- DHA is a long chain polyunsaturated omega-3 (ω-3) fatty acid
- Omega-3 fatty acids constitute a group of fatty acids, present only in rather small amounts in food. However, today we know that they fulfill essential functions in our organism.
- There are several different omega-3 fatty acids, where the most important ones are:
- alpha-linolenic acid (ALA):
This is the most abundant omega-3 fatty acid in our diet, mainly found in specific vegetable oils (e.g. rapeseed oil, linseed oil). Today we know that its main purpose is to supply the basic substance for the synthesis of the so-called "long chain polyunsaturated omega-3 fatty acids (ω-3 LC-PUFA).
- eicosapentaenoic acid (EPA)
- docosahexaenoic acid (DHA).
These are the most important ω-3 LC-PUFA which perform specific essential functions in the organism (see below).
- All omega-3 fatty acids are similar in their basic structure and can be converted into each other in the human organism.
- The basic structure of the omega-3 fatty acids, however, can not be produced in the human organism. Thus we depend on the dietary supply of such "base frame", for this reason these fatty acids are called "essential" in our diet.
- What are the functions of long chain omega-3 fatty acids in the organism?
- Long chain omega-3 fatty acids (particularly DHA) are important constituents of cellular membranes. They enhance the fluidity and permeability of the membranes for an optimal exchange of essential substances between the cells and their ambient media.
- DHA concentrations are particularly high in the brain, in neuronal membranes and also in the retina. Studies have shown that deficiencies in omega-3 fatty acids (especially DHA) may be associated with impaired cognitive and visual functions, which underlines the importance of these fatty acids for the central nervous system and its associated tissues.
- Long chain omega-3 fatty acids supply the base frame for the synthesis of further essential substances in the organism, the group of so-called "eicosanoids". This group comprises highly active agents such as prostaglandins, leukotrienes and thromboxanes. These substances, also called "tissue-" or "signal hormones", are involved in a number of essential processes in the body.
Eicosanoids deriving from omega-3 fatty acids are considered to have anti inflammatory properties and to improve blood circulation. This could be an explanation for the protective effect of omega-3 LCPUFA with respect to the risk of coronary heart disease, which has been shown in numerous clinical and epidemiological studies.
- How can we get DHA?
- DHA and other long chain polyunsaturated omega-3 fatty acids (e.g. Eicosapentaenoic acid EPA) can be synthesised in the human body from the precursor alpha-linolenic acid, which is mainly contained in specific vegetable oils (e.g. rapeseed oil or linseed oil).
- The conversion rate, however, is rather limited - even when there is sufficient alpha-linolenic acid available. There is therefore a risk of a possible undersupply of these long chain omega-3 fatty acids.
- Therefore - for an optimal supply - nutrition committees (e.g. DGE - German Nutrition Society and others) recommend a regular intake of "preformed" omega-3 LC-PUFA (DHA, EPA) with the diet.
- What are good dietary sources of omega-3 fatty acids?
- Basically there is only one group of foodstuffs with significant native amounts of DHA and EPA, fish in particular (especially fatty "cold water fish", such as salmon, mackerel, herring, tuna or sardines).
Thus the regular consumption of fish (1-2 meals per week) is recommended in order to ensure an optimal supply of omega-3 LC-PUFA.
- Most of the other foodstuffs, especially those of vegetable origin, do virtually not contain any "preformed" omega-3 LC-PUFA.
- How much omega-3 fatty acids do we need?
- At present there are no official data existing with regard to the quantities of omega-3 LCP-PUFA to be taken. Several working groups and commissions, however, assume that a daily intake of 250 - 500 mg LC-PUFA (DHA + EPA) is desirable for healthy individuals.
- For pregnant women and breastfeeding mothers it is recommended to take 200 mg DHA per day.
The PKU diet, as a very strict low protein diet, includes mainly food of vegetable origin. Most foodstuffs of animal origin are (almost) not allowed. This, however, means that fish, as the most important dietary source of omega-3 LCPUFA, is excluded from the PKU diet.
Current studies demonstrate a low status of omega-3 LCPUFA, especially DHA, in many PKU patients, despite the fact that the low protein diet usually includes sufficient alpha-linolenic acid from vegetable oils. This can serve as an indication that the endogenous synthesis from the precursor ALA is quite often insufficient.
Furthermore impairment of visual and cognitive functions have been observed in PKU patients, which could be corrected through supply of additional omega-3 LCPUFA (e.g. in the form of fish oil).
Individuals who have to follow a low protein diet have the possibility of getting omega-3 LC-PUFA through:
- Nutritional supplementation with fish oil (-capsules): However, it has to be kept in mind that this concerns quite often gelatin capsules, which contain phenylalanine in the gelatin coat.
- Use of a protein supplement already enriched with LC-PUFA.
- Use of a dietetic food, which supplies DHA-oil in protein-free/Phe-free Softgel capsules.