Lipids play diverse roles in the normal functioning of the body:
- they serve as the structural building material of all membranes of cells and organelles
- they provide energy for living organisms - providing more than twice the energy content compared with carbohydrates and proteins on a weight basis
- they function as molecular messengers and signalling molecules in the body
Lipids are also biomarkers of disease and are involved in several pathological conditions. Lipids are also known to play a role in genetic modification and inﬂuence risk of chronic disease.
Some of the fatty acids need to be taken in diet. This includes essential fatty acids (EFAs), linoleic acid (LA, an omega-6 fatty acid, 18:2n-6), and a-linolenic acid (LNA, an omega-3 fatty acid, 18:3n-3). These help in formation of polyunsaturated fatty acids (PUFAs) used in cellular structures and as precursors for the biosynthesis of many of the body’s regulatory molecules like long-chain PUFAs, arachidonic acid, eicosapentaenoic acid (EPA, 20:5n-3), and docosahexaenoic acid (DHA, 22:6n-3) and eicosanoids. DHA again is necessary for normal neural and retinal development in the infant and young child.
Effects of PUFA
Dietary lipids help in biochemical and physiological functions as modulators of cell actions and genes. For example, the n-6 and n-3 PUFAs bind to the peroxisome proliferator-activated receptors (PPARs) on genes. This PPAR gene is important for lipid and carbohydrate metabolism. These also play a role in chronic diseases like diabetes and inflammatory conditions.
PUFA in diet has been found to reduce risk of cardiovascular disease and cancers. In addition, n-3 fatty acids are known to lessen the severity and minimize symptoms of chronic inﬂammatory diseases, including rheumatoid arthritis and inﬂammatory bowel disease, and may even beneﬁt in correcting psychological disorders.
PUFAs modulate eicosanoid biosynthesis in various tissues and cell types and this can inﬂuence gene expression.
Foods with PUFA
PUFA is present in three forms in food. These are LNA in vegetables, oilseeds, and nuts, and EPA and DHA in cold water ﬁshes and algae.
SDA is rich in plant oils (such as hempseed oil and black currant seed oil) but can be isolated and concentrated from marine ﬁsh. Since n-3 fatty acids cannot be synthesized in the body they must be either ingested directly or formed from LNA.
Food supplements and fortification
The diet needs to be low in saturated fats. Essential fatty acids and n-3 PUFA, however, are important in the diet.
Sources of n-3 PUFAs are also added directly to infant formula to provide sufﬁcient DHA for normal development of the nervous system during early infancy. These supplements are added to both dairy and non dairy products to reduce risk of heart disease, cancer risk and risk of obesity. The n-3 PUFA are contained and added in ﬁsh meal, ﬁsh oil, vegetable oils, linseed oil and canola oil etc.
Lipids and vitamins
A minimum amount of dietary fat is important because it helps in absorption of fat-soluble vitamins (A, D, E and K) and carotenoids.
Lipids and chronic diseases
Fats in diet play a role in chronic diseases. Up to 70% of all cancers in the United States are attributable to diet for example. Around half of the population according to the USDA develops a diet-related chronic disease responsible for the leading causes of death like heart disease, cancer, stroke, diabetes, and arteriosclerosis. This raises the annual health costs to $250 billion in the USA. High fat, especially trans fats and unsaturated fats lead to heart disease, degenerative and inﬂammatory arthritis, osteoporosis, obesity, cancer etc.