Tag: <span>Excess Body Weight</span>

When surgeons talk about the expected weight loss outcomes of bariatric surgery, they talk about the expected percentage of loss of a person’s Excess Body Weight.

For instance, they will say that a typical Gastric Bypass patient can expect to lose 70% of their excess body weight after about 12-18 months.

That’s not 70% of their current weight, but 70% of their excess weight. But how does anyone calculate what their excess body weight is?

Well, I found out that it starts out with calculating my Ideal Body Weight.

Ideal Body Weight

The ideal body weight is meant to represent, as the name suggests, the ideal body weight a person should be for their height and gender.

Unfortunately there is not just one formula used for calculating ideal body weight. There are, in fact, at least five of them! And they all give a slightly different answer about what an ideal body weight should be.

I used this ideal body weight calculator to try and find my ideal weight, based on my height of 188 cm and my gender as male, and got the following results:

  • Peterson formula (2016) – 77.7 kg
  • Miller formula (1983) – 76.0 kg
  • Robinson formula (1983) – 78.6 kg
  • Devine formula (1974) – 82.2 kg
  • Hamwi formula (1964) – 85.8 kg

That’s a range from 76.6 to 85.8 kg – almost a 10 kg difference! So what is the correct value for ideal body weight?

Well to confuse things further, some people prefer to use BMI to calculate the ideal body weight.


BMI, or Body Mass Index, has a target range of between 18.5 and 24.9 defined for a normal weight. It’s calculated as weight divided by height squared – but you can use a BMI Calculator to do the maths.

For me the normal BMI weight range would put me between 65.4 and 88.4 kg – which I suppose more-or-less corresponds with the different ideal body weight calculations above.

Excess Body Weight

To calculate my excess body weight, I need to subtract my actual body weight from my ideal body weight. However, so far there seems to be no single value for ideal body weight I can use. All the different formulas give different results, so which value should I use?

Well I’ve decided to go with the most recent Peterson formula, as it seems to reflect the most recent thinking on ideal body weight, and for my purposes is based upon a target BMI of 22 that’s pretty-much in the middle of the normal BMI range.

The calculation for my Excess Body Weight is:

Weight on Day of Surgery (163.7) – Ideal Body Weight (77.7) = Excess Body Weight (86.0)

Expected Weight Loss

Estimates vary between surgeons, and experiences vary between patients, but the perceived wisdom is that:

  • Gastric Bypass patients can expect to lose 70% of their excess body weight
  • Gastric Sleeve patients can expect to lose 60% of their excess body weight

And so, based on an Ideal Body Weight of 77.7 kg, and an Excess Body Weight of 86.0 kg, and an expected weight loss of 70% from my bypass, that would set me expected weight 18 months after surgery to be 103.5 kg.

A expected weight of 103.5 kg would give me a BMI of around 29, which is still in the overweight range, but at least it’s not in the obese range any more!

So, for now, I guess my goal is to get down to 103.5 kg (or 16 st 4 lbs / 228 lbs)

Surgery Weight

I was curious to find out the average weight loss for gastric bypass patients, so that I could reality-check my expectations.

I have this goal in my head that I’d like to get down to 105 kg, which for a man of my height would take my BMI below 30, and make me officially ‘Overweight’ rather than ‘Obese’. Some might say that I should be aiming for a more ambitious goal, and try and get my BMI down below 25 into the ‘Normal’ weight category. However I wanted my goal to be achievable and realistic.

I found a blog article about how much weight you lose in a month, and I decided to use the information in it to check out if my 105 kg goal is realistic, not ambitious enough, or too ambitious.

The article talks about calculating my Ideal Body Weight, and working from there. And according to their chart, my Ideal Body Weight is 171 lbs or 77.6 kg.

From there I need to calculate my Excess Body Weight, which is the amount of weight I am above my Ideal Body Weight. In my case, on the day of my surgery my Excess Body Weight was 86.1 kg.

Expected excess body weight loss

Different bariatric procedures seem to have different results in terms of the amount of the Excess Body Weight that will be lost:

  • Roux-en-Y Gastric Bypass : 70% of excess body weight will be lost
  • Vertical Sleeve Gastrectomy: 60% of excess body weight will be lost

So with my Excess Body Weight of 86.1 kg, and an expected loss of 70%, then my expected loss is 60.3 kg, and my expected final body weight is 103.4 kg.

As such, my personal goal of 105 kg actually seems about right.

Expected first month weight loss

The article also says that gastric bypass surgery patients generally lose about 17% of their excess weight in the first month.

For me, 17% of my excess body weight is 14.6 kg. But in the first month I lost 10.9 kg, which is just under 13% of my excess weight.

However this 17% goal is based upon a US bariatric post-op diet that seems to be a lot more restrictive than the one I’m on. It has patients on liquids for 2 weeks, pureed food for another 2 weeks, and then soft food for another 12 weeks. Whereas my bariatric team had me on liquids for only 1 day after surgery, then pureed foods for the rest of that week, and soft foods for the next 5 weeks.

So I guess I’ve probably been consuming more calories in my first month than a typical person following the US diet. So I’m not going to worry about not hitting this 17% target.

Surgery Weight