There is a lot of disagreement in nutrition.
But one of the few things people actually agree on is the unhealthy nature of trans fats.
Fortunately, consumption of these horrible fats has gone down in recent years and decades.
But we are still eating way too much of them, which has various detrimental effects on health.
This article takes a detailed look at trans fats... what they are, why they're so bad for you and how to avoid them.
What Are Trans Fats?
Trans fats, or trans fatty acids, are a form of unsaturated fat.
Unlike saturated fats, which have no double bonds, unsaturated fats have at least one double bond in their chemical structure.
This double bond can be either in the "cis" or "trans" configuration, which relates to the position of hydrogen atoms around the double bond.
Basically... "cis" means "same side," which is the most common structure. But trans fats have the hydrogen atoms on opposite sides, which can be a problem.
In fact, "trans" is latin for "on the opposite side," hence the name trans fat.
This chemical structure is believed to be responsible for numerous health issues.
Bottom Line: Trans fats are unsaturated fats with a specific chemical structure, where the hydrogen atoms are on opposite sides of the double bond.
Natural vs Artificial Trans Fats
Natural trans fats have been part of the human diet ever since we began eating the meat and dairy from ruminant animals (such as cattle, sheep and goats).
Also known as ruminant trans fats, they are completely natural, formed when bacteria in the animal's stomach digest grass.
However, dairy and meat eaters do not need to be concerned.
However... the same positive things can NOT be said about artificial trans fats, otherwise known as industrial trans fats or hydrogenated fats.
This process involves high pressure, hydrogen gas, a metal catalyst and is highly disgusting... the fact that anyone would consider them suitable for human consumption is baffling.
After they have been hydrogenated, the vegetable oils have a much longer shelf life and are solid at room temperature, with a consistency similar to saturated fats.
Although humans have been consuming natural (ruminant) trans fats for a very long time, the same is NOT true for artificial trans fats... which are seriously harmful.
Bottom Line: Natural trans fats are found in some animal products and are not harmful. Artificial trans fats are made by "hydrogenating" vegetable oils in a harsh chemical process.
Trans Fats and Heart Disease Risk
In the past few decades, there have been numerous clinical trials studying trans fats.In these clinical trials, people were fed trans fats (from hydrogenated vegetable oils) instead of other fats or carbohydrates.
The health effects were evaluated by looking at known risk factors for heart disease, like cholesterol or the lipoproteins that carry cholesterol around.
Replacing carbohydrates (1% of calories) with trans fats significantly increases LDL (the "bad") cholesterol, but does not increase HDL (the "good") cholesterol.
However, most other fats tend to increase both LDL and HDL cholesterol (13).
Similarly, replacing other fats in the diet with trans fats significantly increases the total/HDL cholesterol ratio and negatively affects lipoproteins (ApoB/ApoA1 ratio), both important risk factors for heart disease (14).
Bottom Line: Both observational studies and clinical trials have found that trans fats significantly increase your risk of heart disease.
Insulin Sensitivity and Type II Diabetes
The relationship between trans fats and diabetes risk is not completely clear.
A large study of over 80,000 women found that those who consumed the most trans fats had a 40% higher risk of diabetes (19).
Several controlled trials in humans have also looked at trans fats and important diabetes risk factors, such as insulin resistance and blood sugar levels.
Most notable was a 6 year study on monkeys which found that a high trans fat diet (8% of calories) caused insulin resistance, abdominal obesity (belly fat) and elevated fructosamine, a marker of high blood sugar (31).
Bottom Line: It is possible that trans fats cause insulin resistance and drive type II diabetes, but the results from human studies are mixed.
Trans Fats and Inflammation
Excess inflammation is believed to be among the leading drivers of many chronic, Western diseases.
This includes heart disease, metabolic syndrome, diabetes, arthritis and numerous others.
There have been three clinical trials investigating the relationship between trans fats and inflammation.
From looking at the evidence, it seems pretty clear that trans fats are an important driver of inflammation... which can potentially lead to all sorts of problems.
Bottom Line: Clinical trials and observational studies both indicate that trans fats increase inflammation, especially in people who are overweight or obese.
Blood Vessels and Cancer
Trans fats are believed to damage the inner lining of the blood vessels, known as the endothelium.
When saturated fats were replaced with trans fats in a 4 week study, HDL cholesterol was lowered by 21% and the ability of arteries to dilate was impaired by 29% (37).
Markers for endothelial dysfunction were also increased when trans fats replaced carbohydrates and monounsaturated fats (38).
Unfortunately, very few studies have looked at the association between trans fats and cancer.
In the Nurses' Health Study, intake of trans fats before menopause was associated with increased risk of breast cancer after menopause (39).
However two review studies have concluded that the cancer link is very weak. No compelling associations have been observed so far (40).
Bottom Line: Trans fats can damage the inner lining of your blood vessels, causing a condition known as endothelial dysfunction. The effect on cancer risk is less clear.
Trans Fats in the Modern Diet
Hydrogenated vegetable oils (the biggest source of trans fats) are cheap and have a long shelf life.
For this reason, they are found in all sorts of modern processed foods.
Fortunately, because the governments and health organizations around the world have been cracking down on trans fats, consumption has gone down in recent years.
The FDA only recently decided to remove the GRAS (Generally Recognized as Safe) status for trans fats, even though these studies have been out for many, many years.
However... even though artificial trans fat consumption is lower than before, it is still way too high and should be reduced to zero.
Bottom Line: Consumption of trans fats has gone down significantly in recent years. However, current intake is still high enough to cause harm.
How to Avoid Trans Fats
Big improvements have been made in recent years, although trans fats are still present in many processed foods.
In the US, manufacturers can label their products "trans fat free" as long as there is less than 0.5 grams of trans fats per serving.
You can see how a few a "trans fat free" cookies could quickly add up to harmful amounts.
To make sure you're avoiding trans fats, read labels. Don't eat foods that have the words "hydrogenated" or "partially hydrogenated" on the ingredients list.
Unfortunately, reading labels isn't enough in all cases. Some processed foods (like regular vegetable oils) can contain trans fats, without any indication on the label or ingredients list.
In order to avoid trans fats, the best thing you can do is eliminate processed foods from your diet.
Take Home Message
Ruminant (natural) trans fats from animal products are safe.
But industrialized (artificial) trans fats from processed foods are downright toxic.
Studies have strongly linked artificial trans fats to cardiovascular problems, including heart disease.
Consumption is also associated with long-term inflammation, insulin resistance and type II diabetes risk, especially for people who are overweight or obese.
Although the amount of trans fats in the modern diet has gone down, the average intake is still dangerously high.
Unfortunately, the labels on junk foods and processed vegetable oils cannot always be trusted. Many "trans fat free" products still contain trans fats.
You have been warned.