interchangeability of proteins, fats and carbohydrates

From what I gather, unused proteins and carbohydrates turn to fat, used fat ought to behave somewhat like carbohydrates, and I’ve also heard that fat people who start exercising tend to gain muscle mass faster. So to some degree, these should all be interchangeable, but how much? I’d guess you’d get less energy out of using one for the other, and perhaps it takes some time to convert, too? Am I right? Lost? Dope, please.

Carbs and Proteins have 4 calories per gram. Fats have 9 calories, obviously fat is a much more efficent fuel.

The body can use protein as fuel too, but it doesn’t like to.

To oversimplify a bit, your body uses protein to build, carbs for everyday energy and fat for long term energy storage and exercising at length.

You will notice when you are running and you hit your “second wind,” that is your body switching from burning carbs to burning fat. Because fat is more than twice as efficent you get your “second wind.”

But your body ALWAYS takes the line of least resistance. Fat people weigh more so, yes they gain muscle faster, 'cause they are in effect lifting more weight. But almost all the muscle comes off when they diet as well.

It is used by bodybuilders because it can work and instead of gaining 15 pounds of muscle a year they’ll have 17 or 18 pounds of muscle. Not much for the average Joe, but it can make the difference between first and second place in a contest.

Your body does need a minimal amount of carbs and fats to process things like vitamins and to do other bodily functions.

Your body needs about 1 gram of protein of per KILOGRAM of weight. Not pound but KILOGRAM. So I weigh 175 pounds, which is about 80kg. So I should be getting about 80grams of protein a day and then I can split the rest of my food intake between carbs and fats.

There are few things in nature more energy-dense than good old-fasioned fat.

One pound of broccoli: 154 calories.
One pound of spaghetti: 712 calories.
One pound of lard: 4,091 calories.

This is a completely uneducated guess by a completely unprofessional person, but might this be simply because fat people have bigger bodies that require more energy to move? If a fat person runs a mile, they’ve done more work (physics definition) than a skinny person.

While it is true that fats have about twice as much calories per mass as carbohydrates and proteins, this doesn’t make them “more efficient” in terms of their utilization by the body. It is harder for the body to break down facts in order to extract the calories, which is a reason why high fat and high protein reducing diets “work” (although they are not healthy sustaining diets) and produces waste products that have to be filtered and excreted. In fact, almost all “low fat” diet food supplants the removed fats with carbohydrates (typically simple sugars) in order to enhance the flavor and fullness, which ironically provides more accessible calories and can cause the consumer to become more fat for the same caloric intake as the excess glucose is converted into fats. This is why it is critical to look at the glycemic index (GI) in addition to gross calories. Breaking down fats requires exercise in the anaerobic regime (where the body is not able to take in or utilize sufficient oxygen to maintain aerobic performance) which, as Markxxx indicates, occurs after the body’s normal glycogen stores which are almost exclusively derived from carbohydrate intake, is exhausted.

Fats, carbs, and proteins are not interchangeable, nor can they be “converted” from one to another any more than lead can be transmuted into gold. All are needed in the correct proportions, which are 40-50% carbs, 25-30% proteins, and 20-30% fats, depending on metabolic state and amount and type of exercise being performed. Carbs provide basic energy for most metabolic functions, including digestion. Proteins are the structural building materials and only a small portion are generally converted to calories. Fats act as a carrier for a lot of non-water soluble vitamins and sterols, and provide a denser and typically more resilient source of calories compared to carbohydrates. Unsaturated fats also help to reduce “bad” cholesterols and provide other micronutrients to various organs including the brain and the dermis that are needed for good function and vitality.

As for “I’ve also heard that fat people who start exercising tend to gain muscle mass faster,” if this is true at all (not going to touch that one) it would be because fat people probably have a diet which supports muscle growth. It’s actually necessary to put on some muscle in order to effectively burn excess body fat (although increasing muscle mass in a particular location, like the abdominal, doesn’t do anything to burn away the subcutaneous fat in that particular location, late night infomercials notwithstanding) and many overweight but physically active people probably already have some decent muscle development concealed under the surface fat. Taking off fat is the most effective way to “gain definition”; it isn’t that it increases muscle mass, but it does make it more visible.