For the final day, I continued with advanced carbohydrate counting/insulin dose adjustment based on intake because this was the method I identified with the most. I believe that this would be the most accurate way to manage blood glucose levels whether you have type 1 or type 2 diabetes, assuming the patient has the motivation and understanding to do it.
This week has been fun, and educational. Compared to the week I spent on the renal (pre-dialysis) diet in my undergrad MNT class, this was a piece of cake (no pun intended). Here’s what I got out of it (in no particular order of importance):
1. I am happy to say I have gotten over my fear of needles. I can’t even watch when someone else gives me a shot. Orientation was the first time I was able to actually stick myself with a needle. In the past, I had to have someone else do it. Now, after sticking myself 3 times a day for 7 days, I’m pretty numb to it.
2. I would make a great diabetic patient. My typical meal pattern is already pretty evenly distributed with carbohydrate. I’m a huge perfectionist and am very organized, and have a good memory for things like checking blood sugar. I almost always have my meals planned out, at least in my head, for the whole day. I have been known to look up the nutrition information of restaurant menus before I go there, so I can decide what I’m getting before I arrive. I realize that it is extremely unlikely that my patients will come equipped with all, if any, of these attributes.
3. Don’t freeze the other half of the large/medium banana for later. Share it with a friend, or just use the whole darn thing and adjust for it. Icky texture change is not worth it!
4. Hooray for wine, a great low carb drink choice!
5. Despite my desire to follow the meal plan precisely, something always came up that caused me to change it in some way or another. That’s life – you just have to be ready to deal with it. I will remember this when working with patients, and will focus on education so that they can adjust for changes in their plan.
6. I love advanced carbohydrate counting! I know I am going to want everyone to get there, but will have to recognize when people are and aren’t ready for this method. For some, the plate method (although I practically loathed it) will be the most appropriate thing to teach.
7. I believe the hardest part about being diagnosed with diabetes would be the perceived loss of freedom and ability to be spontaneous. You can’t just eat or drink whatever or whenever you want, and you always have to carry your supplies with you. You have to be aware of what you’re eating, how much, and how you’re feeling between meals. You have to be prepared and know what to do in case your blood sugar gets to low. I have a feeling that many people probably go through some period of denial/anger after being diagnosed. It will be important to recognize this in patients and only give them the information they are ready to hear so as not to overwhelm them even more.
Sunday, November 14, 2010
Diabetes - Day 6
Today was a very different day for me, food-wise. I was at work and did not eat lunch until after 3pm, so I didn’t need my afternoon snack. We also decided to go out to dinner tonight, at a restaurant I’ve only eaten at a few times. Needless to say, this required some estimation once the food was in front of me. I ordered the cabbage rolls, which were stuffed with beef, rice, and herbs. Using the exchange system, I estimated the carbohydrate content the best I could. When I got home, I looked up the actual information and saw that I was quite close! The restaurant we ate at did not have nutrition information on their website, and they are not a large chain so probably aren’t required to have it available. I used the information for a similar recipe to decide whether my estimation was correct.
I also had two glasses of wine with dinner, which is really a good choice if you have diabetes. A 5 ounce glass of most types of wine (Pinot Noir was my choice) only has about 3 grams of carbohydrate, whereas a 12 ounce glass of beer has 10 grams. I won’t even get into how high some of those mixed drinks/fruity martinis could probably get.
The fact that I’m playing a person with type 1 diabetes, and the fact that I was drinking, made me think of an ex-boyfriend of mine (this was over 10 years ago) who was in that situation. I was only 19 at the time and didn’t really understand anything about his condition, except he was always saying that he had to eat (it was not optional) and of course, had to give himself shots of insulin. On his 21st birthday, he had a huge party at his house and was drinking hard liquor in excess. Early the next morning, I was sitting next to him and he starting having a seizure and passed out. It was terrifying! I screamed for his parents and we called 911. The paramedics arrived and gave him a shot (glucose?) and he woke up and was fine.
For a long time, I thought that this directly resulted from his drinking alcohol, but I now know it was a severe case of hypoglycemia. He hadn’t eaten, and was only drinking hard liquor, which contains no carbohydrate. Maybe if he would have thrown in a beer or two, or had something to eat at some point, the situation would not have escalated the way it did. All I know is that if I hadn’t been sitting right there, it’s possible that no one would have found him for hours since everyone else in the house was asleep. Even then, things were not going great between us and we broke up shortly thereafter, but I still believe that I was meant to be with him long enough to help in that situation.
