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Some corrections from the point of view of an endurance athlete (triathlon). First of all you don't really "eat glucose", that would be an oversimplification. G
by tigerBL00D 10y ago
Some corrections from the point of view of an endurance athlete (triathlon). First of all you don't really "eat glucose", that would be an oversimplification. Glucose is produced by your own body when metabolizing carbohydrates. As a backup mechanism your liver can also produce glucose by converting amino acids (muscle) and even fat, a process known as gluconeogenesis.
Now, if we replace "eat glucose" with "eat carbohydrates", then the statement is still not quite accurate. Experienced marathon runners (and other endurance athletes) will not consume carbs before the run because doing so would spike insulin and effectively shut down breakdown of fatty acids in the liver. Liver can more or less either convert glucose to glycogen and fat, or break down fat, and is not great at doing both simultaneously. Maintaining fat metabolism is hugely important when going the distance since it's the largest energy reserve available in your body (50,000+ calories vs <2000 calories as glucose).
Marathon runners consume moderate amounts of carbohydrates DURING exercise when insulin response is blunted. The idea here is to maintain glucose levels and avoid going into hypoglycemic state (low blood sugar). Ingesting moderate amounts of simple and complex carbs during exercise spares glycogen without necessarily spiking blood glucose to where liver has to regulate toxicity. This way you can keep on going longer.
- CarpetBench 10y ago> As a backup mechanism your liver can also produce glucose by converting amino acids (muscle) and even fat, a process known as gluconeogenesis. Just a quick note, and your explanation is fantastic otherwise: this isn't quite correct. The (human) liver doesn't use fat directly for gluconeogenesis. It's just not efficient for humans: We wouldn't gain enough energy from it. The liver uses fat indirectly through glycerol (which is a product of fatty acid catabolism), but it's important to draw a distinction here because this is why ketosis occurs - if the liver could efficiently break down fat directly, ketosis would never happen at all! Most tissues would much rather use glucose directly if it's an option. While muscle breakdown occurs in small amounts normally it's mostly a last resort that occurs after an extended period of starvation. Which makes sense: You wouldn't want to break down the thing (skeletal muscle) you need to get more food except as a last resort. The amino acids involved in more typical gluconeogenesis largely come from other sources.
- tigerBL00D 10y agoThank you for this clarification. I agree, I took a few too many shortcuts with that statement and it can be misleading.
- steveslegend 10y agoHow does blunted insulin response feel? Is that as simple as feeling burnt out early?
- eggy 10y agoAll of this with the qualifier 'marathon runner' or 'endurance athlete', since explosive, short-duration, powerful sports require immediate energy reserves, which they readily deplete when you do this type of exercise. Fat metabolism would be too slow for the quick, short types of activities. I also believe endurance or extreme endurance activities are more for your enjoyment than fitness. They take their toll on the body's joints, organs and regulatory systems. Moderation is good advice in lots of things.