It does seem to happen regularly in untrained and minimally trained individuals.
Increasing Muscle Mass While Decreasing Body Fat
This predominately works for untrained/minimally trained individuals and especially obese individuals with a well written exercise/followed exercise program, providing they are in a calorie deficit.
That means any diet in which there is a calorie deficit will increase muscle mass and decrease body fat levels for these individuals.
The leaner and more advanced an individual is, the harder it is to gain muscle mass while losing body fat at the same time.
Some diets are definitely more effective than others. Which bring us to...
It seems to happen more often in an environment of low insulin and high caloric intake, which is common in low carb/high fat diets, as well at ketogenic diets
Calories Count
Calories are the "Prime Root" of weight gain or weight loss.
That means any diet that increases calories produces weight gain and any diet that decrease calories produces weight loss.
Insulin: The Anabolic Hormone
High carbohydrates diets increase insulin production. Insulin is "Anabolic". However, it is what is termed...
"Globally Anabolic"
That means the it not only increase muscle mass but fat mass, as well. Metaphorically speaking, insulin is like nuclear power. Under the right condition, it is effective. Under the wrong condition it, your fat cells blow up.
As Nutritionist, Jay Robb put it...
"Insulin is a Fat Maker. Glucagon is a Fat Taker"
Chronic elevated insulin levels mean an increase in body fat and contribute to other health issues.
Low insulin levels allow for body fat to be burned for energy due to an increase in the "Fat Burning Hormones: Glucagon, Nor-epinephrine, Epinephrine, Growth Hormone, Dopamine and Cortisol.
A side note on Cortisol: Acute (short term) increase when training or during fasting allows it to utilize burn body fat for energy. Chronic (long term) levels of Cortisol are catabolic (muscle burning) creating health issues.
The Cortisol Take Home Message
Acute Cortisol increase is good.
Chronic Cortisol level is bad.
Some (Not All) Factors for Low and High Carbohydrate Diets
1) Insulin Sensitive: These individual for the most part do well on a Moderate to High Carbohydrate diet. Usually, younger individuals are Insulin Sensitive.
2) Insulin Resistant: These individual gain weight/fat by just looking at a piece of bread. Moderate to High Carbohydrate Diets weight gain is primarily fat mass with a little increase in muscle mass.
Older individuals tend to be more Insulin Resistant, due in part to the aging process.
3) Sports Energy Systems
a) Phosphagen Energy System: This system is not dependent on carbohydrates. That means glucose is not need when with Sports or Training Method that employ the Phosphagen Energy System, glucose/carbohydrates are not necessary.
b) Glycoltic Energy System: Moderate to high carbohydrate appears to be necessary for Oxidative Energy System Sports. Athletes and Training Method that utilize the Oxidative Energy System are not dependent on glucose, low carbohydrate diet work for this group.
c) Oxidative Energy System: This system is not dependent on carbohydrates. That means glucose is not need when with Sports or Training Method that employ the Phosphagen Energy System.
The low insulin levels make it hard for the body to store fat, while a high caloric intake allows muscle growth.
Low Insulin Levels, High Calorie Intake
Very well stated, lower insulin levels makes it easier to burn fat as well as harder to store fat.
Increasing calories, primarily from fats, ensure weight gain, most likely in muscle mass.
Personal Experience
After losing 23 lbs by combining the Ketogenic Diet and Intermittent Fasting. I decided to gain some of the weight back with the Ketogenic Diet and limited Intermittent Fasting.
By dramatically increasing my fat calorie intake and minimally increasing protein (maintaining 25% or less of calorie intake), I gain back 17 lb.
Some of the weight gain was body fat; calories count.
The Issues of the Ketogenic and High Carbohydrate Diets
1) Ketogenic Diets make you effective at using body fat for energy. However, you become less efficient at accessing glycogen.
2) High Carbohydrates make you glucose dependent; less effective at accessing body at for energy.
3) Diets that restrict one marco group (Low Fat or Low Carbohydrate) ensure failure with the majority of the population.
Intermittent Fasting
Employing this method allows "Metabolic Flexibility"; your body is able to access glucose (carbohydrates) or ketones (body fat).
"Metabolic Flexibility" amount to having a Hybrid Car. It utiized electricity or gas, switching between the two dependent on the task.
Back To Gaining Muscle and Losing Body Fat
This is best accomplished by cycling calories up and down.
1) Bodybuilders "Bulk" and "Cut" phase have demonstrate how effective this is.
2) Layne Norton's "Reverse Dieting" is build on the Traditional Bodybuilding Protocol, above. Norton provide a definitive method to ensure muscle gain and fat loss.
3) Dr John Berardi's (PhD Nutrition) "Bigger-Smaller-Bigger" Intermittent Fasting for increasing muscle mass and decreasing fat mass is built on cycling calories, as is the Traditional Bodybuilding Method and Norton's Reverse Diet Method.
The Take Home Message
The foundation of Periodization Training, cycling training, works for gaining weight or losing weight.
Periodization Dieting via cycling calories up and down up is an effective method of increasing muscle mass and decreasing body fat.
The foundation of Periodization Dieting Foundation for gaining or losing weight (increasing muscle mass and decreasing body fat) is built on calorie. The Diet you chose is secondary.
Kenny Croxdale