Fat is an enigmatic opponent. From both the nutrition side and the weight loss side, fat presents a number of challenges. It's high caloric value, ubiquity, and the fact that it usually tastes delicious make it difficult to effectively control dietary intake of fats. At the same time, once your body has stored excess energy as body fat, it is notoriously difficult to get rid of. Many people find that even when they are "doing everything right" it seems impossible to significantly reduce the amount of fat they are carrying on their bodies. In this post, we'll cover precisely what fat is, how it's digested and absorbed and what metabolic conditions encourage (or inhibit) the human body to "burn off" excess fat stores.
First off, what exactly is fat? Chemically speaking, fat is a combination of fatty acids connected by a glycerol molecule. Because that is probably not a meaningful description for the average person, I have included the
handy image to the left to illustrate this concept. Once the free fatty acids are connected to the glycerol backbone to form one large molecule, it is called a triglyceride. Their are many different types of fatty acids that can be attached to the glycerol backbone, and these differences are what define your different types of fat, such as saturated fat, mono-unsaturated fat, poly unsaturated fat and the ominous trans-fat.
To briefly summarize these different types of fat:
Saturated fat - The primary fat derived from animal sources. It is composed of straight fatty acids that have no double bonds. Because of this, the molecules can pack closely together and form more dense fats. This type of fat is often solid at room temperature. There is also some concern that high levels of dietary saturated fat are correlated with an increased rate of cardiovascular disease. However, most research studies have failed to show a strong causative relationship between saturated fat intake and cardiovascular disease. It is more likely that cardiovascular disease is impacted by total nutrition and lifestyle choices, rather than simply eating saturated fat.
Unsaturated Fat (Mono-unsaturated and Poly-unsaturated) - The primary type of fat found in plant sources. For example, olive oil contains roughly 70% unsaturated fat, in the form of oleic acid (a type of fatty acid). Unlike saturated fat, unsaturated fats are composed of fatty acids that are bent or kinked. As a result, they can't pack together as closely, are often less dense and are often liquid at room temperature. Several studies have suggested that there are a number of potential health benefits from certain types of unsaturated fats, such as those found in olive oil (oleic acid).
Trans Fat - An artificial type of unsaturated fat generated from a chemical process known as partial hydrogenation. Partial hydrogenation is used to make liquid fats more solid, such as in the production of margarine from vegetable oil. Not all partially hydrogenated fats contain trans fat. In fact, with recent research showing that trans fat could potentially increase the risk of coronary heart disease and raise "bad" (LDL) cholesterol levels, many products are now being produced without trans fats.
Probably more important than understanding dietary fat, is understanding how your body processes that fat and how it impacts your own stores of body fat (aka adipose tissue). First off, it is important to keep in mind that a complete fat molecule, a triglyceride, is not readily absorbed by the digestive system. It must first be enzymatically digested into fatty acids and glycerol, which are illustrated in the first image. Unlike the larger triglyceride molecules, free fatty acids are readily absorbed through the intestines. The digestion of triglycerides into free fatty acids is performed by enzymes in the intestines called lipases. These enzymes are the target of the drug orlistat, also known as alli (OTC) and Xenical (Rx). Orlistat prevents the digestion of triglycerides into free fatty acids and therefore prevents the body from absorbing the fat. During treatment with these medications, a substantial amount of ingested dietary fat remains as undigested triglycerides, passes through the digestive system and is excreted in the stool.
Fat contains more calories per gram than carbohydrates or proteins. Fat has approximately 9 calories per gram compared to an average of 5 for carbohydrates and 4 for proteins. Because of that, it is a lot easier to consume excessive calories if you are eating a diet that is high in fat. However, simple caloric intake is not the whole story when it comes to weight gain or loss. In many cases, consumption of fat can be a beneficial part of a healthy diet. Fat is often associated with high protein, low carbohydrate foods, like meats or eggs. Research has suggested that many sources of fat could have beneficial health effects, like olive oil or cod liver oil. A moderate amount of fat in a meal promotes a sensation of satiety that you often don't get with high sugar/high carbohydrate meals. The biggest danger is when you combine high fat food choices with choices that are high in sugars and simple carbohydrates. As we will see in the next section, the combination of high sugar/high fat creates metabolic conditions that favor the storage of large amounts of energy as body fat.
If I had to choose one thing that people need to understand about fat metabolism, it would be this: Blood sugar is the master regulator of metabolism. When your blood sugar is high, your metabolism shifts its focus towards storing energy (making fat). When your blood sugar is depressed, your metabolism focuses on getting more sugar in your blood (burning fat). Blood sugar plays this critical role because it regulates the production of the master metabolism hormones, insulin and glucagon. High blood sugar leads to increased production of insulin, which causes fat cells to absorb free fatty acids and glucose from the blood and turn it into fat. Furthermore, during periods of high blood sugar, the metabolic pathways required for burning fat (e.g. lipolysis) are shut down. Therefore, it is virtually impossible to reduce body fat levels when you have elevated blood sugar levels. This is illustrated in the figure above showing an increase in glucose (blood sugar) causes the pnacreas to release insulin, which inhibits lipolysis in the fat cell. In contrast, low blood sugar levels encourage the metabolic pathways that burn fat because low blood sugar decreases insulin levels and increases levels of glucagon, which encourages the release of stored energy.
