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Naturally occurring fats, also known as ruminant fats, are often compared to trans fats obtained from partially hydrogenated fats, which have been proven to be harmful to health.
Find out what ruminant trans fatty acids (rTFAs) are and what the latest scientific studies say about their health effects.
Where do ruminant trans fatty acids come from?
- Food sources of ruminant trans fatty acids
The most common food sources of naturally occurring trans fats are meat and dairy products from cows, sheep and goats, but also any other ruminant animals. These trans fatty acids have been a part of our diets since the agricultural revolution, around 10,000 years ago.
- The process of creating rTFAs: bio-hydrogenation
The process of rTFAs production is called microbial bio-hydrogenation, where unsaturated fatty acids are saturated with hydrogen by the microbes living in the gut of the ruminants.
During this process, some of these unsaturated fatty acids are converted into saturated fats and some to trans fats. Cows fed with grass produce up to 5 times more of these trans fats than cows fed with grains. (2, 3)
- Where are rTFAs more abundant?
Dairy products contain up to 5% of rTFAs of total fat and beef and lamb up to 9% (in comparison to about 60% of industrial trans fatty acids – iTFAs – in partially hydrogenated oils). (4, 5) rTFAs cannot be removed from dairy products and meat.
In countries that have imposed bans on iTFAs, most TFAs come in the form of milk and other dairy products and meat. Only a negligible amount comes from iTFAs.
For instance, in Denmark, which banned iTFAs in 2004, the average consumption of TFAs is 1.7g per day (ranging from 0.9-2.7g per day), and most comes from ruminant sources. Of the ruminant trans fats, 85% comes from milk and 15% from meat. (6)
- Amounts of naturally occurring trans fats in commonly consumed ruminant products (7)
Food TFA (g/serving) Dairy products Cheese, cheddar (28 g, 1 oz) 0.24 Milk, whole (244 g, 1 cup) 0.21 Yogurt, plain, low-fat (255 g, 1 cup) 0.06 Meat Meat, beef, ground, 20.8% fat, raw (115 g, 4 oz) 0.91 Meat, beef, ground, 22.1% fat, raw (115 g, 4 oz) 1.07
Because of the low contents of rTFAs in dairy and meat products, it is difficult to consume them in high amounts.
In countries where ruminant dairy and meat is consumed, it is estimated that the maximum intake of ruminant fats is 4-5 g daily. (2)
What are the components of ruminant trans fatty acids?
rTFAs mainly consist of two fatty acids:
- Conjugated linolenic fatty acids or CLA (rumenic).
- Vaccenic acid (VA) which makes up about 45% of rTFA and is partially converted to CLA by the bodies of both ruminants and humans.
Potential effects of naturally occurring trans fats
While there are many studies on iTFAs and the evidence of their negative health effects strong, the number of studies on rTFAs are limited by comparison. (9)
The current knowledge of rTFAs is mostly based on observational, epidemiological or animal studies, either in its natural form (e.g. consuming rTFAs in the form of milk) or using its pure components, such as CLA or VA.
The bottom line is that there are no results showing that rTFAs coming from milk and meat in its natural form, increase the risk of cardiovascular disease or cancers or have any other detrimental effect on health.
What has been found so far is that they may even have some positive health benefits (more studies are needed).
- Naturally occurring trans fatty acids (rTFAs) – studies show that a daily consumption of up to 4g of rTFAs is not associated with coronary heart diseases. (2)
rTFAs have been connected with a reduced risk of developing type 2 Diabetes.
- Conjugated Linolenic Acid (CLA) – predominantly, found in milk, CLA is one of the major components of rTFAs and has been shown to have various health benefits: (12, 13, 14)
– Anti-carcinogenic properties (e.g. breast cancer) (15)
– Anti-diabetic properties
– Reduced numbers of myocardial infarctions
– Prevents the development of atherosclerosis
– Promotes fat reduction while improving lean body mass (16)
– Modulates immune responses
– Modulates inflammatory responses
Please note that most of these studies are measuring the effects of extracted CLA, rather than in amounts naturally occurring in rTFAs. (17)
Supplementation with CLAs may have also negative health effects in some people, such as effects on the liver function, glucose metabolism, oxidative stress and insulin resistance, especially in obese men. (18, 19, 20)
- Special note on grass fed vs. grain fed ruminants.
Meat from grass-fed animals contain more Omega-3 fatty acids and CLAs than meats from grain-fed animals.
In fact, the contents of Omega-3 in grass fed cows is high enough to be considered by the Food Standards Australia and New Zealand as a good Omega-3 food source. (21)
- Vaccenic acid (VA) – is another major component in rTFAs (45%).
Vaccenic acid is partially converted to CLAs inside the human body.
When the vaccenic acid was tested in larger dosages (10 times more) than normally consumed from natural foods, it showed detrimental effects similar to those in the high iTFAs diet.
These amounts of vaccenic acid, however, were artificially synthesized in the lab and don’t occur in such quantities in foods. (7)
Main conclusions of the major studies on ruminant trans fatty acids.
A 2015 double-blind, randomized controlled trial showed that when VA was compared gram for gram with iTFAs, the results on total cholesterol and LDL cholesterol were similar.
Although the study suggested that vaccenic acid may have similar effects on the risk of developing cardiovascular diseases (CDA), due to the blood cholesterol increase, it is important to note that although it raised LDL cholesterol, it also raised HDL cholesterol.
Another study found that the circulating blood triglycerides have a higher concentration of vaccenic acid in hyperinsulinemic and hyperglycemic people and higher concentrations were associated with insulin resistance. (28)
IMPORTANT NOTE: The positive effects of rTFAs are sometimes promoted by studies sponsored by the dairy industry. When searching for proof, consider who the sponsors are or any conflicts within the scientific studies.
Problems with the current studies
For ethical reasons, randomized intervention studies, which could show the extent of these fats on human health, may never be conducted. Most studies are done on animals or are observational or epidemiological.
Studies of iTFAs are easier to conduct and more abundant because they can be produced in high quantities using the partial hydrogenation process.
Studies on rTFAs, on the other hand, are harder since they are available in very small amounts in their natural form. (9)
The current knowledge of rTFAs is mostly based on observational studies of these fats, either in their natural form (e.g. consuming rTFAs in the form of milk) or using its pure components, such as CLA or VA.
The rTFAs’ molecular structure is slightly different from the iTFAs’.
Therefore, they have different effects in our body. More studies are needed to clearly show these differences.
Comparing the health effects of these two fats may be difficult, since there are other variables that may alter the results.
For example fats containing iTFAs are mainly unsaturated while rTFAs are mostly saturated. In addition, some fats may have higher omega-3 fatty acids concentration which counteracts many of the TFAs actions, such as inflammation.
CLAs are the most studied component of rTFAs, while VAs have not been investigated as much. (25)
The association with the risk of developing cancer has not yet been well studied. (29)
Some studies show that rTFAs alone (or their individual components, such as CLAs or VAs) may be responsible for some health benefits.
Other studies, however, suggest that the health benefits are due to other components that are present in foods containing rTFAs, such as dairy. (30)