What is fat mass index and how does it impact health

Fat mass index (FMI) is a small part of the total BMI - it accounts for body fat and is the reason high BMI is sometimes misunderstood.

Myupchar September 25, 2019 14:02:35 IST
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What is fat mass index and how does it impact health
  • BMI is a calculation of the total mass in a person's body; however, it does not differentiate between fat and muscle mass

  • So, an otherwise healthy person with a high muscle mass may be considered unhealthy or obese as per the BMI measurements

  • FMI, on the other hand, is not affected by muscle mass and is hence a better parameter for defining fat or lean body types

If you thought you could tell a lot about a person’s health just by looking at their BMI (body mass index), think again.

BMI is our weight to height ratio - cardiologists recommend that we keep our BMI within the healthy range of 18 to 23. A BMI over 25 indicates that we may be overweight and BMI over 30 indicates obesity.

Now, research shows that BMI may have its own Mr Hyde: an evil avatar with no redeeming qualities. It’s called fat mass index or FMI.

What is fat mass index and how does it impact health

Sides of a coin

Saying that high BMI is bad is like saying high cholesterol is bad - without differentiating between the good cholesterol HDL and bad cholesterol LDL. BMI does not distinguish between fat-free mass (which we need a lot of) and body fat (which we need a little bit of).

FMI is a small part of the total BMI - it accounts for body fat and is the reason high BMI is sometimes misunderstood.

It is a well-established fact that being overweight or obese may lead to a disturbance in the physical and physiological functioning of the body, making the person prone to conditions such as heart diseases, stroke and diabetes.

Though BMI is commonly used to measure ideal weight, there is growing evidence that it is FMI that may be the root cause of metabolic disturbances and development of comorbidities in obese people.

Why does FMI matter?

FMI is the measurement of your fat mass/(height)2, where the number 2 is adjusted as per the population it is being used for.

Now researchers at China's Central South University have found that high FMI increases the risk of cardiovascular diseases in people with type 2 diabetes mellitus (T2DM). In other words, if you are fat and diabetic, there is a high chance that you may develop heart disease.

"Lean body mass and fat mass appear to have distinct effects in patients with T2DM across differing BMIs. Increased risk of CVD in patients with T2DM and obesity may be attributed to more fat mass, whereas the protective effect of lean body mass no longer increases when lean BMI is more than 16.7 kg/m2. Thus, patients with T2DM should have sufficient lean body mass and less fat mass to reduce the risk of CVD," wrote Dr Xinqun Hu, the lead author of the study conducted at the Department of Cardiovascular Medicine and Emergency Medicine, The Second Xiangya Hospital, Central South University, China.

The research was published in the Canadian Medical Association Journal, a peer-reviewed journal brought out by the Canadian Medical Association.

FMI versus BMI

BMI is a calculation of the total mass in a person’s body; however, it does not differentiate between fat and muscle mass. So, an otherwise healthy person with a high muscle mass may be considered unhealthy or obese as per the BMI measurements. This can sometimes make BMI an unreliable factor for determining obesity or overweight.

FMI, on the other hand, is not affected by muscle mass and is hence a better parameter for defining fat or lean body types.

Body fats are of two types: Essential body fat and storage fat. We need a bit of both.

We need essential body fat to maintain everyday functions - 2-3% of lean body mass in men and 5-8% of the lean body mass in women is essential body fat (women need a tad bit more for their hormonal functions and for facilitating childbearing). Our bodies need storage fat to provide insulation (heat). So, ideally, our bodies should have a little more than essential fat.

The U.S. Navy has a useful method to trim the fat and get to your FMI quickly: Body fat% * weight.

To get an accurate measurement of your body fat percentage, visit a testing lab, gym or nutritionist who has the equipment installed - since the calculations are sensitive, they are difficult to do at home.

Fat distribution and health

Depending on where we have excess fat accumulation in the body, we can be at higher risk for different health conditions. For example, an excess of fat deposited in the upper body is associated with a higher risk of metabolic disturbances.

Michael D. Jensen, a professor and researcher at the Endocrine Research Unit, Mayo Clinic, Rochester, U.S., explained the harmful effects of excess fat on the body in his 2008 article, Role of Body Fat Distribution and the Metabolic Complications of Obesity.

Jensen explained that excess fat leads to the release of free fatty acids in the bloodstream after every meal. This has a direct impact on the beta-cells of the pancreas - the cells that produce insulin, a hormone that controls blood sugar levels. Which, in turn, can severely impact the walls of our blood vessels, increasing the risk of stroke and heart attack.

The details

For this study, the researchers collected data from 10,251 diabetics over nine years to find the link between lean body mass, fat mass and major cardiovascular conditions. The mean age of participants in the study was around 63 years - more than 60% of participants were men.

The researchers found that diabetics who had higher FMI were more prone to cardiovascular diseases than those who had a normal FMI. However, those with lower than normal FMI were also prone to CVDs, indicating the importance of maintaining FMI within the normal range.

Health articles in Firstpost are written by myUpchar.com, India’s first and biggest resource for verified medical information. At myUpchar, researchers and journalists work with doctors to bring you information on all things health. For more information on this topic, please read our in-depth article on Obesity.

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