So what is the key to creating the metabolic conditions that encourage your body to tap into its stored fat reserves? The answer is two fold. First, you need to avoid the conditions that inhibit fat catabolism (another word for "burning fat"). Those "anti-fat burning" conditions are created by high blood sugar levels. Avoid eating foods that cause large increases in blood sugar, particularly sugars and simple carbohydrates. Of course, it is also important to avoid excessive calorie intake in general (max=2000-2500/day) if you want to maximize your fat burning potential. There are also several prescription drugs on the market that can help you maintain low blood sugar levels. The second key is to encourage your muscles to utilize more glucose, thus lowering blood sugar levels by energy demand. Exercise, obviously, is the most effect way to do this. Both during and after exercise, your muscles have an increased demand for energy. Even resting muscle has an elevated metabolic demand. Increasing your lean muscle mass is also an effective way to encourage a decrease in body fat. In addition to exercise, increasing the amount of protein in your diet encourages the growth and maintenance of lean muscle tissue. In the end, the keys to decreasing your body fat levels sound like much the same advice you've always heard.
1) Avoid sugar and other foods high in simple and processed carbohydrates
2) Avoid excessive calorie intake (more than 2000-2500 calories per day)
3) Exercise
4) Increase your protein intake to encourage development of lean muscle mass
Additional options
1) Explore options about prescription medications that can help you regulate your blood sugar.
2) Explore protein supplements and other natural supplements that can help you increase your lean muscle mass.
References, Background Reading and Additional Information
Books:
How Fat Works
Philip Wood
Eat, Drink and Be Healthy: The Harvard Medical School Guide to Healthy Eating
Walter Willett, MD
Cereal Killer
Alan Watson
Good Calories, Bad Calories: Fats, Carbs, and the Controversial Science of Diet and Health
Gary Taubes
Online Resources:
Fat - Wikipedia
Insulin and Metabolism - Wikipedia
Fatty Acid Metabolism - Wikipedia
The Chemistry of Fat Metabolism
The Science of Acne
Scientific Research Papers:
PPARS and the Complex Journey to Obesity
Evans, et al. Nature Medicine 2004
Fructose Consumption: Considerations for Future Research on Its Effects on Adipose Distribution, Lipid Metabolism, and Insulin Resistance
Stanhope, et al. Journal of Nutrition 2009
Consumption of Resistant Starch (Dietary Fiber) Decreases Postprandial Lipogenesis in White Adipose Tissue in Rats
Higgins, et al. Nutrition Journal 2006
First off, what exactly is fat? Chemically speaking, fat is a combination of fatty acids connected by a glycerol molecule. Because that is probably not a meaningful description for the average person, I have included the
To briefly summarize these different types of fat:
Saturated fat - The primary fat derived from animal sources. It is composed of straight fatty acids that have no double bonds. Because of this, the molecules can pack closely together and form more dense fats. This type of fat is often solid at room temperature. There is also some concern that high levels of dietary saturated fat are correlated with an increased rate of cardiovascular disease. However, most research studies have failed to show a strong causative relationship between saturated fat intake and cardiovascular disease. It is more likely that cardiovascular disease is impacted by total nutrition and lifestyle choices, rather than simply eating saturated fat.
Unsaturated Fat (Mono-unsaturated and Poly-unsaturated) - The primary type of fat found in plant sources. For example, olive oil contains roughly 70% unsaturated fat, in the form of oleic acid (a type of fatty acid). Unlike saturated fat, unsaturated fats are composed of fatty acids that are bent or kinked. As a result, they can't pack together as closely, are often less dense and are often liquid at room temperature. Several studies have suggested that there are a number of potential health benefits from certain types of unsaturated fats, such as those found in olive oil (oleic acid).
Trans Fat - An artificial type of unsaturated fat generated from a chemical process known as partial hydrogenation. Partial hydrogenation is used to make liquid fats more solid, such as in the production of margarine from vegetable oil. Not all partially hydrogenated fats contain trans fat. In fact, with recent research showing that trans fat could potentially increase the risk of coronary heart disease and raise "bad" (LDL) cholesterol levels, many products are now being produced without trans fats.