Today I learned that the greatest challenge of carbohydrate counting/insulin dose adjustment would likely be going out to dinner at an unfamiliar restaurant. You would need excellent skills of estimation, or would need to know what you were going to order before arriving at the restaurant. These days, as many people have access to the internet via their cell phone (I am not one of those people), I could see this being less of a challenge because you could probably locate the needed information very quickly. Also, if the evening was going to involve alcohol, it would be important to be aware of the carbohydrate content (or lack thereof) of the drinks you would likely consume. This would be especially relevant for people with type 1 diabetes, as it is typically diagnosed during the teen years, prior to gaining any kind of experience with alcohol. As with my ex-boyfriend, unawareness of these facts, coupled with the effect that alcohol consumption has on reasoning, situations like this can turn dangerous very easily. I will definitely keep this in mind in the future if and when I work with teenage/young adult patients with type 1 diabetes.
I also had two glasses of wine with dinner, which is really a good choice if you have diabetes. A 5 ounce glass of most types of wine (Pinot Noir was my choice) only has about 3 grams of carbohydrate, whereas a 12 ounce glass of beer has 10 grams. I won’t even get into how high some of those mixed drinks/fruity martinis could probably get.
The fact that I’m playing a person with type 1 diabetes, and the fact that I was drinking, made me think of an ex-boyfriend of mine (this was over 10 years ago) who was in that situation. I was only 19 at the time and didn’t really understand anything about his condition, except he was always saying that he had to eat (it was not optional) and of course, had to give himself shots of insulin. On his 21st birthday, he had a huge party at his house and was drinking hard liquor in excess. Early the next morning, I was sitting next to him and he starting having a seizure and passed out. It was terrifying! I screamed for his parents and we called 911. The paramedics arrived and gave him a shot (glucose?) and he woke up and was fine.
For a long time, I thought that this directly resulted from his drinking alcohol, but I now know it was a severe case of hypoglycemia. He hadn’t eaten, and was only drinking hard liquor, which contains no carbohydrate. Maybe if he would have thrown in a beer or two, or had something to eat at some point, the situation would not have escalated the way it did. All I know is that if I hadn’t been sitting right there, it’s possible that no one would have found him for hours since everyone else in the house was asleep. Even then, things were not going great between us and we broke up shortly thereafter, but I still believe that I was meant to be with him long enough to help in that situation.
Today I learned that the greatest challenge of carbohydrate counting/insulin dose adjustment would likely be going out to dinner at an unfamiliar restaurant. You would need excellent skills of estimation, or would need to know what you were going to order before arriving at the restaurant. These days, as many people have access to the internet via their cell phone (I am not one of those people), I could see this being less of a challenge because you could probably locate the needed information very quickly. Also, if the evening was going to involve alcohol, it would be important to be aware of the carbohydrate content (or lack thereof) of the drinks you would likely consume. This would be especially relevant for people with type 1 diabetes, as it is typically diagnosed during the teen years, prior to gaining any kind of experience with alcohol. As with my ex-boyfriend, unawareness of these facts, coupled with the effect that alcohol consumption has on reasoning, situations like this can turn dangerous very easily. I will definitely keep this in mind in the future if and when I work with teenage/young adult patients with type 1 diabetes.
Diabetes - Day 5
Today I played the role of a person with type 1 diabetes, who must administer the appropriate amount of insulin in order to achieve blood glucose control. I felt that the best meal plan to use for this situation was advanced carbohydrate counting. This is the most precise method for meal planning, and I knew before I even tried it that it would be my favorite.
I don’t like estimations – especially because, as previously mentioned, I noticed that many of the foods I ate did not match up to the estimations used in the exchange system. They were fairly close, but I am concerned that the little differences could add up to a lot over a whole day. If I am going to base my insulin dosage off the foods that I’m eating at each meal, I would want it to be as exact as possible. That’s probably why the carbohydrate counting method is taught to patients who are diagnosed with type 1 diabetes – at least that has been my observation so far at my hospital. We print the exact carbohydrate content of each menu item on the pediatric menu so that patients (and their parents) can use this method while they are inpatients. I also see a lot about carbohydrate counting education in the dietitian’s notes.
