By Dr. Atli Arnarson
The health effects of saturated fats are a controversial topic. In the past, saturated fat was widely believed to be a major cause of heart disease. Today, scientists are not so sure.
However, one thing is clear: saturated fat is not a single nutrient. It is a group of different fatty acids with varying effects on health and metabolism.
This article takes a detailed look at the most common saturated fatty acids, their health effects and dietary sources.
What Is Saturated Fat?
Saturated fat is one of the two main classes of fat, the other being unsaturated fat.
These groups differ slightly in their chemical structure and properties. For instance, saturated fat is generally solid at room temperature, while unsaturated fat is liquid.
The main dietary sources of saturated fat are fatty meat, lard, tallow, cheese, butter, cream, coconut oil, palm oil and cocoa butter.
All fats are composed of molecules called fatty acids, which are chains of carbon atoms. The different types of saturated fatty acids can be distinguished by the length of their carbon chains.
Here are the most common saturated fatty acids in the human diet:
- Stearic acid: 18 carbon atoms long
- Palmitic acid: 16 carbon atoms long
- Myristic acid: 14 carbon atoms long
- Lauric acid: 12 carbon atoms long
- Capric acid: 10 carbon atoms long
- Caprylic acid: 8 carbon atoms long
- Caproic acid: 6 carbon atoms long
It's rare to find saturated fatty acids other than these in the diet.
Saturated fatty acids that are less than six carbon atoms long are collectively known as short-chain fatty acids.
These are produced when gut bacteria ferment fiber. They are created in your gut from the fiber you eat and can also be found in trace amounts in some fermented food products.
Bottom Line: Saturated fatty acids are one of the two major categories of fat. Common dietary saturated fatty acids include stearic acid, palmitic acid, myristic acid and lauric acid.
How Does Saturated Fat Affect Health?
Most scientists now accept that saturated fats are not as unhealthy as previously assumed.
This doesn't necessarily mean that saturated fats are unhealthy. It simply suggests that certain unsaturated fats are protective, while saturated fats are neutral.
In comparison, replacing saturated fat with carbs doesn't provide any health benefits and even impairs the blood lipid profile. This is a measurement of the levels of lipids in your blood, such as cholesterol and triglycerides (5).
Although it is clear that some saturated fats may raise the "bad" low-density lipoprotein (LDL) cholesterol, the association between cholesterol levels and heart disease is a bit more complex than that.
For more information on the issue, read this article.
Bottom Line: Saturated fats are not as harmful as previously believed. Growing evidence suggests there are no strong links between saturated fat and heart disease.
1. Stearic Acid
Stearic acid, which consists of 18 carbon atoms, is the second most common saturated fat in the American diet (8).
Compared with carbs or other saturated fats, stearic acid lowers the "bad" LDL cholesterol slightly or has neutral effects. This suggests it may be healthier than many other saturated fats (9, 10, 11).
Research shows that stearic acid is partly converted to oleic acid, a healthy unsaturated fat, within the body. However, according to some estimates, the conversion rate is only 14 percent and may not have much relevance to health (12, 13).
The main dietary source of stearic acid is animal fat. The levels of stearic acid are usually low in plant fat, with the exception of coconut oil, cocoa butter and palm kernel oil.
Stearic acid is considered a healthy saturated fat.
It does not appear to raise the risk of heart disease. This seemed to be true even in a study of people whose stearic acid intake constituted up to 11 percent of their total calorie intake for 40 days (9).
Bottom Line: Stearic acid is the second most common saturated fat in the American diet. It appears to have neutral effects on the blood lipid profile.
2. Palmitic Acid
Palmitic acid is the most common saturated fat in plants and animals. It is 16 carbon atoms long.
In 1999, palmitic acid made up an estimated 56.3 percent of the total saturated fat intake in the U.S. (8).
The richest dietary source is palm oil, but palmitic acid also makes up approximately a quarter of the fat in red meat and dairy, as shown in the chart below.
Compared to carbs and unsaturated fats, palmitic acid raises the levels of total cholesterol and LDL cholesterol without affecting the levels of "good" high-density lipoprotein (HDL) cholesterol (9, 11, 14).
