How well do you know clinical nutrition: Basic review (11)

FATS

Fats are essential for the construction of cell membranes and as a source of energy. Fats are, in fact, different forms of fatty acids. These can be long chain, with 16, 18, or more carbon units, or short chain fatty acids, such as the three carbon butyric acid. Fatty acids are stored in the body.

They are sometimes present in food as triglyceride, which is composed of three fatty acids attached to a backbone of glycerol. Over-consumption of the high fat food choices can predispose to obesity, elevated cholesterol, atherosclerosis, heart disease, stroke, gallstones, and other health problems.

Patients should be educated about the fat content of their food choices. For example even after cooking, "extra-lean" ground beef obtains more than half its calories from fat. More than 70% of the energy content of cheese comes from fat. However, the quality of fat is as important as the quantity. Some fats support the process of healing; other fats contribute to disease processes.

Saturated and Unsaturated Fats

Especially harmful is saturated fat, which is found high amounts in animal derived foods - meat and dairy. However, monounsaturated fats (with one unsaturated carbon to carbon bond) seem to decrease serum cholesterol, while polyunsaturates, including the essential fatty acids, are more easily oxidized, but less atherogenic. In general, naturopathic physicians follow the recommendations of the major nutritional authorities in advising patients to restrict the amount of saturated fat in their diet.

Essential Fatty Acids

Some fatty acids are termed "essential fatty acid (EFAs) because they cannot be synthesized from other fatty acids and must be obtained from food. They play a critical role in the manufacture of prostaglandins, locally acting messengers that exert control over inflammatory activity, blood vessel tone and clotting. Many natural vegetable oils contain the essential fatty acids, provided that they have not been overly processed. Longer-chain derivatives of the essential fats are found in the oils from fish. In this case, it is from the meat of the fish, not from fish liver oils, which are used as vitamin A and vitamin D supplements.

Trans Fatty Acids

Trans fats can be dangerous. These fatty acids have the same chemical formula as a normal fatty acids (cis configuration), but the spatial orientation of hydrogen atoms around a carbon to carbon double bond has been altered. Trans fats occur in small amounts in nature, but are chiefly created in the processing of oils, including the manufacturing of margarine, vegetable shortening, and deep frying oils.

In this case the aim of fat processing is to make a product that is more stable at room temperature and more resistant to heating. Trans fats replace fats of the cis configuration in cell membranes and reactions, and have been linked to increased risk of cardiovascular disease. Increasingly, food is being processed using alternative methods and prepared commercially without using trans fats.

OMEGA-3 AND OMEGA-6

EFAS Essential fatty acids are omega-3 or and omega-6 in type. The omega nomenclature refers to the position of the first double bond in the chain of carbon molecules in the fatty acid. -A fatty acid with a double bond at carbon 6 (from the terminal end of the fatty acid) would be omega-6, at carbon 3. omega-3. Both omega series have fatty acids that are considered essential. They can be used to form prostaglandins and other eicosanoids (prostaglandins were first discovered in the prostate gland of sheep and were so named). Specifically, the omega-3 class of fatty acids help reduce inflammation and platelet aggregation.

This class of EFAs includes gamma linolenic acid (GLA) and eicosapentaenoic acid (EPA) found in fish, and arachidonic acid (AA) found in meats and peanut oil. The inflammatory cascade begins with arachidonic acid being cleaved from a phospholipid in the cell membrane, which allows it to enter the pathway of prostaglandin/leukotriene synthesis.

Omega-6 fats are important, for energy and, in the case of the omega-6 linoleic acid, for conversion to eicosanoid molecules, which act as molecular switches for-inflammation, blood clotting, and other actions.

There is no strictly defined ratio of omega-6 to omega-3 fats in the diet; however, many plant-eating animals consume more omega 3 than 6.

Humans on a natural hunting and gathering diet have large amounts of omega-3. Modern humans on a Western diet often have much more omega-6 than omega-3. This can be considered out of balance and likely to promote inflammation in the body. A healthy ratio of omega 6 to 3 would be somewhere from 1:1 to 4:1, with the lower ratio being desirable for those with inflammatory diseases who need to maintain an optimal eicosanoid balance.

Fat Processing and Storage Patients should be encouraged to consume fats that have not been otherwise chemically modified. For example, vegetable oils high in polyunsaturates are often stripped of their antioxidants (beta-carotene and vitamin E) during processing, even though we know these oils are susceptible to oxidation. Heating of these oils, for purposes of extraction from seeds or for cooking, can lead to the formation of epoxides and trans fats. Epoxides are a combination of oxygen and fatty acids that generate free radicals in the body, which influence the disease process.

Cold-pressed oils are recommended. In this process, neither heat nor chemical solvents are used to extract the oil from the seed. Oils should be protected from light, which can lead to rancidity, especially in polyunsaturates. Olive oil is high in monounsaturates and can be obtained as "extra virgin" olive oil, which means the first pressing. Flaxseed oil, an excellent source of linoleic acid and linolenic acid, should never be used for cooking because it becomes a rancid linseed oil, unfit for consumption.

Recommended Daily Fat Intake:

65 g per day on a 2000 kcal diet, of which no more than 20 g should be saturated.