Tyler Robbins Fitness

B.Sc. Biochemistry, Certified Strength and Conditioning Specialist (CSCS), Certified CrossFit Trainer (CCFT/CF-L3), USA Weightlifting Level 1

Filtering by Tag: Body Fat

Does exercise actually burn fat?

How absurd is this?

How absurd is this?

So, does exercise really actually burn or melt body fat? Well, a very plain and simple answer would be no, not really. The answer is certainly more complicated than that, and I plan on explaining myself further, but this is certainly a topic that most people get wrong, or are greatly misinformed.

Sure, a lot of you may read this blog and think, "Your argument is just semantics. Exercise (in a roundabout way) burns fat!" Well, maybe. Maybe this could be considered semantics, but I personally believe this plays a crucial role in how people perceive not only the role of exercise, but the role of food and their diet as well!

Heavy science jargon and content ahead. I have done my absolute best to explain what is going on here. You've been warned. If you're still here, let's dive in.

I came across this interesting review the other day:

Abdominal fat reducing outcome of exercise training: fat burning or hydrocarbon source redistribution?

Abstract

Fat burning, defined by fatty acid oxidation into carbon dioxide, is the most described hypothesis to explain the actual abdominal fat reducing outcome of exercise training. This hypothesis is strengthened by evidence of increased whole-body lipolysis during exercise. As a result, aerobic training is widely recommended for obesity management. This intuition raises several paradoxes: first, both aerobic and resistance exercise training do not actually elevate 24 h fat oxidation, according to data from chamber-based indirect calorimetry. Second, anaerobic high-intensity intermittent training produces greater abdominal fat reduction than continuous aerobic training at similar amounts of energy expenditure. Third, significant body fat reduction in athletes occurs when oxygen supply decreases to inhibit fat burning during altitude-induced hypoxia exposure at the same training volume. Lack of oxygen increases post-meal blood distribution to human skeletal muscle, suggesting that shifting the postprandial hydrocarbons towards skeletal muscle away from adipose tissue might be more important than fat burning in decreasing abdominal fat. Creating a negative energy balance in fat cells due to competition of skeletal muscle for circulating hydrocarbon sources may be a better model to explain the abdominal fat reducing outcome of exercise than the fat-burning model.

Lots of science talk, let's break things down and give some thoughts as to what is being discussed here.

Fat burning, defined by fatty acid oxidation into carbon dioxide, is the most described hypothesis to explain the actual abdominal fat reducing outcome of exercise training.

This is one of these popular "facts" making its way around the internet lately. The idea that as you exercise and burn fat, the fat then just starts melting and you magically breathe it out as carbon dioxide. Sure, carbon dioxide is a by product of metabolism and respiration, and you certainly burn some fat during exercise, but it isn't really that simple.

This hypothesis is strengthened by evidence of increased whole-body lipolysis during exercise. As a result, aerobic training is widely recommended for obesity management.

Right. This has been heard for years. This is actually one point that seems to be at least somewhat well-known to be a mistruth now. That just because adipose tissue (body fat) is only burned in the presence of oxygen (oxidation), then low-level exercise must be best for burning fat. Right? Go for a nice long, easy run on the treadmill and you will get thin and sexy. Well, not exactly. My readers should know that intense exercise is better suited for reducing body fat by now so lets move on.

anaerobic high-intensity intermittent training produces greater abdominal fat reduction than continuous aerobic training at similar amounts of energy expenditure.

Study after study after study has shown just this - high intensity interval training is more effective for reducing body fat than steady state cardiovascular exercise.

significant body fat reduction in athletes occurs when oxygen supply decreases to inhibit fat burning during altitude-induced hypoxia exposure at the same training volume

Ah good, now things get interesting. So what this states is that body fat is reduced more in individuals that have decreased oxygen supply. Doesn't oxygen need to be present to burn body fat? Well, as the previous statement pointed out to us, high intensity exercise - you know, the type that has you gasping for air (oxygen deprived), is actually best at obtaining or maintaining an optimal body fat percentage.

Lack of oxygen increases post-meal blood distribution to human skeletal muscle, suggesting that shifting the postprandial hydrocarbons towards skeletal muscle away from adipose tissue might be more important than fat burning in decreasing abdominal fat.

This gets into the meat of this paper's argument, and one that I will elaborate on below. People need to stop thinking of exercise as a fat burner, and instead consider exercise (both resistance training and "cardio") as a means to make your body a better fat-burning machine.

