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Valarie, Nurse (RN)
Category: Health
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Experience:  36+ yrs exprience medical, surgical, wound/skin care, nutrition, geriatrics, rehab, management
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After gastric bypass surgery, patients have reported 100

Resolved Question:

After gastric bypass surgery, patients have reported 100 pounds weight loss in 5 weeks. That is 20 pounds per week, or 2.857 pounds per day.
My question is, how can someone lose 2.857 pounds per day? If the amount of weight lost is the daily intake of calories minus daily expenditure of calories, losing 2.857 pounds in a day would require 'burning' 10,000 calories per day.
How is this possible? Even if a person ate nothing, one would only expect to burn ~2,500 calories per day at resting metabolism. Where does the excess ~7,500 calories come in? Working out 12 hours per day at a 625 calorie per hour rate (this is difficult to do - equivalent of intense bicycling effort for 12 hours straight) would do it, but I doubt these bypass surgery patients were eating nothing and working out 12 hours per day.
So how does anyone, even a gastric bypass patient, lose 100 pounds in 5 weeks?
Submitted: 6 years ago.
Category: Health
Expert:  Valarie replied 6 years ago.

Hello. Thank you for coming to JustAnswer with your question, and welcome.

Where did you hear that patients lose this amount of weight in 5 weeks?

Customer: replied 6 years ago.
1) Scientific American Frontiers had an episode where two people with gastric bypass surgery were followed to show their results after the surgery. I can't remember exactly what the loss was but it was certainly more than 1 pound per day, which isn't the same scale as the 2.857 pounds per day of 100 lbs in 5 weeks, but is still more than I would expect someone to be able to lose.

2) On this website a person talks about their weight loss after gastic bypass and they specifically claim "more than 100 pounds in 5 weeks":

(check the first question in the FAQ link on that site)

3) Here is a link from a medical organization that would suggest something similar:

The claim here is that "The average patient will lose about 75 to 80% of their excess body weight by the end of the first year following surgery."

If a person weighs 400 lbs and their "ideal" weight is 150, then the loss would be 75 - 80% of 250 lbs, which is about 195 lbs in 1 year. This is about 0.5 pounds per day. Even this rate of loss suggests something more than just "calorie burn" is the cause, as 0.5 lbs per day is ~1750 calories per day, and I am not sure how anyone can maintain a 1750 calorie deficit every single day for a year.

I guess it would be good to have some more concrete numbers though; it's hard to tell what the average or maximum weight loss is for gastric bypass patients over the short interval directly following the surgery.

If you search on the web it is easy to find stories of people who claim (apparently legitimately, part of normal discussion groups and not for-profit web sites) to have lost 200 lbs in one year. So I feel like losing 1/2 lb a day is not unheard of by any means. I just don't understand the physiology of losing that much weight that rapidly - can it really be explained by 'burning calories' - or is there something else to it? Maybe on average really heavy people lose a percentage of water for each lb of fat they lose (fat cells get smaller and need less non-fat tissue to support the smaller quantity of fat), and that explains some of it?
Expert:  Valarie replied 6 years ago.

As you are probably aware, bariatric surgery (there are a number of different types of procedures) basically causes your intake to be drastically restricted, and in some cases there is a "malabsorption" of nutrients going on as well.

Having dealt with many patients in my life who basically stop eating for various reasons, I know that 1 lb a day or more is possible even with people who have no excess calories stored (fat).

So, losing up to 80% of excess weight (which would be fat) in a year's time is not unreasonable with some people. When anyone loses that much weight however, there is also more than just fat lost. Many of these people can also have nutrient deficits, just like anyone else whose diet is too restrictive.

Generally, however, I think the more average person having this type of surgery can expect 50 to 60% of excess weight lost after a year or two. And then, some of those will regain a few pounds by the 2 to 4 year point.

As far as calories burned, you can only lose (3500 calories per lb of fat basically) the amount that your body uses (if you don't replace the calories). Some people will have fluid loses at first which account for quite a bit of weight depending on their health concerns when they have the procedure done. Fluid is very heavy. And many people who have this done are so overweight that they have other health issues, heart problems, fluid retention, etc.

In the lady's blog you posted, she went from 500 lbs to 158 in about 4 years, which would be an overall average of a little over 7 lbs per month. This is very possible. Her pictures look great (if they are real---it is a blog), and I am sure she had surgery afterward for excess skin etc. And if you look at her weight graph, the weight loss slowed down quite a bit after the first few weeks, so she probably had some fluid retention problems as a result of her normal intake and weight issues. Still....its a lot for 5 weeks.

The other site from University of Maryland Medical Center is a realistic view of the average person's results from bariatric surgery.

As far as stories on the web......well, they are stories. Everyone has one. Some will be true, many will be at least greatly exaggerated.

So again, to answer your question:

There is more than restriction of calories. There is fluid loss due to decreased intake of calories and sodium. Just being overweight can cause fluid retention. There may also be some component of malnutrition after a time, which results in your body not functioning properly.....this can also account for more loss than simple burning of calories. Severe restriction of food can cause loss of muscle tissue as well.

Customer: replied 6 years ago.
Thank you for your response.

Just as a final followup, is it then safe to say that the only mechanism for losing fat is to utilize that fat as calories, and that anyone who loses 1 lb of fat must have 'burned' 3500 excess calories. Additional weight loss beyond the fat itself can be explained by fluid and other tissue loss. The sum of the loss of fat (due to utilizing the fat for metabolic processes) and loss due to non-fat tissue and fluids can approach 1 lb per day but beyond that is highly unusual and even if achieved is still achieved using the same mechanisms as normal weight loss.

What I was wondering is if there is some other way that the fat is being lost (like being excreted by the body at a rate faster than the uptake that was previously sustained through extreme caloric intake, not being metabolized but instead being secreted in some way, i.e. defacated somehow), but I believe your answer is to say that there is no other process beyond metabolization of fat to eliminate fat from the system.

Therefore, I would conclude that reports of excess weight loss where that weight loss would not be explainable by reduced caloric intake and increased physical exercise, and in additionally, for extremely heavy people, contributed to by loss of retained fluids and cell material that supported the large fat stores, are more than likely due to exaggeration of either the amount or the time scale over which the amount was lost.
Expert:  Valarie replied 6 years ago.

Yes, you are correct. Fat is basically stored calories. It does not need anything to maintain itself (calories, I mean). The cells basically shrink or get larger depending on the use of, or the storage of fat.

Of course, this is a very simplistic way to explain how weight loss works. There are other things that influence weight loss and/or gain. (metabolism, nutrients, hormones, genetics...) But it is basically correct.

There is no other way for the body to rid itself of fat. It can be surgically removed, but beyond needs to be used as energy to shrink.

And yes, I would say that the stories you read are largely exaggerated. (Who wouldn't want to exaggerate their weight loss success?) Bariatric surgery is necessary and effective for some people with extreme weight problems, but it is by no means a miracle cure. There are still issues to deal with for most people, even after massive amounts of weight have been lost. And some people I know who had it done will figure out a way to regain the weight by just eating more frequently in very small amounts.

Just FYI: here is an article about How Fat Cells Work.

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