How to Measure Body Composition – Women and Fasting Part 4

In last week’s post we discussed the importance of understanding your body composition.  The scale only tells us our total body weight but not what are body is composed of.   We don’t want to have a very low body weight if we are weak, brittle and mostly made up of fat.  In this week’s blog, we’re going to discuss how you can measure your body composition, so you can have a better understanding of your overall health status.


Magnetic Resonance Imaging (MRI)

Having an MRI is the gold standard for knowing your body composition.  The problem is it’s very difficult to get an MRI.  They’re very expensive tests and many hospitals and clinics often have very long wait times.  Don’t worry – there are other great alternatives that are much more economical and time efficient than an MRI.


DEXA Body Composition Scan

Most of us have heard of DEXA scans that measure our bone mass density, but you can have a DEXA scan that measures your total body composition.  It’s a low radiation scan, so it’s quite safe for women who aren’t pregnant to have.

What can you learn from a DEXA body composition scan?

  1. Your total fat mass and where it is distributed within the body
  2. The amount of lean mass you have and where it is located
  3. The weight and general quality of your bone mass
  4. Your resting metabolic rate (RMR)

How often should you go for a scan?

Most DEXA body composition scans cost around $100.  Some clinics will let you purchase packages of three or six scans at a discounted price per scan.  I know that can be a bit pricy for some, but you don’t have to go very often.  It takes awhile for your body composition to change.   Below is how often I recommend my patients, who can afford to, go for a scan:

  1. Baseline

It is always good to know where you’re starting from and have measurements to go back to later if you decide to do any future scans.

  1. Every 4 to 6 months

Body composition is slow to change.  You will see very small changes from month to month, but those changes add up to be significant changes in larger chunks of time.  As a result, going for scans too frequently can be a waste of time and money.

  1. Feeling stuck

It is good to go for a scan if you start to see the scale creep up and you’re feeling nervous.  Often, we’re just gaining lean mass, which is great!  We want to be have strong bones and muscle to protect us as we age.  Having a body composition done during these times can give you a real peace of mind since you can see you’re losing body fat and gaining bone and muscle mass.

  1. When you think you’re at your ideal weight

This is the only time I’m pushy with some patients.  A lot of them will come in and say they don’t’ want to lose anymore weight since they’ve reached their goal on the scale, but I know they still have a very poor body composition because of their metabolic numbers in their labs.  People who weigh very little can be extremely obese if they have a poor body composition.  Having a scan done can often be a reality check to encourage the patient to continue to fast but to start being more active in order to put on healthy weight.

Are there any limitations of DEXA scans?

While these scans are the next best thing to MRIs, they aren’t without flaws.  There are two major things to consider while interpreting your results:

  1. They report a reduction in organ fat as muscle loss

DEXA scans interpret the fat in organs as muscle mass.  If you have a fatty liver, the scan is going to measure your large liver as a muscle rather than fat.  This is problematic for interpreting your results, especially if you do a repeat scan after losing liver fat.  Losing any organ fat is a great thing, but the scan will make it appear like you’ve lost muscle mass.  This is something to be cautious of.  I always recommend that patients have a baseline abdominal ultrasound to check to see if they have a fatty liver, pancreas or spleen.  This way we can help interpret the DEXA scan results more accurately.

  1. Glycogen stores can make you look like you have more lean mass

If you have a wild, carb filled weekend, you’re body is going to store a lot of those carbs as glycogen in your liver and in your muscles.  This will make your liver and muscles appear to be much larger on the DEXA scan than they are, so you end up thinking you’ve got more muscle mass than you really do.  It’s best to wait a week or two after feasting on carbs to go for your scan to ensure you’re getting the most accurate reading possible.

Interested in getting a DEXA scan in the Greater Toronto Area (GTA)?  A good friend of mine, Dr. Suleiman Furmli, who is a family doctor, came to shadow me in clinic one day.  He was never really taught about body composition in medical school, and he realized during our time together how important body composition is.  He went to try to book a DEXA scan for himself and realized that there weren’t many available in his area.  He was concerned that the lack of availability would prohibit his patients for going for this test, which he thinks is very important.  He went on to co-found with colleagues of his to try to provide more centres for body composition analysis across the GTA.

Watch this video to learn more about DEXA body composition analysis. 


