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Why does eating saturated fat increase blood cholesterol?

Why does eating saturated fat increase blood cholesterol?


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I am interested in the biochemistry of diet and the way we have been advised to eat for the past forty years.

In researching an explanation for the relationship between dietary fat and blood cholesterol I came across the following: "It is clear that eating too much saturated fat increases the levels of cholesterol in the blood, especially our "bad" cholesterol which doctors refer to as LDL". This is from heartuk.org.uk.

"It is clear… " - really?

I am mystified! I understand that dietary fat, other than very short chain fatty acids, does not immediately enter the blood stream but is transported via the lymphatic system as triglycerides packaged in protein assemblies called chylomicrons, finally entering the blood via lymph nodes under the armpits. Once in the blood the triglycerides are hydrolysed into fatty acids and transported to appropriate cells in albumin complexes.

Where does LDL feature in this transportation? And, by the way, why just saturated fats? Surely the small intestine doesn't differentiate between saturated and unsaturated fats, or does it?


In short: It may not be saturated fat by itself but high saturated/unsaturated fat ratio and high animal/plant fat ratio in the diet that increases the risk of heart disease.

A systematic review of the effect of dietary saturated and polyunsaturated fat on heart disease (NMCD Journal, 2017)

Reducing saturated fat and replacing it with carbohydrate will not lower cardiovascular events or CVD mortality although it will reduce total mortality. Replacing saturated fat with mono- or poly-unsaturated fats or high-quality carbohydrate [from whole-grain food] will lower cardiovascular events.

Saturated Fatty Acids and Cardiovascular Disease: Replacements for Saturated Fat to Reduce Cardiovascular Risk (PubMed, 2017)

Replacing dairy fat with carbohydrates from refined starches and added sugar was not associated with increased or decreased risk of coronary heart disease (CHD), stroke or total cardiovascular disease (CVD). However, replacing dairy fat with carbohydrate from whole grains reduced the risk of CVD, CHD and stroke. Relative to other animal fats, dairy was found to have less impact on CVD. When 5% of energy from dairy fat was replaced with animal fat from non-dairy sources, risk of CHD increased by 6%. However, when 5% of energy from dairy fat was replaced with an isocaloric amount of polyunsaturated fats, risk of CHD was reduced by 26% and CVD risk was reduced by 24% [41].

A basic explanation of the underlying mechanisms:

The liver produces low-density lipoproteins (LDL) and high-density lipoproteins (HDL). Lipoproteins are composed of triglycerids, phospholipids, cholesterol and proteins.

LDL caries cholesterol from the liver to the peripherial tissue, including arterial walls, where it can accumulate and cause atherosclerosis. This is why LDL is called "bad cholesterol" (even if LDL is only a carrier for cholesterol). HDL clears excessive cholesterol from the blood and carries it to the liver for disposal, so it is called "good cholesterol. (Heart.org.uk)"

High LDL levels are associated with an increased risk of coronary heart disease (Bentham Open).

One possible mechanism by which saturated fats increase (LDL) cholesterol (PLOS):

Saturated fat is thought to increase LDL-C primarily through down-regulation of hepatic LDL receptor activity, leading to reduced clearance of LDL particles [from the blood].


Lean meat and heart health

The general health message to the public about meat consumption is both confusing and misleading. It is stated that meat is not good for health because meat is rich in fat and cholesterol and high intakes are associated with increased blood cholesterol levels and coronary heart disease (CHD). This paper reviewed 54 studies from the literature in relation to red meat consumption and CHD risk factors. Substantial evidence from recent studies shows that lean red meat trimmed of visible fat does not raise total blood cholesterol and LDL-cholesterol levels. Dietary intake of total and saturated fat mainly comes from fast foods, snack foods, oils, spreads, other processed foods and the visible fat of meat, rather than lean meat. In fact, lean red meat is low in saturated fat, and if consumed in a diet low in SFA is associated with reductions in LDL-cholesterol in both healthy and hypercholesterolemia subjects. Lean red meat consumption has no effect on in vivo and ex vivo production of thromboxane and prostacyclin or the activity of haemostatic factors. Lean red meat is also a good source of protein, omega-3 fatty acids, vitamin B12, niacin, zinc and iron. In conclusion, lean red meat, trimmed of visible fat, which is consumed in a diet low in saturated fat does not increase cardiovascular risk factors (plasma cholesterol levels or thrombotic risk factors).


New perspectives challenge the idea that saturated fats cause heart disease

In science, sometimes a new perspective can turn our interpretation of the data upside-down, and necessitate a paradigm shift.

