I have been wondering this for a while now. The average amount of calories per day varies between men and women, 2000 for women and 2500 for men, my question is, if you ate 2500 calories worth of fat would that be burnt of by the body, or because your eating that much of it be stored as fat, same goes for if you ate 2500 calories with of protein etc? I know also that this 2500 Mark is more than enough to do all your bodily functions like walk, sleep, brain activity etc. So it’s maybe better to take the base amount for this, I’m not sure what the basic requirements are but think it must be about 1300ish for a man.
I think if all your calories came from fat, you wouldn’t have a nutritionally balanced diet and it would affect your metabolism, which would in turn affect how many calories you could consume to maintain weight. Also, I think you’d have some health issues because the body requires protein to maintain muscle mass and carbohydrates for energy.
A human being simply could not maintain health on a fat-only diet.
Your body breaks all foods that it eats down to simple sugars, amino acids, and fatty acids. These produce, roughly, 4, 4, and 9 Calories per gram. That process is called digestion.
One inside the body, these building blocks are used for energy, are built up into the components of the body that need adding to or replacing, or are converted to fat and stored.
How much of each type is used depends on both the basic metabolic rate that the body has settled into and the amount of work (effort, exertion) that the body does over the course of the day.
That’s why the body needs a variety of foods (even ignoring micronutrients like vitamins). If you eat 2500 calories only of protein or only of fat, the body would try to salvage as many building blocks out of it as necessary. Without the other two this would not be sufficient. Any amino acids or fatty acids not used would be excreted or converted into fat and stored by the body. It’s impossible to give an exact number because the body would cannibalize itself to used the stores of energy, muscle, and fat already present to try to make what it needs.
Over time, the body would start to break down. But not because of the raw numbers of calories not being eaten, but because three building blocks are necessary and you are only providing one.
Your body needs approx 11 calories per pound to maintain its own weight.
So I weigh 175. I need 175 X 11 = 1925 and that is to maintain the weight I have. If I were to work out vigorously I would need more. Basically the 1,925 represent, just daily activities to maintain.
Your body also need 1 gram of protein per KILOGRAM (not pound). So 175lbs is about 79 kilos. So I need 79 grams of protein per day to maintain my body
As another poster stated protein has 4 calories per gram. So 79 X 4 = 316.
So to maintain my 175lbs, 316 of those 1,925 calories need to be from complete proteins. 1,925 - 316 = 1,609. These 1,609 calories can come from fats and carbs or proteins.
Your body also needs a certain amount of fats and carbs per day.
Whatever is not used by the body is converted to sugars and stored as fat.
Normally your body uses carbs as fuel for everyday. It only switches into fat burning mode, if you’re exercising heavily. It does this because fat has 9 calories per gram, more than twice that of carbs and protein. Thus fat is a more efficient fuel.
The idea behind diets like Atkins is that you eat very little carbs and your body is forced to burn fat for everyday fuel instead of carbs.
The two cases are definitely NOT the same. The thermic effect of fat is only 0-3% while thermic effect of protein 20-30%, so far fewer of those calories will be available for fat storage in the protein-consumption case.
Ok I get it now, this will help with my diet 
cheers fo the reply guys.
This type of analysis is really not the right way to go about dieting.
If you eat nothing but fat, you’ll probably suffer digestive issues first. I would expect that you will start passing more undigested fats and you’ll get malnourished even faster. The digestive system needs some amount of fiber to work properly.
I expect you’d have runny stools, anal leakage and, although you’d might be eating X am’t of calories, you’ll absorb something less than X.
The most startling thing awaits you though: When you eat fiber or carbs again, you’ve just signed up to be a food zombie. Bah… what do several billion case studies really mean when you got it figured out?
Good luck! Anal leakage: Good times!
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I average about 3 minutes for 30mml
Not sure if that’s competitive.
What’s a food zombie?
Wow. That’s a good number. You should consider competing in your local anal leagueage.
From Google, the only other person who could compete with me is the Russian semi-pro Vladimir Skitrovitch. Not much chance of us ever meeting up though. Unless he defecates to the West.
A food zombie is someone who has gone on a diet that is impractical for the body, and when they try to return to anything resembling a normal diet, the have no will power and slowly trend back up to their previous weight and likely beyond.
Most diets see most people become food zombies, with a scarce few not becoming completely zombified. The most ridiculous diets are sure winners to produce food zombies.
We could get all scientific, but what’s the point really?