Dietary Fats

Dietary Fats; which ones are recommended?

The foods we eat contain nutrients that provide energy and other things the body needs.
These nutrients fall into three major groups; carbohydrates fats and proteins and three minor groups; vitamins, minerals and water.

Fats are important for many body processes. Dietary fats protect the body organs, keep the body warm, help the body to absorb and move nutrients around, and help hormone production. However, some fats are better than others and having too much of any type is not good.

Dietary fats can be classified into four main groups according to their structure:
Each group behaves differently inside the body. All four types of fat consist of 'fatty acids' (various combinations of carbon and hydrogen molecules).

The four main types of dietary fats are;

1. Saturated Fats
   Saturated Fats are saturated with hydrogen molecules. They are mostly found in animal products. Sources include beef, lamb, milk, cheese and other dairy products and some processed foods containing hydrogenated vegetable shortenings, such as pastries and fried fast foods. NB: Saturated fats contribute to the risks of heart disease by boosting blood cholesterol levels.
2. Mono-unsaturated Fats
   Mono-unsaturated fats have fewer hydrogen molecules attached to them. They tend to lower blood cholesterol when used in the diet, but have a lesser impact than poly-unsaturated fatty acids. Sources include avocado, olive oil, canola oil and peanuts (or peanut oil and butter). NB: Mono-unsaturated fats are considered the most beneficial to health because they lower LDL levels and maintain, or even raise, HDL cholesterol levels.
3. Poly-unsaturated Fats
   Poly-unsaturated Fats also have fewer hydrogen molecules attached to them, thus tend to lower blood cholesterol when used in the diet, but have a larger impact than mono-unsaturated fatty acids. Sources include fish oils, seafood and vegetable oils - especially safflower, sunflower, and corn or soy oils. NB: Polyunsaturated fats lower LDL levels, but some studies have shown that they can also cause a decrease in the levels of HDL, the 'good' blood cholesterol.
   Polyunsaturated fats can be divided into two categories: omega-6 and omega-3 fats:
   Omega-6 fats sources include; nuts, seeds and plant oils (corn, soy and safflower).
   Omega-6 fats lower LDL “bad” cholesterol levels in the blood, thus lower the risk of heart diseases and strokes.
   The omega-3 fats sources include; fish, seafood, lean meat, plant foods (cereal grains, seeds, nuts, legumes, dark green leafy vegetables, figs), plant oils (soybean, canola, linseed and walnut), oily fish (such as mackerel, salmon, trout, tuna, sardines, herring and gem fish) Omega-3 fats lower LDL “bad” cholesterol and triglycerides (fats) levels in the blood, lower the risk of heart disease and strokes, reduce blood pressure, reduce the risk of cancer, improve blood vessel elasticity and lessen blood vessel damage, thins the blood and makes it less sticky and less likely to clot, produces anti-inflammatory compounds called leukotrienes, which can help ease a variety of inflammatory disorders, such as psoriasis, rheumatoid arthritis, ulcerative colitis and inflammation of blood vessel walls associated with atherosclerosis and contributes to the normal development of foetal brain.
   NB: Very high intake of omega-6 fat can compete with the omega-3 fats and stop them from doing their good work, which may lead to an omega-3 fatty acid deficiency. For a healthy balance, it is recommended that the ratio of omega-6 to omega-3 should be less than 5 to 1. This can be achieved by consuming a variety of plant oils and spreads.
4. Trans Fats
   Trans Fats are rare in nature. They are naturally found in small amounts in milk, cheese, beef and lamb. They are created in the rumen of cows and sheep, and They can also be created during the manufacturing of some table margarines and solid spreads used in the food industry to make baked products such as pies, pastries, cakes, biscuits and buns.
   NB: Trans-fatty acids are considered to behave like saturated fats in the body; they raise LDL “bad” cholesterol levels and increase the risk of heart disease. Unlike saturated fats, they tend to lower HDL “good” cholesterol, so are potentially even more damaging. However, they are found in much smaller amounts in the diet than saturated fats and do not pose as great a risk of heart disease as saturated fats.
   The amount and type of trans-fatty acids in the diet may result in the narrowing or widening of the arteries, which has the effect of altering the flow of blood and the tendency for blood clotting. People should be more concerned about the trans-fats produced during food manufacturing than the trans-fats present naturally in certain foods. Look for margarine that has less than one per cent trans-fats on the label or choose foods with the Heart Foundation Tick.
   Limit how much takeaway food and packaged snack foods you eat. These are important factors which influence the risk of developing cardiovascular disease.

Energy density of dietary fats and disease

Dietary fat has more than twice the amount of kilojoules per gram (37) present in carbohydrate and protein (17), making it energy dense.

A high fat diet has been associated with Coronary Heart Disease (CHD) because it narrows the arteries and increases the pressure used by the heart in pumping blood during circulation.

A high fat diet is also associated with Diabetes because it over-burdens the pancreas in producing the hormone glucagon to convert glycogen back to glucose for energy. This puts extra work on the pancreas and it eventually becomes weak and less effective in producing insulin to convert glucose to energy, thus high glucose levels remain in the blood.

A high fat diet is associated with overweight and obesity because the excess fat in the food which the body does not utilize is stored as adipose tissue and increases the body weight.
A high fat diet is linked to liver diseases because its metabolism over burdens the liver and may affect its effectiveness in performing its elimination duties.

A high fat diet raises the level of LDL “bad” cholesterol because it is present in some dietary fats such as saturated and trans fats and may contribute to the narrowing and silting up of the arteries.
NB: Saturated fats tend to raise LDL levels.

The saturated fats which contain mainly palmitic and myristic fatty acids are the most powerful in raising blood cholesterol levels. However, not all saturated fats raise LDL cholesterol levels. Those containing stearic acid are a better choice.

Palmitic acid is the major fatty acid in palm oil. It is also found in cottonseed oil, lard, cocoa butter, beef tallow, in many fast foods and commercial products, such as biscuits and pastries.
Mystiric acid is found in dairy foods, particularly in cheese. Stearic acid is found predominantly in meat, dairy products and chocolate and does not appear to affect blood cholesterol levels.

Current Recommendations

Nutritionists recommend that we limit the amount of fats in the daily diet, particularly saturated and trans-fats.

• Trim visible fat from all cuts of meat.
• Include one or two fish or seafood meals a week. Oily fish preferable.
• Do not batter fish or fry it in animal or hydrogenated vegetable fats; pan-frying and deep-frying may decrease the omega-3 content of the fish.
• Instead of frying foods, try steaming, stir-frying or baking.
• Switch to reduced fat or non-fat varieties of milk and other dairy products.
• Limit takeaway foods, butter, potato chips, biscuits and cakes, and other processed foods containing vegetable shortenings.
• Choose fat from unrefined sources - for example, oily fish, nuts, soy, avocado, seeds (in bread) and virgin/cold pressed oils.
• Use a variety of different oils - for example, virgin olive oil, canola oil or peanut oil.
• Use non-stick pans to cut back on the amount of fats that are used solely to stop the food from sticking.

Remember that fat is an important part of a healthy diet. However, some fats are better than others.

• Saturated fats increase blood cholesterol.
• Mono-unsaturated and
• Polyunsaturated fats tend to lower blood cholesterol. Omega-6 and omega-3 fats can benefit your health when well combined.
• Trans-fats are potentially harmful and are used to make baked products, pies, cakes, biscuits and buns.

References: Better Health Channel (Australian -Victorian Government website)