There has been, and continues to be, fierce disagreements in nutrition science as to what constitutes a healthy diet. A key controversy is the role of saturated fats in health and disease. Saturated fats are known to increase blood cholesterol levels, and increased blood cholesterol is often observed in people who develop cardiovascular disease.

It has been thought for more than half a century that saturated fats in the diet promote heart disease by increasing blood cholesterol. However, a new model explains why this so-called "diet-heart hypothesis", which has had a major influence on dietary guidelines, may have an alternative explanation.

In a new article published today in the American Journal of Clinical Nutrition, three scientists have raised a question that challenges the diet-heart-hypothesis: Why do saturated fats increase blood cholesterol, and why should this be dangerous? After all, saturated fats occur naturally in a wide variety of foods, including breast milk.

"Cholesterol is a critically important molecule for all cells in the body," explains associate professor Marit Zinöcker, the lead author at Bjørknes University College, Oslo, Norway. "A cell is surrounded by a fluid membrane that controls cell function, and the cells depend on the ability to incorporate a certain amount of cholesterol molecules, so that their membranes don't become too stiff or too fluid."

"The basis of the model is that when saturated fats replace polyunsaturated fats in the diet, less cholesterol is needed in the cell membranes," she explains. The opposite is true when eating more polyunsaturated fatty acids, which include omega-3 and omega-6 fatty acids. "This is because polyunsaturated fats from the diet enter our cell membranes and make them more fluid. The cells adjust the fluidity of their membranes by incorporating cholesterol recruited from the bloodstream. According to the model presented by the researchers, this can explain why blood cholesterol levels decrease when we eat more polyunsaturated fats.

The authors have named the model the "Homeoviscous Adaptation to Dietary Lipids" (HADL) model.

"Cells need to adjust their membrane fluidity according to changes in their environment, such as the access to different types of fat", says co-author Simon N. Dankel, researcher at the Department of Clinical Science, University of Bergen, Norway.

"This phenomenon is called homeoviscous adaptation, and has been described in both microorganisms, vertebrates and in human skin cells. We argue that this is a critical principle in human physiology. Our cells are normally capable of adjusting their cholesterol content according to changes in dietary fats."

"Nutrition research often focuses on what changes in the body, but the question of why something, such as the blood cholesterol, changes, is of equal importance", says co-author Karianne Svendsen, postdoctoral fellow at the Department of Nutrition, University of Oslo, Norway.

This is where the new HADL model comes into play, providing an explanation based on adaptive human physiology. "From the perspective of the HADL model, we find logical explanations for why cells need to change their cholesterol content, and thereby the blood cholesterol, when fats in the diet change," says Zinöcker.

In the paper, other reasons for elevated LDL-cholesterol in people with cardiovascular disease are discussed, such as low-grade inflammation and insulin resistance. This indicates that elevated blood cholesterol caused by metabolic disruptions must be uncoupled from elevated blood cholesterol caused by a major change in intake of dietary saturated fatty acids. It also questions the benefit of lowering blood cholesterol by adding polyunsaturated fatty acids to the diet, and not addressing the root cause.

"There is at best weak evidence that a high intake of saturated fat causes heart disease," says Dankel. "The overall data are inconsistent and unconvincing, not to mention the lack of a logical biological and evolutionary explanation."

"Also, people with metabolic disorders often do not show the expected changes in blood cholesterol when changing their fat intake, suggesting loss of the normal response."

"The research and reasoning that the HADL model is based on indicates that the effect of dietary fats on blood cholesterol is not a pathogenic response, but rather a completely normal and even healthy adaptation to changes in diet." Zinöcker concludes.

The authors state that although the model is based on existing knowledge of cellular mechanisms, the model still needs to be verified. The authors therefore urge researchers to discuss the HADL model using #HADLmodel and to test the model.

The paper was published online on January 20 and can be found here:

Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.


Fatty Meals Affect Arteries

In the small study, published in the Journal of the American College of Cardiology, researchers looked at the effects on 14 healthy adults of eating a meal high in saturated fat or polyunsaturated fat. Study participants had such a meal on two separate occasions, one month apart.

Each meal consisted of a slice of carrot cake and milk shake made with either saturated or polyunsaturated fat.

The meals were tailored to each participant and designed to contain 1 gram of fat for every 2.2 pounds of body weight. That amount of fat is equivalent to a double cheeseburger, a large order of fries, and a large milk shake for a 150-pound person.

The researchers found that three hours after eating the saturated fat meal, the endothelium, or inner lining of blood vessels, in study participants showed reduced ability to expand and increase blood flow.

