From: Lyle McDonald Newsgroups: misc.fitness Subject: Carbohydrate.info.part1 Date: Mon, 25 Apr 94 20:02:50 -0500 Well, at long last, here's the sports nutrition primer that I've been promising for four months. I had originally planned to start with protein but cannot find some of the references that I need. So, first I'l like to talk a little about carbohydrates: what they are, how they are digested, what they do in the body, athlete's requirements, etc. What they are: As the name suggests, carbohydrates are carbon chains with hydrogen and hydroxyl (OH) groups attached. They tend to occur in 6 carbon chains which have a tendency to form into rings. Single chain carbs are called monosaccharides or simple sugars. This includes glucose (blood sugar), fructose (fruit sugar) and galactose. When monosaccharides join, they form disaccharides. Examples are sucrose (which is a glucose joined to a fructose), lactose (glucose + galactose), and maltose (glucose + glucose). Multiple unit chains of monosaccharides form polysaccharides or starches, also referred to as complex carbohydrates. How it is digested: Digestion of carbs start in the mouth during chewing due to the action of ptalin or salivary amylase where polysaccharides (chains of multiple monosaccharides) are broken down. In the small intestine, pancreatic amylase continues the breakdown of starches. Then specialized enzymes (maltase breaks down maltose, lactase breakse down lactose, etc) continue the breakdown into monosaccharides (glucose, fructose, and galactose). FYI, you may have heard of a condition called lactose intolerance. This disease afflicts many people and is the inability to digest lactose. It is cause by a decrease in the enzyme lactase and can be treated with lactase supplements (Lact-Aid and Dairy Ease are two) which are taken with dairy products. Symptoms of lactose intolerance include gas, diarrhea, and indigestion when dairy foods are eaten. Some people find yogurt easier to digest than milk or cheese presumably due to the presence of active yogurt cultures which aid in digestion. The fate of broken down sugars varies. Glucose and galactose are generally stored as glycogen (strings of glucose) in the blood and muscle. Fructose is further digested in the liver and can be converted into glucose, lactic acid, or triglyceride (a type of fat). If large amounts of glucose reach the bloodstream, some may be stored as fat. However, conversion of carbo to fat is only about 70% efficient meaning that, of 100 extra calories taken in as carbs, only about 70 will actually be stored with the other thirty being used up to fuel the conversion process. Another factor which may affect carbs being stored as fat is the glycemic index (which I'll cover in a little bit). When carbs are eaten, insulin is released, the amount of insuling depending on a number of factors. Insulin moves carbs (and amino acids) into muscle cells and also into fat cells. Some have suggested that it is extremely high insulin levels which promote fat storage but I'm getting ahead of myself. Lyle References: 1. "Contemporary Nutrition: Issues and Insights" 1992 by Mosby-Year Books, Inc. From: Lyle McDonald Subject: Carbohydrate.info.part2 Date: Mon, 25 Apr 94 20:04:24 -0500 This time I want to talk about the uses of carbohydrate in the body. Carbohydrate's main use in the body is for energy needs. Whether it is to fuel immediate energy requirements (during exercise) or to be stored for future use (as glycogen in the muscle) it's main purpose is to provide energy. However, it pales in comparison to fat as an storage depot for energy. A sedentary person can store about 1700 calories as glycogen (with 400 of that in the liver) while fat stores may total up to 35000 (more than 10 marathon's worth) calories (assuming 10lbs of fat). An athlete may be able to store as many as 4000 calories as carbohydrate due to training adaptations, but this is still limited compared to the 10000-30000 calories stored as fat. In any case, glycogen is limited and ,if carbohydrate is not supplied regularly, stores become rapidly depleted. Ideally, during exercise, only fat would be used as it is essentially limitless. Unfortunately, this is not chemically possible as some carbohydrate must be available for fat to be oxidized. Another use of carbohydrate (and one which is related to energy needs) is to spare protein. When I talk about protein and nitrogen balance, this will make a little more sense. For now, let me say that inadequate carbohydrate intake will raise protein requirements. Another form of carbohydrate (which I didn't mention in part 1) is fiber. There are two types of fiber (soluble and insoluble). Fiber serves many purposes in the body including softening the stool and decreasing blood cholesterol levels (I'll go into more detail in the section on fats). Another function of fiber is to slow gastric emptying and digestion. This serves to slow the release of carbohydrate into the bloodstream and helps to keep insulin levels steadier. Recommendations are 25-30 grams per day. Average intake