

(26)

. These data

highlight the need to better understand the physiological

effects of dietary docosapentaenoic acid.

Options for increasing intake of EPA and DHA

Clearly, one option to increase intake of EPA and DHA is

to encourage increased consumption of oily ﬁsh. However,

given that young adults (18–24 years) appear to consume

only small amounts if any, education in this area needs to

start at a very young age and be built into an increased

awareness of diet and health in general. Another option is

to encourage the increased use of ﬁsh oil supplements such

as capsules. However, data from the recent UK Low

Income Diet and Nutrition Survey

(32)

indicates that habi-

tual use of ﬁsh oil capsules in this population is very much

less than that found in the National Diet and Nutrition

Survey

(21)

, suggesting that encouragement to increase use

would have less uptake in populations that are perhaps at

greatest risk.

A further option is EPA and DHA enrichment of foods

that are consumed in relatively large quantities by a large

proportion of the population and that are amenable to en-

richment. Animal-derived foods are key targets in this

context since changes to the animals’ diet can be used to

bring about enrichment of the food products.

Enriching animal-derived foods with EPA and DHA

There have been many studies aimed at improving the

EPA and DHA concentration in animal-derived foods in

relation to chronic disease (for reviews, see Givens

(33)

and

Pisulewski et al.

(34)

), although few studies have attempted

to connect the potential for enrichment with current and

projected patterns of food consumption. Assuming that

consumption of enriched foods would be the same as the

current intake of normal foods, estimates have been made

of the potential for enrichment of a wide range of animal

foods and how these foods could contribute to additional

EPA and DHA intake

(23)

. The ﬁndings for milk and milk

products, meat and eggs are summarised in Table 4, which

shows that enrichment of animal-derived foods has the

potential to provide a daily intake of EPA + DHA of about

230 mg, with poultry meat providing the largest potential

intake (74 mg). Other useful contributions could be pro-

vided by eggs and full-fat cheese, although the average

contributions from liquid milk and other meats are likely to

be modest based on current food consumption data.

Enrichment of poultry meat

The EPA and DHA content of poultry meat can in theory

be relatively easily modiﬁed by dietary means. As early as

1963 it was noted that the fatty acid compositions of

broilers’ breast, thigh and skin tissues are similar to those

of the broilers’ diet

(35)

, and it was demonstrated that

feeding ﬁsh oil to turkeys increases the concentrations of

EPA and DHA in their depot fat and muscle lipids

(36)

considerable amount of work has been done to enhance the

EPA and DHA content of poultry meat by dietary means in

ways that will result in nutritionally-meaningful intakes of

these fatty acids by individuals who consume these pro-

ducts (for review, see Rymer & Givens

(37)

Despite the volume of work, there are few data relating

to the relative ability to enrich the meat of modern geno-

types of broiler chickens and turkeys

(37)

. A study was there-

fore carried out to determine the effect of different species

and genotypes of poultry on their response as measured by

increases in the EPA and DHA content of their edible tis-

sues to increased concentrations of ﬁsh oil in their diet

(38)

Some key ﬁndings for skinless white chicken meat are

shown in Table 5. Overall, the results show that in modern

broiler genotypes there is no signiﬁcant difference in the

Table 4. Potential mean intakes of EPA and DHA by adults in the

UK from enriched animal-derived foods (from Givens & Gibbs

(23)

)

Food

Intake

(g/week)*

Concentration†

(mg/g) of

Intake of

EPA + DHA

(mg/d)

EPA DHA

Milk products

Whole milk 337 0

106 0

141 11

Semi-skimmed milk 877 0

045 0

060 13

Skimmed milk 215 0

008 0

011 0

Cream 12 1

064 1

406 4

Other milk 42 0

080 0

105 1

Cottage cheese 9 0

104 0

137 0

Other cheese 98 0

745 0

984 24

Butter 22 2

181 2

882 16

Total milk products 71

Meat

Beef and veal 249 0

24 0

053 10

Sheep meat 51 0

82 0

97 13

Pork 63 0

13 0

167 2

Bacon and ham 105 0

072 0

093 2

Poultry 374 0

60 0

80 74

Sausages‡ 68 0

012 0

015 0

Other products‡ 216 0

036 0

006 1

Total meat products 105

Eggs 194 0

06 1

90 54

Total intake 231

*Intake of milk and milk products and meat from the National Diet and

Nutrition Survey

(21)

and eggs from British Egg Information Service

(22)

†Values for milk based on Chilliard et al.

