So, you’ve read the science, you’ve asked the experts and you know that weight loss is about creating a calorie deficit. If you burn more calories than you consume, you will lose weight.

You also know that the most effective way to burn calories is through strenuous aerobic activity. So, if you drastically reduce your calories, put on your running shoes and hit the road for an hour a day, you should lose weight, right? You’re probably reading this, and throwing your arms up in the air in a mix of agreement and frustration, saying, EXACTLY, SO WHAT THE HELL AM I DOING WRONG?
Unfortunately the human body is infinitely complex and can’t be reduced to a simple calories in vs calories out equation. Don’t get me wrong, creating a calorie deficit is still the crux of the matter, but there are other factors at play. The key to weight loss lies in how you create a calorie deficit. Let me explain.
In my experience, weight loss happens when you replace the idea of WEIGHT LOSS with FAT LOSS in your approach to shedding those unwanted pounds. So, when I use the term weight loss, take it to mean fat loss. With that said, the golden rule of weight loss is:- Always look after your muscle mass first! Here’s why:-
Resting Metabolic Rate (RMR) is the amount of energy the body expends during rest, and accounts for about 70% of daily energy expenditure (American College of Sports Medicine, 2001). By increasing your RMR, you can significantly increase daily energy expenditure, creating a net negative energy balance, thereby increasing weight loss.
Fat Free Mass (FFM) is the portion of your body mass made up of muscle, bone and organs (not fat). RMR is significantly correlated with FFM. In short, if you increase your muscle mass (FFM), you will increase your RMR and expend more energy in a day, resulting in an enhanced ability to lose weight.
So, the perfect weight loss recipe is:- create a calorie deficit whilst increasing muscle mass (FFM), thereby increasing RMR.
To return to the question: “WHAT THE HELL AM I DOING WRONG?” (aerobic exercise on a very low calorie diet), here’s your answer:-
Firstly, very low calorie diets tend to slow your RMR and also result in a loss of muscle mass.(FFM). The addition of aerobic exercise whilst on a very low calorie diet may result in an even greater loss of FFM, which further serves to depress RMR. Your body’s ability to burn calories becomes severely restricted, and weight loss becomes increasingly more difficult.
So where to from here? (Weights to lose Weight)
I don’t advocate very low calorie diets, for their effect on depressing your RMR and because of a host of other health complications associated with nutrient deficiencies. If however you are on a very low calorie diet, ditch the cardio for weights! Studies have shown that it is possible to maintain FFM and maintain or increase RMR whilst weight training, on very low calorie diets (800Kcal per day). Cardio however will have the opposite effect when combined with very low calorie diets, and, as your FFM and RMR decreases, you may find yourself gaining more fat!
Ideally however, you should aim to create a healthy calorie deficit of between 500 and 1000 calories per day (more than that may result in a loss of muscle mass, and a depressed RMR, which, as explained is counter-productive), and do more weight training than aerobic exercise. This way, you increase your FFM and RMR whilst creating a calorie deficit – the perfect recipe to shed that unwanted fat.
High volume strenuous weight training (several sets at a moderate intensity) has also been shown to significantly increase EPOC (Excess Post Exercise Oxygen Consumption) – the period after recovery from exercise, when the metabolic rate is elevated above resting values. This means that for several hours after weight training, your RMR is elevated and your energy expenditure is higher. Note that the training needs to be strenuous, so beginners should build slowly, and weight train at first primarily to increase their FFM. As you progress, you will reach a level at which point the effect of weight training on your EPOC become more significant (Jeffrey, L. Alexander, MS, Strength and Conditioning Journal, February 2002).
Hormones play a major role in the regulation of weight and metabolic processes. The mechanisms through which hormones interact are complex. What is important to know for the purposes of weight loss however is that weight training stimulates the production of hormones that bring about fat oxidation. In addition, the production and uptake of anabolic (building up) hormones such as testosterone, growth hormone and IGF results in an increase in muscle mass and a relative increase in RMR.
Finally, weight training has been shown to increase fat usage after exercise. For several hours after exercise, your body uses carbohydrate (a nutrient that may otherwise be stored as fat) to replenish muscle glycogen at an elevated rate. It is thought that through glycogen replenishment after intense exercise, the body uses fat as a primary source of energy, resulting in a potential increase in the loss of body fat.
Weight training and aerobic exercise will benefit you, from an overall health perspective and in your efforts to lose weight, so do both. The golden rule of weight loss is: Create a calorie deficit whilst increasing your FFM, to increase RMR. If you are on a very low calorie diet (and you shouldn’t be), ditch the cardio for weight training. Ideally, however, create a healthy sustainable calorie deficit and build your exercise programme around strenuous, high volume, moderate intensity (load) weight training (slowly progress to this point if you’re a beginner).
As far as cardio is concerned, HIIT (high intensity interval training) has a greater muscle sparing effect than steady state cardio, so this should be your focus. (two sessions per week should suffice for the average person). Throw in some low to moderate intensity cardio to add balance and burn calories whilst undergoing some active recovery, and you’re on the right track to becoming a fat burning machine!.