DEXA, ALMI, FFMI, VAT and all the other Acronyms

The DEXA has traditionally been used in elderly women to diagnose osteoporosis and osteopenia. While this test can confirm that you have neither disease of bone density, for most of my patients we were not overly concerned about the presence of this disease process. While I always look at bone mineral density and plot a general trajectory in the decades to come, it would be an atypical finding to see a red flag pop up in many of my male patients. Instead, the main reason I order the DEXA scan is to look at body composition. Specifically I like to look at three main measures. ALMI, FFMI, and VAT. Let's look at each one:

ALMI:

ALMI stands for appendicular lean mass index. This is the measure of how much muscle is in your arms and legs normalized by your height. Because the DEXA scan cannot differentiate between muscle mass and organ mass (such as your liver and spleen) ALMI is often a better measure of your lean mass/muscle mass than the next measure we will talk about (FFMI) because it excludes the variation of the internal organs. Having and maintaining lean muscle mass is essential for metabolic health and functional capacity as one ages. Muscle mass peaks in the late 30s and early 40s, and then predictably declines with age, often about 10% a decade then accelerating to 15% per decade and more once you are in your 70s. Thus the key is to build as much of a reserve of muscle mass as you can early on, and then delay the decline over the decades. As you enter into the decades where falls become a major risk for morbidity and mortality, the optimal strategy to surviving this stage is not to have stronger bones in the fall, but to avoid the fall altogether. A combination of balance/coordination and muscle mass to catch yourself before the fall are essential. Aiming for superlative ALMI is ideal, keeping cut off above the 95th or 97th percentile for your age.

FFMI:

FFMI stands for Fat Free Mass Index. This is similar to the ALMI but includes the entire body. Since DEXA basically sees three buckets: bone, fat, and everything else, including the torso in the measurement adds internal organs to the 'everything else' bucket and thus to what we are considering lean mass. When FFMI and ALMI are discordant I usually put more weight in the ALMI.

VAT:

The last measure I usually look at is the VAT. This is a measure of the Visceral Adipose Tissue. Let's contrast VAT from subcutaneous (SubQ) adipose tissue. SubQ fat is by definition the fat tissue we can see and feel directly under the skin. While often the focus of concern for many individuals because of cosmetic reasons, the SubQ fat is rather inert. While it is not fully inert, giving off signaling molecules such as adipokines, the point I want to express is that this SubQ fat is less a driver of poor metabolic health than an outcome or proxy if you will for poor metabolic health. That is, accumulation of SubQ fat is often a downstream indication that there is poor metabolic health in the body, not the initiator of that poor metabolic health. This is directly in contrast to the Visceral Adipose Tissue. Your VAT is the fat that accumulates in and around your internal organs. This fat is highly inflammatory and is implicated in driving metabolic illness. It clogs the liver and pancreas, causing dysfunction and disease. What is so interesting about VAT is that it is a relatively small amount of fat compared to SubQ fat. For example, it is not uncommon for a metabolically healthy 200 lb man to carry 40-50 lbs of SubQ fat on them. No problem. However, if you get even over 1 lb of visceral fat in you, you can start having major metabolic issues. Everyone has a different amount of SubQ fat they can carry before it starts 'spilling over' into VAT. The only way to really know this is to get imaging to look at it through DEXA or MRI. I like to aim for a VAT under 1 lb and/or under 10th percentile for age.