Fish oils have received both positive and negative press regarding their effects on health. The quality of fish oils on the market varies widely, so what should you be looking for when buying fish oils. There are several primary factors to consider when selecting fish oils:

• Purity
• Freshness
• Concentration
• Bio-availability

Given the scale of pollution in the oceans, the purity of fish oils has to be the primary concern of any consumer. Oils must meet standardised international standards for heavy metals, PCBs, dioxins, and any other potential contaminants.

Omega 3 are susceptible to becoming rancid from oxidation, which means that the fish oils are more likely to contribute the diseases and ailments that they are being used to prevent, given that rancid oils are inflammatory. Therefore, it should be ensured that the fish oils are fresh.

Adequate levels of EPA and DHA are required within the fish oils, in order to induce an anti-inflammatory effect, meaning concentration is critical.

The chemical structure of the fish oil has an impact on the ability to absorb the beneficial components. Therefore bioavailability of the fish oil source should be taken into consideration.

Several fish contain many toxic chemicals and heavy metals, such as arsenic, cadmium, mercury and lead, PCBs, and dioxins which can cause disease. Whilst fish only represents a small proportion of the diet containing these chemicals, chronic consumption may significantly expose individuals to high levels of these chemicals. In order to remove toxins, fish oil is put through a process called molecular distillation, which reduces toxins below a safety threshold for consumption. If you have any doubt, contact the manufacturer, and request a certificate of analysis (COA) (which is carried out by independent labs, to measure ingredients and confirm or reject claims made by the manufacturer).

Rancid fish oils cause oxidative stress and inflammation, which promote disease. Unsaturated fats are particularly susceptible to oxidation. EPA and DHA (long-chain) unsaturated fats are the most unsaturated of the fats and therefore the most susceptible to oxidation. Once fish oil has oxidised and become rancid, it will cause the opposite effect to that which is desired. In order to assess rancidity, check the COA for the peroxide level, which will give a figure of the level of oxidation and rancidity which has occurred during storage. The peroxide value should be below 5meq/kg.

If you open a capsule once purchased, there should be a fishy smell but not one of rotten fish. Moreover fruit smells are often tell-tale signs of masking agents to hide rancidity. Another common technique is to freeze a capsule and if the contents become cloudy, they are deemed to be rancid and oxidised. However given the saturated and monounsaturated composition of the fish oil (from whole fish), they will appear to be cloudy.

It is particularly important to consume sufficient DHA (1-3g per day) in order to elicit the optimal therapeutic effect of fish oils on inflammation. To take a real world example, an individual would have to consume 170g of salmon roe to acquire 1g of DHA, which equates to approximately £20 so not as cost effective as consuming fish oil capsules. However not all fish oils contain sufficient levels of DHA. Therefore it is necessary to check the label to ensure that each capsule contains 200-300mg DHA per capsule to achieve a clinical dose, without the necessity to consume copious quantities of pills.

The capacity to the absorption capacity of fish oil is dependent on the molecular shape. Generally, the more natural the structure, the greater the bio-availability. There are three forms of fish oil available on the market:

Natural triglyceride oil: essentially oil extracted directly from whole fish, and the closest thing to eating whole fish. However, it is not concentrated or purified meaning low concentrations of EPA and DHA as well as the potential for impurities and contaminants, like heavy metals, PCBs and dioxins.

Ethyl Ester Oil: produced through the concentration and molecular distillation of natural triglyceride oil in order to lower the level of impurities and contaminants, and increase the levels of EPA and DHA by up to three times. The fish oil remains in a semi-natural state owing to an intrinsic chemical function.

Synthetic Triglyceride Oil: produced when natural triglycerides are converted to ethyl esters and subsequently converted to synthetic triglycerides, meaning that carbon bonds move position, which alters molecule structure, which effects the bioavailability

Bioavailability is greatest in natural triglyceride oil followed by ethyl ester oil and then synthetic triglyceride oil. Moreover fish oils are most optimally absorbed when consumed in conjunction with a meal consisting of a high fat content.

If you take the following factors into consideration when purchasing fish oils, you can be confident to confer all the benefits from consuming them.