So, needless to say, today was my favorite day so far. I liked the freedom of eating what I wanted (within reason) for my meals, and I loved the accuracy that this method provides. I believe this would truly be the best way to manage blood glucose levels, but I understand that it might take someone awhile to arrive at a level of readiness for this – especially if they were not used to reading nutrition information. They would also have to be at the appropriate level of literacy, as well as motivation, for this to be appropriate. But for me (the self-proclaimed perfectionist) as the patient this week – I am in heaven!
I don’t like estimations – especially because, as previously mentioned, I noticed that many of the foods I ate did not match up to the estimations used in the exchange system. They were fairly close, but I am concerned that the little differences could add up to a lot over a whole day. If I am going to base my insulin dosage off the foods that I’m eating at each meal, I would want it to be as exact as possible. That’s probably why the carbohydrate counting method is taught to patients who are diagnosed with type 1 diabetes – at least that has been my observation so far at my hospital. We print the exact carbohydrate content of each menu item on the pediatric menu so that patients (and their parents) can use this method while they are inpatients. I also see a lot about carbohydrate counting education in the dietitian’s notes.
So, needless to say, today was my favorite day so far. I liked the freedom of eating what I wanted (within reason) for my meals, and I loved the accuracy that this method provides. I believe this would truly be the best way to manage blood glucose levels, but I understand that it might take someone awhile to arrive at a level of readiness for this – especially if they were not used to reading nutrition information. They would also have to be at the appropriate level of literacy, as well as motivation, for this to be appropriate. But for me (the self-proclaimed perfectionist) as the patient this week – I am in heaven!
Thursday, November 11, 2010
Diabetes - Day 4
Today, I took advantage of the “exchange” property of the exchange system and switched up my meals a little. I woke up really wanting French toast, so I had two slices of that instead of a cup of cereal. I still had the banana, and instead of milk I had yogurt. The almonds that would have gone in my cereal were switched out for Smart Balance on the toast. I used about a tablespoon on lite syrup…I don’t like much, anyway. Normally, I would have put powdered sugar on top, but I didn’t really miss it.
I like the idea of the exchange list, because it really teaches people about the carbohydrate content of foods and the fact that carbohydrate can have the same affect on blood sugar regardless of its source. Working at the hospital, I find that many patients are surprised that fruit and milk have carbohydrates. They usually think carbs are only found in bread and sweets. “Sugar free” foods are also very misleading. We have “sugar free” cake on our menu, and it still counts as two carbohydrate exchanges…the same as the “non sugar free” cake. What’s the point?
The only problem I have with the exchange system is that it is merely an estimate. This is helpful, but I found that some of the foods I consumed were actually quite off from the carbohydrate content supposed by the exchange system. For example, two slices of the bread I buy has only 22 grams of carbohydrate, rather than 30. It’s true, it is a little under an ounce per slice, and I seek out bread that does not have large amounts of added sugar in the ingredients-but the point is that most people would not scour the label for this information.
On that note, I’m really looking forward to the next 3 days when I will be using advanced carbohydrate counting for my meal planning. That means I’ll be using the actual food labels to determine the carbohydrate content of the foods I’m eating.
Wednesday, November 10, 2010
Diabetes - Day 3
Today I moved on to the exchange system for meal planning. I like this method much better, because it is more flexible and I don't feel like my plate has to look a certain way. On that note, I put everything in a BOWL this morning for breakfast. I had my favorite - oats made with skim milk, banana, and walnuts. I used the other half of the banana from the other day, which I put in the freezer (I am waaaaay to cheap to throw that away!). Well, I found out the hard way that previously frozen bananas are not so good. I sliced it up straight from the freezer and put it in the hot oatmeal to thaw it. Yuck, what a mushy mess it became. I've put "on the edge" bananas in the freezer before to use for banana bread later, but never tried eating one. Well, I won't be doing that again. I'd rather adjust my exchanges so I can put the whole thing in my cereal.
