Out of the Frying Pan – the Chemistry

There is a lot of confusion about the terminology used in describing fats and oils e.g. cis and trans, saturated and unsaturated and hydrogenated and partially hydrogenated. This is an attempt at disambiguation, that new word you see so often in Wikipedia which, incidentally does not mean “deciding what sex you are at last”.

Trans-fats are man-made, (commonly in margarine) and rarely found in nature. But they are found far too often in many retail food products where partially hydrogenated solid baking fats and margarines have been included in the recipe. The list below illustrates the diversity:

  • Crackers, cakes, muffins, pie crusts, pizza dough, and breads / hamburger buns.
  • Margarine and vegetable cooking fats
  • Pre-mixed cake mixes, pancake mixes, and chocolate drink mixes
  • Fried foods, including doughnuts, French fries, chicken nuggets
  • Snack foods, including chips and packaged or microwave popcorn
  • Frozen dinners

Trans-fats are always unsaturated i.e. contain double bonds, which would be a good feature if they were classed as “cis” fats. But being trans-fats many believe, including the FDA, that they should be avoided in our diet and we should see the trans fat content  written on the packaging. Cis trans oleic acidIn brief “cis” means “same side” and “trans” means opposite sides” within the fat molecule. This can arise because  groups of atoms on either side of a double bond are held rigidly in the plane of the structure. This means that if the groups on opposite sides of the double bond are different to each other, two arrangements of the atoms become possible as illustrated below in the case of a simple fat molecule called oleic acid diagrammed right The two fat molecules are totally different in shape and it is not surprising that the body has trouble metabolising the rather awkward looking trans form, which leaves a big question mark about what happens in the body to the trans forms of fats, a question which has not been satisfactorily answered yet, but suspicions are that it accumulates in places where it can be a danger to health. Fat Belly

The possibility that trans-fats were unhealthy led to an ironic advertising campaign which said — “Avoid trans-fats – eat butter and cheese and eggs!” Foods that we have been told to avoid because they were blamed for high LDL levels and heart attacks. So how come we have been well exposed for the last hundred years or so to these alien trans molecules which are rarely found in nature but allegedly raise our LDL levels more than the cis fats do? In the increasingly affluent 1800’s, butter shortages were common and its price was inordinately high. Eventually in 1901 a fiendishly clever chemist found that vegetable oils containing carbon to carbon double bonds (hence the name “unsaturated”) could be made solid and butter-like by partial hydrogenation of their cis double bonds and then adding salt and a bit of yellow dye. This seemed an ideal solution to the problem of butter shortages in an affluent society, or shortages in those countries without a dairy industry. It sold like the hot cakes, the very cakes in which those fats slept peacefully for the best part of a century, whilst quietly chipping away at our arteries, or so they say.

crisco-ad-3The first partially hydrogenated cottonseed  oil came onto the market in 1911, as “Crisco”. It was a huge success especially as they gave away free cookbooks in which every recipe called for Crisco. Prior to 1910, dietary fats had consisted primarily of butterfat, beeftallow, and lard. Later  the hydrogenation process made it possible to stabilize and solidify and convert the cheaper whale oil  and fish oils into “margarine”, as it was eventually called, a practice which was kept secret to avoid consumer distaste. (I always thought that first post war ice-cream I had as a child aged 7 in 1946 tasted a bit funny. Now I know why, and I’ll never forget the gooey waxy white globules between watery ice crystals). Naturally the whales were not amused at man’s ingenuity and thankfully, whale oil eventually came off the menu when international whale conservation legislation was approved. That was of course to all except the Inuit (quite rightly) and those intrepid Japanese researchers who apparently keep losing the notes to their research projects so they have to repeat the tests, kill more whales, ad nauseum, and are forced to sell the meat at a huge profit on the quayside.

The main problem with the partial hydrogenation process is that the healthy cis oils in animal or vegetable oils don’t like the temperatures used. During the heating cycle of the process they convert into the trans forms. The result of this molecular tango, this “slipping into something more comfortable” is  that the end product contains higher concentrations of trans-fats, whereas the original animal or vegetable oil may have had little or none. Eventually rapeseed and other vegetable oils became economically available from arable sources and replaced  whale oil in the manufacture of margarine and cooking fat, hence those bright yellow sneeze-inducing farmers’ fields that you may have noticed sprouting up throughout the land. You might think think you will avoid all trans fat and oil by not eating cakes etc. and by doing your cooking in vegetable oil.

13166255498476Unfortunately after a few days of repeatedly frying your dodgy fish and chips in vegetable oil much of the cis molecules will covert into trans molecules, so to stay healthy and trans free you need to change your 2 litres of vegetable oil  more often. At this juncture your saviour is clearly stir fry, so you could say that this would get you out of the frying pan and into the wok! (Sorry). Fresh oil methods of cooking like spray oil and stir-fry are one way around the problem if your love of fried food is, like mine, a dark secret. In the developed world, opinions vary as to the effect of trans-fats on health. In the USA, where they believe that there is a link between trans-fats, affluence and morbidity statistics, food labelling regulations were part of the attack on trans-fats. The UK government mustered up the courage to recommend that only 2% of our daily calorific requirement should come from trans-fats. The investigating panel left labelling out of the equation, leaving you to do your own extensive internet research and the maths. So if we can’t avoid trans-fats and oils, what limits should be put on our consumption of them?

One source says that if you consume 2000 calories per day then 2 grams of trans-fat is the limit for that day, a mere grease spot on your pullover no less! However if the trans-fat content is not on the label you’ve got no chance of making an informed choice. As of 2006, American manufacturers and importers have been required by the FDA to list trans- fat content on food labels and as a result, health-conscious shoppers can be more discerning. The problem is that due to powerful lobbying in the UK, a law making it compulsory to label food packaging with trans-fat content was suppressed and we cannot make informed choices about trans fats in our diet. As our metabolisms have been fed for millions of years with cis fats to the exclusion of trans fats which are very rare in nature, it seems reasonable to assume that habitually consuming trans fats could be bit risky to say the least. Trans free sources like the time honoured – butter, cheese and eggs are still readily available so perhaps we should use these as our fat sources – or should we?

Neville Layhe C.Chem, MRSC

Leave a Reply


This message is only visible to admins.

Problem displaying Facebook posts.
Click to show error

Error: An access token is required to request this resource.
Type: OAuthException