Interesting study on fat metabolism

Most of you have heard me talk over and over about the frustrating but highly rewarding (and certainly healthier overall) fat adaptation process, which teaches your body to prioritize stored fat as the primary fuel of choice for daily living and physical activity.

Doing fasted cardio exercises to “burn” fat, as many advocate, is certainly not enough: fat burning stops the moment you hit that big red STOP button on the treadmill. It takes much more to transition your body from a “carb-burning engine” to a “fat-burning engine”.

I’m only saying this to provide context to an interesting study just released (you can read the full study here):

Here is a summary along with my observations:

The Study 

Comparison of “Fat Oxidation” at rest and during exercise between young “Sedentary Lean (SL)” and “Sedentary Obese (SO)” individuals.

Fat Oxidation means the body’s ability to “burn fat” for energy. I found it interesting that both groups in this study (Obese and Lean) were both “young and sedentary” – this means that any differences in Fat Oxidation between SO and SL are likely to be even more pronounced if SO were to be compared to physically active individuals.

Another interesting element is that both groups (SO and SL) were young, generally healthy, and with the same fasting blood glucose level (i.e. even the Obese group did not have high fasting blood sugar). So essentially, you are comparing obese vs. lean among generally healthy, young, and sedentary people.

The Findings & Discussion

Findings regarding Insulin levels (all measured at rest):


  • SO group showed Insulin levels 3 times higher than the SL group. This means that while the SO individuals are not diabetic, their pancreas is working 3x harder even when fasting – this is alarming as an overworked pancreas is a primary cause of diabetes

  • SO group showed Insulin Resistance to be almost 4 times higher than SL group! This means that even though the SO group is producing 3x more insulin, their liver and muscles (which are supposed to respond to insulin by removing glucose from the blood) are becoming less sensitive to all that insulin circulating in the blood – basically, they’re ignoring that message being sent from the pancreas telling them to remove glucose.

This is indeed alarming, because a combination of high insulin levels and high insulin resistance presents the absolute ideal circumstances for diabetes to develop.

Findings regarding physical ability:


  • Max Power output on a stationary bike: the SO group produced 21.5% less power on the bike vs. the SL group. Again this is interesting because both groups are young, generally healthy, and sedentary. So the SL group did not produce more power because they’re physically fit or active, but only because they are “leaner”.

  • HRmax for SO: 168bpm, while HRmax for SL: 183bpm. This is the max heart rate scored during exercise on the stationary bike (i.e. how high you can get your heart rate before you have to stop). Once again, a big difference was recorded between the 2 groups, even though the SL group was just as untrained and sedentary at the SO group.

I suppose I should not be surprised by this, but it is an interesting observation nonetheless: obese sedentary individuals suffer from impaired strength (power on bike) and cardiovascular ability (heart rate) when compared to their sedentary leaner individuals. I would have expected this in a weight-bearing exercise (such as running or cycling outdoors), but I did not expect this to be so clear-cut on a stationary bike.

Findings related to fat burning efficiency:

The findings here were the most interesting from my perspective:


  • Sedentary Obese individuals were found to burn more fat at rest and lower intensity exercise compared to the SL group. This reversed at higher intensities: the SL group was able to maintain fat burning at higher intensities, while the SO group’s ability to burn fat fell off. No, this is not a license to sit around watching TV, because…

  • …the more interesting observation was that while the SO group burned more fat at rest and low intensity exercise, their bodies’ efficiency at burning fat was actually lower than that of SL.

In other words, the only reason the SO group showed more fat burning at rest and low intensity exercise is because they have more of it to burn, but they are far less efficient at doing so.

In other words, the SL group is a fuel-efficient car with a 30L tank burning 0.5L/km, while the SO group is a pre-diabetic car with a 60L tank but burning 1.5L/Km.


Tony