Severely eating under BMR - Why not dead?

[Humble]

If a person was to severely eat under their BMR, lets say they ate 500 calories for 7 days straight. Why wouldn't that person be dead if their BMR is 1500 calories per day?

 

Im guessing the answer will be, the body will use body fat as energy and hence this is how weight loss is achieved?

If so, then is body fat not essential for a persons growth, lets say ages 10-20,  as long as they are getting adequate micro nutrients, protein and fats?

Could a person grow perfectly fine, say height wise at 10% bf all through out their teens, if they get adequate micro nutrients, protein and fats?

 

[FellowshipOfTheRon]

well if their bmr is 1500 cals and they just eat 500 cals, body wont necessarily be burning the difference (1000cals) in fat. more like the body will start by drawing from glycogen first once those stores are out the person will be performing like shit, then body will slowly begin the process of burning what's needed from the fat stores to stay alive. eventually muscle starts burning too in case of severe undereating but i think that takes a coulpe weeks for the catabolic process to start...unless of course the person is also trying to be very active coupled with being close to the point of starvation

 

fat loss can be acheived in many ways and eating way under BMR/starving oneself is by far the least efficient way... ultimately people who live this way just end up having that shitty skinny fat look (used to undereat for my activity levels and was exactly like that lol!)

 

there is essential bodyfat which is the minimum amount of fat required to function which is around 5% in adult males not sure if they've ever done such testing on young teens lol.

Essential body fat is necessary to maintain life and reproductive functions. The percentage of essential body fat for women is greater than that for men, due to the demands of childbearing and other hormonal functions. The percentage of essential fat is 2–5% in men, and 10–13% in women.

http://en.wikipedia.org/wiki/Body_fat_percentage#Typical_body_fat_amounts

I'd say 10% or possibily little higher even 12~14%bf year round for a teen is a fairly healthy level to aim for. You can easily obtain that and just lean bulk forever. It's not so much that you need to eat restrictively (so your parents and other elders/supervisors don't see you as developing unhealthy/anorexic type eating habbits) and will find that level of fat responds well for mass gains. If you ever notice that you are going through growth spurts (family that you see like once a week will be 1st to tell you that you're getting taller etc.) make sure that if you're in a cutting period you switch up to bulk straight away, probably the only precaution you'd need to take to make sure you don't mess with your natural growth.

 

[holdenman]

If a person was to severely eat under their BMR, lets say they ate 500 calories for 7 days straight. Why wouldn't that person be dead if their BMR is 1500 calories per day?

 

Im guessing the answer will be, the body will use body fat as energy and hence this is how weight loss is achieved?

YES.

If so, then is body fat not essential for a persons growth, lets say ages 10-20,  as long as they are getting adequate micro nutrients, protein and fats?

SOME IS REQUIRED.

Could a person grow perfectly fine, say height wise at 10% bf all through out their teens, if they get adequate micro nutrients, protein and fats?

 A TEEN WOULD GROW ABSOLUTELY FINE AT 10%BF AND LOTS DO.

[Dinahlady]

The key is getting adequate macros and micros. It's questionable if you would be able to get those requirements and sustain healthy growth and development during ages 10 - 20 on 500 calories. Undereating macronutrients and micronutrients as well as total caloric intake during adolescence can cause issues with growth (height), bone density, hormone function and reproductive system development that can cause long term or irreversible damage - eg females can fail to develop reproductive ability due to undereating during teens. 

You also need to take into account your activity levels. Roughly calculated reccommended caloric intakes for adolescence for healthy development as suggested by the american dietetic association are: 

For males: 

Age 12 - 16:
Sedentery: 1800 - 2200 
Moderately active: 2200- 2600 
Active: 2400 - 2800 

Age 16 - 20: 
sedentery: 2200 - 2600 
Moderately active: 2600 - 2800
Active: 2800 - 3200

20 - 24
sedentery: 2400 
Moderately active: 2800
Active: 3000 

 

For Females: 

Age 12 - 13:
Sedentery: 1600
Moderately active: 2000
Active: 2200

Age 14 - 18: 
sedentery: 1600-2000
Moderately active: 2000 - 2200
Active: 2200-2400 

19 - 24
sedentery: 2000
Moderately active: 2200
Active: 2400

 

Having a low body fat but within the normal range is fine and healthy - but restricting calories too severely can cause issues with health as mentioned. You can only mobilise a certain amount of adipose tissue per day and eating less doesnt mean you are going to be using more fat stores. To reduce bodyfat you shouldnt need to much eat less than 200 calories below what is recommended for your activity level.