Trans Fatty acids: Unhealthy or Undebated 2

The American Heart Association (AHA) recommends limiting saturated fat intake to less than 10% of calories and trans fat to less than 1% of calories. One would assume the evidence from prior studies suggests that limiting trans fat intake to less than 1% of calories prevents changes that might increase the risk of cardiovascular disease.

However, if I consume 3% of calories daily as trans fat am I at increased risk of heart disease? What about 5%? In other words, is there a graded increase in risk above 1%? More than that, who in their right mind has a clue what % of calories they consume daily as trans fat; moreover, if I somehow manage to find out I consume 3 grams of trans fat, unless I do a caloric analysis of all I eat, how would I know what % of total daily calories that 3 grams represents? I understand the dilemma, the AHA wants to give the public advice in the language of panel findings; however, it’s useless, impractical information that the public can’t really digest. Not just that, physicians and dieticians on the front line, have the added burden of translating the advice to an undereducated public. The question then is: How do we give the public advice with a measure that’s useful? I’ll address that concern later. First the evidence.


The Evidence(Clinical and Basic Science Studies)
A very nice review of some of the clinical evidence showing the effects of dietary trans fats was published in Nutrition Research by J. Edward Hunter in 2005. I won’t review all the important information he presented, but will offer a bulleted list of some important numbers:

• Frying oils used in restaurants and other food dispensing operations range in trans fat content from 0 to 35% of total fats.
  
• Most current tub and stick margarines contain very little to no trans fat (however, check the nutrition label)
  
• Baking shortenings (still a bad player) contain approximately 15% to 30% fat as trans fat
  
• Beef and dairy fat contains approximately 3% trans fat
  
• On average Americans consume 2.6% of daily energy as trans fat or 5.3 g per person (Allison et al J. Am. Dietetics Assoc 1999;99(2):166-74). That percent has most likely dropped due to the campaign against trans fat and the new labeling initiative-.
  
• Europeans consume less at 2.1% of daily energy.

A large number of studies have analyzed just how trans fat intake might impact normal physiology. A fairly consistent finding reveals that as someone consumes an increasing amount of trans fat, the following happens:

• High Density Lipoprotein cholesterol (HDL-C) decreases
• Low Density Lipoprotein cholesterol (LDL-C) increases

Increased LDL-C and decreased HDL-C increases the risk over time of developing atherosclerosis or coronary heart disease. Eating saturated fatty acids increases both LDL-C and HDL-C, thus total cholesterol is elevated to a greater extent with saturated fatty acid consumption than trans fat.

According to a study conducted by Ascherio et al, in 1999, pooling the data from 17 other clinical studies found that LDL and HDL were significantly altered at the following % intake of trans fat;

• LDL was statistically elevated at 4% trans fat (of total calories)
• HDL was statistically decreased at 5-6% of total calories

Therefore putting the above information together, the average American and European consumes somewhere in the range of 2% of calories as trans fat (and probably less in the current market), but a statistically significant elevation of markers for increased risk of heart disease is roughly twice that value at 4-5%.

The dilemma addressed at the beginning of this presentation is what should the AHA tell the average individual about trans fat? What advice should they give? That's a problem not properly addressed or even considered by the AHA, because the answer is more than they are willing to take on. The bottom line, in my opinion, is to choose your fats carefully. Knowing the science of trans fatty acids is without question a starting point for anyone interested in the association between the foods we eat and our long-term health.

My advice: Learn what you can and make informed choices. That might sound trite and worn, and possibly even evasive, but without reading and understanding the science, we are doomed to the wisdom of concensus statements and what someone else has decided for us. That said, to substitute butter (or saturated fat) for margarine to avoid trans fat, is apparently a bad idea.