Body Composition Scales

Not everyone has access to DEXA scans in their area, and I get asked a lot about body composition scales.  I’ve tried hundreds of them and have compared them to my DEXA scan results.  The expensive ones aren’t that much better or more accurate than some of the inexpensive ones.  You can often find a decent one on Amazon for around $50.  They have the same limitations as the DEXA scan, so be mindful if you have one at home and check your composition regularly.  Also, you always want to be checking at the same time of day, preferably first thing in the morning after you’ve fasted and have gone to the bathroom.  Keep in mind they’re not being calibrated by professionals on a routine basis.  I’ve found that they function the best for the first year but start to become unreliable after that.

Waist Circumference

Measuring and noting changes to your waist circumference is a great and affordable way to measure your metabolic health.  Its biggest limitation is that it can’t tell us how much dangerous organ fat (visceral fat) or less dangerous non-organ fat (subcutaneous fat).  If a patient doesn’t have a lot of subcutaneous fat, they may appear to be very slender despite having metabolic syndrome.  This doesn’t rule out any visceral fat, which is the biggest issue with taking measurements in this patient population.

I also encourage patients to take their measurements everywhere and track how much they lose all over their bodies over time. You might not feel like any weight is coming off but being able to quantify the size of your stomach, hips, thighs, arms, etc., can demonstrate to you that progress is being made.

Progress Photos

The cheapest and easiest way to note changes is to take progress pictures.   I encourage patients to take photos monthly so there is enough time to see changes.  It’s hard to tell how much your body is changing when you’re regularly seeing yourself in the mirror, but you’ll be surprised how much you’ve actually changed if you can go back and look at photos of yourself two months ago

2018-11-29T10:44:24-04:0013 Comments

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My weight has not changed in a year of clean fasting with a four hour feasting daily window. Nor have my body measurements, but my belly fat continues to melt away. It’s amazing to watch the transformation.

IF for life.


How is it possible that your belly fat is melting away if your measurements have not changed? What is now at your waist measurement in place of the belly fat…


What do you think of the BodPod in terms of body fat composition? I have access to have this done monthly for free. I have done three already and have dropped 10% in body fat. The one drawback I see is that it only distinguishes between body fat and “everything else”. So no breakdown of what “everything else” is in terms of bone, lean muscle, etc. Thanks for this series Megan. I have not seen the scale move in theee weeks, yet am seeing a difference in how my clothes fit. I am learning not to be as dependent on… Read more »


Does anyone know if there is anywhere in Calgary that you can have a DEXA scan done?

Patti A Johnson

Great info, Megan! TYVM!!! 🙂 <3


Thank you for that series, It came at a great time for me as am at a weight loss plateau (not in the scale but according to my clothes) so I’m trying a 24h twice a week fast. Your articles encourage me to try the longer fast as the 18/6 stopped working for me.
Thanks again for encouraging us women to fast & not be afraid of fasting.


Using numbers from a DEXA report, here’s the formula that will extrapolate the weight someone would see on their bathroom scale for any desired fat mass percentage they might like to reach:

scale weight = (lean mass + bone mass) / (1 – desired fat percentage)

This of course, assumes that they didn’t transform to either an Arnold Schwarzenegger or Danny De Vito between their the first and follow up scans!


Given that the accuracy specs of DEXA say it can mis-state your body fat % by 5% (or more) I don’t see how it is useful. And don’t get me started on the body fat scales. They use lookup tables to make assumptions about your body composition based on sex and age. So when I lost 10 pounds of fat and gained 10 pounds of muscle, the scale showed exactly the same body fat. What use is that? (More evidence is how the “athlete” setting gives wildly different results, but it makes no sense that there is a hard break… Read more »


Thanks for the Great comment.


Can dexa differentiate edema and water weight from fat and lean mass? My husband has a lot of daily weight
variation due to water retention so I feel like dexa wouldn’t be helpful for him unless it can tell.


I’m very new to fasting as a 61 yr old woman.. mostly trying 16/8 18/6 .. want to step it up and try to get some exercise.. I’ve notuced when I walk upstairs, or try exercising I don’t seem to have any energy in my legs.. tire in seconds.. my arms too.. prob thro years of dieting low fat regimes ..
I’m 4-5 stones overweight.. BMI 35.. lost 1 stone in 6 weeks doing keto and above regime..
how can I proceed in the right direction .. any ideas welcome


Magnesium supplements help me when my legs feel like lead when going upstairs.


Can we in Ontario just request doctor refer us for Dexa? and is it covered by OHIP? I read about various blood tests etc and have never asked for specific workups (didn’t think we could- had to be physician referal only) nor do I receive copies of blood test, MRI, etc results.