I developed a meal pattern, based on my usual intake, to use for my exchange system meal plans. I more or less followed the plan today - except I didn't put cheese on my sandwich at lunch (hadn't been to the store yet), and didn't end up having a piece of bread with dinner. It just looked like I already had way too much food on my plate.
I haven't commented on checking my blood sugar yet. I have remembered to do it three times per day, and have chosen sporadic times in order to get a wider range of values. This morning my blood sugar was 74, which is in the normal range but somewhat low compared to the rest of my values. I wonder if it was due to my using the plate method for my meals. I definitely felt like I was eating less than normal, and certainly taking in much less carbohydrate than I'm used to.
Today felt a lot more "normal" for me, as the exchange system allows you to individualize your pattern, and switch things out. For example, I could easily trade out a starch serving for a milk or a fruit, since they all have about the same carbohydrate content. The goal is to keep carbohydrate intake fairly even throughout the day, at meals and snacks. This was relatively easy since I was already doing this fairly well. The one thing I have to keep reminding myself of is that potatoes and potato chips count as a starch, not a vegetable, because their carbohydrate content is higher. I'm used to counting them as a vegetable when I plan my meals according to the MyPyramid guidelines.
I developed a meal pattern, based on my usual intake, to use for my exchange system meal plans. I more or less followed the plan today - except I didn't put cheese on my sandwich at lunch (hadn't been to the store yet), and didn't end up having a piece of bread with dinner. It just looked like I already had way too much food on my plate.
I haven't commented on checking my blood sugar yet. I have remembered to do it three times per day, and have chosen sporadic times in order to get a wider range of values. This morning my blood sugar was 74, which is in the normal range but somewhat low compared to the rest of my values. I wonder if it was due to my using the plate method for my meals. I definitely felt like I was eating less than normal, and certainly taking in much less carbohydrate than I'm used to.
Today felt a lot more "normal" for me, as the exchange system allows you to individualize your pattern, and switch things out. For example, I could easily trade out a starch serving for a milk or a fruit, since they all have about the same carbohydrate content. The goal is to keep carbohydrate intake fairly even throughout the day, at meals and snacks. This was relatively easy since I was already doing this fairly well. The one thing I have to keep reminding myself of is that potatoes and potato chips count as a starch, not a vegetable, because their carbohydrate content is higher. I'm used to counting them as a vegetable when I plan my meals according to the MyPyramid guidelines.
Tuesday, November 9, 2010
Diabetes - Day 2
I used the plate method again to plan my meals today. My morning started, as always, with my coffee and small glass of OJ before my workout which, today, was an hour long walk. I decided to try and fit my breakfast into the plate model, so I made scrambled eggs and piece of toast, with yogurt on the side. I put Smart Balance and a small amount of pumpkin butter on the toast.
Lunch was cashew curry chicken salad on a bun with leftover vegetable soup and garlic broccoli from yesterday. A perfect plate!
I raked leaves today for about 2 hours, which was incredibly exhausting! I was dying for my afternoon snack...vanilla Chai tea (no cream or milk added) with Stevia, fruit cocktail, and Wheat Thins with the last of the Gouda cheese (sob).
We ordered takeout from a Thai restaurant for dinner tonight. I would normally order the Drunken (Spicy) noodles or Pad Thai, but both are almost 100% noodles, and not very appropriate for my current meal planning method. I scoured the menu for the best choice, and decided on a vegetable stir fry with chicken, with the rice on the side so I could control how much of it I had.
For dessert, I had another bowl of sugar free chocolate pudding (no picture).
Day two, overall , was just as good as day one. The biggest challenge I encountered was choosing something suitable from the Thai takeout place. However, the optimist in me is happy because I got to try something new (and delicious!).
I'm looking forward to tomorrow because I'll be using the exchange list for meal planning. This method is a bit more precise and is much more flexible, and will allow me to more easily include the foods I typically eat (sandwiches with two slices of bread....oatmeal....oh how I've missed you).
Lunch was cashew curry chicken salad on a bun with leftover vegetable soup and garlic broccoli from yesterday. A perfect plate!
I raked leaves today for about 2 hours, which was incredibly exhausting! I was dying for my afternoon snack...vanilla Chai tea (no cream or milk added) with Stevia, fruit cocktail, and Wheat Thins with the last of the Gouda cheese (sob).
