Analyzing low carbohydrate diets
Let me first put it out there; I am not claiming to be a low carb guru or anything.
My knowledge comes from 2nd hand sources. I NEVER participated in a low carb diet for any extended period. With this in mind, my thoughts on a low carb diet are purely from a technical and research point of view. I have no bias one way or another. Next let me just reiterate that I am not a nutritional scientist, and my views are purely amateur and based on personal research. Take my information and opinions for what they are worth.
What does the term "low carb" mean? That's not as easy to answer as it first may seem. There are a lot of people and companies out there pushing "low carb" diets these days. Their definitions depend solely on who you are talking to or reading from. In general there are two main categories of low carbohydrate diets. The first being the most extreme approach, these are called ketogenic diets, where carbs are kept so low that the body remains in a state of ketosis. The second is a non-ketogenic low carb diet. Where carbohydrate levels are kept lower than the FDA recommended amounts, but not so low that the body enters a ketogenic state. I will attempt to briefly outline both, give the low down on how they generally effect the body, and summarize how I feel low carbohydrate diets should be used.
The human body uses 3 forms of macronutrients as fuel. Carbohydrates, fats, and protein are all considered food and fuel for the body. While all 3 macronutrients can be used as energy, evolution has chosen carbohydrates as the primary fuel source for the human body. Dietary carbohydrates (carbs with value to the human body) come in two forms, fiber and non-fiber. Fiber is indigestible to the body and plays a role as a cleaner and digestion governor in the body. Non-fiber carbohydrates can be broken down into sugars and eventually turned into glucose for energy in the body. Glucose is the primary energy source the human body uses. Carbs are broken down quickly in the stomach and intestines and transported mainly to the liver where they are recombined into glucose and distributed throughout the body. When there aren't enough carbohydrates coming in, the body relies on dietary fat, dietary protein, stored fat, and lean tissue to produce its energy. The process of converting fats to energy is somewhat slower than glucose production. Protein is the slowest conversion rate of the three and is usually considered the last resort. The human brain requires glucose or ketones for energy as does the central nervous system. The energy derived from fat cannot be used to fuel the brain directly as free fatty acids (FFA) that can substitute for glucose in many organs and muscle groups are large molecules, and cannot pass the blood-brain barrier. This means that in order for the brain to use alternate fuel, that fuel must first be converted in the liver to glucose or ketones. The body knows how to do this, but the process is slower, and produces less total energy to do so (called the Krebs or citric acid cycle). When there isn't enough carbohydrate in-take to satisfy all energy requirements, the body prioritizes any carb. conversion for the brain, the rest of the body must take what it can from the rest, using fat and protein to balance out its fuel.
When we lower our carbohydrate in-take levels enough, in the short term the body does not make any changes, stored glycogen in the liver and muscles will take up the slack for a period of days or weeks depending on how low our total caloric in-take is. Eventually though, the lowering of carbohydrates depletes glycogen stores, when the stores are depleted enough, the body will begin producing more and more ketones, these ketones take over for the role of glucose in the body, providing energy. By itself this is not a bad thing, but many things happen when we move from a glucose metabolism to a ketogenic metabolism. Without making an informed and conscious choice to choose ketogenisis, you could be putting your body and your health at risk.
Lowering carbohydrate levels to a point where they affect your energy balance does a few things chemically. First and foremost, it changes the amount of water in the body. Because glucose is mainly distributed and stored in a water based solution called glycogen, hundreds of grams of water are no longer needed in the body. As hydration levels lower, weight goes down. In some cases, a person can drop as much as 20 lbs of water weight in a matter of a few days or weeks. "Dieters" and people touting low carb diets for weight loss flaunt this fact as "proof" of weight loss, but it's nothing but a temporary weight loss, no real fat stores have been lowered because of these phenomena. It should be known that once carbohydrate in-take is restored, the water levels will quickly return to their former state and you will gain that water weight back. When protein is used for energy instead of as a building block for lean tissue, it has by-products. Those by products include carbon dioxide, water, urea, and ammonia. The last two, urea and ammonia need to be expelled from the body as they are considered poisons. This forces the liver and kidneys to work harder (stressing them). It is unknown as of yet, whether this can have a long term detrimental effect on a healthy adult, but common sense says that when we increase the work being done by an organ over the long term, the extra stress can be detrimental to its health. Obviously, someone with liver or kidney issues should never be on this type of high protein, low carb. diet, without consulting their doctor first.
There are many studies that have been done recently (over the last 10 to 20 years) that have looked at the long term effects of a low carb diet vs. a balanced nutritional diet with a modest calorie deficit. In diets lasting longer than 6 months, participants generally had statistically insignificant differences in total weight lost. In some cases other systems benefitted from a low carb technique, such as blood cholesterol.
For those with reasons other than weight loss for their dietary changes, there are well documented and perfectly valid reasons to go on a low carbohydrate and/or ketogenic diet. Epilepsy is one reason. Without going into specifics, changing the brain's fuel levels and source has a profound effect on the amount and strength of seizures. Cancer research is also being done on fuel sources. On main theory is that cancer cells rely solely on glucose as fuel and thus starve if not provided, I have not delved deeply into this topic though, and would suggest talking to an oncologist for more details.
As to low carb as a way to quickly and efficiently shed pounds; I don't see the benefit. Studies don't show any additional fat loss from low carb diets over a normal, moderate calorie reduction diet. And the consequences for high intensity work are significant. Once glycogen levels are depleted, someone on a very low carbohydrate diet will take much longer to restore those glycogen levels, severely restricting their ability to perform anaerobic activity for any extended period. This limits the amount of weight training or high intensity (anaerobic) cardiovascular work you can do in any one period. Also hydration levels must be closely monitored, as dehydration can have serious and very dangerous side effects. Couple this with the unknown possible long term consequences of kidney and liver stress; I cannot endorse this method as a weight loss tactic. There is much great work being done in this area in the scientific community, and the facts change almost daily. I have merely hit the main points and barely scratched the surface of low carb. If you want to know more, I urge you to talk to many sources, not just the proponents of one type. There are benefits and drawbacks to low carbohydrate diets. But one thing I can tell you with certainty, it’s not a "quick fix", and done right, it's not easy or cheap. If you wish to be a "low carb. convert", walk into that lifestyle with eyes wide open, realizing that you will have to closely monitor yourself, and be aware of the side effects, and know that doing it short term does nothing for you.
I have not touched on low carb diets as a diabetic treatment or low carb. For those who have nutrient allergies or celiac disease. These are specific cases in which the treatment can have high benefit. Please talk to experts in your specific field if you wish to pursue this avenue. And best of luck to you!