The vitamins can be split into fat soluble and water soluble categories. While the fat soluble vitamins are stored in body compartments, the water soluble vitamins, generally, are not. As intakes of fat soluble vitamins fall due to dietary variability, stores of the vitamin can be mobilised in order to make up the shortfall. However, as intakes of water soluble vitamins fall, detrimental metabolic effects can be observed in a relatively short time. Like the fat soluble vitamins, essential minerals are also stored to some extent. The skeleton is the most obvious storage compartment of minerals, but the teeth and soft tissue also store minerals. Therefore fluctuations in dietary levels are not so detrimental as fluctuations in the water soluble vitamins. The body also has a need for two essential fatty acids, and these can be said to have vitamin status. Because the essential fatty acids can be stored in lipid membranes and adipose tissue there is not a requirement for them to be consumed every day.
The two essential fatty acids are alpha linolenic acid (ALA, C18:3 (n-3)) and linoleic acid (LA, C18:2 (n-6)). Plant oils are a good source of LA and so generally the diets of most individual contain adequate LA. However ALA is more difficult to obtain in the diet and so intakes are generally below recommended levels. However, ALA is metabolised to eicosapentaenoic acid (EPA, C20:5 (n-3)) and docosahexaenoic acid (DHA, C22:6 (n-3)) in humans and these fatty acids can be consumed directly from fish oils negating the requirement for ALA. Most non-vegetarians obtain their n-3 (omega-3) fatty acid requirement from non plant sources. Studies have investigated the ability of fish oils to accumulate in body tissues. For example, in one study1, researchers administered cod liver oil to human volunteers. The accumulation of the fatty acids in the plasma lipoproteins was then measured directly in a longitudinal study. In addition the amounts of other fatty acids in the lipoproteins was also measured.
The doses of the fish oils fed to the subjects were 1.4, 2.3, 4.1 and 8.2 grams per day and consumption lasted 4 weeks. At all doses a shift in the plasma lipoprotein fatty acid composition was seen, with increases in the n-3 fatty acids EPA and DHA. As lipoprotein concentrations of the omega-3 fatty acids rose, concomitant falls in the omega-9 fatty acid oleic acid (OA, C18:1 (n-9)) and LA were observed. Measurements of sterol esters in plasma showed that only levels of EPA increased in this regard. The length of time to reach maximum accumulation of n-3 fatty acids in lipoproteins varied from between 1 and 2 weeks, with higher intakes causing a more rapid accumulation. However, two weeks after the last ingestion of the fish oil supplements, levels of fatty acids had returned to baseline readings. As has been shown previously fish oil supplements caused a significant reduction in plasma triglyceride levels as measured by the very low density lipoprotein (VLDL) particle.
Dr Robert Barrington’s Nutritional Recommendation: Fish oils are the most efficient way to obtain adequate levels of n-3 fatty acids. Incorporating fish oils into the diet can improve health because it allows the correct balance of n-3 to n-6 fatty acids to be achieved, and this then has systemic anti-inflammatory effects. A large contributory factor in the detrimental health effects of the typical Western diet has been shown to be due to an imbalance in the n-6 to n-3 fatty acid ratio in the diet which leads to inflammation and oxidative stress. After increasing intakes of fish oils it can take a number of weeks for the n-3 fatty acids to accumulate in tissues and health effects to be seen. However once accumulated these fatty acids act as a store of essential fatty acids negating the requirement for a daily intake. The current recommendation to eat fatty fish two to three times per week will therefore be adequate for the purpose of supplying n-3 fatty acids for metabolic needs. However, consuming fish at higher intakes initially may reduce the period before beneficial effects are seen. Fish oils supplements will have similar effects.
RdB