High levels of LDL cholesterol are a well-known risk marker of heart disease.
Although palmitic acid raises the levels of total LDL cholesterol, this is mainly due to an increase in large LDL particles. Many researchers consider high levels of large LDL particles to be less of a concern, but some people disagree (6, 16, 18).
Additionally, when other fatty acids, such as linoleic acid, are eaten at the same time, they can offset some of palmitic acid's effects on cholesterol (19).
These aspects of palmitic acid need to be studied further before clear conclusions can be reached.
Bottom Line: Palmitic acid is the most common saturated fatty acid, making up over half of all the saturated fat eaten in the US. It raises LDL cholesterol levels without changing HDL cholesterol.
3. Myristic Acid
Myristic acid consists of 14 carbon atoms.
Consuming myristic acid causes a significant increase in total cholesterol and LDL cholesterol compared to consuming palmitic acid or carbs. However, it doesn't appear to affect levels of HDL cholesterol (11, 25).
These effects are much stronger than those of palmitic acid. Yet similar to palmitic acid, myristic acid appears to increase the levels of large LDL particles, which many scientists consider to be less of a concern (6).
Myristic acid is a relatively rare fatty acid, not found in high amounts in most foods. Yet certain oils and fats do contain decent amounts, as shown in the chart below.
Although coconut oil and palm kernel oil do contain relatively high amounts of myristic acid, they also contain other types of fats, which may offset the effects of myristic acid on the blood lipid profile (26).
Bottom Line: Myristic acid is a long-chain, saturated fatty acid. It raises LDL cholesterol more than other fatty acids.
4. Lauric Acid
Lauric acid is 12 carbon atoms long, making it the longest of the medium-chain fatty acids.
It raises the levels of total cholesterol more than most other fatty acids. However, this increase is largely due to an increase in the "good" HDL cholesterol.
In other words, lauric acid reduces the amounts of total cholesterol relative to HDL cholesterol. These changes are associated with a reduced risk of heart disease (27).
In fact, lauric acid appears to have more beneficial effects on HDL cholesterol levels than any other saturated fatty acid (11).
Lauric acid makes up approximately 47 percent of palm kernel oil and 42 percent of coconut oil. In comparison, other commonly eaten oils or fats contain only trace amounts of it.
Bottom Line: Lauric acid is the longest medium-chain fatty acid. Although it raises total cholesterol significantly, this is largely due to an increase in HDL cholesterol, which is beneficial for health.
5–7. Caproic, Caprylic and Capric Acid
Caproic, caprylic and capric acid are medium-chain fatty acids (MCFAs). They range from 6–10 carbon atoms in length.
Their names are derived from the Latin "capra," which means "female goat." They are sometimes referred to as capra fatty acids, due to their abundance in goat's milk.
MCFAs are metabolized differently than long-chain fatty acids. They are more easily absorbed and transported straight to the liver where they are rapidly metabolized.
Evidence suggests that MCFAs may have the following benefits:
- Weight loss: Several studies indicate that they may slightly increase the number of calories burned and promote weight loss, especially when compared with long-chain fatty acids (28, 29, 30, 31, 32).
- Increased insulin sensitivity: There is also some evidence that MCFAs increase insulin sensitivity, compared to long-chain fatty acids (33).
- Anti-seizure effects: MCFAs, especially capric acid, may have anti-seizure effects, especially when combined with a ketogenic diet (34, 35, 36).
Because of their potential health benefits, MCFAs are sold as supplements, known as MCT oils. These oils usually consist primarily of capric acid and caprylic acid.
Capric acid is the most common of these. It constitutes around 5 percent of palm kernel oil and 4 percent of coconut oil. Smaller amounts are found in animal fat. Otherwise, it is rare in foods.
Bottom Line: Capric, caprylic and caproic acid are medium-chain fatty acids with unique properties. They may promote weight loss, increase insulin sensitivity and reduce the risk of seizures in certain epileptic patients.
8–10. Short-Chain Fatty Acids
Saturated fatty acids that contain fewer than six carbon atoms in their chains are known as short-chain fatty acids (SCFAs).