We ordered takeout from a Thai restaurant for dinner tonight. I would normally order the Drunken (Spicy) noodles or Pad Thai, but both are almost 100% noodles, and not very appropriate for my current meal planning method. I scoured the menu for the best choice, and decided on a vegetable stir fry with chicken, with the rice on the side so I could control how much of it I had.
For dessert, I had another bowl of sugar free chocolate pudding (no picture).
Day two, overall , was just as good as day one. The biggest challenge I encountered was choosing something suitable from the Thai takeout place. However, the optimist in me is happy because I got to try something new (and delicious!).
I'm looking forward to tomorrow because I'll be using the exchange list for meal planning. This method is a bit more precise and is much more flexible, and will allow me to more easily include the foods I typically eat (sandwiches with two slices of bread....oatmeal....oh how I've missed you).
Monday, November 8, 2010
Diabetes – Day 1
For the next seven days, I will play the role of a person with diabetes. That means I’ll be planning my meals, controlling my intake of carbohydrate containing foods, and checking my blood sugar. I don’t really feel too intimidated by this assignment, because I have the impression that I already control my intake in this way. I’m pretty balanced with my food choices throughout the day, and I never binge on candy or eat large portions of high carb foods in one meal. Except when we order Chicago style pizza…which I conveniently did LAST night.
Today I used the Plate Method for meal planning. This is generally considered the simplest form of meal planning for people with diabetes, or people who just want to control their intake and lose weight. So far, my impression of this method is that it is overly simple and does not really fit in with my personal eating plan. For example, I always have cereal for breakfast and a sandwich for lunch. I also eat mixed dishes for dinner fairly often. Under the plate method, you are supposed to divide your plate into three sections: ¼ for meat, ¼ for grains or starchy vegetables, and the rest for non-starchy vegetables. Milk and fruit go on the sides, and are optional at meals. It is recommended that these foods are used for snacks. At any rate, snacks and desserts should be kept at very small portions.
Here’s what my plates looked like today:
Morning/pre-workout snack (not pictured): I always have a cup of coffee with fat free half and half, sweetened with Equal or Stevia, and ½ cup of orange juice in the morning before I work out. I usually work out for about an hour, and this keeps me going all the way until I eat breakfast.
Breakfast: small bowl of bran flakes cereal with skim milk and 1/2 banana, and a fried egg
Lunch: 1/2 turkey sandwich with Gouda cheese (yum!), a small bowl of Campbells Light Southwest vegetable soup, and fat free/no sugar added yogurt.
Afternoon snack: about ½ cup of fruit cocktail in lite syrup, and 6 Wheat Thins with peanut butter
Dinner: Extra lean beef hamburger with Gouda (yum again!), a small hamburger bun, and roasted garlic broccoli. I did have a few roasted potato wedges and about a tablespoon of ketchup. Hey, you’ve gotta have it!
Evening snack/dessert: bowl of sugar free/fat free chocolate pudding.
My overall reflection of day 1: this isn’t really that difficult. All of the foods I ate are normal for me. I often use artificially sweetened products like the yogurt and pudding. I normally would have had a whole sandwich for lunch, but this method of meal planning made me feel like I could only have one slice of bread since it fits on that part of the plate. I also would have had a lot more potatoes with my burger, but probably the same amount of broccoli.I remembered to check my blood sugar three times. Today I checked it when I got up, after my workout, and 2 hours after I ate lunch.
Today I used the Plate Method for meal planning. This is generally considered the simplest form of meal planning for people with diabetes, or people who just want to control their intake and lose weight. So far, my impression of this method is that it is overly simple and does not really fit in with my personal eating plan. For example, I always have cereal for breakfast and a sandwich for lunch. I also eat mixed dishes for dinner fairly often. Under the plate method, you are supposed to divide your plate into three sections: ¼ for meat, ¼ for grains or starchy vegetables, and the rest for non-starchy vegetables. Milk and fruit go on the sides, and are optional at meals. It is recommended that these foods are used for snacks. At any rate, snacks and desserts should be kept at very small portions.
Here’s what my plates looked like today:
Morning/pre-workout snack (not pictured): I always have a cup of coffee with fat free half and half, sweetened with Equal or Stevia, and ½ cup of orange juice in the morning before I work out. I usually work out for about an hour, and this keeps me going all the way until I eat breakfast.