Six hours after the meal high in saturated fat, the "good" HDL cholesterol's protective ability to prevent inflammation was also impaired, the researchers found. Inflammation has been linked to plaque buildup in the arteries.

In contrast, six hours after eating the meal high in polyunsaturated fats, HDL's protective effects were enhanced. The researchers found fewer inflammatory agents in the participants' arteries than they did after the saturated fat meal.

"We have a situation where consumption of a single meal containing a high level of saturated fat is associated with . impairment of a normal protective property of HDL," says Nicholls. "In contrast, consumption of a meal high in polyunsaturated fat results in HDL that is more protective."

Sources

SOURCES: Nicholls, S. Journal of the American College of Cardiology, Aug. 15, 2006 vol 48: pp 715-720. News release, American College of Cardiology. News release, The Cleveland Clinic Foundation.


Grapefruit

Shutterstock

If you are taking certain cholesterol-lowering drugs, grapefruit can be one of the worst foods you can eat. Not because it may increase cholesterol levels, but because it can negatively interact with your medication. If you are on a cholesterol-lowering drug, ask your doctor if you should be avoiding grapefruit before you indulge in the sweet-tart treat.


Does One Meal Matter?

A single fatty meal won't put you at risk for heart disease. Nor is it likely to change your cholesterol levels or test results. But over time, a diet high in saturated fats and carbohydrates can greatly increase your risk.

Other risk factors include obesity, smoking and a lack of exercise, according to the Mayo Clinic. Genetics, older age and conditions like diabetes can also be risk factors.

The best way to manage your risk for high cholesterol and triglycerides — and reduce your risk of heart attack or stroke — is to follow a healthy diet, exercise regularly and to quit smoking.

Discuss your cholesterol with your doctor. In some cases, you may also be prescribed medication to help manage your risk.


Does Eating Saturated Fat Cause High Cholesterol

The foods that you consume might determine your health. It is true that you could get various essential substances from your foods such as carbohydrate, protein, vitamins, and minerals. On the other hand, the foods that you consume also contain various substances that might harm your health as well such as fat and cholesterol. Fat is considered as one of the causes of various health problems. Some people might say that eating fats could raise the level of cholesterol in your blood. However, there are also several types of fats that are safe for your health. In fact, you might need these types of fat since they could give several health benefits for you. To find out whether eating certain types of fat could cause high level of cholesterol, there are several important aspects that you should know about cat and cholesterol.

Details about High Cholesterol

Before you learn about the connection between certain type of fat and cholesterol level, the first thing that you should know is the details about high cholesterol. Basically, cholesterol is the type of fat that is produced by your body. Cholesterol is needed by your cells and it could be found in your blood. On the other hand, your body also could get cholesterol from the foods that you consume as well. If the level of cholesterol in your blood is average, it will not bring any problems to your health. But when the level of cholesterol becomes too high, there are several health problems that might appear.

Different Types of Cholesterol

The next thing that you should know about cholesterol is that there are several different types of cholesterol. The first type of cholesterol is LDL. This type of cholesterol is also known as bad cholesterol. When the LDL level becomes too high in your blood, it could clog your arteries. This type of cholesterol is the type of cholesterol that you should lower. The next type of cholesterol is HDL or also known as good cholesterol. HDL is the type of cholesterol that will help cleaning the fat in your blood. Unlike LDL, you need to increase the level of HDL in your blood. The last type of cholesterol is triglycerides. Triglycerides are usually connected with LDL. When the level of both LDL and triglycerides is high you will have higher risk of having heart attack.

The Cause and the Symptoms of High Cholesterol

Since the high cholesterol might cause health problems, high cholesterol itself could be considered as health problem. Just like any other health problems, there are some symptoms that might be shown by high level of cholesterol in your blood. Basically, the symptoms of high cholesterol might be quite undetected. High cholesterol will not cause any pain and you will not feel sick when you have high cholesterol. However, when you find out that your cholesterol level is high, it’s better for you to get treatments immediately to prevent further issues. Besides the symptoms, you also might need to know about what cause high cholesterol. Basically, there are several causes that might trigger high cholesterol. The main cause of high cholesterol is the types of food that you consume. Foods that contain high amount of saturated fats, cholesterol, and trans-fats could make your cholesterol level becomes higher. So now it’s clear for you that saturated fats indeed could cause high cholesterol. Other factors that might cause high cholesterol are including overweight, age, family history, and certain health disease.