(41)

, beef from Scollan et al.

(51)

, sheep

meat from Cooper et al.

(61)

, poultry meat from Rymer & Givens

(37)

and eggs

from Simopoulos

(62)

‡Unchanged relative to non-enriched.

276 D. I. Givens and R. A. Gibbs

Proceedings of the Nutrition Society

https://doi.org/10.1017/S0029665108007167 Published online by Cambridge University Press

efﬁciency with which EPA and DHA are incorporated

into edible tissue. There is also little evidence to suggest

that there is any inherent difference between broilers and

turkeys in their ability to incorporate EPA and DHA into

their edible tissues, except perhaps for EPA in white

meat. There is evidence that white chicken meat is a richer

source of DHA than dark meat and also has greater en-

richment efﬁciency than dark meat for DHA. This ﬁnding

is promising since in the EU the consumption of white

poultry meat far outweighs the consumption of dark meat.

This result is not perhaps surprising as EPA and DHA

preferentially accumulate in the phospholipids, which are

much more prevalent in the white meat compared with the

dark meat. As shown in Table 5, diets containing 40 g ﬁsh

oil/kg give rise to white chicken meat containing about

140–160 mg EPA + DHA/100 g, which has the potential to

make a real contribution to dietary EPA + DHA intake.

The same study also examined the birds’ ability to con-

vert dietary ALNA to EPA and DHA and then deposit

these fatty acids in the edible tissues

(38)

. The evidence

from this experiment suggests that, as in man, the process

is extremely limited, which is in agreement with the con-

clusion of an earlier study

(39)

. The latter study suggests that

although the birds may be capable of converting ALNA to

EPA and DHA to some extent, these acids are not then

deposited in skeletal muscle but rather sequestered in the

liver or transported to other tissues. It therefore seems that

ALNA cannot be used to make worthwhile enrichment of

EPA and DHA in poultry edible tissues and that currently

reliance continues to be on the use of ﬁsh oil.

There are some potential drawbacks to enriching poultry

meat with EPA and DHA. These factors are the potentially

reduced oxidative stability and hence shelf-life of the pro-

ducts and the possible negative effect that EPA and DHA

enrichment may have on the organoleptic qualities of

poultry meat. Current work in the author’s laboratory indi-

cates that most problems of this type can be overcome by

the use of additional vitamin E in the diet of the bird.

Enrichment of milk

As a result of extensive biohydrogenation in the rumen and

the inability of ruminant tissue to synthesise PUFA, typical

levels of linoleic acid (18:2n-6) and ALNA in milk fat are

extremely low. Even when high amounts of PUFA from

plant oils and oilseeds are included in the diet, absolute

increases in linoleic acid and ALNA are relatively small.

In relation to EPA and DHA, milk from cows fed conven-

tional diets based on forages and cereal-based concentrates

has extremely low concentrations (typically < 1 g/100 g

fatty acids

(40)

). It is possible to increase levels of EPA and

DHA in milk fat by including some ﬁsh oil in the diet

of the cow, although the extent of enrichment in milk fat

is very low, with a typical efﬁciency of transfer of EPA

and DHA from the diet into milk of 2

6% and 4

respectively

(41)

. These values are much lower than the

transfer efﬁciencies of 18–33 % and 16–25% seen for EPA

and DHA respectively when ﬁsh oil is infused post-

ruminally

(41)

. The poor transfer of EPA and DHA into milk

when marine lipids are fed arises from extensive (between

74% and 100 %) biohydrogenation in the rumen (for

example, see Shingﬁeld et al.

(42)

) and preferential parti-

tioning of these fatty acids into plasma phospholipids and

cholesteryl esters, which are poor substrates for mammary

lipoprotein lipase

(43)

. Table 6 shows the typical effect of

including ﬁsh oil in the diet of the cow on EPA and DHA

concentrations. Whilst milk from the ﬁsh oil-containing

diet is to some extent enriched with EPA and DHA, a side

effect of this process is the substantial increase in the

trans-fatty acids and conjugated linoleic acid content of

the milk fat. Unlike industrially-hydrogenated products the

majority of the increased trans-fatty acids is trans-vaccenic

acid (trans-11 18:1)

(42)

. Whilst most evidence indicates

that trans-vaccenic acid is not a risk factor for CVD

(44)

there are few data from human studies, which have mostly

evaluated trans-fatty acids from industrial sources. A study

is currently underway to directly compare the effects of

trans-fatty acids from milk and industrial sources on CVD

risk factors in healthy human subjects

(45)

There have been various approaches developed to pro-

tect ﬁsh and other marine lipids from biohydrogenation in

the rumen, including encapsulation of oils and the creation

of calcium salts of fatty acids or fatty acyl amides. Most of

these technologies have been developed to overcome the

negative effects on animal performance of feeding high

levels of lipid, but can also allow sizeable and strategic

changes in milk fatty acid composition.

