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lipid intakes

Saturday 29 December 2018

Humans have a requirement for certain essential fatty acids, such as linoleic acid (an omega-6 fatty acid) and alpha-linolenic acid (an omega-3 fatty acid) in the diet because they cannot be synthesized from simple precursors in the diet.

Both of these fatty acids are 18-carbon polyunsaturated fatty acids differing in the number and position of the double bonds.

Most vegetable oils are rich in linoleic acid (safflower, sunflower, and corn oils).

Alpha-linolenic acid is found in the green leaves of plants, and in selected seeds, nuts and legumes (flax, canola, walnuts and soy).

Fish oils are particularly rich in the longer-chain omega-6 fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). Most of the lipid found in food is in the form of triacylglycerols, cholesterol and phospholipids.

Most of the saturated fatty acids (as triacylglycerols) in the diet are incorporated into adipose tissue stores, because the absence of double bonds allows a higher energy yield per carbon than is obtained from oxidation of unsaturated fatty acids.

The longer chain fatty acids are incorporated into cell membranes as phospholipids regardless of degree of saturation. Since dietary fatty acids are exchanged with membrane fatty acids, dietary fat composition is reflected in membrane lipid composition.

Thus dietary fatty acids can influence cell function through effects on membrane properties. Dietary fat provides an average energy intake which is approximately twice that of carbohydrate or protein.

A minimum amount of dietary fat is necessary to facilitate absorption of lipid vitamins (vitamin A, vitamin D, vitamin E and vitamin K) and carotenoids.

High fat intake

High fat intake contributes to increased risk of obesity, diabetes and atherosclerosis. Abnormal levels of certain lipids, particularly cholesterol (in hypercholesterolemia) and trans fatty acids, are risk factors for heart disease amongst others.

Atherosclerosis is the primary cause of coronary and cardiovascular diseases and is primary due to the buildup of plaque on the inside walls of arteries.

Plaque is made up of cholesterol-rich low density lipoproteins (LDL), macrophages, smooth muscle cells, platelets, and other substances.

In North America and most other western countries, atherosclerosis is the leading cause of illness and death, almost doubling the number of deaths from cancers.

Despite significant medical advances, coronary artery disease and atherosclerotic stroke are responsible for more deaths than all other causes combined.

A substantial amount of scientific evidence supports the impact of dietary fatty acids on cardiovascular health.

Saturated fatty acids have a profound hypercholesterolemic (increase blood cholesterol levels) effect and tend to increase plasma LDL.

Saturated fatty acids are found predominantly in animal products (butter, cheese and meat) but coconut oil and palm oil are common vegetable sources.

Intake of monounsaturated fats in oils such as olive oil is thought to be preferable to consumption of polyunsaturated fats in oils such as corn oil because the monounsaturated fats apparently do not lower high-density-lipoprotein (HDL) cholesterol levels.

Keeping cholesterol in the normal range not only helps prevent heart attacks and strokes but may also prevent the progression of atherosclerosis.

Statins are a class of drugs that lowers the level of cholesterol in the blood by inhibiting the enzyme HMG-CoA reductase, a key enzyme involved in the biosynthesis of cholesterol in the liver.