Despite the enormous global burden caused by chronic respiratory diseases (CRD) there is less reliable data available on the effect of diet on CRD due to various reasons. Among them, different definitions of CRD for epidemiological studies, lack of standardisation of different aspects of dietary surveys and different approaches for the assessment of long-term nutritional intake, which should be typical to reflect a habitual diet. Among dietary assessment methods there is no ideal method that could provide a quick, cheap and reliable assessment of individual dietary intake and the written methods Validation of dietary assessment is an important issue while analysing dietary impact on the health status of the individual and the role of individual nutrients in this process. External objective reference parameters, such as biological markers of intake, are often needed to evaluate the validity of dietary assessment. At present only a few nutrients have biological markers that respond to changes in dietary intake with sufficient sensitivity. For instance, fatty acid composition in adipose tissue is a reflection of longterm dietary fat intake. Biochemical measurements of nutrients in blood and urine correlate well with a shortterm intake of lipids, vitamins, sodium and potassium.

Using different methods, associations have been reported between CRD (mainly asthma and chronic obstructive pulmonary disease (COPD)) and the intake of fruits, fish, whole grain, antioxidant vitamins, fatty acids, sodium, magnesium, alcohol and other factors. Obesity has also been associated with the increased risk of asthma and lower lung function.

Polyunsaturated fatty acids (PUFAs) intake of 6–10% needs special discussion. PUFAs consist of n-6 PUFAs and n-3 PUFAs (or omega-6 and omega-3 PUFAs). The most important n-6 PUFA is linoleic acid, which is abundant especially in soybean and sunflower oils. The most important n-3 PUFAs are eicosapentaenoic acid and docosahexaenoic acid, found in fatty fish and seafood, and α-linolenic acid, found in vegetables. N-6 PUFAs lower plasma total and low-density lipoprotein (LDL) cholesterol concentrations, while the biological effects of n-3 PUFAs are wide ranging from beneficial – powerful lowering of serum triglycerides, lowering of blood pressure, improvement of cardiac function, arterial compliance, endothelial function, vascular reactivity and potent anti-platelet and anti-inflammatory effects – to the harmful – they raise serum LDL cholesterol. In view of this, appropriate balance between n-6 and n-3 PUFAs is beneficial for cardiovascular diseases.

From the CRD point of view, n-6 PUFAs (including arachidonic fatty acid) are considered to be proinflammatory due to higher levels of inflammatory mediators (prostaglandins PGE2 and leukotrienes LTB4) and this pro-inflammatory effect should be also balanced by the anti-inflammatory effect of n-3 PUFAs. However, more studies are needed to determine the optimal balance of these fatty acids.

Several large-cohort studies have found that intake of trans fatty acids increases the risk of coronary heart disease. Most trans fatty acids are contributed by industrially hardened oils, deep fried fast foods and baked goods.

There is only very limited evidence about the effect of trans fatty acids on asthma. In those countries that have higher levels of trans fatty acids intake, a higher prevalence of asthma is observed and a cross-sectional study found that higher levels of margarine consumption increased the risk of asthma. In view of this the PNG of trans fatty acids consumption (less than 1% of total energy) could have a beneficial effect on CRD. However, more studies are needed in the area of CRD where trans fatty acids consumption could be validated by fatty acid composition in adipose tissue.

Monounsaturated fatty acids (MUFAs) are beneficial for cardiovascular disease by lowering plasma total and LDL cholesterol. There is little evidence on the effect of MUFAs on CRD. There are some data on the harmful effects of MUFAs, which promote allergic sensitisation. The only nutritionally important MUFA is oleic acid, which is abundant in olive and canola oils and also in nuts. Thus, more studies are needed, and the recommendation to consider MUFAs by difference: total fat (saturated fatty acids+ PUFAs + trans fatty acids) should not be harmful for CRD, in particular if the consumption of n-3 PUFAs is adequate.