Defining obesity

Posted on December 11, 2024 by - General, Medical Podcast, Podcasts

In this episode of PodMD, Melbourne-based surgeon and researcher, Dr Sean Mackay, will be discussing the topic of defining obesity.



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  • Transcript
    Please note this is a machine generated transcription and may contain some errors.
    *As always, all in this PodMD podcast is intended for health professionals and the comments are of a general nature. Information given is not intended as specific medical advice pertaining to any given patient. If you have a clinical issue with one of your patients please seek appropriate advice from a colleague with expertise in the area.

    Today I’d like to welcome to the PodMD studio, Sean Mackay. Sean is a consultant surgeon in the Upper GI and Hepatobiliary Surgical Unit at Box Hill Hospital, which is part of Eastern Health. He’s an associate professor in the Eastern Health Clinical School, which is part of Monash University. He practises in private at Eastern Epworth Hospital where his practise includes Upper GI Hepatobiliary and bariatric surgery and of course, he is one of the founders and principles of PodMD.

    We do hope you enjoy this podcast but please remember that the advice here is of a general nature and is not intended as specific advice about a given patient. The views and opinions expressed in this podcast are those of the doctor, not PodMD.
    If you do have a patient on whom you require specific advice then please seek advice from a colleague with appropriate expertise in that area.

    Question 1
    So Sean, welcome today. As we said to the PodMD studio and believe you’re going to be talking today a series of podcasts actually that you’re making in relation to obesity, having just returned from an international conference on the topic.

    Sean: That’s right, Caroline. And in fact, I didn’t have to return very far, cause we were very lucky that the International Conference for the If so, the International Federation for the surge of obesity and metabolic disease actually came to Melbourne in August, so that was very convenient and it was a very good conference. The other major group in obesity and metabolic surgery is the American Society for Metabolic and Bariatric Surgery. So these two groups are the two big groups for surgeons and increasingly for bariatric physicians.

    Question 2
    Well, the conference sounds great. We really look forward to hearing your information about it. Maybe we should start with defining obesity Sean?

    Sean: Of course, as you know, the BMI has long been the measure that we’ve used to define obesity, and that is the patients weight in kilogrammes divided by the square of the patients, height in metres, and that is an easily done and reproducible index of the patients obesity, although it’s not perfect, but in day-to-day practice, in most cases it’s it’s all that we need.

    Question 3
    Well, today we’re talking mostly about obesity. So what is an actual obese level according to the BMI?

    Sean: The stated normal range for BMI is 18.5 to 25, with the 25 to 30 range being considered overweight and BMI above 30 being classified as obese. And in days gone by, we’ve used the term morbid obesity for those with a BMI of greater than 40 who would be considered suitable for bariatric surgery even without comorbidities. But in the recent years, there’s been a move to classifying the BMI over 30 into class one, two and three obesity and the ranges are 30 to 35, 35 to 40, and 40 and above. So what used to be called morbid obesity is now called Class 3 obesity.

    Question 4
    So BMI is certainly one of the measures that you utilise. Where does that sort of maybe come unstuck or where are there other sort of areas that we need to consider?

    Sean Well, as I mentioned in clinical practice the BMI is all you need most of the time, but there are two things that it doesn’t do. It doesn’t take note of the individual patients natural physical build and it doesn’t take note of the distribution of the fat within the patient’s body. And both of those things can be important.

    Question 5
    So to deal with the first of those, what about the patients build?

    Sean: Caroline, someone who is naturally fixed, set broad shouldered, broad in the hips, will naturally have a higher BMI than the average person, and so any if they do gain weight, any degree of obesity will be overestimated by the BMI. And likewise, someone who has a relatively slender build, their degree of obesity will be underestimated by the BMI. And in fact, in clinical practice there are certain definable groups in whom we have to make an adjustment. Of most relevance in Australia is people from a Southeast Asian background, and we in fact add on 2.5 BMI points for people from a Southeast Asian background, rather than adjusting those BMI cut offs of 30, 35 and 40. It’s also true in the literature and not so much of an issue in Australia, but in the American literature, that African Americans we actually take off 2 BMI points, understanding that in general that they tend to be solidly built.

