Some thoughts.. There is so much discussion about different diet approaches to loosing body fat. I have not settled on one yet, although, I am trying the "Targeted Keto Diet" now.
So here are some of the pieces I understand to loosing body fat.
1) Glucagon is the hormone produced by the pancreas that tells the body to utilize body fat to be metabolized for energy.
2) Glucagon is activated in times of low blood sugar / glucose ... opposite to Insulin.
So as I understand it.. the rate and degree to which one can loose body fat depends on when the glucagon hormone is active which is directly proportional to the frequency and duration of keeping blood sugar (glucose low).
The type of food, the amount of food, and the frequency of eating will all influence the above. Additionally, the total calories the body burns (bmr, activity level, etc) and hence the glucose draw from the blood stream and liver (not including glycogen in the muscles).
So I think any of the diets can accomplish this, its then a question of which one will produce the greatest rate of fat loss (and prevent muscle loss which I'll mention next). I believe (only opinion on my part right now) the the order of the diets from those that will cause slow fat loss to those that will provide rapid fat loss are:
1) regular diet which simply lowers carbs a small amount to effect a 500 calorie per day deficit.
2) carb cycling which greatly reduces carbs to bringing them back up to a full load usually cycled over 3 to 4 days.
3) targeted keto diet. standar keto diet, but add carbs targeted just before workout with the aim that they support workout intensity and are burned off as a function of the workout. During times of no carb, low blood sugar activates glucagon to casue fat burn through keto.
4) cyclic keto diet. loads carbs to a person specific level to fill muscle glycogen ie. on a Fri eve and Sat., then allows for a specific workout routine which will draw down no more than the carbs loaded. i.e. M, T weights; W, TH low intensity cardio, F weights or circuit workout. The abscence of carb intake after saturday and to Fri eve keep blood sugar low during the week activating glucagon to cause fat burn through keto.
5) standard keto. no carb loads or targets..
So which one prevents muscle loss or could cause more muscle loss..
Here is how I understand we loose muscle:
1) over training in the gym: overtraining occurs when the glycogen in the muscle is depleted, there is no glucose in the bloodstream to draw on and the liver has provided what it stored to the bloodstream already. What prevents overtraining? Eating strategically, and not working out so long on a given muscle group in terms of sets, reps, and rest period. Muscle groups can not share their store of glycogen with another muscle.
2) we have voluntary and involuntary muscles: in the abscence of carbs and fat consumed calories, the body will then seek protein first in the blood (as in the protein you drink) the it resorts to protein in the liver, muscles, then other organs ... (called gluconeogenesis) in that priority. if there is no mechanical activity required of the voluntary muscles (ie the couch potatoe) then there is no energy consumption. But our involuntary muscles are still consuming energy for vital life support. Your brain consumes 20% of your calories!
So how do you prevent muscle loss.. dont let your bodily energy requirements deplete you carb and fat calories which includes the glycogen in the muscles, glucose in the blood stream, and glycogen in the liver... and of course provide the protein/amino acids for muscle rebuilding if we are considering that.
So now, how do you activate fat burning (activating glucagon, by low glucose level in the blood stream) while at the same time have the calories for the muscles? I think from the above, you can figure the answer.
My fear with diets that just lower the carbs to create a calorie deficit is that there is not enough to fully activate the glucagon (pancreas) to draw on fat for energy, yet the muscle may be running on a glycogen and glucose deficit (as well as liver glycogen) and have to resort to gluconeogenesis (protein break down).
Thats why Im more receptive to the keto diet. It is producing ketones to supply energy/glucose etc. Obviously not enough ketones if one is still doing intense workouts.. But that is where the cyclic and targeted ketosis diets come in where they ensure the carbs are in place to support the workout and prevent muscle loss. In the case of the cyclic, the workout energy draw has to match the carb load from the weekend. In the case of the targeted keto, the carb load is specific to the exercise sets and is taken just before the workout.
Im not convinced which diet, the cyclic keto or the targeted keto, will have the most rapid fat loss. I have a feeling the cyclic, but it takes a little more coordination. I believe both will prevent muscle loss better than a diet that just reduces carbs for a calorie deficit.
So.. just my opinion based on my current knowledge.
I'd appreciate informed comments as Im still trying to develop a thorough understanding of this myself.