weight loss

Evolution. The muscles in the lower body, mostly "dark meat," have evolved in such a way that the body powers them by burning fat. Body fat provides an almost limitless source of energy, allowing the muscles to be used for long periods of time, while walking long distances. Lower body exercise like walking, running or biking taps into these muscles' ability to burn fat. The muscles in the upper body are mostly "white meat" and have evolved to be powered by burning glycogen stored in the muscles themselves. These muscles evolved for quick bursts of activity, such as throwing, grasping, tearing or lifting, instead of sustained activity. Since it takes more time to get energy out of stored fat, the glycogen serves as a quick start system. The white muscles will burn fat, but the body resists letting them do it until their glycogen reserves are depleted. Likewise, the dark muscles will burn glycogen for quick bursts of speed, but are optimized to burn fat. The two types of muscle correspond roughly to aerobic and anaerobic exercise, swimming having a large anaerobic component provided by the resistance of the water. Since more muscle mass can store more glycogen, working muscles anaerobically will cause the body to react by building muscle. Exercise that is more aerobic will build less muscle, since the the muscle mass isn't necessary to store glycogen to power the muscles that way. To put that all into the context of your question, when you run, you are not building very much muscle, but you are burning fat. You're losing fat weight without building muscle weight. When you swim, even though you lose fat, you will not lose it as efficiently as when running because the muscles in use don't draw on the fat reserves as readily. Meanwhile, you're also building muscle when you swim, which offsets the weight you lose from fat. You also mentioned the hunger that comes from swimming. That's a direct result of glycogen depletion. When you burn the glycogen out of your muscles, your body will want to replenish it as quickly as possible in order to be ready for the next burst of activity. When you burn fat through lower body exercise, the body tends to keep running on the fat reserves for a while once the process has gone into high gear, and it thinks that it doesn't need any additional fuel. Thus hunger is suppressed. For many swimmers trying to lose weight, the loss of glycogen causes a craving for carbohydrates. Carbs are the quickest way to replenish the glycogen in the muscles. The problem is that eating carbs without a balancing portion of protein causes them to hit the blood system as sugar more quickly than the muscles can absorb them, and the blood sugar level spikes. To counter that spike, the body releases insulin. Insulin triggers the formation of fat; it causes the sugar to be taken out of the bloodstream and stored for future use in the fat cells. Tell me if this sounds familiar: You get out of the pool starving. You eat something starchy to satisfy your hunger. But half an hour later you desperately want a nap, and if you don't get it your brain goes into a fog. That's caused by an insulin spike. Your body wants glycogen, so you give it carbs. Insulin is released to get rid of the excess. It works too well, so your blood sugar goes a little low. When your blood sugar goes low, your body responds by trying to shut down for a while to recover. You can avoid that by eating some protein with your carbs. The protein is more difficult to digest, and when it is mixed with the carbs in the digestive system it prevents them from being absorbed as rapidly. Thus, the body can keep up with the sugar entering the system without releasing an insulin spike, thus avoiding issuing a command to the body to store fat. Finally, that business about running keeping you from being hungry because it jostles your internal organs is a wives' tale. You can pound on someone's abdomen with a billy club, but if his muscles are depleted of glycogen he'll still be hungry.

Evolution. The muscles in the lower body, mostly "dark meat," have evolved in such a way that the body powers them by burning fat. Body fat provides an almost limitless source of energy, allowing the muscles to be used for long periods of time, while walking long distances. Lower body exercise like walking, running or biking taps into these muscles' ability to burn fat. The muscles in the upper body are mostly "white meat" and have evolved to be powered by burning glycogen stored in the muscles themselves. These muscles evolved for quick bursts of activity, such as throwing, grasping, tearing or lifting, instead of sustained activity. Since it takes more time to get energy out of stored fat, the glycogen serves as a quick start system. The white muscles will burn fat, but the body resists letting them do it until their glycogen reserves are depleted. Likewise, the dark muscles will burn glycogen for quick bursts of speed, but are optimized to burn fat. The two types of muscle correspond roughly to aerobic and anaerobic exercise, swimming having a large anaerobic component provided by the resistance of the water. Since more muscle mass can store more glycogen, working muscles anaerobically will cause the body to react by building muscle. Exercise that is more aerobic will build less muscle, since the the muscle mass isn't necessary to store glycogen to power the muscles that way. To put that all into the context of your question, when you run, you are not building very much muscle, but you are burning fat. You're losing fat weight without building muscle weight. When you swim, even though you lose fat, you will not lose it as efficiently as when running because the muscles in use don't draw on the fat reserves as readily. Meanwhile, you're also building muscle when you swim, which offsets the weight you lose from fat. You also mentioned the hunger that comes from swimming. That's a direct result of glycogen depletion. When you burn the glycogen out of your muscles, your body will want to replenish it as quickly as possible in order to be ready for the next burst of activity. When you burn fat through lower body exercise, the body tends to keep running on the fat reserves for a while once the process has gone into high gear, and it thinks that it doesn't need any additional fuel. Thus hunger is suppressed. For many swimmers trying to lose weight, the loss of glycogen causes a craving for carbohydrates. Carbs are the quickest way to replenish the glycogen in the muscles. The problem is that eating carbs without a balancing portion of protein causes them to hit the blood system as sugar more quickly than the muscles can absorb them, and the blood sugar level spikes. To counter that spike, the body releases insulin. Insulin triggers the formation of fat; it causes the sugar to be taken out of the bloodstream and stored for future use in the fat cells. Tell me if this sounds familiar: You get out of the pool starving. You eat something starchy to satisfy your hunger. But half an hour later you desperately want a nap, and if you don't get it your brain goes into a fog. That's caused by an insulin spike. Your body wants glycogen, so you give it carbs. Insulin is released to get rid of the excess. It works too well, so your blood sugar goes a little low. When your blood sugar goes low, your body responds by trying to shut down for a while to recover. You can avoid that by eating some protein with your carbs. The protein is more difficult to digest, and when it is mixed with the carbs in the digestive system it prevents them from being absorbed as rapidly. Thus, the body can keep up with the sugar entering the system without releasing an insulin spike, thus avoiding issuing a command to the body to store fat. Finally, that business about running keeping you from being hungry because it jostles your internal organs is a wives' tale. You can pound on someone's abdomen with a billy club, but if his muscles are depleted of glycogen he'll still be hungry.