My girlfriend asserts that extremely obese people can lose about a pound a day on a starvation diet.
When I think about this from a biological perspective, I get confused.
A pound of fat is about 500 grams and each gram of fat is 10 Calories. Therefore a pound of fat is 5000 Calories. I’m wondering how an obese person, presumably inactive, could burn 5000 Calories a day. An average person burns about 2500 Calories per day. By my calculations, a person can only burn 1/2 pound a day.
Perhaps more mass equals more energy burned.
Can anyone help?
Larger organisms burn more calories than small ones, this is why a 100 pound dog needs more food than a 10 pound lapdog.
So a larger person needs more food than a smaller person. However, fat deposits don’t require very much metabolic maintenance compared to muscle and organs that are metabolically active.
Also extremely obese people on extreme diets like this can also lose tremendous amounts of weight just by losing water. Boxers will go to extremes to cut weight before weigh-in, but a very large fraction of that is water weight.
I agree, that is pushing the limits of what is possible. In the early stages of weight loss, it might be possible to lose that with help from fluid loss. I can’t see it being sustainable for any length of time though.
With this calculator you can see how many calories are required to maintain body weight at various levels. To maintain a 600 lb weight requires nearly 5000 calories a day. Cutting that back to 2000 calories a day (medically supervised) would probably get you in the ballpark but not quite reach 1 lb/day.
As to the water weight, I’ve managed to lose 10+ lbs a week at the start of a weight loss program but that’s not sustainable.
One correction to the OP - a pound of fat has about 3,500 calories. There’s been a few threads lately about the complexity of losing weight, so you might want to search through those for some good discussion.
This. Fat cells, just like muscle cells, are alive; they require a constant supply of fuel and oxygen to sustain themselves through the usual process of cellular respiration. A 240-pound professional body builder requires more calories per day to maintain all of his muscle mass than a 240-pound couch potato requires to maintain all of his fat reserves - but each of them requires more calories than a 160-pound adult with normal levels of fat and muscle.
I lost 25 pounds in 2 weeks when I became a diabetic. It was mostly water loss as discussed above, and honestly, I don’t recommend it.
People are often disappointed when the rapid loss of water weight in the first few days ends. On a starvation diet it’s difficult to burn calories, your metabolism slows down and you rapidly become too tired for much activity.
Also, using averages for calorie consumption and expenditure isn’t very useful, people have different sizes, the components of the body like bone, fat, and muscle vary in percentages, and a body adjusts to changing conditions like food intake and energy expended.
To answer the OP, the fastest way a person can lose weight is by surgery.
Such as liposuction, an immediate surgical removal of accumulated fat. Other weight-loss surgeries (gastric bypass, balloon, sleeve, etc.)are restrictive measures, designed to limit eating to reduce weight & keep it off over a long term.
But I’m not sure if this is what the OP wanted to know.
You neglect to mention the rapid weight loss that can be achieved by selected extremity amputation!
Hop in a pool of lava. The pounds will just melt away right before your eyes (melt)!
I was thinking, “being targeted by anti-aircraft fire”.:eek:
Cutting off your legs.
Amateur, just get yourself vaporized in a nuclear explosion, it’s faster and more effective.
If you watch the show my 600 lb life, it isn’t uncommon for a 600 lb person to lose 50-70 lbs in the first month.
How much weight can you lose?
It is mostly calories in vs calories out. How many calories a day do you burn due to your natural biology and activity level, vs how many do you consume each day?
A person who weighs 600 lbs who is a male (men have more muscle) may be burning 8,000 calories a day. An hour of walking will probably burn another 1000 calories. So if a 600 lb person walks 2 hours a day, that is a 10,000 calorie a day demand.
If they are only eating 1,000 calories a day, then they will burn 9,000 stored calories. Most (maybe all, not sure) of that energy is going to come from fat. Since there are 3500 calories in a pound of fat, a person that large can lose about 2.5 lbs of fat a day.
But a woman who weighs 110 lbs can’t lose 2 lbs of fat a day, its pretty much impossible unless she finds a way to run a 7000 calorie a day deficit (which I guess she could if she did severe activity all day and ate almost nothing, but she’d probably pass out).
Anyway, its a question of calories in vs calories out. How big is the deficit. If you are burning 8000 calories a day and eating 2000, you have a 6000 calorie a day deficit which is almost 2 lbs a day.
As a metaphor, it is like if you want to drain your bank account as fast as possible. How do you drain your account? Increase your spending and decrease your external income. Someone who starts buying a ton of luxury items and quits their job will see their savings depleted faster than someone who lives normally and keeps their job. Its the same with weight loss.
There is also speculation that a lb of fat can only mobilize so many calories a day, but I’m not sure how true that is. I’ve heard 31, but I think you can mobilize more after that but you’ll lose lean tissue. I’d wonder if things like carnitine would increase that number.
Clearly losing too much weight too fast is unhealthy. So I have a different spin on the question. What is the fastest an ideal human specimen* would lose weight under “ideal” circumstances?
If this hypothetical person were stranded on the proverbial desert isle with very little water (so enough to stay alive but not enough to add more than a trivial amount of water weight) and no food, during the period with the most rapid weight loss how much would they lose per day? (Assume that before they starve to death they are rescued).
*By ideal I mean a person with the height, weight, and metabolism that would allow them to lose weight the fastest without dying. E.g. I would assume someone weighing 200 lbs could lose more weight more quickly than someone who weights 95 lbs.
I weighed about 235lb when I decided to try the Atkins diet. (5’10", male). I lost about 12 lb in 2 weeks, and continued to lose about a pound every day or two. Never had any health problems, other than really weak and tired the first few days.
(In fact, I got down to 208lb - went from size 38 or 40 pants to size 33; but of course put it all back on over the next few months with my usual eating habits… and then some.)
It’s a common misconception (and one I had myself) that liposuction is a weight-loss strategy. It ain’t.
Angus Barbieri weighed 456 lbs. and didn’t eat anything for 382 days, hitting his goal weight of 180. That’s an average loss of .72 lbs. a day.
How do you survive more than a year without calories??