Foods with High Amount of Saturated Fats

After you know that saturated fats might cause high cholesterol, it’s very important for you to limit or even prevent consuming foods that contain high amount of saturated fats. There are several types of foods that are known for their high amount of saturated fats, including butter, suet, tallow, lard, several types of cheese, pate, sausage, fish oil, whipped cream, dark chocolate, coconut oil, palm oil, dried coconut, macadamia nuts, cashew, sesame seeds, pine nuts, and vegetable shortening. If you want to have lower level of cholesterol, you should reduce or prevent consuming these types of foods since they contain high amount of saturated fats. You also need to pay attention to the label of processed foods as well. if you find out that processed foods contain one of those foods as the ingredients, the processed foods might contain high level of saturated fats.

Planning Your Diet

Eating saturated fats definitely could make the level of cholesterol in your body becomes higher. However, you could prevent it by planning your diet carefully. These days, there are various diet plans that you could choose if you want to lower your cholesterol in more effective way. Before deciding which diet plan that you’re going to follow, it’s better for you to consult your personal nutritionist so that you could get the best results from your diet plan. You also need to make sure that your diet plan could allow your body to get the nutrition that it’s needed as well. By choosing the right diet plan, you will be able to lower your cholesterol level without causing other health problems.

Doing Some Exercises Might Help

Besides planning your diet, high level of cholesterol also could be lowered by performing certain types of exercises. Basically, there are various types of exercises that you could choose if you want t lower your cholesterol level such as walking, running, jogging, bicycling, and swimming. With regular exercise, the level of cholesterol in your blood could be lowered in more effective way. Exercise also allows you to maintain ideal body weight as well so that you could have healthier body.


Trans Fat

Trans fats (or trans fatty acids) are created in an industrial process that adds hydrogen to liquid vegetable oils to make them more solid. Another name for trans fats is &ldquopartially hydrogenated oils.&rdquo

Trans fats raise your bad (LDL) cholesterol levels and lower your good (HDL) cholesterol levels. These changes are associated with a higher risk of heart disease.

Trans fats are found in many fried foods. Baked goods, such as pastries, pizza dough, pie crust, cookies and crackers also can contain trans fats.

Since 2006, the FDA has required trans fat content to be listed on the Nutrition Facts panel of packaged foods. In recent years, many major national fast-food chains and casual-dining restaurant chains have announced they will no longer use trans fats to fry or deep-fry foods.

The American Heart Association recommends that adults who would benefit from lowering LDL cholesterol eliminate trans fat from their diet.

To find the amount of trans fats in a particular packaged food, look at the Nutrition Facts panel. Companies must list any measurable amount of trans fat (0.5 grams or more per serving) in a separate line in the &ldquoTotal Fat&rdquo section of the panel, directly beneath the line for &ldquoSaturated Fat.&rdquo This means if a food package states 0 grams of trans fats, it might still have some trans fats if the amount per serving is less than 0.5 g. Make sure to check the ingredients list for &ldquopartially hydrogenated oil.&rdquo


by J. Clifford and A. Kozil* * (9/17)

Quick Facts…

  • In healthy amounts, fat and cholesterol help our bodies function properly. However when consumed in excess, they may promote disease.
  • Overweight, obesity, and high intake of saturated fats are major risk factors for elevated LDL (‘bad’) cholesterol levels.
  • Saturated fats and trans fats have a significant effect in raising blood cholesterol levels.
  • Elevated blood cholesterol levels are a risk factor for heart disease and atherosclerosis (hardening of the arteries).
  • Most Americans consume too much fat and cholesterol—mostly from animal fat, prepackaged foods, and processed foods.

Cholesterol

Cholesterol is a waxy, fat-like substance found in all animals including humans and is essential to every cell in the body. Cholesterol is used to make certain hormones, like estrogen and testosterone, and it is part of a chemical called bile, which helps to digest fats. A special form of cholesterol found in the skin has the ability to change into vitamin D when exposed to sunlight. There are two different types of cholesterol:

  1. Blood, or serum, cholesterol—this type circulates in the blood and is mostly made by the body.
  2. Dietary cholesterol—this type comes from foods and beverages of animal origin.

How is blood cholesterol transported by the body? Cholesterol is transported in the blood by different carriers. The relative amounts of cholesterol transported by each carrier can affect one’s risk for heart disease. The two major blood cholesterol carriers are LDL (low density lipoprotein) and HDL (high density lipoprotein). LDL cholesterol is known as “bad” blood cholesterol, and functions to deliver cholesterol to cells throughout the body and can be deposited as “plaque” on artery walls. HDL cholesterol is known as “good” blood cholesterol, and functions as a vehicle in the blood to remove cholesterol waste from the body via the liver (Table 1).