is around 10-15 grams per day. Ok, well what about carbohydrate recommendations for athletes and other folks. With all the recent fervor over heart disease, the trend has been to increase carbohydrate intake in this country in lieu of fat. General recommendations are for 65-75% of total calories to come from carbohydrates with no more than 10% in the form of simple sugars. Actual American intake hovers around 45% of total calories. There is no RDA for carbohydrates. From: Lyle McDonald Subject: Carbohydrate.info.part3 Date: Mon, 25 Apr 94 20:06:33 -0500 Well, before I talk about specifics about carb intake, let me talk a little about insulin. Insulin is a hormone which is released from the pancreas after carbohydrate is digested. Insulin has a couple of functions. One is to drive glucose into the muscle cells by increasing glucose transport. Another is to drive glucose and fat into fat cells by stimulating an enzyme called lipoprotein lipase (LPL). Thus, insulin is a double edged sword when it comes to athletic performance. Without it, glucose cannot reach the muscle cells where it is needed, but an excess will contribute to fat storage. Well, depending on certain factors (which I'll cover in the next post), you may or may not want a high insulin level. The amount of insulin released is basically a factor of how quickly glucose is released into the bloodstream. Rapid release will result in a large insulin response. Sometimes, too much insulin is released leading to low blood sugar as too much of the ingested carbohydrate is shunted into the muscle/fat cells which results in hunger and impaired performance. The general thinking was always that complex carbohydrates (rice, potatoes, etc) released less insulin than simple carbohydrates (fruit, etc). However, in the last 10-15 years, this idea has been challenged by the introduction of something called the glycemic index (GI). The GI was developed for diabetics who need to keep a lid on their insulin release as their bodies are not capable of dealing with the excess (or any) insulin. Basically, the GI is a measure of how much insulin is released by a given food. Glucose is defined as 100 and all values are relative to it. Unfortunately, only a handful of foods have even been tested as it is quite expensive to do. Also, there is a lot of individual variability so treat these numbers as guidelines only. Please note that these values only apply if the food in question is eaten by itself. As soon as you combine foods off of this list, the value changes. And, if the food in question is eaten with fat, protein or fiber, the GI drops as digestion, and hence, gastric emptying is slowed lessening the insulin response. Oh, yeah, number closer to 100 release more insulin than numbers farther from it. Sugars Grains/cereals Legumes glucose 100 white bread 69 beans fructose 20 wheat bread 72 soy 15 maltose 105 brown rice 66 baked 40 sucrose 59 white rice 72 butter 36 spaghetti kidney 29 Vegetables white 50 chick peas 36 beets 64 wheat 42 peas (frzn) 51 carrots 92 corn 59 lentils 29 potatoes cornflakes 80 instant 80 oatmeal 49 yams 51 shredded wheat 67 Fruits Dairy products MIsc. apples 39 ice cream 36 honey 87 bananas 62 milk, skim 32 Mars bar 68 oranges 40 whole 34 peanuts 13 potato chips 51 You may notice that fructose (fruit sugar) has a very low GI. This has prompted some to suggest it as the optimal form of carbo for exercise. This is not the case as too much fructose in one's diet can cause diarrhea and elevate blood triglycerides. Next time, I will talk about the consequences of the GI for both athletes and sedentary people. References: 1. Glycemic Index reprinted from Science Digest" January 1984. From: Lyle McDonald Subject: Carbohydrate.info.part4 Date: Mon, 25 Apr 94 20:08:59 -0500 Last time, I introduced somthing called the Glycemic Index (GI) which is a measure of how much insulin is released by a given carbohydrate food (relative to glucose). Now, I want to talk about the consequences of the GI at different times during the day. Sedentary person: Let's say you eat a carbohydrate meal during the day. If you eat a high GI food, you will get a high insulin response and, since glycogen levels are high, glucose will be stored equally to skeletal muscle and adipose (fat) tissue equally. So, you should try to stick with low GI foods for most of your meals. Before exercise: For a long time, it was thought that taking in carbs before exercise might be detrimental as it would cause an insulin burst and ultimately lower blood glucose levels. This was found in several studies. However, if carbs are taken in at least an hour before exercise, insulin levels have a chance to return to normal and exercise performance is not impaired. (1) Also, low GI foods (beans, etc) make an excellent pre-exercise carb source as they don't realease much insulin anyway. During exercise: At this time, the situation changes and some interesting things are going on hormonally. The body releases epinephrine and nor-epinephrine which increase heart rate in addition to other things and