I just started reading Blindfaith's post about the CKD, but I was curious what the biggest differences are between the CKD, the SKD, and the TKD?
Ketogenic Diet Summary.
A Ketogenic Diet is a muscle-sparing fat-loss diet that works by forcing the body into ketosis through carbohydrate deprivation. Ketosis is a state where the body converts fat into ketones that the brain can use for fuel when glucose (carbohydrates) are in short supply. It's metabolic trickery that has some major advantages over a regular, carb-based diets.
It's a common misconception, even among doctors, that the brain can only use glucose for fuel. In actuality, it can burn either glucose or ketones, but under normal circumstances ketones aren't produced by the body. Most of the time, everyone in the world has their brain burning glucose. The only time the body would create and burn ketones in large quantities is when insufficient glucose is available as a fuel source. The way to make glucose (a basic sugar) unavailable, is to simply restrict carbohydrate consumption to 30g/day or less. For example, if you stop eating all carbs at, say, 6:00 PM on Sunday, and then do a heavy weightlifting workout Monday and Tuesday, this will deplete your liver and bloodstream of and glucose, and your muscles of glycogen. At that point, your liver will start producing ketones, so the brain has a fuel to work with, and if you consume no carbohydrates at all, the body will start converting protein into glucose as it will still need at least 30g glucose per day.
There are many benefits of ketodieting, among them are: Your body burns fat as it's primary fuel source 24 hours a day, 7 days a week. Thus, if you restrict calories, you will burn off adipose bodyfat at a rate no carb-based diet can match. Next, people in ketosis very often eat much less than when they're on carbs. For most people, being in ketosis strongly blunts hunger feelings, which makes it much easier to restrict calories. Ketodiets also naturally spare lean muscle mass, far more than normal diets, when adequate protein is consumed (50-150g/day minimum, 1g/lb bodyweight recommended). Sparing lean muscle mass is incredibly important to dieters, as it helps to keep your metabolism from slowing down, which helps both in keeping the fat loss going, and with maintaining the fat loss once you're off the diet.
Ketodieting does have it's disadvantages though. Many people think that ketodieting is very unhealthy due to the high amount of fat and cholesterol that you can consume on the diet (relative to 'normal' diets). But, if you make wise food choices, you can stay on a ketodiet while eating very very healthy. (Click on the Health link to the left for more details). Another disadvantage is that it's very restrictive in the fact that carbohydrates are in most foods people eat on a day to day basis, and this can make ketodieting tough at first. Please be sure to review the foods list thoroughly so the diet is still healthy, and not boring to the palette! Next, when weightlifting, your lifts will go down very significantly (10% or more), because your muscles use glucose to produce the energy needed for lifting. This can be a bit depressing, but the strength is easily regained when carbs are refed. One last problem can be bad breathe, one of the ketones your body produces is Acetone, which can be exhaled noticably. This can produce 'fruity' and not-great smelling breath in some people.
There are three major ways to do a ketodiet, the first is a 'Standard Ketogenic Diet', or a SKD. This is where you just restrict carbs, go into ketosis, and stay there for long periods until you've reached your fat loss goals, sometimes going back on carbs for a couple days or a week at a time. Personally, I recommend against SKDs, or any ketodiet where weightlifting isn't being performed. Next is a 'Targeted Ketogenic Diet', or TKD. A TKD is the same as an SKD, but you take in 25-50 grams of carbs about 30-60 minutes before weightlifting workouts to supply energy for the muscles (Note: These carbs will be burned during the workout, and should not be counted towards the 30g/day limit). For some people this can help maintain strength while on the ketodiet. Last is a 'Cyclic Ketogenic Diet', a CKD, which is much more complex. On a CKD, you go into ketosis during the week, and do 'carb-ups' on the weekends. Proper CKD instruction is beyond the current scope of this website, we recommend reading Lyle McDonalds book, 'The Ketogenic Diet' completely before trying a CKD.
As for the details of the ketogenic diet, the rules are minimal carbs, 30 grams per day or less. Now, even though you'll eat very few carbs, you still need close to your normal amount of calories per day (depending on your personal maintenance level of calories, let's use a 175lb male at 2500 cals/day as an example). To get that many calories from protein, you would need to eat 625 grams of protein per day, and the body simply cannot handle that much every day, too much protein is very hard on the liver and kidneys. An excellent level of protein for weightlifters is about 1 gram per pound of bodyweight. For our example would be only 175 grams of protein per day, or 700 calories! If your calorie intake is that low, your metabolism WILL start slowing down, and fat loss will stop. We recommend going no lower than 1000 calories below maintenance level. So if we had this 175lb man at 2500 cals maint level, 1500 would be the lowest he could go, so the rest of his calories must come from fat, or a full 800 caloires. Restricting caloires further than 1000 cals/day might be possible with drugs, such as T3, but we strongly recommend against this.
This allows for some wild food choices, bacon, hamburgers, steak, ham, whole eggs, chicken, fish, olives, and full-fat cheese just to name a few. Now, most people usually have kittens when they hear this, because those are mostly 'EVIL' foods, high in cholesterol, and high in saturated fats. The thing is, during the ketogenic diet, and only during a ketogenic diet, your body's primary fuel source is always 100% FAT (or ketones made from fat). For most people, the cholesterol never gets a chance to do damage, as not only is all the fat you eat converted to energy or ketones if you're doing things right, but also stored bodyfat is being burned at the same time! Many people actually see a marked REDUCTION in overall cholesterol levels, and LDL/HDL ratios because of this. We do recommend having your cholesterol checked both before the diet, and after 4-8 weeks of dieting.
Side effects of the diet include: Possible intermittant bad breath due to acetone respiration. Feeling nauseous during the first couple times when you switch over from glucose to ketones. The solution to this is to add a few carbs back in each day, say an extra 10-15 grams or so. The first week is usually wierd, but after that your brain will get used to it. What happens is that the first time you ketodiet, your brain can still only use 100% glucose for fuel, so the liver creates glucose from protein using a process called gluconeogenesis. After three weeks in ketosis, the brain can get up to 70-75% of it's fuel from ketones, which is when you really start feeling 'normal' again.
That pretty much covers the basic theory without going into the nitty gritty details. We really don't recommend trying a ketodiet without further information, please consult your doctor and get a good checkup along with cholesterol bloodwork, and we *STRONGLY* recommend reading 'The Ketogenic Diet' by Lyle McDonald. It's available from http://www.netrition.com. Another good starting point is 'The Atkins New Diet Revolution' by Dr. Atkins, it's a little more biased in favor of ketodiets, but works well too.
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Wow, lots of information; thanks Bobo.