Table 5. Effect of ﬁsh oil in the diet and breed of broiler chicken on the mean EPA and DHA concentration (mg/100 g meat) in white chicken

meat (from Rymer & Givens

(38)

)

Diet*... Control Loﬁsh Hiﬁsh Statistical signiﬁcance (P) of:

Breed... Ross 308 Cobb 500 Ross 308 Cobb 500 Ross 308 Cobb 500 Breed Diet

EPA 7

917

420

027

230

8NS < 0

001

DHA 39

638

654

964

3 118 126 NS < 0

001

*Contained ﬁsh oil at (g/kg): control, 0; loﬁsh, 20; hiﬁsh, 40.

Table 6. Effect of including ﬁsh oil in the diet of the dairy cow on

EPA, DHA, trans-18:1 and conjugated linoleic acid (CLA) in milk fat

(from Shingﬁeld et al.

(42)

)

Fatty acids

(/100 g total fatty acids) Control diet

Diet containing

herring and mackerel

oil (250 g/d)

EPA (mg) 50 110

DHA (mg) 0 100

Total trans-18 :1 (g) 4

514

Total CLA (g) 0

39 1

How can the diet n-3 content be improved? 277

Proceedings of the Nutrition Society

https://doi.org/10.1017/S0029665108007167 Published online by Cambridge University Press

Another approach is to directly fortify milk with ﬁsh oils

during processing to provide EPA and DHA, and in theory

this process is much more efﬁcient and controllable than

inclusion in the diets of dairy cows. Over the last 10 years

milk fortiﬁed with EPA and DHA has been available

commercially in several countries. In the UK, for example,

the St Ivel Advance

brand (Dairy Crest Group plc, Esher,

Surrey, UK) markets a fortiﬁed whole milk and a semi-

skimmed milk that contain respectively 113 and 63 mg

EPA + DHA/250 ml

(46)

, and in Spain Puleva omega3

(Puleva Food SL, Madrid, Spain) provides approximately

66 mg EPA + DHA/100 ml

(47)

. The effect of consuming the

latter product on CVD risk factors has shown positive

effects

(48)

, although the milk used in this study was also

fortiﬁed with oleic acid, folic acid and other vitamins and

had its SFA content reduced substantially.

Overall, enriched and fortiﬁed milk products are likely

to provide generally small increases in EPA + DHA intakes

at normal levels of consumption, but as noted earlier many

populations have substantially suboptimal intakes, and for

them the availability of such milk may be very valuable.

Enrichment of eggs

Eggs enriched with EPA and DHA can also be produced

by the addition of ﬁsh oil to the diet of the hen. A study

has been carried out involving diets containing no addi-

tional lipid (control), 150 g ﬁsh oil/kg or 50, 100 or 150 g

linseed/kg

(49)

. The n-3 PUFA were found to be higher in

eggs produced from hens fed ﬁsh oil or linseed compared

with the control. In another study that used linseed to in-

crease the n-3 PUFA content of eggs the work was ex-

tended to examine the effects of consumption of the eggs

produced on plasma and platelet lipids in male sub-

jects

(50)

. Diets containing 0, 100 and 200 g ground linseed/

kg were used and key results are summarised in Table 7.