also inhibits insulin release. This causes insulin levels to drop increasing the mobilization of free fatty acids from adipose tissue. Since glycogen is being used up, there occurs an increase in glucose transport to the muscle which is insulin independent. Thus, it is best to drink a high GI fluid (preferably glucose or glucose polymer) as it will empty from the stomach quickly and reach the muscles faster than a low GI carbohydrate would. This applies for any exercise session lasting 1.5-2 hours. If you are exercising more than two hours, something else is going on. In addition to depletion of muscle glycogen, liver glycogen is also being used up. Thus, it is best to combine glucose (or polymer) with fructose (which preferentially increases liver glycogen) and drink it constantly during exercise. But, how much carbohydrate should be used during exercise. The composition of drinks during exercise has been the study of much research and advertising. The first drink on the market was Gatorade and it has been joined by dozens of others (Cytomax, Endura, and Hydra Fuel to name a few). Without going into too many details regarding the research that has been done which deals with not only concentration, type of carbohydrate, absorption, gastric emptying and a lot of other stuff, I'll cut to the chase and make recommendations. The first problem during exercise that must be dealt with is fluid replacement. Without adequate fluids, dehydration sets in rapidly and fluid loss can be 1 liter/ hour during intense exercise. So, adequate fluid intake is crucial to athletic performance. At a dehydration level of 1%, performance suffers by 3%. At a dehydration level of 5% or more, death can result. The second is maintaining carbohydrate levels during exercise. Well, unfortunately, the addition of carbohydrate to water tends to retard gastric emptying of the water and thus impairs fluid replacement. A good guideline is to take in 100-200 calories of carbs (25-50 grams) every half hour split into 2 8oz feedings. Basically, this works out to a 5-8% concentration of carbohydrate which has been found to maximize gastric emptying while still maintaining blood glucose levels. Up to 2-3% of this may be fructose. Higer fructose concnetrations may cause gastro-intstinal upset (i.e. diarrhea) and should be avoided. Most commercial drinks fall somewhere into this concentration range. (2) Also, many drinks add electrolytes (sodium and potassium) to their drinks. This has been found to increase glucose and water uptake and also increases the palatibility of the drinks making it more likely that the athlete will drink the mfrequently. As to which drink is the best, that's a touch call. Most have some reason to claim being the best. Cytomax has alpha-poly-lactate which is supposed to buffer lactic acid. Endura has extra magnesium as they claim endurance athletes are chronically depleted. Basically, pick one that you like the taste of. No matter how good one of these drinks is, they are useless if you don't like the taste and don't drink it. To digress slightly, protein is not needed during exercise unless it is extremely intense and of long duration (i.e. Tour De France, Race Across America, etc). References: 1. Andrew Shields Ed. "The Health for Life Training Advisor" Health For Life 1990. 2. Jacqueline Berning "Sports Nutrition for the 90's" Aspen Pubications 1991. From: Lyle McDonald Subject: Carbohydrate.info.part6 Date: Mon, 25 Apr 94 20:12:30 -0500 Ok, to wrap up carbohydrates, let me talk a little about how much carbohydrate athletes need. For endurance athletes, it's a little more clear cut than for weight training in terms of how much one needs. However, when I talk about fats, we'll see that the old ideas regarding carb intake may not necessarily be correct. The general thinking is that carbs should make up anywhere from 65-75% of the diet of an endurance athlete. Since may calories are expended during training, sufficient carbs must be ingested to maintain muscle glycogen so that training can continue. One study found that people ingesting 40% calories from carbohydrates slowly depleted their muscle glycogen to the point that they could not exercise. By contrast, a group eating 70% carbs was able to maintain muscle glycogen levels even with daily training. What about for strength athletes? Well, here the waters muddy a bit and, quite honestly, I haven't seen a lot of research. One theory has it that, as with endurance athletes, the majority of calories should be in the form of carbs. Other sources suggest that only enough carbs should be taken in to prevent ketosis (buildup of incompletely burned fatty acids) with the remainder of calories coming from protein. Ultimately, the amount of carbs necessary to maintain athletic performance will vary with the athlete and the type and amount of training. The 65-75% of calories should provide a good guideline. As a brief teaser, let me mention that there is some more recent research that indicates that less carbs and more fat may be more conducive to athletic performance and bodyfat loss but you'll have to wait a little for me to get to that. From: Lyle McDonald Newsgroups: misc.fitness Subject: Carbohydrate.info.part5 Date: Mon, 25 Apr 94 20:11:21 -0500 Continuing from last time, I would like to talk about carbo intake immediately after exercise. At this point, assuming you have worked out a sufficient amount, muscle glycogen is depleted immediately after workout, even if you took in carbs during exercise. This has a couple of consequences. First, and foremost, glucose transport is high due to low levels of muscle glycogen. Also, glycogen synthase (the enzyme responsible for turning glucose into glycogen) activity is high. Now, two things can happen. 