Strength Training and Fat Loss

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I wanted to start my informational blog, by revisiting a topic I put together from social media. This is a topic I have discussed numerous times, as I think it is important to highlight the role that strength training plays in assisting weight loss and improving body composition. Specifically in regards to the loss of body fat.

One of the most common themes I come across in client consultations - particularly with females - is the desire to lose weight and get stronger, but that there is a fear that weight training will lead to becoming 'bulky.' This is somewhat of a myth and as I'll cover here, increasing or decreasing your body mass index is inextricably linked to your metabolic rate and the number of calories that you consume. One other reason for this myth persisting is the societal conditioning associating weight loss with cutting calories/going on a diet, and prioritising aerobic exercise and cardio training as the primary means to achieve this. 

Therefore, some of the themes that I'll cover here will include:

  • The different training approaches for losing body fat
  • The role of resting metabolic rate and energy expenditure
  • The difference between aerobic and resistance training, and their effects on body composition
  • The importance of building and maintaining muscle mass for fat loss
  • And, how strength training effects your metabolism
As mentioned, we have been preconditioned as a society to associate weight loss (and fat loss) through prioritising aerobic exercise and cutting calories. You may have done a HIIT class at some point and been told about the 'afterburn' effect and the increased calorie expenditure after the 30 min class has finished? This is not strictly incorrect as the effect of high intensity exercise on energy expenditure does increase slightly in the period immediately after exercise, but only by about 10%. For example, if you expended 300kcal in a 30 min aerobic class, you would only expect to expend an additional 30kcals over your 'normal' energy expenditure in the hour after exercise.

You would struggle to expend a similar amount of calories during the same amount of time under a strength/resistance-based approach. However, the overall increased expenditure throughout the day would end up being roughly the same. So why is strength training overlooked as an approach for fat loss? The answer would have something to do with the amount of calories burned during the aerobic approach being greater initially. However, this immediate increase in energy expenditure does not necessarily equate to losing body fat.

So how do we understand and determine energy expenditure? Your daily energy expenditure consists of three components:
  • Resting Metabolic Rate (RMR)
  • Thermic Effect of Food (TEF)
  • Physical Activity
The goal of any fat loss programme is to create a deficit between your calorie intake and your calorie output. Essentially, you want to expend more calories than you consume. Extreme low-calorie approaches do not necessarily equate to reducing body fat by encouraging the body to use stored energy as fuel. This brings us back to the role that muscle mass plays in fat loss. Muscle, as an active energy source, is easier for the body to use as a fuel source and has a direct impact on your RMR. The lower your muscle mass, the lower your metabolic rate Reducing calorie intake without taking measures to maintain, or improve, muscle mass can result in calorie reduction ceasing to work. For example, if you used to burn 2000kcal per day, and through a combination of reducing calories and increasing aerobic exercise, you lose a couple of kilograms of muscle, your metabolic rate may lower to 1800kcal per day. Therefore, you would have to keep reducing your intake in order to keep losing weight. Ending up with drastically reducing calories to the point where you can't sustain daily functions through lack of energy.

All this links back to the role that muscle mass plays in your metabolic rate. Your metabolic rate is the total energy expended by your body, and can be separated into the three parts discussed earlier: RMR, TEF, Physical Activity. 
  • Your RMR is the energy that the body needs to consume for basic functions without any additional activity. Breathing, brain function etc. This accounts for 60-70% of your total energy expenditure. 
  • TEF - or the energy required to digest food - accounts for 10-20%
  • The rest of your energy expenditure is made up from physical activity (moving), and will account for 20-30% depending on the individual. 
Energy expenditure does differ from person to person, but these figures provide a basic reference for how the calories consumed are used. Your metabolic rate is controlled by the thyroid, and yet it is also influenced by the percentage of muscle mass in your body. The higher the percentage of muscle mass as body weight equals the higher the individual RMR. It is for this reason why it is important to develop, work and maintain muscle mass through strength training. 

This can be done through the types of physical activity pursued, as physical activity is the easiest part of your metabolic rate to understand and adjust. Increasing physical activity will result in more energy being required for daily functions, which in turn leads to a calorie deficit if intake is managed correctly. Increasing activity through aerobic exercise only will not maintain muscle mass, and can end up lowering your metabolic rate. An important point to expand upon here is that strength training will not result in getting 'bulky' if you are maintaining a calorie deficit. The goal with this approach is to develop and maintain muscle whilst attempting to lose body fat.

In conclusion, the reason why strength training should be incorporated into any fat loss programme lies with the role of muscle in influencing RMR. If you are strengthening and developing existing muscle mass, your body will burn more calories at rest as a result. This is due to muscle being an active component in the metabolism. As RMR increases, the calories required for maintaining muscle increase, ensuring that any calorie deficit does not have to be as drastic. And, if more of your those calories are required to maintain muscle mass, the likelihood of your body using its stored energy (fat) for fuel increases. 

I'll expand on these topics in future posts. Specifically on nutrition and the role of protein. But if you have any questions or would like to know more, please leave a comment. Thank you.

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