This is a rather long post but I hope you will persevere with the story because I am very interested to hear some other opinions on this subject matter:
Last Thursday I had a DEXA scan which produced the following results:
Total Mass (TM
): 69.0 kg
Fat Mass (FM
): 15.63 kg
Lean Mass (LM
): 50.72 kg
Bone Mineral Content (BMC
): 2.60 kg
Visceral Fat (VAT): 1.03 kg (included in FM)
The clinical exercise physiologist (CEP) who did the scan told me the following:
"Your visceral fat result of 1.0kg is not good. It should be 0.4kg or less. Ideally it should be zero. I suggest a calorie reduction program to help you lose more weight and I suggest you make an appointment with our registered dietician to get some guidance about this."
Eeeeek Ö.. the very mention of the words Ďregistered dieticianí made me want to flee for the front door but I lingered to ask some questions:
Q: I have lost more than 25kg of weight in the last 16 months. Do you have any idea what my visceral fat would have been when I was still obese with a body weight of 94 kg?
A: I donít know but for sure it would have been worse.
Q: OK but you must have done many of these DEXA scans. What is the worst amount of visceral fat you have ever measured?
A: Yes, I have done more than 900 DEXA scans on male subjects and the worst amount of visceral fat I have seen is 4 kg.
Q: Is there a safe level of visceral fat?
A: No all visceral fat is bad.
Q: How much extra weight do you think I need to lose in order to bring my visceral fat below 0.4kg?
A: You need to discuss that with the dietician but I also suggest that you come back for repeat scans every 3 months to see if your visceral fat is reducing.
The CEP also emailed me my results and added the following:
"Regarding your lean mass value, please refer to the following link which shows that someone of your age, sex, height & weight should have at least 49.7-54.0 kgs of lean mass, depending on which formula used (although I prefer The James Formula as it is the most recent). Your lean mass of 50.72 kg is at the lower end of your matched average population range, and therefore this would indicate that you would benefit from a strength/resistance programme to build lean mass, once you have reduced your visceral fat mass." LBM Calculator
All of this was a little bit disheartening because in fact I have already been following a strength/resistance program ever since I commenced low carb so I decided to do some research and analysis.
The fist thing I realized is that the CEPís comparison of the DEXA lean mass (LM) result (50.72kg) with the lean body mass (LBM) estimates from the calculator.net weblink is wrong.
All of the LBM formulae are based on LBM being equal to Total Body Mass minus Fat Mass, such that
TM = FM + LBM
The DEXA scan separately measures bone mineral content , such that
TM = FM + LM + BMC
Checking: 15.63 + 50.72 + 2.60 = 68.95
Hence LBM must include bone mass and therefore it should be compared with the sum of the DEXA lean mass and bone mass results and not just the LM by itself. In my case LM + BMC
= 53.3 kg
The LBM formulae from the calculator.net weblink give the following estimates:
Boer formula: 53.5 kg
James formula: 54.1 kg
Hume formula: 49.8 kg
My research lead me to discover the following:
The Hume formula is the oldest correlation (1966) and should not be used at all.
The Boer formula should actually be referred to as the Hume & Weyers formula and dates from 1971
The James formula is not the most recent and badly underestimates LBM for overweight and obese subjects.
The most recent formula is one, which is not included in the calculator.net weblink. It is the Janmahasation formula dating from 2005 and is considered an improvement of the Hume & Weyers formula. For my height and weight it produces a LBM estimate of 53.2 kg Ė remarkably close to the DEXA result for LM + BMC of 53.3 kg.
So I am feeling less concerned that I have to do something about my Ďapparentlyí low lean mass.
But what about that pesky visceral fat (1 kg of it) which the CEP says I need to lose before
attempting to build extra lean mass? Well my research revealed the following:
1) There appears to be no data to determine what is a 'safe level' of visceral fat but plenty of commentary saying that any amount is bad.
2) I found one highly interesting and useful paper,
which indicates that there is an allometric relationship between visceral fat and total fat mass.
After this I found that by combining the allometric relationship between visceral fat and total fat mass together with estimates of fat mass from the Janmahasation LBM formula I was able to extrapolate upwards and downwards from my current weight and deduce the following:
1) A person my height would have to weigh around 112 kg with a BMI of ~40 in order to have around 4kg of visceral fat (i.e. the maximum which the DEXA scan physiologist says she has ever come across).
2) When I started low carb and my weight was 94 kg my visceral fat was probably around 2.6 kg.
3) Extrapolating in the direction of lower weight shows that I would need to achieve a total body weight of around 55kg or less in order for visceral fat to be reduced to 400g or less. Even if I got down to around 63 kg (my weight when I was a distance runner some 30 years ago) the visceral fat level would still be 0.8kg.
Therefore my final conclusion is that the DEXA scan physiologist is suggesting a visceral fat target which is impossible but I guess it is good for business if people believe it and keep coming back for scans to check their 'progress'.
Should I nonetheless be concerned about having 1 kg of visceral fat? Well Iím not sure but I do wonder how much of it might actually be necessary fat. I understand that organs like the kidneys naturally sit in a layer of fatty tissue called the adipose capsule/perinephric fat. I have no idea what mass this might represent but I rather suspect that some of what the DEXA scan measures as apparently Ďnasty visceralí fat is probably just this essential perinephric fat.