The most important SCFAs are:
- Butyric acid: 4 carbon atoms long
- Propionic acid: 3 carbon atoms long
- Acetic acid: 2 carbon atoms long
SCFAs are formed when beneficial gut bacteria ferment fiber in the colon.
Their dietary intake is minimal compared to the amounts of SCFAs produced in the colon. They are uncommon in food and only found in small amounts in dairy fat and certain fermented food products.
SCFAs are responsible for many of the health benefits associated with fiber intake. For instance, butyric acid is an important source of nutrition for the cells lining the colon (37).
For more information on the potential health benefits of SCFAs, read this article.
Bottom Line: The smallest saturated fatty acids are known as short-chain fatty acids (SCFAs), which are formed when friendly bacteria ferment fiber in the colon. They have many potential health benefits.
Take Home Message
Not all saturated fat is the same. Its health effects vary depending on the type.
Although certain types of long-chain saturated fat may raise your levels of "bad" LDL cholesterol, no strong evidence proves any of them cause heart disease.
Reposted with permission from our media associate Authority Nutrition.
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By Ana Maldonado-Contreras
- Your gut is home to trillions of bacteria that are vital for keeping you healthy.
- Some of these microbes help to regulate the immune system.
- New research, which has not yet been peer-reviewed, shows the presence of certain bacteria in the gut may reveal which people are more vulnerable to a more severe case of COVID-19.
You may not know it, but you have an army of microbes living inside of you that are essential for fighting off threats, including the virus that causes COVID-19.
How Do Resident Bacteria Keep You Healthy?<p>Our immune defense is part of a complex biological response against harmful pathogens, such as viruses or bacteria. However, because our bodies are inhabited by trillions of mostly beneficial bacteria, virus and fungi, activation of our immune response is tightly regulated to distinguish between harmful and helpful microbes.</p><p>Our bacteria are spectacular companions diligently helping prime our immune system defenses to combat infections. A seminal study found that mice treated with antibiotics that eliminate bacteria in the gut exhibited an impaired immune response. These animals had low counts of virus-fighting white blood cells, weak antibody responses and poor production of a protein that is vital for <a href="https://doi.org/10.1073/pnas.1019378108" target="_blank">combating viral infection and modulating the immune response</a>.</p><p><a href="https://doi.org/10.1371/journal.pone.0184976" target="_blank" rel="noopener noreferrer">In another study</a>, mice were fed <em>Lactobacillus</em> bacteria, commonly used as probiotic in fermented food. These microbes reduced the severity of influenza infection. The <em>Lactobacillus</em>-treated mice did not lose weight and had only mild lung damage compared with untreated mice. Similarly, others have found that treatment of mice with <em>Lactobacillus</em> protects against different <a href="https://doi.org/10.1038/srep04638" target="_blank" rel="noopener noreferrer">subtypes of</a> <a href="https://doi.org/10.1038/s41598-017-17487-8" target="_blank" rel="noopener noreferrer">influenza</a> <a href="https://doi.org/10.1371/journal.ppat.1008072" target="_blank" rel="noopener noreferrer">virus</a> and human respiratory syncytial virus – the <a href="https://doi.org/10.1038/s41598-019-39602-7" target="_blank" rel="noopener noreferrer">major cause of viral bronchiolitis and pneumonia in children</a>.</p>