Table 1: Characteristics of HDL and LDL blood cholesterol carriers.
LDL HDL
Full Name: Low Density Lipoprotein. High Density Lipoprotein.
What it does: Takes cholesterol from the liver to the rest of the body. Primarily takes cholesterol from body tissue back to liver.
Effect on the risk for heart disease: High amounts increase risk. High amounts reduce risk.
Nickname: “Bad” cholesterol. “Good” cholesterol.

Where do we get cholesterol? Our bodies have the ability to make all of the cholesterol needed for proper functioning once we reach childhood, but most people also get cholesterol from foods. Different foods vary in the amount of cholesterol they contain. Only animal products have cholesterol plant based products may contain fat, but they do not contain cholesterol.

Is cholesterol harmful? Cholesterol is necessary for a healthy body, but a high blood level of total cholesterol is a major risk factor for atherosclerosis (hardening of the arteries), heart disease, and high levels of LDL cholesterol. The risk continues to increase as blood cholesterol levels elevate. For more information on cardiovascular disease, see fact sheet Heart Health: Managing Heart Disease through Diet.

While the 2010 Dietary Guidelines for Americans recommended limiting consumption of dietary cholesterol to 300 mg per day, this recommendation is not included in the updated 2015-2020 edition of the Dietary Guidelines. This change reflects new research that suggests that dietary cholesterol, consumed in moderate amounts, does not affect health risks, including heart disease, for the majority of people unless a person has diabetes. Consuming solid fat (saturated fat), not cholesterol, is what increases heart disease risk for most people. Still, the healthy eating patterns highlighted in the 2015 Dietary Guidelines contain approximately 100 to 300 mg cholesterol per day, in keeping with the previous 2010 recommendations. The Institute of Medicine also recommends individuals eat as little dietary cholesterol as possible as a part of a healthy eating pattern. In general, foods that are higher in dietary cholesterol, such as fatty meats and high-fat dairy products, are also higher in saturated fats.

Table 2: Classifications of a Fasting Lipoprotein Profile.
Total Cholesterol (mg/dL) 1
Desirable < 200
Borderline High 200 – 239
High > 240
LDL Cholesterol
Optimal < 100
Borderline High 100 – 129
Borderline High 130 –159
High 160 – 189
Very High > 190
HDL Cholesterol
Low < 40
High 2 > 60
Triglycerides
Normal < 150
Borderline High 150 –199
High 200 – 499
Very High > 500
1 Milligrams per Deciliter (mg/dL).
2 An HDL of 60 mg/dL and above is considered protective against heart disease.

The National Cholesterol Education Program (NCEP) recommends a blood test known as a “lipoprotein profile” every five years for those ages 20 and older. This test reveals information about the total cholesterol, LDL cholesterol, HDL cholesterol, and triglyceride levels in the blood (Table 2). Triglycerides are also a type of fat found in the blood. The results of the blood test, along with other factors such as age, gender, family history, smoking, hypertension, diabetes, and obesity, can help determine one’s overall risk for heart disease.

What is dietary fat? Fat is a necessary component of a healthy diet. It is a part of every cell in the body and makes up about 60% of the brain. Fat is essential in the absorption of fat-soluble vitamins A, D, E and K and also makes up parts the hormones that regulate important body functions. Dietary fat provides essential fatty acids, such as linolenic (omega-3) and linoleic (omega-6) acids, which the body cannot produce on its own. Essential fatty acids are necessary for brain and eye development in infants and children and the maintenance of healthy skin in children and adults.

Dietary fat may improve the taste of food, aid in cooking, and increase satiety. Yet, eating too much fat may lead to increased weight, as it has more than twice as many calories per ounce as sugar, starch or protein. Consuming fatty foods in excess may increase total and LDL cholesterol levels, while increasing the risk of heart disease and some forms of cancer.

Types of Fat

Are all fats the same? There is not a single type of fat. Rather, the word “fat” is often used to refer to all of the fatty substances found both in food and in the body.

Lipids: Scientific term referring to fat, cholesterol and other fat-like substances.

Triglycerides: Scientific name for the main form of fat found in in the body and in foods. Most of the fat in the body is stored as triglycerides, but triglycerides circulate in the blood as well. Triglycerides are made of three fatty acids and one glycerol molecule. These three fatty acids may include any combination of saturated fatty acids, monounsaturated fatty acids (MUFAs), and polyunsaturated fatty acids (PUFAs). Triglycerides in the blood stream trigger the liver to make more cholesterol, so high triglyceride levels are often associated with high levels of total and LDL cholesterol.