Breakfast: small bowl of bran flakes cereal with skim milk and 1/2 banana, and a fried egg
Lunch: 1/2 turkey sandwich with Gouda cheese (yum!), a small bowl of Campbells Light Southwest vegetable soup, and fat free/no sugar added yogurt.
Afternoon snack: about ½ cup of fruit cocktail in lite syrup, and 6 Wheat Thins with peanut butter
Dinner: Extra lean beef hamburger with Gouda (yum again!), a small hamburger bun, and roasted garlic broccoli. I did have a few roasted potato wedges and about a tablespoon of ketchup. Hey, you’ve gotta have it!
Evening snack/dessert: bowl of sugar free/fat free chocolate pudding.
My overall reflection of day 1: this isn’t really that difficult. All of the foods I ate are normal for me. I often use artificially sweetened products like the yogurt and pudding. I normally would have had a whole sandwich for lunch, but this method of meal planning made me feel like I could only have one slice of bread since it fits on that part of the plate. I also would have had a lot more potatoes with my burger, but probably the same amount of broccoli.I remembered to check my blood sugar three times. Today I checked it when I got up, after my workout, and 2 hours after I ate lunch.
Thursday, November 4, 2010
Fatty Acid Synthesis: How fat is made
Fat is made and stored in the body any time that excess calories are taken in. It does not matter if these calories come from fat, carbohydrate, or protein. Actually, the major source of the carbon used to make fat is from carbohydrate. In general, both glucose and amino acids can be changed to Acetyl CoA, which is made into fatty acids, which is made into triglycerides, which is packaged into VLDL and circulates in the blood. Fatty acids may also be made into glycerophospholipids, which have a glycerol backbone, 2 fatty acids, and a head group.
Fatty acids are made in the liver. This is stimulated by the hormone insulin that is released after a meal. The creation of fatty acids is basically the reverse of oxidation, or the breakdown of fatty acids for energy in that, instead of breaking off two carbon units at a time, it adds them on until the long chain fatty acid palmitate is formed. However, fatty acid synthesis occurs through a different pathway with different enzymes involved. Also, fatty acids are synthesized in the cytoplasm - while oxidation occurs in the mitochondria.
In order for fatty acids to be made, acetyl CoA is needed in the cytoplasm. However, acetyl CoA cannot cross the mitochondrial membrane to get there. Acetyl CoA exists in the mitochondria because it is synthesized from pyruvate from glycolysis, using the enzyme pyruvate dehydrogenase. Normally it would enter the Krebs cycle to make energy, but when excessive carbohydrate is taken in, there is excess CoA. At that point, a special reaction takes place so that the CoA can enter the cytoplasm and make fatty acids.
With a carboxylation reaction requiring the enzyme pyruvate carboxylase and the water soluble vitamin biotin, oxaloacetate (OAA) is formed from pyruvate. This combines with acetyl CoA through a condensation reaction, forming citrate. Citrate can cross through to the cytosol, and once there it breaks back into Acetyl CoA and OAA. The acetyl CoA can now be used for fatty acid synthesis, and the OAA is changed back to pyruvate and starts the conversion process over again. This happens by first changing OAA to malate through a dehydrogenase reaction, which requires NADH. Then, malic enzyme removes one carbon and releases CO2 and NADPH, changing the malate (a 4 carbon molecule) to pyruvate (a 3 carbon molecule). The NADPH produced is then used in fatty acid synthesis. This is important, because fatty acid synthesis requires a lot of NADPH. This reaction, along with the pentose phosphate pathway, are the major sources of NADPH for fatty acid synthesis.
Acetyl CoA is converted to malonyl CoA by adding CO2 in a carboxylation reaction that requires both biotin and ATP. Malonyl CoA is the intermediate used in the fatty acid synthase complex, so at this point we are ready to make some fatty acids!
Fatty acid synthase is a large enzyme system that consists of a pantothenyl sulfhydral (P-SH) group and a cysteinal sulfhydral (C-SH) group. Acetyl CoA attaches to the P-SH group, then to the C-SH group. Malonyl CoA attaches to the P-SH group. Condensation occurs, releasing CO2 from the malonyl part. Next, a series of 4 more reactions occur which results in the addition of 2 carbons.