Chronic Disease and Microbes<p>Patients with chronic illnesses including Type 2 diabetes, obesity and cardiovascular disease exhibit a hyperactive immune system that fails to recognize a harmless stimulus and is linked to an altered gut microbiome.</p><p>In these chronic diseases, the gut microbiome lacks bacteria that activate <a href="https://doi.org/10.1126/science.1198469" target="_blank" rel="noopener noreferrer">immune cells</a> that block the response against harmless bacteria in our guts. Such alteration of the gut microbiome is also observed in <a href="https://doi.org/10.1073/pnas.1002601107" target="_blank" rel="noopener noreferrer">babies delivered by cesarean section</a>, individuals consuming a poor <a href="https://doi.org/10.1038/nature12820" target="_blank" rel="noopener noreferrer">diet</a> and the <a href="https://doi.org/10.1038/nature11053" target="_blank" rel="noopener noreferrer">elderly</a>.</p><p>In the U.S., 117 million individuals – about half the adult population – <a href="https://health.gov/our-work/food-nutrition/2015-2020-dietary-guidelines/guidelines/" target="_blank" rel="noopener noreferrer">suffer from Type 2 diabetes, obesity, cardiovascular disease or a combination of them</a>. That suggests that half of American adults carry a faulty microbiome army.</p><p>Research in my laboratory focuses on identifying gut bacteria that are critical for creating a balanced immune system, which fights life-threatening bacterial and viral infections, while tolerating the beneficial bacteria in and on us.</p><p>Given that diet affects the diversity of bacteria in the gut, <a href="https://www.umassmed.edu/nutrition/melody-trial-info/" target="_blank" rel="noopener noreferrer">my lab studies show how diet can be used</a> as a therapy for chronic diseases. Using different foods, people can shift their gut microbiome to one that boosts a healthy immune response.</p><p>A fraction of patients infected with SARS-CoV-2, the virus that causes COVID-19 disease, develop severe complications that require hospitalization in intensive care units. What do many of those patients have in common? <a href="https://www.cdc.gov/mmwr/volumes/69/wr/mm6912e2.htm" target="_blank" rel="noopener noreferrer">Old age</a> and chronic diet-related diseases like obesity, Type 2 diabetes and cardiovascular disease.</p><p><a href="http://doi.org/10.1016/j.jada.2008.12.019" target="_blank" rel="noopener noreferrer">Black and Latinx people are disproportionately affected by obesity, Type 2 diabetes and cardiovascular disease</a>, all of which are linked to poor nutrition. Thus, it is not a coincidence that <a href="https://www.cdc.gov/mmwr/volumes/69/wr/mm6933e1.htm" target="_blank" rel="noopener noreferrer">these groups have suffered more deaths from COVID-19</a> compared with whites. This is the case not only in the U.S. but also <a href="https://www.washingtonpost.com/world/europe/blacks-in-britain-are-four-times-as-likely-to-die-of-coronavirus-as-whites-data-show/2020/05/07/2dc76710-9067-11ea-9322-a29e75effc93_story.html" target="_blank" rel="noopener noreferrer">in Britain</a>.</p>
Discovering Microbes That Predict COVID-19 Severity<p>The COVID-19 pandemic has inspired me to shift my research and explore the role of the gut microbiome in the overly aggressive immune response against SARS-CoV-2 infection.</p><p>My colleagues and I have hypothesized that critically ill SARS-CoV-2 patients with conditions like obesity, Type 2 diabetes and cardiovascular disease exhibit an altered gut microbiome that aggravates <a href="https://theconversation.com/exercise-may-help-reduce-risk-of-deadly-covid-19-complication-ards-136922" target="_blank" rel="noopener noreferrer">acute respiratory distress syndrome</a>.</p><p>Acute respiratory distress syndrome, a life-threatening lung injury, in SARS-CoV-2 patients is thought to develop from a <a href="http://doi.org/10.1016/j.cytogfr.2020.05.003" target="_blank" rel="noopener noreferrer">fatal overreaction of the immune response</a> called a <a href="https://theconversation.com/blocking-the-deadly-cytokine-storm-is-a-vital-weapon-for-treating-covid-19-137690" target="_blank" rel="noopener noreferrer">cytokine storm</a> <a href="http://doi.org/10.1016/S2213-2600(20)30216-2" target="_blank" rel="noopener noreferrer">that causes an uncontrolled flood</a> <a href="http://doi.org/10.1016/S2213-2600(20)30216-2" target="_blank" rel="noopener noreferrer">of immune cells into the lungs</a>. In these patients, their own uncontrolled inflammatory immune response, rather than the virus itself, causes the <a href="http://doi.org/10.1007/s00134-020-05991-x" target="_blank" rel="noopener noreferrer">severe lung injury and multiorgan failures</a> that lead to death.