Join Date: Mar 2012
Location: Helena, MT
sorry this is so long! I think it might be worth reading though, if anybody wants to know how low-carb diets work.
I get to use my (kind of...) vast knowledge of physiology!
Both people above me are correct. Above a certain level of carbohydrates, when metabolism is functioning relatively properly (the way we either evolved or the way we were made, depending on what you "believe"), calories are calories, and that's why high-fat diets tend to pack on the pounds just as much as high-carb diets. Calories *tend* to be calories, regardless of what they're from. As rpmcduff noted, most of your energy when you are not at rest is taken from glycogen tanks. Glycogen is a modified storage carbohydrate found in muscle tissue and the liver. Glycogen tanks are quite large; they can sustain most people throughout whatever workout they have. However, have you ever worked out so hard that you felt like you just hit a wall, and suddenly it became very hard for you to continue? That's the glycogen tanks running out- and now your body is searching for another source of energy, and it's difficult!! That is why a lot of runners will take "energy packs" (they're gel-filled shiny packs that runners can consume quickly without stopping) or refuel with higher-calorie gatorade when running in races. You want to make sure that those tanks are as full as they can get to fuel yourself so you don't hit that wall, and why so many runners have 60% or more coming from carbs. As glycogen is a carbohydrate, it is easier to get that from carbs than from proteins and fats, which are metabolized different.
Carbs go through the typical metabolic process known as respiration to get ATP (aka, "energy"). Fats and proteins go through a separate process- even their digestion is different! While carbs begin chemical digestion in the mouth, proteins start in the stomach, and fats in the intestines. Proteins and carbs, usually hydrophilic, can be transported easily in the blood stream, but fats have to be specially packaged into something called a chylomicron- basically, the fat is broken down into a triglyceride and fatty acids, then transported inside another cell where it gets reassembled into the full fat again, and then it's transported out- and not into the blood stream but in the lymphatic system to THEN be transported into the blood stream.
So I'm sure most if not all of you learned about cellular respiration during some biology course: you take a sugar, add in oxygen, combustion occurs and you get carbon dioxide, water, and energy. But, as we know, we get energy from fats and proteins- they enter into the same cycle as the sugars as an intermediate, but they (quite obviously) have to shed off a lot of their excess "stuff." Proteins enter in as pyruvate, acetyl CoA, or other intermediaries in the citric acid cycle- but as a result, they have to get rid of their nitrogen... in the form of ammonia. Ammonia is actually *very* toxic and must *very* watered down to be "safe" for animals, hence why only fish excrete pure ammonia. In us, it's converted to urea, which in turn is excreted by the kidneys.
This is why proteins are actually NOT good for us to have in bulk. With oxygen, glucose respiration is not toxic. But, because our bodies have not been "designed" or selected to deal with high amounts of ammonia, too much protein taxes the liver (where ammonia is converted to urea) and the kidneys (where urea is filtered out of the blood). Urea also takes energy to make- but I want to say (though I might be wrong) that this is taken into consideration when talking about the usable calories in a gram of food.
Anyway, with fats, the byproducts are called ketones- which is where "ketosis" (really, ketoacidosis- what you want to be "in" during Atkins) gets its name- the ketones are released inside the body and excreted, again, through the urine (and please remember- our kidneys really are not supposed to filter out a large quantity of ketones at a time over an extended period of time). You NEED to be in ketosis to function on a low-carb diet, by the way. Brain cells can only gather energy through either glucose or the ketones, so if you are restricting carbs beyond a certain level but aren't yet to the point of ketosis, you're going to see loss of cognitive functioning and even some cell death. When you're in ketosis, the brain can take in those ketones and use that for energy (though it is NOT preferred- it can be used to synthesize other lipids, though, because some ketones are out of the body within 5 hours).
So, basically, my point is: when you eat low-carb, your brain is forced to find a new way to get energy, and that comes from ketones. Because proteins do not offer the brain any energy, it will take up the ketones found in the blood stream- and this is where I begin speculating because I truthfully have not studied this enough.
