Nutrition
Smoke signals
by Jennifer Bowden
We all know smoking cigarettes is unhealthy, but what about eating smoked fish?
Question: When fish is smoked, does it lose any of its nutritional value? Is the omega-3 fat content of oily fish such as salmon adversely affected by smoking? And are there any health hazards in the smoking of fish?
Answer:
Although nutritionists keep banging on about ensuring your food isn’t smothered in excessive smoke while being barbecued, we accept our food will inevitably get a little smoke on it. But surely eating purposely smoked meat or fish can’t be a good idea, can it?
Traditionally, commercially smoked fish is gulleted, then covered in a mixture of sugar and salt for a while, before being cleaned and placed on racks in a kiln for drying and smoking. Smoking occurs at different temperature ranges – cold, semi-warm or hot – with cold smoked salmon, for example, staying in a kiln at around 20°C for 8-12 hours.
Smoke was originally generated in the same chamber as the fish. However, many commercial operators, like Regal Salmon, now use indirect smoking: the smoke is added to the kiln on a controlled basis from a separate chamber, where wood chips and sawdust are heated on a hot plate. Other modern variations include using “liquid smoke” or “smoke flavourings”. So there is no longer one clear definition for smoked food.
Smoke, and therefore smoked foods, may contain polycyclic aromatic hydrocarbons (PAHs) which are created by the incomplete combustion of inorganic material such as wood. Unfortunately, this family of chemical compounds includes several carcinogens. In addition, high-salt foods, such as those that are smoked, may increase the production in our gut of N-nitroso compounds, which are thought to contribute to stomach cancer.
Whether smoked fish contains PAHs depends on the processing technique. For starters, hardwood fuels such as oak, hickory, beech and manuka burn more cleanly and produce fewer PAHs than softer woods. Indirect smoking methods and filtering also lower the PAH content, as does heating wood chips on a hot plate rather than burning them, moving the fish further from the heat source, reducing smoking times, and washing or water-cooling the product after smoking – according to the New Zealand Food Safety Authority.
Regal Salmon, which supplies over a third of supermarket smoked salmon, uses beech wood for its smoked salmon range, which is good news, as is its use of an indirect smoking process and heating of wood chips (rather than burning).
There is only limited evidence, of quite poor quality, that smoked foods may cause stomach cancer, according to the World Cancer Research Fund’s Second Expert Report on diet and cancer. And most evidence is from studies involving smoked meat rather than fish. The report also says there is limited evidence that grilled and barbecued meat are a cause of stomach cancer.
Salmon’s omega-3 fats are a precious asset and, thankfully, smoking has little effect on them, with around 3g of omega-3 fats per 100g of either fresh or smoked salmon. Omega-3 fats in New Zealand king salmon appear well protected, according to University of Auckland researchers, who found minimal losses occurred when salmon fillets were poached, steamed, microwaved, pan-fried, oven-baked or deep-fried.
However, smoked fish typically contains significantly more sodium than fresh fish: for example, about 600mg of sodium per 100g of smoked salmon, compared with just 20-30mg of sodium per 100g of raw salmon. So although commercially smoked fish is nutritious and relatively safe, it shouldn’t form the foundation of your diet. Ensure your diet also includes meats and fish prepared by other cooking methods, and lots of fruits and vegetables – research suggests fruits and veges may reduce the risk of stomach cancer. Which goes to show it’s all about balanced eating at the end of the day.