Saturated Fat Acids (SFAs): Usually solid at room temperature, saturated fats have all of the hydrogen atoms they can hold (saturated with hydrogen). Saturated fats are primarily from animal products, but are also found in tropical plant oils, such as coconut and palm as well as other plant based foods, though in smaller amounts. The 2015 Dietary Guidelines for Americans suggests limiting saturated fats in the diet to less than 10% of daily calories. See Table 3 for the health effects of saturated fats in the diet.

Monounsaturated Fats (MUFAs): Liquid at room temperature, monounsaturated fats are missing one pair of hydrogen atoms. Monounsaturated fats are primarily derived from plants and include olive oil, canola oil, peanut oil, and avocados. See Table 3 for the health effects of monounsaturated fats in the diet.

Polyunsaturated Fats (PUFAs): Liquid at room temperature, polyunsaturated fats are missing two or more pairs of hydrogen atoms. Many common vegetable oils, such as corn, soybean, safflower and sunflower oil as well as fish are high in polyunsaturated fats. See Table 3 for the health effects of polyunsaturated fats in the diet.

Essential Fatty Acids: Fatty acids that are essential to human health but not produced in the body must be obtained through food. Only two types of fatty acids are considered essential omega-3 fatty acids and omega-6 fatty acids, both polyunsaturated fats. The 2015 Dietary Guidelines for Americans emphasize vegetable oils (mono- and polyunsaturated fats) as part of healthy eating pattern because they are the major source of essential fatty acids and vitamin E.

  • Omega-3 Fatty Acids: OOmega-3’s are a group of polyunsaturated fatty acids that include alpha-linolenic acid (ALA), eicosapenaenoic acid (EPA), and docosahexaenoic acid (DHA).. DHA and EPA are mainly found in higher-fat, cold-water fish, such as salmon, mackerel, sardines and herring. ALA is found in canola oil, chia seeds, flaxseed oil, soybean oil, and walnuts, and some of that ALA can be converted into DHA and EPA by the body. Diets high in EPA and DHA may help reduce the risk of heart disease by helping to thin the blood and prevent blood platelets from clotting and sticking to artery walls, causing blockages. Research also suggests that EPA and DHA may lower levels of triglycerides in the blood, may prevent hardening of the arteries, and may moderately reduce blood pleasure. In addition, consuming DHA during pregnancy (2 servings of oily fish per week) is linked with better cognitive development and vision in infants. For more information on omega-3 fatty acids, see fact sheet Omega-3 Fatty Acids.
  • Omega-6 Fatty Acids: Omega 6 fatty acids are found in meats and vegetable oils, such as, soybean, corn, and safflower. Polyunsaturated omega 6’s, such as linoleic acid (LA), are thought to promote heart health by lowering LDL cholesterol levels, especially when replacing saturated fats and trans fats in the diet. Linoleic acid (LA) can be converted to a long chain omega-6 fatty acid called arachidonic acid (AA), which in excess, may be linked to inflammation and other chronic health conditions. Another type of omega 6 fatty acid, called conjugated linoleic acid (CLA), found in dairy foods, beef, and lamb, may be associated with a decrease in certain types of cancers and improved body composition. Research is still exploring these connections.

Hydrogenated Fats: These are unsaturated fats that are processed to become solid at room temperature. Hydrogen atoms are added to unsaturated fat through a process called hydrogenation. This turns unsaturated fats into saturated fats. Hydrogenated fats can either be fully or partially hydrogenated, and are used in foods to enhance texture, extend shelf life, and prevent rancidity. Packaged and processed foods such as cookies, crackers, and margarine most commonly contain these types of fats.

Trans Fatty Acid: Trans fats occur naturally in some foods derived from cattle and sheep, but generally, this type of fat is formed during the process of hydrogenation. Only partially hydrogenated fats contain trans fats, where fully hydrogenated fats do not. Trans fatty acids mimic the properties of saturated fats in the body, and have been shown to increase LDL cholesterol and lower HDL cholesterol, which may increase the risk for heart disease. The 2015 Dietary Guidelines for Americans suggest limiting trans fats in the diet. Trans fat may be found in partially hydrogenated margarines, peanut butters, and snack foods.

In 2015, the Food and Drug Administration (FDA) stated that partially hydrogenated oils were no longer recognized as safe for use in foods, as they are the primary source of dietary trans fatty acids. The food industry was given 3 years to comply with the ruling and remove TFA’s from food products.The FDA stated that removing partially hydrogenated oils from processed foods could prevent thousands of heart attacks and deaths each year.

