Study under review: Vaccenic acid and trans fatty acid isomers from partially hydrogenated oil both adversely affect LDL cholesterol: a doubleblind, randomized controlled trial
Fatty acids are broadly classified as saturated, monounsaturated, or polyunsaturated based on how many double-bonds exist within the fatty acid tail (zero, one, and more than one, respectively). Unsaturated fats most commonly come in the cis- isoform, meaning that the double-bond creates a kink in the tail that causes bending. These kinks prevent the fatty acids from gathering close to one another, which lowers the fat’s melting point and explains why unsaturated fats are oils at room temperature.
In contrast, a trans- configuration causes the tail to remain straight, mimicking the structure of a saturated fat. These trans-fatty acids (TFAs) exist in nature alongside their cis- counterparts, but in far lower quantities. The most common naturally occurring TFA in the human diet is vaccenic acid, which is produced via microbial fermentation of plant matter in the stomachs of ruminant animals, and subsequently obtained in our diets through consuming the meat, fat, and milk of these animals. Additionally, vaccenic acid can be further metabolized into cis-9, trans-11 conjugated linoleic acid (c-9, t-11 CLA) within the ruminant stomach.
Although humans have been consuming ruminant TFAs throughout evolutionary history, they made up an incredibly small portion of the diet and are not the TFAs that come to mind when the term is used today. Rather, TFAs have become synonymous with partially hydrogenated oils. These industrial trans-fatty acids (iTFAs) are produced when unsaturated oil is reacted with hydrogen in the presence of a chemical catalyst (usually powdered nickel). This technique appeared within the last century, with the first marketed iTFA being a partially hydrogenated cottonseed oil called Crisco that appeared on American shelves in 1911.
The primary iTFA is elaidic acid, which is essentially oleic acid with the double-bond in a trans- rather than cis- configuration, meaning the kink in the chain is removed. Vaccenic acid (whose structure is shown in Figure 1) also has 18 carbons like oleic acid and elaidic acid, but its trans- double-bond is farther down the chain. CLA is most similar to linoleic acid as both have two double-bonds; however, CLA has its second double-bond in the trans- configuration whereas linoleic acid has two cis- double-bonds.
The health effects of iTFAs are well documented, to the point that most major health authorities recommend limiting intake to as little as possible, preferably less than 1% of energy intake. The FDA has even revoked their Generally Recognized as Safe status and required that they be removed from the American food supply over the next three years. However, the FDA defines the TFA term based on chemical structure rather than metabolic or functional aspects. As such, the origin of the TFA does not matter for the FDA definition, and they must be labelled when falling under their definition of “all unsaturated fatty acids that contain one or more isolated double bonds in a trans configuration.”
Based on the FDA’s definition, vaccenic acid but not CLA must be included in the label for TFAs because CLA contains conjugated double bonds (meaning that there are two double-bonds separated by one single-bond) in the trans- configuration. But the health effects of these fatty acids are far less investigated than those of partially hydrogenated oils. Therefore, the current study evaluated the effects of iTFAs and ruminant TFAs on blood lipid risk markers for cardiovascular diseases (CVD) in the context of a highly controlled dietary intervention.
The detrimental effect of partially hydrogenated oils and their trans-fatty acid component on cardiovascular disease risk is well-established. However, the effects of naturally occurring trans-fatty acids such as vaccenic acid and conjugated linoleic acid are far less investigated. The current study aimed to compare iTFA and TFAs from ruminants in a highly controlled dietary intervention study.
Other Articles in Issue #14 (December 2015)
Investigating vitamin D as a performance enhancer
Having sufficient vitamin D levels has been associated with better muscle recovery. This trial not only looks at the question of causality, but also addresses some potential mechanisms of vitamin D’s benefit for exercise.
High versus low fat diets for insulin sensitivity
More body weight means more risk for metabolic syndrome. But the question of whether more fat (and especially saturated fat) impacts insulin sensitivity hasn’t been adequately addressed until now.
Exercise, with a (tart) cherry on top!
Berries have burst onto the research scene in recent years. Tart cherries have shown some of the most promise in certain areas, leading to this study of powdered tart cherry on exercise recovery.
Interview: Dan Pardi MS PhD(c)
Dan Pardi is an entrepreneur and researcher whose life’s work is centered on how to facilitate health behaviors in others.
Root rage: The impact of ashwagandha on muscle
So called “adaptogens” like ashwagandha are typically studied for stress-easing potential. A randomized trial looked into this popular herb for a different purpose: bolstering adaptations to weight training.
Does the Food Guide make my butt get fat?
By Francy Pillo-Blocka, RD
We’ve covered antioxidants and strength training before. This study is a bit different — it investigates whether vitamin C and vitamin E might impact adaptations to endurance exercise.
I <3 green tea
When it comes to curbing cardiovascular disease, it’s not all about reducing cholesterol. Green tea may help prevent oxidation of LDL, as is explored in this trial looking at green tea catechins both in vivo and in vitro.
Investigating slow carbs for metabolic rate
Glycemic index, glycemic load, insulin index: only one of these is widely known by the public. But when it comes to keeping weight off, does glycemic index and total carb content actually have any impact?