1. Two hydrogen are added from NADPH at the 2nd carbonyl carbon
2. Water is removed, making a double bond
3. NADPH gives more hydrogen to make the bond saturated.
4. SH is flipped to make the pantothenyl group open.
At this point, a 2 carbon unit has been added, and malonyl CoA can attach again and start the cycle over until palmitate has been made.
At this point, triglycerides may be made, or the fatty acids may be elongated or desaturated. Highly unsaturated fatty acids and a class called eicosanoids are needed for important processes in the body, including usage by the brain. However, the human body cannot desaturate an 18:1 fatty acid to 18:2 (linoleic acid) or 18:3 (linolenic acid). That's why we call these two fatty acids essential - we must obtain them from the diet.
Triglycerides are synthesized from fatty acids in the liver and adipose tissue. The process requires glycerol 3-phosphate, which is made in different ways in both tissues. The liver contains the enzyme glycerol kinase, which can change glycerol to glycerol 3-P by using ATP. The liver can also reduce the dihydroxyacetone phosphate (DHAP) from glycolysis using NADH. The adipose tissue can only do the latter, because it does not contain glycerol kinase. Either way, 2 fatty acyl CoA's are added to the glycerol 3-P to form phosphatidic acid. The phosphate group comes off, making it into a diacylglycerol. Last, another fatty acid group comes in to form a triglyceride.
The triglycerides in the liver are packaged together with cholesterol, cholesterol esters, phospholipids, and proteins (mainly ApoB-100) to form a VLDL. VLDL is composed mostly of triglyceride. Upon entering the blood the VLDL is a nascent, or new/young VLDL. As it circulates, it acquires Apo C2 and Apo E proteins from HDL, making it a mature VLDL particle. Apo C2 activates lipoprotein lipase (LPL) located at adipose and muscle cells. LPL digests the VLDL, causing triglycerides to come off. Since muscle cells need fatty acids for energy, its LPL activity is high even when the level of VLDL and chylomicrons in the blood are low. However, adipose tissue's major function is to store fatty acids. Therefore, it only uses its LPL when VLDL levels are very high, or following a meal. A meal rich in carbohydrates (namely simple sugars) results in a large amount of triglyceride being produced, leading to overproduction of VLDL. This condition is known as transient hypertriglyceridemia. As TG is broken down by the LPL in the adipose tissue, fatty acids go to storage and glycerol returns to the liver. This is how excess sugar in the diet is stored as fat and results in weight gain.
Eventually the VLDL becomes and IDL, then LDL as more of it its triglyceride content is digested.
In the fasted state, level of insulin goes down and the level of glucagon goes up. This stimulates the release of triglycerides from adipose lipase. The triglycerides are digested to fatty acids and glycerol and go to the liver. Fatty acids go through oxidation for energy, or are used to make ketones. Glycerol can be used in gluconeogenesis, or the making of glucose from non carbohydrate sources, and used for energy.
Fatty acids are made in the liver. This is stimulated by the hormone insulin that is released after a meal. The creation of fatty acids is basically the reverse of oxidation, or the breakdown of fatty acids for energy in that, instead of breaking off two carbon units at a time, it adds them on until the long chain fatty acid palmitate is formed. However, fatty acid synthesis occurs through a different pathway with different enzymes involved. Also, fatty acids are synthesized in the cytoplasm - while oxidation occurs in the mitochondria.
In order for fatty acids to be made, acetyl CoA is needed in the cytoplasm. However, acetyl CoA cannot cross the mitochondrial membrane to get there. Acetyl CoA exists in the mitochondria because it is synthesized from pyruvate from glycolysis, using the enzyme pyruvate dehydrogenase. Normally it would enter the Krebs cycle to make energy, but when excessive carbohydrate is taken in, there is excess CoA. At that point, a special reaction takes place so that the CoA can enter the cytoplasm and make fatty acids.