The Relationship Between Fat and Cholesterol

How are fats related to blood cholesterol? Research shows that the amount and type of dietary fat consumed can affect blood cholesterol levels. Dietary fat, especially saturated and trans fats, may raise blood levels of total and LDL cholesterol. Replacing some saturated fats with polyunsaturated and monounsaturated fats (especially olive and canola oil) can help lower blood cholesterol. Recall that high total blood cholesterol levels and LDL cholesterol levels increase risk of heart disease, while lower levels reduce risk. Higher levels of HDL cholesterol help lower the risk for heart disease.

What foods contain fat and cholesterol? In some foods, fats are obvious, like noticeably greasy, fried or oily foods, or meats with visible marbling. In other foods, such as dairy, eggs, and some meats, fat and cholesterol is harder to see. Fats are found in both plant and animal foods, but cholesterol is only found in foods of animal origin. A food can be high in fat and cholesterol (fried egg), high in fat but low in cholesterol (peanut butter and avocado), low in fat and high in cholesterol (shrimp), or low in both (fruit). The nutrition facts label is a useful tool to determine the amount of fat or cholesterol in a particular food item.

Monitoring Intake of Fat and Cholesterol

Dietary fat and cholesterol are necessary components for a healthy diet. Though, when consumed in excess, they may be harmful to the body and increase one’s risk for obesity, atherosclerosis, and heart disease. Keep in mind, however, that dietary cholesterol does not have as much of an effect on blood cholesterol as saturated fat. It is important to regulate ones intake of dietary fat in order to regulate blood LDL, HDL, and triglyceride levels.

Summary

  • The two types of cholesterol in the blood are LDL (bad) and HDL (good) cholesterol. Excessive LDL deposits plaque on artery walls, while HDL acts to remove cholesterol from the body.
  • Our body has the ability to make all of its own cholesterol. In the diet, it is obtained only through animal products.
  • High blood levels of LDL and total cholesterol as well as low levels of HDL, are risk factors for heart disease.
  • Triglycerides are the primary form of dietary fat found in the body, and may contain a combination of three fatty acids: saturated fatty acids (SFAs), polyunsaturated fatty acids (PUFAs), or monounsaturated fatty acids (MUFAs).
  • Essential fatty acids cannot be not produced by the body and must be obtained from the diet these include omega-3 and omega-6 fatty acids.
  • Trans fats are derived from partially hydrogenated fats and mimic the function of saturated fatty acids in the body. They may increase risk for heart disease, and are most often found in processed foods and fast foods.
  • Dietary fat and cholesterol are closely related types of dietary fat (saturated and trans fat) can lead to an increase in blood cholesterol levels.
  • Follow the USDA’s 2015 Dietary Guidelines for Americans to ensure proper intake of fats in the diet.
  • Follow the 2010 USDA Guidelines to ensure proper intake of fat and cholesterol.

References

Advanced Nutrition: Macronutrients, Micronutrients, and Metabolism (2009). Boca Raton, FL: CRC Press, Taylor & Francis Group.

Duyff, R. L., Academy of Nutrition and Dietetics. (2017). Complete Food and Nutrition Guide 5th Edition. New York, NY: Houghton Mifflin Harcourt Publishing Company.

Mahan, L. K., Escott-Stump, S., Raymond, J. L., & Krause, M. V. (2012). Krause’s food & the nutrition care process. St. Louis, Mo: Elsevier/Saunders.

United States Department of Agriculture. (2016). 2015 Dietary Guidelines for Americans. Retrieved from: http://health.gov/dietaryguidelines/2015/guidelines/

* J. Clifford, Colorado State University Extension food and nutrition specialist , A. Kozil, graduate student. Original fact sheet revised by L. Bellows, Colorado State University Extension food and nutrition specialist and assistant professor and R. Moore, graduate student. 5/96. Revised 9/17.


Study: Doubling Saturated Fat in the Diet Does Not Increase Saturated Fat in Blood

COLUMBUS, Ohio – Doubling or even nearly tripling saturated fat in the diet does not drive up total levels of saturated fat in the blood, according to a controlled diet study.

However, increasing levels of carbohydrates in the diet during the study promoted a steady increase in the blood of a fatty acid linked to an elevated risk for diabetes and heart disease.

The finding “challenges the conventional wisdom that has demonized saturated fat and extends our knowledge of why dietary saturated fat doesn’t correlate with disease,” said senior author Jeff Volek, a professor of human sciences at The Ohio State University.