A progressive increase in the ALNA concentration of the

eggs was observed relative to linseed inclusion. EPA was

not found to be increased but DHA concentration was

increased, although no signiﬁcant difference was found

between the two rates of linseed inclusion (DHA content

equivalent to 51, 81 and 87 mg per egg respectively for 0,

100 and 200 g linseed/kg diet). It thus seems that laying

hens have some capacity to synthesise DHA from ALNA,

with little restriction of the process at the EPA level, a

mechanism presumably designed to provide the embryo

and chick with a source of DHA. Four eggs per d from

each treatment were subsequently fed to the subjects for 2

weeks. No signiﬁcant effects were seen in total cholesterol,

HDL-cholesterol or plasma TAG concentrations but in-

creases in total n-3 fatty acids and DHA contents of pla-

telet phospholipids were recorded in subjects who ate the

eggs from the diets containing linseed. Thus, eggs modiﬁed

by the inclusion of sources of ALNA in the diet of the hen

could provide a useful source of EPA and especially DHA

without the use of ﬁsh oils. Some studies have shown that

enhanced concentrations of EPA and DHA can also occur

in ruminant meat as a result of in vivo synthesis from diet-

ary ALNA (for example, see Scollan et al.

(51)

), although

the efﬁciency of this process is normally very low and it is

not likely that this route could be used with conﬁdence.

Alternatives to the use of ﬁsh oil

Essentially, all approaches to increase intake of EPA and

DHA rely directly or indirectly on the use of ﬁsh oils.

There are concerns, however, that the continued and pos-

sibly increased use of ﬁsh oils in the food chain is not sus-

tainable and that alternatives are needed. Although some

data are available (for review, see Givens et al.

(52)

), further

work on the potential of industrially-produced microalgae

as dietary sources of EPA and DHA would seem war-

ranted, although to date this process has proved to be very

expensive.

A reason for the poor conversion of ALNA to EPA

appears to be low activity of D6 desaturase

(53)

, and thus an

alternative strategy for increasing EPA supply would be to

provide the product of D6 desaturase, stearidonic acid

(18:4n-3). A number of recent studies (for example, see

Miles et al.

(54)

) do indeed indicate that dietary stearidonic

acid may be a useful means of increasing the EPA content

of human lipids. Although certain oils, such as that in the

seed of Echium plantaginium, contain some stearidonic

acid (approximately 13 g/100 g total fatty acids), this con-

centration may not be high enough to make diet mani-

pulation easy, and currently the plant is not of major

agricultural importance. The potential for discovering

plants with much higher concentrations of stearidonic acid

in their seed oil would seem large.

It is also noteworthy that efforts are ongoing into the

genetic modiﬁcation of certain plants in order that they

will synthesise EPA and DHA in their seeds from shorter-

chain precursors

(55)

. This process involves the introduction

of cloned algal genes into the plant. If successful and

accepted by the consumer this approach could prove to be

a major breakthrough in the long term.

Reducing intake of n-6 fatty acids

A number of studies, including the review of Ailhaud

et al.

(56)

, have concluded that over the last 40–60 years

intake of n-6 fatty acids, notably linoleic acid, has in-

creased very substantially in most Western societies, lead-

ing to a much increased dietary n-6 fatty acids:n-3 fatty

Table 7. Effect of including linseed in the diet of laying hens on

EPA, DHA and other fatty acids in the lipid fraction of eggs (from

Ferrier et al.

(50)

)

Fatty acid

(/100 g total

fatty acids)

Linseed inclusion in

diet of hens (g/kg)

0 100 200

a-Linolenic acid (g) 0

EPA (mg) 100 200 200

DHA (mg) 1000

1700

1800

Total n-3 (g) 2

Total n-6 (g) 21

n-6:n-3 9

Total SFA (g) 32

a,b,c

Values with unlike superscript letters were signiﬁcantly different (P < 0

05).

278 D. I. Givens and R. A. Gibbs

Proceedings of the Nutrition Society

https://doi.org/10.1017/S0029665108007167 Published online by Cambridge University Press

acids. This situation has led to concerns that competition

between n-6 fatty acids and ALNA for the n6 desaturase

enzyme has led to reduced efﬁciency of conversion of

ALNA to EPA. This area has recently been reviewed by an

expert group with the conclusion that the n-6 fatty acids:

n-3 fatty acids is not a useful concept and distracts atten-

tion away from increasing absolute intakes of LC n-3 fatty

acids

(57)

. However, some evidence was reported that intake

of linoleic acid can inﬂuence the proportion of EPA and

DHA in membrane lipids, with higher intakes lowering

the proportion of EPA and DHA. The long-term effect of

the substantially increased intakes of linoleic acid seen

over the last half century would seem to warrant further

attention.

Acknowledgements

This work was supported by LIPGENE, an EU Sixth

Framework Programme Integrated Project (2004–2009)

(http://www.lipgene.tcd.ie).

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