Research Review: Fat Burning

 In Blog

The term fat burning get’s thrown around a lot – but it’s actually a concept that’s grounded in sports medicine. If you can tap into your body’s ability to burn fat, you can get in great shape.

Not all calories are created equal. You have three main sources of energy: fat, carbohydrate, and protein. So when you’re burning calories, it’s usually a combination of the three. Since proteins make up your muscles, burning your calories from protein is a big NO-NO. Protein isn’t easy to break down as energy to do work (i.e. calorie burning) but your body will do it if it has to. To some extent this will affect your muscle mass and possibly have detrimental effects on your metabolic rate.

So that leaves us with sugar (carbs) and fat. Ideally, we’d all want to burn fat as much as possible. But a ton of factors can have an effect on what you burn at rest, such as your training status, type of workout, diet, and amount of sleep (stress doesn’t help either). That’s by no means a complete list. In the end you can be working out a lot but if you’re still burning sugar most of the time, you’re going to have trouble losing weight.

As a fitness nerd I love to read studies. The title of this study caught my eye, and being a good personal trainer means sharing the knowledge with the masses. This research sheds some light on the idea of fat burning so let’s take a closer look at “Individual Responsiveness to Exercise Induce Fat Loss is Associated with Change in Resting Substrate Utilization. (1)”

I realize that title might not be as appealing to you guys as it is to me, so let me break it down for you.

Subjects: 55 women participated in this study, which is really cool since women tend to burn more sugar at rest (compared to men). They had an average age of 35 along with a bodyfat percentage of 39%. So this puts the subjects close to middle age and, as a group, they’d be considered obese. Half the subjects had a family history of Type II diabetes. Each subject had their RQ measured, which tells us the type of calories you’re burning. In this case, most subjects burned a majority of their calories from sugar.

Protocol: There was a lot of measuring and testing, but in a nutshell, these hardworking women trained for 7 weeks. They started at 3 – 30 minute workouts per week and built up to 5 days of 60 minutes. These workouts were all endurance based, so subjects trained at 65 to 80% of their predicted heart rate maximum. This is probably a brisk walk to a hard run. There was no other type of training in this study.

Results: Just to show the individual differences when it comes to training, some women lost up to 6.5 pounds of fat mass. Pretty awesome, right? We’re not talking just scale weight here, but all those 6.5 pounds came from bodyfat stores. Shockingly, some women gained weight – even up to 5.5 pounds! Remember that RQ thing? Regardless of how many calories were burned through exercise, the subjects that had the greatest shift to fat burning lost the most weight. So some subjects worked out but didn’t manage to lose weight because they couldn’t shift their bodies into that coveted fat burning mode.

My Takeaway: The study shows what a lot of personal trainers struggle with: the differences between clients. But it also highlights another issue: the subjects in this study were told to record their dietary intake. We know for a fact that people are terrible at this, so bad that they can underestimate their calorie intake b 50% (2).  So who knows what kind of results we would have had with a nutritional intervention.

I’m not a huge fan of endurance exercise as the main source of training. It would be interesting to see how people responded to a protocol of endurance training along with circuit training with weights.

If you want a concluding thought to things it’s this: you need to work hard at training but in order to reap the benefits you need to consider what you do outside of the gym. Smart choices in terms of what you put in your mouth, when and where you eat (like not in front of the TV), your sleep patterns and how much stress you place on yourself. Take care of your body outside of the gym and you’ll definitely turn into a fat burning machine.


1. Barwell, N.D. et al. “Individual Responsiveness to Exercise Induced Fa Loss is Associated with Change in Resting Substrate Utilization.” (2009) Metabolism Clinical and Experimental 58. 1320-1328

2. Donnelly, Joseph E. Smith, Bryan K. “Is Exercise Effective for Weight Loss With Ad Libitum Diet? Energy Balance, Compensation, and Gender Differences.” (2005) Exercise and Sport Science Reviews 33;4. 169-174

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