Probably more important than understanding dietary fat, is understanding how your body processes that fat and how it impacts your own stores of body fat (aka adipose tissue). First off, it is important to keep in mind that a complete fat molecule, a triglyceride, is not readily absorbed by the digestive system. It must first be enzymatically digested into fatty acids and glycerol, which are illustrated in the first image. Unlike the larger triglyceride molecules, free fatty acids are readily absorbed through the intestines. The digestion of triglycerides into free fatty acids is performed by enzymes in the intestines called lipases. These enzymes are the target of the drug orlistat, also known as alli (OTC) and Xenical (Rx). Orlistat prevents the digestion of triglycerides into free fatty acids and therefore prevents the body from absorbing the fat. During treatment with these medications, a substantial amount of ingested dietary fat remains as undigested triglycerides, passes through the digestive system and is excreted in the stool.
Fat contains more calories per gram than carbohydrates or proteins. Fat has approximately 9 calories per gram compared to an average of 5 for carbohydrates and 4 for proteins. Because of that, it is a lot easier to consume excessive calories if you are eating a diet that is high in fat. However, simple caloric intake is not the whole story when it comes to weight gain or loss. In many cases, consumption of fat can be a beneficial part of a healthy diet. Fat is often associated with high protein, low carbohydrate foods, like meats or eggs. Research has suggested that many sources of fat could have beneficial health effects, like olive oil or cod liver oil. A moderate amount of fat in a meal promotes a sensation of satiety that you often don't get with high sugar/high carbohydrate meals. The biggest danger is when you combine high fat food choices with choices that are high in sugars and simple carbohydrates. As we will see in the next section, the combination of high sugar/high fat creates metabolic conditions that favor the storage of large amounts of energy as body fat.
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If I had to choose one thing that people need to understand about fat metabolism, it would be this: Blood sugar is the master regulator of metabolism. When your blood sugar is high, your metabolism shifts its focus towards storing energy (making fat). When your blood sugar is depressed, your metabolism focuses on getting more sugar in your blood (burning fat). Blood sugar plays this critical role because it regulates the production of the master metabolism hormones, insulin and glucagon. High blood sugar leads to increased production of insulin, which causes fat cells to absorb free fatty acids and glucose from the blood and turn it into fat. Furthermore, during periods of high blood sugar, the metabolic pathways required for burning fat (e.g. lipolysis) are shut down. Therefore, it is virtually impossible to reduce body fat levels when you have elevated blood sugar levels. This is illustrated in the figure above showing an increase in glucose (blood sugar) causes the pnacreas to release insulin, which inhibits lipolysis in the fat cell. In contrast, low blood sugar levels encourage the metabolic pathways that burn fat because low blood sugar decreases insulin levels and increases levels of glucagon, which encourages the release of stored energy.
So what is the key to creating the metabolic conditions that encourage your body to tap into its stored fat reserves? The answer is two fold. First, you need to avoid the conditions that inhibit fat catabolism (another word for "burning fat"). Those "anti-fat burning" conditions are created by high blood sugar levels. Avoid eating foods that cause large increases in blood sugar, particularly sugars and simple carbohydrates. Of course, it is also important to avoid excessive calorie intake in general (max=2000-2500/day) if you want to maximize your fat burning potential. There are also several prescription drugs on the market that can help you maintain low blood sugar levels. The second key is to encourage your muscles to utilize more glucose, thus lowering blood sugar levels by energy demand. Exercise, obviously, is the most effect way to do this. Both during and after exercise, your muscles have an increased demand for energy. Even resting muscle has an elevated metabolic demand. Increasing your lean muscle mass is also an effective way to encourage a decrease in body fat. In addition to exercise, increasing the amount of protein in your diet encourages the growth and maintenance of lean muscle tissue. In the end, the keys to decreasing your body fat levels sound like much the same advice you've always heard.
1) Avoid sugar and other foods high in simple and processed carbohydrates
2) Avoid excessive calorie intake (more than 2000-2500 calories per day)
3) Exercise
4) Increase your protein intake to encourage development of lean muscle mass
Additional options
1) Explore options about prescription medications that can help you regulate your blood sugar.
2) Explore protein supplements and other natural supplements that can help you increase your lean muscle mass.
References, Background Reading and Additional Information
Books:
How Fat Works
Philip Wood
Eat, Drink and Be Healthy: The Harvard Medical School Guide to Healthy Eating
Walter Willett, MD
Cereal Killer
Alan Watson
Good Calories, Bad Calories: Fats, Carbs, and the Controversial Science of Diet and Health
Gary Taubes
Online Resources:
Fat - Wikipedia
Insulin and Metabolism - Wikipedia
Fatty Acid Metabolism - Wikipedia
The Chemistry of Fat Metabolism
The Science of Acne
Scientific Research Papers:
PPARS and the Complex Journey to Obesity
Evans, et al. Nature Medicine 2004
Fructose Consumption: Considerations for Future Research on Its Effects on Adipose Distribution, Lipid Metabolism, and Insulin Resistance
Stanhope, et al. Journal of Nutrition 2009
Consumption of Resistant Starch (Dietary Fiber) Decreases Postprandial Lipogenesis in White Adipose Tissue in Rats
Higgins, et al. Nutrition Journal 2006