Creating a negative energy balance in fat cells due to competition of skeletal muscle for circulating hydrocarbon sources may be a better model to explain the abdominal fat reducing outcome of exercise than the fat-burning model.

Once I dove deeper into this paper, I got a better sense of what point the authors were trying to prove. Your muscle cells and fat cells both have the ability and goal in mind to store energy. In fact, there seems to be a competition between the two. Your body is constantly varying its sources of energy based on your level of activity. When you are exercising intensely, your body is primarily using glucose as a fuel source, for example. Sure, there is some fat being oxidized, but the primary fuel source is glucose.

Compare that to the amount of fat being burned between aerobic exercise, resistance exercise, and non-exercise. Sorry resistance trainee camp, not even you can argue that resistance training is "better" than aerobic exercise for burning fat - at least not directly.

This one is telling for the "exercise until you puke" camp. The notion that the harder you exercise, the more fat you burn is total b.s. as well. Do I think intense exercise is important? Absolutely. Do I think intense exercise is necessary for weight loss and body fat reduction? Not really, or at least not primarily. Some is good, but only to a certain level.

So what is the point to all of this? Well this is where the semantics comes in.

The current understanding is that when you are exercising, your body is literally burning away those love handles as you crank through all those burpees or squats. As we saw in figure A above, this is simply not the case. Yes, intense exercise promotes lower body fat percentages, but not because the fat is literally being burned and exhaled as carbon dioxide. Ok, then it must be the post-workout "burn" where metabolism is revved up. That is a common theme, correct? Again, not the case. Because oxygen must be present in order to burn fatty acids as a fuel source, by exercising intensely, you are specifically forcing your body to turn to glucose as a primary energy source.

So low-level exercise is better for burning fat, right?

Well, no. Research has proven time and time again that shorter, intense exercise is not only more efficient and effective than low-level, steady-state exercise to improve cardiovascular health and a healthy body-fat percentage.

So what gives?

As this review points out, the mindset as to what exercise actually does to your body and how body fat is reduced is the most important part. Exercise, and more specifically, intense exercise (ideally with external resistance, i.e. weights) not only builds strong muscles, but it turns your muscles into energy consuming machines. This causes a domino effect.

  1. Body fat (adipose tissue) and lean tissue (muscle) are constantly competing over consuming incoming calories. The body seems to give preferential treatment to muscles the harder they work.
     
  2. Energy that is not consumed and stored in muscles goes to body fat.
     
  3. Carbohydrates are broken down into glucose. When your body is not active, glucose is not being burned as readily by muscles, so there is more glucose present and glucose becomes the primary energy source even during low-level activity (most of the day).
     
  4. Fatty acids from adipose tissue are the primary energy source for majority of your day (i.e. the time you aren't working out intensely). But if glucose is present, blood sugar (glucose) becomes the energy source of choice.
     
  5. If your body is using blood glucose as an energy source, body fat deposits are not reducing.
     
  6. If your muscles are consuming large amounts of energy, especially carbohydrates, then your body primarily uses fatty acids (adipose tissue) as the energy source.

Conclusions

So although this isn't necessarily different than what most people should already know - intense exercise makes you thin and keeps you healthy, the mindset for how this works should change. Resistance training is used to not only strengthen the connective tissues of the body, but to make your muscles greater calorie-burning machines.

Carbohydrates should be consumed almost entirely just prior to, and/or immediately following a workout in order to reduce the amount that is stored as body fat.

Although intense activity is great and very important for overall health, the more active you are the rest of the day during "low-level activity" (walking, working, playing, etc.), the more effective your body will be at reducing your body fat percentage.





"Skinny Fat" is Dangerous

The BMI (Body Mass Index) scale, to be honest, hasn't been universally welcomed for some time now. An arbitrary relationship between an individual's height and weight, and the theoretical level of "health" based on this magical formula has received much scrutiny in the past. Despite the lack of faith put in this system by many experts in the field of health and fitness, it still receives a fair bit of attention from physicians and health care workers looking to promote a healthy lifestyle amongst patients.

It is not uncommon that individuals who use even a moderate amount of resistance training in their workout program can be pushed into the "overweight" or even "obese" category on the BMI scale. Fat free mass, such as muscle, is very dense, which can increase an individual's overall weight and therefore skew their BMI score.