I assume that when you are on a diet like Atkins, your brain, in desperate need of energy, will first sap up all of the glycogen stored up, and then will send hormones for the further respiration of fats. As other organs, tissues, and cells can use fats and proteins found in the blood stream to make energy, your body isnít set to starvation mode, because it is still getting adequate calories for that. So, basically, it is your brainís need to function in such an environment that drives the fat loss.
And this is where I know stuff again :P So, the brain needs ketones in the blood stream, but again, these ketones will be filtered out in the urine. Once the fat molecule is used for ketones, it canít be stored again- so any excess ketones will be excreted. This is why you see such a huge weight loss on Atkins and low-carb diets. While the brain needs some glucose to function (those 20 grams a day are actually important!), it gets the rest from ketones from the breakdown of fats in the body, and there will be excess that cannot be stored. You arenít burning more energy; youíre wasting it!
Ironically, this is the same process that can happen in diabetics. If you donít know, one sign of diabetes is unintended weight loss- thatís because the body canít regulate glucose levels in the body anymore. Some diabetics will go into ketoacidosis- and this is very risky for them (though the biggest issue is with the glucose- because they still have glucose; they just canít utilize itÖ). Personally, I find it a bit odd that otherwise healthy people find something that can be fatal to others for cosmetic purposes.
Anyway, back to a 40/30/30 diet. This is typically NOT enough of a carb restriction to put your body in ketosis- and really what you will begin to see in any carb-restricted diet is sluggishness and potential damage to the kidneys and liver if you arenít careful (I know a couple people who had to be hospitalized for dehydration despite drinking as much as they could and even renal failureÖ They were on Atkins, though- not a 40/30/30), though I hope you arenít taking in more than 175 grams of protein (I could go on about protein requirements in the body if youíd like :P) It really is not the best ratio when working outÖ even when youíre weight lifting, itís carbs you want after a workout, not protein.
Now then, onto the other question regarding your activity level needing to be higher with an increase in carbs:
Not completely true. Though your body might be more in need of ketones than usual at a 40% level, the amount needed is not enough (in my opinion) to justify staying at that level when you're having difficulties already. You probably are not restricting enough to be in full ketosis (it's not just % but overall grams), as I just said, so really all it will do is lower the amount of taxation on the vital organs and give you more energy to workout. If indeed you do need to expend any more energy during the day to still lose weight, trust me, when you work out, it will just come naturally. You can push yourself harder and often times will without even noticing it. Workouts will become easier- performance increase! And that doesn't mean you're burning less. It means you're using your body the way it was meant to function. Personally I prefer that!
Everybody has their own ďgolden ratioĒ though- at least, I think so. For me, Iím best at 60-65% carb intake, 20-25% protein intake, and around 10-15% fat intake. I function my very best when Iím getting around 290-305 grams of non-fibrous carbohydrates, 90-105 grams of proteins, and less than 35-40 grams of fat. I actually lack an enzyme to break down certain fats, so I end up feeling really sick when I eat those- and theyíre the kind most commonly found (like butterÖ). Thus, itís harder for me to go into ketosis with any shred of safety, and as a student studying long hours to make a double major and minor meet (I kid you not, I am in lecture, lab, or studying probably 10-12 hours a day), supplying my brain with adequate glucose is a must. Your own personal ratio will be different, obviously, but donít get stuck in the ďso and so said this was the best ratio for what I want to do, and he has a book/TV show/movie/masterís in nutrition/whatever!Ē mindset. The BEST thing to do is to try to see where you physically feel best.
Remember the goal of weight loss is NOT to lose weight as quickly as possible. It's to find a lifestyle you can sustain and watch the weight shed after that. Too many people "diet," but if you feel awful while you do it, will you really want to keep doing that?
Good luck though! And if you do feel best at 40/30/30, try added-fiber foods, like Fiber One cereal, or sugar-alcohol products (1-3 calories per gram instead of 4), like those breads or various products that have usually boast a low net carbs, if you feel like you need more to eat.