The Facts about Fats
As we discovered when discussing Carbohyrates , there are many misconceptions about their role in our diet. This is even more so when we talk about FATS . The food industry has done much to foster the belief that Fats are bad by their emphasis on Low fat or No fat foods. While the low fat approach to eating has helped some individuals, as a nation it has not helped us control weight or become healthier. The incidence of Obesity is increasing at an alarming rate, especially in children. As a consequence, the incidence of Diabetes is also increasing dramatically.
So what is the answer to this problem? To answer that question, again,we must understand the Facts about Fats
- What are Fats ?
- What is the function of Fats in our body ?
- Classification and sources of Fats.
- What is the optimum amount of Fat in our diet ?
Fats usually describe a wide range of substances that generally will dissolve in organic solvents, but are largely insoluble in water. There are many other terms used to describe fats namely lipids,triglycerides, oils and waxes. The term “Fat” is usually used to refer to fats that are solid at room temperature, while “oils” refers to those that are liquid at room temperature. “Lipids”, is used to refer to both solid and liquid fats , along with other related substances. There are many different kinds of fats, each being a variation on the same chemical structure. All fats consist of fatty acids. Natural fats , whether they are derived from animal or plant sources are composed of three fatty acid molecules (that’s the “tri” in triglycerides) bound to one glycerol (a type of alcohol ) molecule. The properties of any specific fat molecule depends on the particular fatty acids of which it is composed. There are about 25 different fatty acids that can be attached to the glycerol backbone structure.
Function of Fats in our Body
Fats are important for many body processes. Almost all foods contain some fat. Even so called fat free foods such as carrots and lettuce contain small amounts of this nutrient. You need to eat some fat in your diet. Even if the diet contains no fat, the body will convert excess protein and carbohydrate to fat and store them as such. Fats play a vital role in maintaining healthy skin and hair. Fat protects and insulates body organs against shock, keeps you warm and helps maintain body temperature. It helps your body absorb and move nutrients around; eg the fat soluble vitamins A,D,E and K. It also helps hormone production. Fat also serves as a useful buffer against many diseases. When a substance reaches unsafe levels in the blood stream, the body can store the offending substance in new fat tissue. This helps protect vital organs until such time as the offending substances can be metabolised and/or removed from the body. While it is nearly impossible to remove fat completely from the diet, it would be unhealthy to do so. Some fatty acids are essential nutrients for numerous chemical processes. They cannot be produced in the body from other compounds and need to be consumed in small amounts ( See 3a & 3b below). The two essential fatty acids are linoleic and alpha- linoleic acid All other fats required by the body are non-essential and can be produced in the body from other compounds.
Classification and source of Fats
Dietary fats are classified by their structure. Different types of fats react differently in the body. Dietary fat can be classified into four main groups:
1. Saturated Fats
2. Mono-unsaturated Fats
3. Poly-unsaturated Fats can be divided into 2 categories. (a) Omega -3 fats (b) Omega-6 fats
4. Trans Fats
1. Saturated Fats are fats that are solid at room temperature and come mainly from animal food sources, including meat and dairy products. Examples are fatty beef, lamb, pork, poultry with skin, beef fat (Tallow), lard and cream, butter, cheese and other dairy products made from whole or reduced-fat milk.
In addition, many baked goods and fried foods can contain high levels of saturated fats. Some plant foods, such as palm oil, palm kernel oil and coconut oil, also contain primarily saturated fats, but do not contain cholesterol. These foods also contain dietary Cholesterol. Increased blood cholesterol is an important risk factor in coronary heart disease.
2. Mono-unsaturated Fats are typically liquid at room temperature but start to turn solid when chilled. Olive oil, canola and peanut oils are good examples. They are also found in avocado and nuts such as peanuts, hazelnuts, cashews and almonds. One of their beneficial effects is to lower LDL-cholesterol levels.
3. Poly-unsaturated Fats can be found mostly in grain products, fish and sea food, vegetable oils such as safflower,corn or Soy oils, nuts such as walnuts and brazil nuts and seeds. Foods like mayonnaise and soft margarine may also be good sources, but nutritional factors can vary by style and brand.
( a ) Omega-3 Fats are found in both plant and marine foods. Plant food sources include linseed, walnuts, canola and soy oils and canola based margarine. It is the omega-3 from fish, fish oil and seafood, that has the strongest evidence for health benefits, including reducing the risk of heart disease. Oily fish such as Atlantic salmon, mackerel, herring, Southern blue fin tuna , trevally and sardines have a high omega-3 content. There has been some evidence suggesting omega-3 fatty acids can reduce prostate tumour growth, reduce the tendency to blood clotting, lower triglyceride levels, reduce inflammation and support the immune system.
( b ) Omega-6 Fats are found primarily in foods that come from plant sources such as nuts, seeds and plant oils such as corn, soy, sunflower and safflower. These may also reduce the risk of cardiovascular disease. The omega-3 fats provide the essential fatty acid alpha-linoleic acid, while the omega-6 fats provide linoleic acid
4. Trans Fats are rare in nature. They are only created in the rumen of cows and sheep and are found naturally in small amounts in milk, cheese, beef and lamb
Commonly they are fats created when a vegetable oil undergoes a process called hydrogenation. The liquid vegetable oil is heated in the presence of hydrogen gas. The process is used to make liquids more solid and to improve the stability and extend shelf life of processed foods . This occurs in the manufacture of some table margarines and in solid spreads used in the food industry to make baked products such as pies , pastries, cakes biscuits and buns. Fully hydrogenating a vegetable oil creates a fat that acts like a saturated fat. Trans fats are far worse than saturated fats when it comes to heart disease.
What is the optimum amount of Fat in our Diet ?
- As we have seen, almost all foods contain some fat. Most experts recommend that adults restrict their fat intake to no more than 30% of each day’s Kilojoules. Some authorities say this should be lower, with10-25% frpm mono-unsaturated fats and 8 -10% from poly-unsaturated fats.
- Research has shown that the total amount of fat in the diet isn’t really linked to obesity or disease. What really matters is the type of fat in the diet. Since no one eats by percentage of daily kilojoules (or calories ), a good rule of thumb is to choose unsaturated fats instead of saturated as far as possible.
- Bad fats - saturated and trans fats - increase the risk for developing certain diseases, while Good fats, mono-unsaturated and poly unsaturated fats, can have a positive effect on the heart and other parts of the body .
- Researchers have found that people who have a high intake of mono-unsaturated fats from olive oil, ( for example, those from Mediterranean countries such as Greece and Italy), tend to have a low incidence of coronary artery disease, regardless of their body weight. The other important factor in the diet of people from these regions is the high intake of vegetables, legumes, fruits and cereals which are also rich in antioxidants
The Take Home Message when discussing Fats is - Look for foods with the least amount of saturated fat and a good mixture of unsaturated fat especially those containing the essential fatty acids.
In my next article I will talk about the relationship of Fats and Cholesterol