    Question 6
    So you mentioned the distribution of fat and the pattern of the person’s obesity. Tell us more about that.

    Sean: Well. When someone is overweight, obviously that has inherent issues for them in terms of mobility issues with arthritis perhaps, and that will not vary. Depending upon the distribution of the obesity. But in terms of the complications of obesity that relate to the metabolic syndrome to endothelial dysfunction, it’s visceral adiposity that causes that. So it’s intraperitoneal fat deposition. And in terms of those risk factors, you know a woman, for example, who has a gynoid pattern and has all of her weight on her buttocks and thighs probably doesn’t have an elevated risk of diabetes, hypertension compared to a male who has the classic pot belly and an entirely intraperitoneal obesity. So the same BMI can represent 2 quite different risk profiles, and that needs to be considered when thinking about metabolic syndrome as an indication for obesity surgery.

    Question 7
    Well, metabolic syndrome is going to be a topic of another podcast that you’re kindly going to make for our listeners and that’ll be interesting to hear. But what about when BMI is not a perfect indicator of metabolic syndrome? Cause it’s certainly a huge problem in today’s society.

    Sean: Thanks, Caroline. I think the easiest way is perhaps to give an example. If we imagine a male with a BMI of 33 and hypertension but doesn’t have diabetes, although he has a bad family history of diabetes and that BMI of 33 comprises entirely intraperitoneal fat. He’s tried to lose weight, but he’s been unsuccessful. It’s pretty clear that he is going to develop diabetes in time and the complications thereof, and it seems unreasonable to deny him surgery. And I do note that Metabolic surgery, which is weight loss Bariatric surgery for type 2 diabetes, is an accepted treatment at a BMI of 30 or even 28 in some health jurisdictions. So in that situation, I think that one seriously has to ask, why should we keep this patient waiting. In that situation I’ll typically present the case to a surgical colleague and get that person’s opinion, and sometimes ask my patient to go and see the other doctor for a formal second opinion. I don’t think that there’s enormous value in doing testing of body fat percentage, that could be the subject of more than one podcast probably it’s an interesting area. Body fat percentage is a better index than BMI, but it’s just not practical to do accurately. Anyway, so I think that the patient who is on the margin as long as it it’s not the typical patient in a bariatric surgeons practice I think it’s reasonable under appropriate circumstances to offer surgery which is a little outside the guidelines.

    Question 8
    Well thank you for that terrific podcast today, giving us the latest definitions of obesity. We look forward to more podcasts in the series. We need to for our listeners just wrap up with the three take home messages, Sean. So what would they be today.

    Sean: I think the first message is that the BMI is still the mainstay of our objective assessment of the patient’s degree of obesity, and there are some new definitions there with Class One, Class 2 and Class 3 as we mentioned. I think the second point is that there are patients who are not really perfectly well served because they’re on the margins of an indication, for example, for surgery. But I’m not embarrassed to fall back on good old fashioned clinical judgement from time to time. And the third take home message is that although there is just so much to read, We have put up a link, the DOI link. You can follow it directly to an important consensus paper from 2022, where if so, and a SMBs, they’re the two umbrella organisations I mentioned at the start, have set out a very thorough and very powerful review and then recommendations for indications for metabolic and bariatric surgery.

    Well, we look forward to the rest of the obesity podcasts in the series. Sean, thanks so much for joining us today.

    Sean: Thanks Caroline.

*As always, all in this PODMD podcast is intended for health professionals and the comments are of a general nature. Information given is not intended as specific medical advice pertaining to any given patient. If you have a clinical issue with one of your patients please seek appropriate advice from a colleague with expertise in the area.