07 January 2021


Section 3: How much weight will I lose?


Excess weight loss

Specialist bariatric surgeons, dietitians and nurses use the term ‘excess weight loss' as a measure of your progress following surgery. Excess weight is defined as:

Pre-surgery weight (in kilograms) minus ideal weight (in kilograms)

Your ideal weight is defined as your weight at a Body Mass Index of 25kg/m2. This is calculated by multiplying your height in metres squared (i.e. multiplied by itself) by 25.

For example, if your height is 1.65m, multiply this by itself to make 2.7225 and then multiply this by 25 to obtain your ideal weight in kilograms (68kg). 

Weight loss after the gastric bypass and gastric sleeve

Generally, gastric bypass and sleeve patients lose up to 3lb (1.5kg) per week in the initial stages after surgery. This tends to slow to 1-2lb (0.5kg to 1kg) per week by six months following surgery.

The average weight loss after three years is*:

  • 55-70% of your excess weight with a gastric bypass.
  • 55-60% of your excess weight with a gastric sleeve.

However, the majority of this is lost in the first 12-18 months.

(*Source: National Bariatric Surgery Registry, Second Registry Report, 2014)

The dietitian will discuss your excess weight loss at each of your postoperative appointments.

The rate of, and total weight loss, depend on several factors:

  • Your initial weight – People with more weight to lose tend to see a greater week-by-week loss (especially initially after surgery). However, it’s important to remember excess weight loss; if you had ten stone to lose and have lost a stone, you have lost 10%, but if you had five stone to lose and have lost a stone, you have lost 20%.
  • Your gender – Men have a higher muscle mass than women and, given that muscle is more metabolically active than fat, men do tend to lose weight faster than women.
  • Your dietary choices – To get the best results from the surgery, it is important to eat healthily whilst limiting high calorie foods and alcohol. Follow up appointments and our general guidelines on life with a bypass or sleeve will explain the diet after surgery in more depth.
  • Your exercise levels – Patients who increase their physical activity level lose more weight than those who do not. Your ultimate aim should be to ensure that you do some sort of exercise that increases your heart rate for 30 minutes, five times a week. See Physical Activity for more information.

Judge your progress by how your clothes fit, as well as by actual weight loss. Sometimes, your weight loss may slow but you could be losing inches, especially if you are exercising (See Physical Activity).

How to get the best results

In order to achieve the best results, you MUST stick to the eating regime AND follow the dietitian’s advice:

  • Take small bites, chew properly, eat slowly, and never binge eat. Poor eating technique can cause pain on eating and/or vomiting and stretch the stomach. (See bypass/sleeve risks of surgery, potential complications, side effects.)  This may jeopardise your potential to maximise your weight loss and can increase the risk of weight regain.
  • Be prepared to realistically change your lifestyle, i.e., eat at regular intervals, eat a varied diet, cut down on high calorie foods/drinks and alcohol, and increase exercise.
  • Actively ensure that you have regular follow-up appointments. Let us know if any proposed dates are not convenient, and we can reschedule them or arrange a telephone consultation.

What if I am not losing weight?

  • Call us to arrange a video, telephone, or if necessary, face-to-face appointment with a dietitian. It may be that you need to change the way you are eating to work with the surgery, not against it. Remember – dietitians working in weight loss surgery are here to help you get the best from the surgery, not just tell you how to eat healthily!
  • Increase your physical activity.
  • Keep a positive attitude, and set realistic targets throughout your weight loss journey. Evidence shows that people who have something to focus on mentally often have the best results. Perhaps you have a wedding to attend, have booked a holiday abroad and want to look good on the beach, or have health problems and want to feel better. Whatever your situation, find something realistic yet personally important and aim for it at all times.

You should be aware that surgery is not a quick fix or a magic cure for obesity; you will need to work with it, and therefore there are no guarantees.

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