“It’s unusual for a marker to track so closely with carbohydrate intake, making this a unique and clinically significant finding. As you increase carbs, this marker predictably goes up,” Volek said.The researchers found that total saturated fat in the blood did not increase – and went down in most people – despite being increased in the diet when carbs were reduced. Palmitoleic acid, a fatty acid associated with unhealthy metabolism of carbohydrates that can promote disease, went down with low-carb intake and gradually increased as carbs were re-introduced to the study diet.In the study, participants were fed six three-week diets that progressively increased carbs while simultaneously reducing total fat and saturated fat, keeping calories and protein the same.

When that marker increases, he said, it is a signal that an increasing proportion of carbs are being converted to fat instead of being burned as fuel. Reducing carbs and adding fat to the diet in a well-formulated way, on the other hand, ensures the body will promptly burn the saturated fat as fuel so it won’t be stored.

“When you consume a very low-carb diet your body preferentially burns saturated fat,” Volek said. “We had people eat 2 times more saturated fat than they had been eating before entering the study, yet when we measured saturated fat in their blood, it went down in the majority of people. Other traditional risk markers improved, as well.”

The research is published in the Nov. 21, 2014, issue of the journal PLOS ONE.

Volek and colleagues recruited 16 adults for the study, all of whom had metabolic syndrome, defined as the presence of at least three of five factors that increase the risk for heart disease and diabetes (excess belly fat, elevated blood pressure, low “good” cholesterol, insulin resistance or glucose intolerance, and high triglycerides).

After getting them to a baseline reduced-carb diet for three weeks, researchers fed the participants the exact same diets, which changed every three weeks, for 18 weeks. The diets started with 47 grams of carbs and 84 grams of saturated fat each day, and ended with 346 carb grams per day and 32 grams daily of saturated fat.

Each day’s meals added up to 2,500 calories and included about 130 grams of protein. The highest-carb level represented 55 percent of daily calories, which roughly matches the estimated daily percentage of energy provided by carbs in the American diet.

Compared to baseline, there were significant improvements in blood glucose, insulin and blood pressure that were similar across diets. Participants, on average, lost almost 22 pounds by the end of the trial.

When looking at palmitoleic acid, however, the scientists found that it consistently decreased on the high-fat/low-carb diet in all participants. The fatty acid then showed a step-wise increase in concentration in the blood as carbs were progressively added to the diet. Elevated levels of palmitoleic acid in the blood have been linked to obesity and higher risk for inflammation, insulin resistance, impaired glucose tolerance, metabolic syndrome, type-2 diabetes, heart disease and prostate cancer.

The study does not address what happens to palmitoleic acid levels when high carbs are combined with a diet high in saturated fat. Instead, Volek hoped to identify the carb-intake point at which participants began to store fat.

“That turned out to be highly variable,” he said. “Everyone showed increased palmitoleic acid levels as carbs increased, but values varied widely between individuals, especially at the highest carb intake. This is consistent with the idea that people vary widely in their tolerance to carbohydrates.”

Participants’ existing health risks were not a factor in the study because everyone ate the exact same diet for 18 weeks. Their bodies’ responses to the food were the focus of the work.

“There is widespread misunderstanding about saturated fat. In population studies, there’s clearly no association of dietary saturated fat and heart disease, yet dietary guidelines continue to advocate restriction of saturated fat. That’s not scientific and not smart,” Volek said. “But studies measuring saturated fat in the blood and risk for heart disease show there is an association. Having a lot of saturated fat in your body is not a good thing. The question is, what causes people to store more saturated fat in their blood, or membranes, or tissues?

“People believe ‘you are what you eat,’ but in reality, you are what you save from what you eat,” he said. “The point is you don’t necessarily save the saturated fat that you eat. And the primary regulator of what you save in terms of fat is the carbohydrate in your diet. Since more than half of Americans show some signs of carb intolerance, it makes more sense to focus on carb restriction than fat restriction.”

Volek sees this palmitoleic acid as a potential biomarker to signal when the body is converting carbs to fat, an early event that contributes to what he calls “metabolic mayhem.”

“There is no magical carb level, no cookie-cutter approach to diet, that works for everyone,” he said. “There’s a lot of interest in personalized nutrition, and using a dynamically changing biomarker could provide some index as to how the body is processing carbohydrates.”

Co-authors include Brittanie Volk, Laura Kunces, Brian Kupchak, Catherine Saenz, Juan Artistizabal and Maria Luz Fernandez of the University of Connecticut Daniel Freidenreich, Richard Bruno, Carl Maresh and William Kraemer of Ohio State’s Department of Human Sciences and Stephen Phinney of the University of California, Davis.



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