So how does current
government advice that “we” should try to eat at least
two servings of fish a week, including one serving of oily fish, as
part of a healthy balanced diet translate into dietary advice for vegetarians?
And what should you do if your GP suggests fish oils for creaking joints
or to thin your blood? Well, the first thing to remember is that the
vegetarian diet is widely recognised as being protective against heart
disease, the main ailment that the advice is aimed at, so vegetarians
have a head start already, and of course the general population don’t
exactly eat much oily fish, or indeed offal, the other “good” source
of omega 3 fats.
To begin with we must distinguish between the two polyunsaturated fatty acids
which are termed essential because they can not be made in the body and therefore
must be present in the diet. They are linoleic acid (LA), an omega 6 fat, which
is widely available in a vegetarian diet, being present in large quantities
in most oils and other vegetable based fatty foods, and alpha-linolenic acid
(ALA), an omega 3 fat, which is not so widely available in a vegetarian diet,
and is generally considered to be the more beneficial of the two EFAs.
Alpha-linolenic
acid is what is known as an omega 3 fat, and is a precursor of the
longer chain omega 3 fats eicosapentaenoic acid (EPA) and docosahexaenoic
acid (DHA) - ie EPA and to a lesser extent DHA can be made in the body
from ALA. These two fatty acids are the ones available in significant
amounts in oily fish, and fish oil supplements. All three omega 3 fats
have been shown to offer numerous physiological benefits, notably their
anti-inflamatory properties and their ability to offer cardioprotective
effects especially in people with pre-existing cardiovascular problems,
though EPA and DHA are more potent than simple ALA.
Generally, vegetarian,
and especially vegan, diets are relatively low in ALA compared with
LA, and provide little EPA and DHA directly (though a certain amount
of DHA is found in eggs, especially from hens fed on flax seeds or
algae), and tissue levels of long chain omega 3 fatty acids have been
shown to be relatively low in vegetarians and vegans, even though ALA
intake varies little across vegans, vegetarians and omnivores.
Taking an overview
of the various fatty acids intake recommendations worldwide, and the
confounding factors surrounding the common vegetarian diet, leads to
a conclusion that an ALA intake of 1.5% of total energy is optimum
for vegetarians – or roughly 4g a day. This should provide enough
of the parent omega 3 fat to ensure significant amounts of EPA and
DHA are formed by the body (conversion rates are around 5-10% for EPA
and 2-5% for DHA). However it is also important for vegetarians to
ensure that their intake of LA is not too high compared with ALA since
a higher intake of LA interferes with the process in which the human
body converts ALA into the even more beneficial EPA and DHA, so a LA
to ALA ratio of around 4 to 1 or slightly lower is considered to be
the optimum, but any steps to bring down an excessively high amount
of omega 6 fats in the diet would be beneficial. |
| Practical
steps
There are a number
of steps to take to ensure that the optimum levels of all the omega
3 fats are present in the body.
1.
Make sure you include a good source of ALA in your diet, the simplest
source would
be one teaspoon of flax seed oil a day, taken either on its own or
mixed into dressings etc. Flax oil is also available in vegetable capsules.
Alternately include 4 to 5 teaspoons of ground flax seeds, or rape
seed oil in your diet – though do not heat any of the oils, and
only add the flax seeds to any foods at a late stage since heating
will destabilise the ALA. It is important that the flax seeds are ground
or at least crushed, if left whole much of the fat will be unavailable.
2. Replace fats
high in omega 6 oils, such as sunflower oil or corn oil, with fats
higher in monounsaturated fats, such as olive oil or rape seed oil
which do not disrupt the formation of EPA and DHA.
3. Other foods can add to your intake of ALA. Most of the little fat
in leafy green vegetables is ALA – broccoli has 0.13g per 100g,
cabbage 0.11g per 100g, so simply eating your greens is making a positive
addition to your
intake. Walnuts and tofu are also good sources but are comparably high in LA.
Pregnant or nursing
mothers who are uncertain whether their diet is providing enough omega
3 fats may wish to consider supplementing their diet with a direct
source of DHA since this appears to play an important part in the development
of immature brains. DHA supplements derived from algae and encased
in non gelatine capsules are now available. It has also been suggested
that DHA supplements may be of help to children with certain behavioral
or learning difficulties.
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