</p><p>Several studies <a href="https://doi.org/10.1016/j.trsl.2020.08.004" target="_blank" rel="noopener noreferrer">described in one recent review</a> have identified an altered gut microbiome in patients with COVID-19. However, identification of specific bacteria within the microbiome that could predict COVID-19 severity is lacking.</p><p>To address this question, my colleagues and I recruited COVID-19 hospitalized patients with severe and moderate symptoms. We collected stool and saliva samples to determine whether bacteria within the gut and oral microbiome could predict COVID-19 severity. The identification of microbiome markers that can predict the clinical outcomes of COVID-19 disease is key to help prioritize patients needing urgent treatment.</p><p><a href="https://doi.org/10.1101/2021.01.05.20249061" target="_blank" rel="noopener noreferrer">We demonstrated</a>, in a paper which has not yet been peer reviewed, that the composition of the gut microbiome is the strongest predictor of COVID-19 severity compared to patient's clinical characteristics commonly used to do so. Specifically, we identified that the presence of a bacterium in the stool – called <em>Enterococcus faecalis</em>– was a robust predictor of COVID-19 severity. Not surprisingly, <em>Enterococcus faecalis</em> has been associated with <a href="https://doi.org/10.1053/j.gastro.2011.05.035" target="_blank" rel="noopener noreferrer">chronic</a> <a href="https://doi.org/10.1016/S0002-9440(10)61172-8" target="_blank" rel="noopener noreferrer">inflammation</a>.</p><p><em>Enterococcus faecalis</em> collected from feces can be grown outside of the body in clinical laboratories. Thus, an <em>E. faecalis</em> test might be a cost-effective, rapid and relatively easy way to identify patients who are likely to require more supportive care and therapeutic interventions to improve their chances of survival.</p><p>But it is not yet clear from our research what is the contribution of the altered microbiome in the immune response to SARS-CoV-2 infection. A recent study has shown that <a href="https://doi.org/10.1101/2020.12.11.416180" target="_blank" rel="noopener noreferrer">SARS-CoV-2 infection triggers an imbalance in immune cells</a> called <a href="https://doi.org/10.1111/imr.12170" target="_blank" rel="noopener noreferrer">T regulatory cells that are critical to immune balance</a>.</p><p>Bacteria from the gut microbiome are responsible for the <a href="https://doi.org/10.7554/eLife.30916.001" target="_blank" rel="noopener noreferrer">proper activation</a> <a href="https://doi.org/10.1126/science.1198469" target="_blank" rel="noopener noreferrer">of those T-regulatory</a> <a href="https://doi.org/10.1038/nri.2016.36" target="_blank" rel="noopener noreferrer">cells</a>. Thus, researchers like me need to take repeated patient stool, saliva and blood samples over a longer time frame to learn how the altered microbiome observed in COVID-19 patients can modulate COVID-19 disease severity, perhaps by altering the development of the T-regulatory cells.</p><p>As a Latina scientist investigating interactions between diet, microbiome and immunity, I must stress the importance of better policies to improve access to healthy foods, which lead to a healthier microbiome. It is also important to design culturally sensitive dietary interventions for Black and Latinx communities. While a good-quality diet might not prevent SARS-CoV-2 infection, it can treat the underlying conditions related to its severity.</p><p><em><a href="https://theconversation.com/profiles/ana-maldonado-contreras-1152969" target="_blank">Ana Maldonado-Contreras</a> is an assistant professor of Microbiology and Physiological Systems at the University of Massachusetts Medical School.</em></p><p><em>Disclosure statement: Ana Maldonado-Contreras receives funding from The Helmsley Charitable Trust and her work has been supported by the American Gastroenterological Association. She received The Charles A. King Trust Postdoctoral Research Fellowship. She is also member of the Diversity Committee of the American Gastroenterological Association.</em></p><p><em style="">Reposted with permission from <a href="https://theconversation.com/a-healthy-microbiome-builds-a-strong-immune-system-that-could-help-defeat-covid-19-145668" target="_blank" rel="noopener noreferrer" style="">The Conversation</a>. </em></p>
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