On the other end of the spectrum, and a topic that has been studied recently in the American College of Physicians publication, is that despite having a "normal" BMI, one can still be considered unhealthy and have a greater risk of all-cause mortality.

Relationship Among Body Fat Percentage, Body Mass Index, and All-Cause Mortality: A Cohort Study

Background: Prior mortality studies have concluded that elevated body mass index (BMI) may improve survival. These studies were limited because they did not measure adiposity directly.

Objective: To examine associations of BMI and body fat percentage (separately and together) with mortality.

Design: Observational study.

Setting: Manitoba, Canada.

Participants: Adults aged 40 years or older referred for bone mineral density (BMD) testing.

Measurements: Participants had dual-energy x-ray absorptiometry (DXA), entered a clinical BMD registry, and were followed using linked administrative databases. Adjusted, sex-stratified Cox models were constructed. Body mass index and DXA-derived body fat percentage were divided into quintiles, with quintile 1 as the lowest, quintile 5 as the highest, and quintile 3 as the reference.

Results: The final cohort included 49 476 women (mean age, 63.5 years; mean BMI, 27.0 kg/m2; mean body fat, 32.1%) and 4944 men (mean age, 65.5 years; mean BMI, 27.4 kg/m2; mean body fat, 29.5%). Death occurred in 4965 women over a median of 6.7 years and 984 men over a median of 4.5 years. In fully adjusted mortality models containing both BMI and body fat percentage, low BMI (hazard ratio [HR], 1.44 [95% CI, 1.30 to 1.59] for quintile 1 and 1.12 [CI, 1.02 to 1.23] for quintile 2) and high body fat percentage (HR, 1.19 [CI, 1.08 to 1.32] for quintile 5) were associated with higher mortality in women. In men, low BMI (HR, 1.45 [CI, 1.17 to 1.79] for quintile 1) and high body fat percentage (HR, 1.59 [CI, 1.28 to 1.96] for quintile 5) were associated with increased mortality.

Limitations: All participants were referred for BMD testing, which may limit generalizability. Serial measures of BMD and weight were not used. Some measures, such as physical activity and smoking, were unavailable.

Conclusion: Low BMI and high body fat percentage are independently associated with increased mortality. These findings may help explain the counterintuitive relationship between BMI and mortality.

What the study found was that despite an individual being within a "healthy" or "normal" weight range on the BMI scale, a greater body fat percentage was linked to a greater risk of all-cause mortality.

In other words, the term "skinny fat" has been used in the media before which this study exemplifies. Just because you are within a healthy weight range for your height does not meant that you are at an advantage health-wise.

What this tells us is that it is important to focus more on keeping a body fat percentage within a healthy range rather than focusing on overall weight. Not only that, but resistance training an adequate protein consumption are extremely effective tools to promote the growth of fat free mass, improving our overall health.





Fasted Training for Greater Fat Loss?

I actually receive this question from clients quite often, but someone asked me about it again the other morning which inspired me to write about it. The question was, and this goes along with conventional "broscience," is fat burning more effective if you workout fasted?

It is common for individuals to workout first thing in the morning, which many end up doing in a fasted state (haven't eaten anything prior to exercising). Let me start off by saying that I commonly workout in a fasted state, and in fact, have done so for many years. Having said that, I have recently changed my daily routine based on my work schedule so my workouts tend to get pushed to later in the day now. This gives me ample opportunity to eat prior to working out, and although what I am about to say is based off of relatively short period of time and is anecdotal, I have felt like my strength and performance has been much better, but we can discuss more of that later.

Anyways, so the training when fasted theory goes something like this. If you are training fasted, then that means that your circulating blood sugar is low, priming your body to be more conducive to fat metabolism. This is a theory, however, and doesn't quite play out as simply as you would think. To discuss exactly what is going on here, let's break this down into 2 topics of interest.

1. Your body is never entirely using one source of energy over another.

Source: http://ausfit.net.au/understanding-your-body-energy-systems/

Source: http://ausfit.net.au/understanding-your-body-energy-systems/

So you have three energy systems in your body: the Phosphagen System, the Glycolytic System, and the Oxidative System. Without nerding out too far, the Phophagen System produces a lot of power, but can only last for a few seconds (think 3 or less repetitions of something heavy or a short sprint). The Glycolytic System can produce a little less power but can last a bit longer (higher rep resistance training or a longer run, up to about 2 minutes). The Oxidative System cannot generate a lot of force, but is much more lasting in nature (less intense activity such as walking, etc.). The Oxidative System is just that, oxygen-based, so that the amount of breathing you do keeps up with the energy demands of your activity. Oxygen, along with fat, produces energy in the Oxidative System. Your breathing may increase a bit during a brisk walk, for example, but you are never pushed to a point of exhaustion.

