04/02/2009 (The Nation UAE) - The topic of which fats are healthy and which are not is complex enough to confuse even those with a biochemistry degree, let alone the average shopper. There are monounsaturated fats, cis fats, trans fats, omega-3s, omega-6s and interestified fats, to name but a few. Their effects in the body are as varied as their names.

A recent study has appeared to make the topic harder still to comprehend by reversing the commonly expressed view that we should cut our intake of omega-6 fatty acids, which are found in vegetable oils, and certain nuts and seeds.

Previous studies seemed to suggest that omega-6s might have a role in promoting the spread of cancer. Research in 2006 found that a substance called prostaglandin E2, which can be produced from omega-6 fatty acids, could promote the spread of prostate cancer cells to the bone marrow. The suggestion was that the tumours used the fats as a source of energy.

There have also been concerns that omega-6 fatty acids can promote inflammation and in so doing increase the risk of cardiovascular disease. For example, arachidonic acid, which can be formed from the most common omega-6 fatty acid, linoleic acid, is considered to lead to inflammation.

The latest research, published in Circulation: Journal of the American Heart Association, suggests however that the omega-6 fatty acids can help to maintain a healthy heart.

A team of nine researchers say that the body limits the amount of harmful by-products it makes from linoleic acid, so consuming extra omega-6 fatty acids will not cause these levels to increase.

Also, the scientists insist that other substances that can be made from omega-6 fatty acids actually work to reduce inflammation by preventing the synthesis of molecules that can narrow arteries, a condition characteristic of heart disease.

One of the authors of the study, Dr Penny Kris-Etherton, is a distinguished professor in the department of nutritional sciences at Pennsylvania State University. “Our message is don’t decrease intake of them [omega-6s], they’re not bad, and our particular studies have shown they are good,” she says.

Chemically, fatty acids all have what is known as a carboxyl group at one end. This consists of a carbon atom that has a double bond to an oxygen atom, and a single bond to an OH, or the hydroxyl group. Carbon atoms tend to have four bonds, and the final bond that carbon atoms form often makes it possible to form the extended chains of molecules present in carbon-based compounds.

But in saturated fats, each carbon atom in the chain is linked to hydrogen atoms, or “saturated”, so there can be no double bonds between the carbon atoms. This makes these fats harder to break down, giving them a tendency to collect in the body. There is no argument among scientists that these fats, which tend to have higher melting points, are bad for you. Common in foods such as lard and cheese, saturated fats have been linked to heart disease and atherosclerosis, the narrowing of the arteries.

In unsaturated fats, some hydrogen atoms are missing and there are double bonds between at least two of the carbon atoms in the chains. Omega-3s and omega-6s are a type of polyunsaturated fatty acids, meaning that they have multiple double bonds between the carbon atoms in the chain.

Polyunsaturated fatty acids are required for good health – they are known as essential fatty acids – but like most vitamins, they cannot be synthesised by the body, so they must be obtained from food.

Some nutritionists have indicated that the level of omega-3s or omega-6s is not important. Instead, it’s maintaining an appropriate ratio between the two that is integral for optimal health. Scientists have suggested that people should cut their intake of omega-6s to create an optimal ratio of omega-6 to omega-3 in the diet.

While most people are said to have a ratio of between 14:1 and 20:1 in their diets, the ideal is thought to be much lower, at between 5:1 and 10:1 or perhaps much lower.

However, the recommendation from the recent paper, which analysed the results of four previous studies, is that people should try to obtain between five and 10 per cent of their calories from omega-6s and that cutting their intake is not necessary. The ideal amount is between about 12 grams and 22 grams per day, depending upon gender, age and exercise levels.

“I think for now we are eating adequate amounts of omega-6s,” Dr Kris-Etherton says. “Do not decrease intake – they’re not bad and studies have shown that potentially they’re good.

“If people are concerned about the balance of omega-6s and omega-3s, then the way to deal with this is not to cut omega-6s, but for people to make sure they consume omega-3s. Both these fats are good.”

Popular sources of omega-3s include fish, linseed oil, walnuts and pecans.

The recent positive news about omega-6s represents a return to favour for a substance that was well thought of several decades ago.

“In the early 1970s, we appreciated the benefits of high omega-6 foods like corn oil and soya bean oil that had cholesterol-lowering properties,” she said.

“People were drinking these small cups of omega-6 vegetable oil and what happened? We gained weight.

“As soon as you tell people this is good or that’s good, they eat more of it. People overdo it and that’s a message to be avoided.”

Dr Kris-Etherton herself uses a variety of oils when cooking and says keeping a diverse diet is a good thing.

“As nutritionists we say people should eat a variety of foods,” she says. “I use corn oil, safflower oil, it depends what I’m cooking. For salads I might use olive oil or sometimes I use Chinese stir/fry.”

To maintain health, Dr Kris-Etherton says people should continue to avoid foods that are high in saturated fats, such as animal fats, palm oil, palm kernel oil and coconut oil. Also, it is best to be wary of ghee, an oil commonly used in Indian cookery. “People should avoid it or limit their intake.”