With a carboxylation reaction requiring the enzyme pyruvate carboxylase and the water soluble vitamin biotin, oxaloacetate (OAA) is formed from pyruvate. This combines with acetyl CoA through a condensation reaction, forming citrate. Citrate can cross through to the cytosol, and once there it breaks back into Acetyl CoA and OAA. The acetyl CoA can now be used for fatty acid synthesis, and the OAA is changed back to pyruvate and starts the conversion process over again. This happens by first changing OAA to malate through a dehydrogenase reaction, which requires NADH. Then, malic enzyme removes one carbon and releases CO2 and NADPH, changing the malate (a 4 carbon molecule) to pyruvate (a 3 carbon molecule). The NADPH produced is then used in fatty acid synthesis. This is important, because fatty acid synthesis requires a lot of NADPH. This reaction, along with the pentose phosphate pathway, are the major sources of NADPH for fatty acid synthesis.
Acetyl CoA is converted to malonyl CoA by adding CO2 in a carboxylation reaction that requires both biotin and ATP. Malonyl CoA is the intermediate used in the fatty acid synthase complex, so at this point we are ready to make some fatty acids!
Fatty acid synthase is a large enzyme system that consists of a pantothenyl sulfhydral (P-SH) group and a cysteinal sulfhydral (C-SH) group. Acetyl CoA attaches to the P-SH group, then to the C-SH group. Malonyl CoA attaches to the P-SH group. Condensation occurs, releasing CO2 from the malonyl part. Next, a series of 4 more reactions occur which results in the addition of 2 carbons.
1. Two hydrogen are added from NADPH at the 2nd carbonyl carbon
2. Water is removed, making a double bond
3. NADPH gives more hydrogen to make the bond saturated.
4. SH is flipped to make the pantothenyl group open.
At this point, a 2 carbon unit has been added, and malonyl CoA can attach again and start the cycle over until palmitate has been made.
At this point, triglycerides may be made, or the fatty acids may be elongated or desaturated. Highly unsaturated fatty acids and a class called eicosanoids are needed for important processes in the body, including usage by the brain. However, the human body cannot desaturate an 18:1 fatty acid to 18:2 (linoleic acid) or 18:3 (linolenic acid). That's why we call these two fatty acids essential - we must obtain them from the diet.
Triglycerides are synthesized from fatty acids in the liver and adipose tissue. The process requires glycerol 3-phosphate, which is made in different ways in both tissues. The liver contains the enzyme glycerol kinase, which can change glycerol to glycerol 3-P by using ATP. The liver can also reduce the dihydroxyacetone phosphate (DHAP) from glycolysis using NADH. The adipose tissue can only do the latter, because it does not contain glycerol kinase. Either way, 2 fatty acyl CoA's are added to the glycerol 3-P to form phosphatidic acid. The phosphate group comes off, making it into a diacylglycerol. Last, another fatty acid group comes in to form a triglyceride.
The triglycerides in the liver are packaged together with cholesterol, cholesterol esters, phospholipids, and proteins (mainly ApoB-100) to form a VLDL. VLDL is composed mostly of triglyceride. Upon entering the blood the VLDL is a nascent, or new/young VLDL. As it circulates, it acquires Apo C2 and Apo E proteins from HDL, making it a mature VLDL particle. Apo C2 activates lipoprotein lipase (LPL) located at adipose and muscle cells. LPL digests the VLDL, causing triglycerides to come off. Since muscle cells need fatty acids for energy, its LPL activity is high even when the level of VLDL and chylomicrons in the blood are low. However, adipose tissue's major function is to store fatty acids. Therefore, it only uses its LPL when VLDL levels are very high, or following a meal. A meal rich in carbohydrates (namely simple sugars) results in a large amount of triglyceride being produced, leading to overproduction of VLDL. This condition is known as transient hypertriglyceridemia. As TG is broken down by the LPL in the adipose tissue, fatty acids go to storage and glycerol returns to the liver. This is how excess sugar in the diet is stored as fat and results in weight gain.
Eventually the VLDL becomes and IDL, then LDL as more of it its triglyceride content is digested.
In the fasted state, level of insulin goes down and the level of glucagon goes up. This stimulates the release of triglycerides from adipose lipase. The triglycerides are digested to fatty acids and glycerol and go to the liver. Fatty acids go through oxidation for energy, or are used to make ketones. Glycerol can be used in gluconeogenesis, or the making of glucose from non carbohydrate sources, and used for energy.
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