1. If you don't take in any carbs after your workout, the body will take protein (muscle) and lactate and go through a process called gluconeogenesis (literally the making of new glucose) and convert it into glucose. This is bad as it has the potential to break down muscle tissue. 2. You can take in carbs, satisfying your muscle's needs and avoid muscle breakdown. This is the better choice. But, what kind of carbs are best for glycogen repletion? My professor suggested that low glycemic index carbs be used so that an insulin response would be avoided which would impair muscular glycogen repletion. However, glycogen synthase activity only stays elevated for 2 hours after exercise so low GI carbs may be too slow in digesting to be of any use. Michael Colgan suggests glucose polymers with a little pure glucose so that insulin will be stimulated to increase glucose transport into the cell. He contends that the high insulin response won't push glucose into the fat cells since the muscles will take it up too quickly (1). One study found that simple carbohydrates (high GI) were better than complex, fiber-rich carbs (low GI) for glycogen repletion after six hours but that no difference was found after 20 hours for muscle glycogen (2). Another study found that combining 112 grams of carbs with 40.7 grams of protein maximized muscle glycogen due to a higher insulin response when compared to either the carbs or protein taken separately (3). And, finally, a recent muscle magazine suggested taking in simple carbs while doing low intensity exercise so that insulin independent glucose transport could occur withoutfear of insulin response (4). To me, this last suggestion makes the most sense. With it, you neither risk an insulin response (which may or may not drive some glucose into fat cells) and get good quick glucose uptake and synthesis by the muscles. The key is to make the exercise intensity low enough that you aren't depleting more carbohydrate than you are ingesting. The magazine suggests 10 minutes of easy exercise during which time 75-100 grams of simple carbs (like fruit juice) are sipped. In actuality, a study was done that backs this up indirectly (5). The study was looking at carbs immediately prior to exercise (which as stated has been found to cause an insulin response and reactive hypoglycemia or low blood sugar) to see if mild exercise would blunt the insulin response. A warm up done consisting of 5 minutes easy spinning, and 20 minutes of slightly harder riding with 10 sec intervals thrown in. During this time, a variety of carb drinks were ingested at either 300 or 600 ml. At the onset of exercise, increased blood glucose levels were found with only a slight increase in insulin levels after a seven minute break. So, carbs taken during light exercise have the capacity to increase blood glucose (and presumably muscle glycogen when it is depleted) without an insulin response. The magazine suggests 10 minutes of easy exercise. Every supplement company makes some type of post-workout carb drink. Personally, I've used Twinlab Ultra Fuel and Gatorlode. Gatorlode is good because it's cheap but it doesn't have a lot of the bells and whistles like chromium (which may help) or even fructose as it is mainly glucose polymer. Another option is plain fruit juice although you have to drink quite a bit to get a lot of carbs (figure 3-4 cups to get 60-90 grams of carbs). Also, it may not be a bad idea to use a drink containing some fructose (or add some yourself) to help replenish liver glycogen which can be very depleted following exercise. When I talk about protein, I'll complete this explanation and talk a little more about protein after exercise. Next time, carbohydrate needs for athletes. Lyle References: 1. Colgan, M. "Optimal Sports Nutrition" 2. Kiens, B. et al. "Benefit of Dietary Simple Carbohydrates on the Early Postexercise Muscle Glycogen Repletion in Male Athletes" Med Sci Sports Exercise (Abstract) 3. Zawadzki, K. et al. "Carbohydrate-protein complex increases the rate f muscle glycogen storage after exercise" J. Appl. Physiol. 72(5): 1854- 1859. 4. Ron J. Clark "Insulin Management accelerates Muscle growth in drug-free bodybuilders" Muscle Media 2000. Dec-Jan 1994. 5. Brouns F. et al. "Effect of carbohydrate intake during warming-up on the regulation of blood glucose during exercise" Int. J. Sports Med. 10: S68-S75, 1989.