Fish Oils and Inflammatory Bowel Disease

Much interest has been shown recently in the use of fish oils for the treatment of IBD.
Eicosapantaenoic acid (EPA) is the essential fatty acid found in fish and is also produced by the desaturation and chain lengthening of linolenic acid which is found in soya bean and rapeseed oil. Commercially prepared capsules of fish oil are made up of EPA, e.g. Max EPA.

Fish oils in the past have had varying degrees of success, mainly due to their unpalatability and side effects, e.g. heartburn, belching, diarrhoea, flatulence and bad breath. Relatives living with patients taking the capsules sometimes found the odour intolerable.

Essential fatty acids (EFAs) are important in the production of substances called prostaglandins, which have an effect on the inflammation in the body and the clotting of the blood. EFAs belong to either the n-3 or n-6 groups of fatty acids and must be obtained from the dietary intake of plant sources, e.g. vegetable oils and nuts, as both humans and animals are unable to synthesise their own.

Linolenic acid belongs to the n-3 group, which is transformed along the Omega 3 pathway into a series of highly polyunsaturated fats, the most important being EPA. This pathway is extremely active in marine animals and fish is a rich source of EPA.

Linoleic acid belongs to the n-6 group and is transformed into two important fatty acids:

  • Gamma Linolenic Acid (GLA). Evening Primrose oil is a rich source.
  • Arachidonic Acid.

Prostaglandins derived from arachidonic acid are very potent whilst those formed from GLA and EPA are less so. It is the disturbance in the metabolism of prostaglandins, which is thought to contribute to many inflammatory conditions such as rheumatoid arthritis, asthma, psoriasis and certain clot-forming conditions such as coronary artery disease.

Marine oils in man obtained from the diet or supplementation may alter the clotting of the blood, thereby possibly reducing the risk of clots forming in the vessels. Eskimos in Greenland have a diet rich in fatty whale and seal meat thus containing a higher proportion of EPA to arachidonic acid and tend to have a prolonged bleeding time with a reduced death rate from coronary thrombosis (blood clots in the heart).

Clinical trials have shown fish oils (EPA) to be effective in IBD, probably due to the increased production of less potent prostaglandins at the expense of the more potent one, (i.e. from arachidonic acid).

A double-blind crossover study conducted by Stenson and colleagues which involved patients with active ulcerative colitis taking both fish oils, (Max EPA) and placebo, showed improvement in sigmoidoscopic and clinical scores whilst taking the fish oils. Although patients continued their present medication, i.e. corticosteroids and 5-ASAs, a  steroid sparing effect was noted when fish oils were taken.

Another study by McColl and colleagues reported a decline in disease activity in a 12-week open study using Max EPA. Results may have been subjective as both patients and doctors were aware that they were receiving fish oils. However, colonic mucosa was found to contain increased amounts of EPA.

New preparations of EPA, which are enteric coated, have meant a dose reduction (1/3 of that previously) with consequently fewer side effects and therefore increased compliance, making long-term treatment more acceptable.

A study by Belluzzi and colleagues in Italy showed that an enteric coated (EC) fish oil preparation (pur EPA) was effective in reducing the rate of relapse of Crohn's disease (CD) patients in remission.

78 patients with CD were randomised to receive either 3 capsules of fish oil 3 times daily or 3 capsules of placebo 3 times daily (there was no difference in odour between the two). Patients were clinically in remission and off medication three months before trial entry - blood tests, however, indicated a mild increase in inflammation. Out of 39 patients in the fish oil group, 11 relapsed compared to 27 out of 39 in the placebo group. After one year of treatment 23 patients in the fish oil group were still in remission compared to only 10 in the placebo group.

The actual mechanism for the effect of the EPA is not clearly understood and more research is needed to determine this. It has been speculated that the lack of an enzyme involved in the Omega 3 and Omega 6 pathways is responsible for the susceptibility of certain individuals to these conditions and that by supplementing the diet, this acts as a form of replacement therapy.

  • Several factors have been shown to influence the one-year relapse rate of Crohn's disease:
  • Diet (45%)
  • Long-term 5-ASA treatment (40%).
  • Metronidazole following ileal resection (shows the relationship of bacteria in the lumen and inflamed mucosa).
  • Quitting smoking (40%).

Perhaps a diet rich in fish oils could reduce the relapse rate. The Japanese have a fish-rich diet and low incidence of IBD, however, this is not so in Scandinavia (where fish consumption is also high!) However, a general consensus has yet to be reached and research continues.