During regular, every day activity, our bodies are constantly transitioning between the three energy systems. Walking, talking, general daily activities tend to keep us in our Oxidative state. If we bend down to pick up something heavy, suddenly we transition to either the Glycolytic or Phosphagen system for that quick burst of energy. However, throughout the day, our bodies are constantly metabolizing energy from all 3 energy systems in some ratio depending on the activity.

So how does this change based on whether or not we exercise in a fasted state or not? It doesn't really. Our bodies are great at storing and utilizing energy based on our needs and demands. It doesn't matter when your last meal was, if you need a quick surge of energy to pick up something heavy then you have stored energy for that.

Sure, activity at low intensities when in a fasted state may illicit a greater promotion of fat oxidation, but I would like to think that most people now realize that training in a specific heart rate zone to maximize one energy system over the other is far less beneficial (for overall body composition and health) than exercising intensely.

Not only that, but research tells us that when you are in a fasted state, your body may increase adipose tissue breakdown in order to increase blood triglyceride levels, but the production far outweighs the demand. In other words, the Oxidative System is slow moving and only produces energy at a certain pace - a slow pace at that! So even if you're in a fasted state and your body is increasing blood triglyceride levels, that doesn't mean that those increased levels in the blood are going anywhere. In fact, once you're done exercising, they get shuttled back into your fat cells.

Also keep this in mind: the more carbohydrates you burn during a workout, the more fat you will burn after the workout is over.

Neither the Phosphagen or Glycolytic system require oxygen for their immediate energy output but the Glycolytic System does utilize oxygen in order to replenish spent energy stores. If oxygen demand is not met through respiration during exercise, our bodies go into a state called EPOC, or Excess Post-Exercise Oxygen Consumption. This is oftentimes also called the "afterburn" because calories are still being used to replenish spent energy stores through respiration. This is also why you are still breathing heavy long after an intense workout session.

So let's sum this up.

Low-intensity exercise primarily uses aerobic metabolism (fat oxidation) to generate enough energy for the activity demand. Going for a brisk walk, for example. There may even be some truth to the body metabolizing a higher ratio of fat oxidation when fasted, however this is such a relatively small amount of calories burned compared to much higher intensity exercise.

Performing high intensity exercise will favour more of a carbohydrate-burning metabolism, which sort of defeats the purpose of training fasted. The amount of EPOC you can create for yourself, or in other words, the more intense your workout is, therefore causing a substantial "afterburn" will yield greater calorie burn and fat oxidation.

On top of all of that, research shows that training in a glycogen-depleted state causes the body to burn far more tissue proteins for energy rather than stored energy sources. Muscle protein can account for nearly twice the amount of calories burned in a fasted state versus that of a fed state. In other words, eat before you workout, but train hard!

2. Who really cares how many calories you burn during a workout anyways?

There is a flip side to this coin, however.

I try and remind clients about this on a consistent basis. Keep this thought in your head from now on and it will save you a lot of time and aggravation: Exercise is for your brain and your body. Sure, it burns calories, but you are doing it to keep your machine (your body) running at optimal levels. Body composition is largely controlled by the diet that you eat and the overall net balance of calories in versus calories out.

Doing an hour of light exercise to attempt to stay in your "fat burning zone" will burn such a minuscule amount of calories (in the grand scheme of things) that there really isn't any point in even counting them. Similarly, the amount of calories you may or may not be burning in a fasted state is negligible.

There should be two main factors that your training should focus on if you wish to optimize the amount of adipose tissue you wish to eliminate. First, make sure you are including enough resistance training to work as much muscle during your training sessions as possible. Compound movements involving our primary movers and joints are great for this. Compound movements include such things as squats, deadlifts, presses, rows, etc.

Secondly, your training should be intense. As mentioned above, if you're training intensely, the net amount of calories burned from the exercise itself, followed by the burn long after your workout is over, is far more beneficial from a calorie burning and hormonal response standpoint than trying to target fat loss specifically at a lower heart rate.

Between carrying around more lean mass (muscle), and exercising intensely, your body will be primed to have a much higher resting or basal metabolic rate to maximize your calories burned on a day to day basis.