Myth 1: “Fat burning zone training is optimal for weight loss”
Low intensity cardio training in the so called “fat burning zone” has long been claimed to be the best type of training for weight loss. The “fat burning zone” is the intensity range where the body oxidizes (“burns”) fat as a primary fuel. As intensity increases the body starts gradually reducing fat oxidation and increasing the use of carbohydrates as fuel. Advocates therefore believe that it leads to a greater loss of body fat, and thereby weight loss.
Training in the “fat burning zone” – is it effective?
It is true that the proportion of fat oxidized is high in the “fat burning zone”, but since intensity is low the total energy expenditure will also be low.
It is important to realize that “burning” high amounts of fat during a workout does not lead to reduction of body fat per se. For a reduction of body fat to occur it is necessary to achieve a state of energy deficit. This forces the body to tap on its energy stores (body fat). The more energy you expend during a workout (regardless of if comes from fat or carbohydrates), the greater the energy deficit you create.
Training at higher intensities, using training methods like HIIT (high intensity interval training) can lead to a larger energy expenditure per minute. Therefore, when comparing two training sessions of equal length (low intensity vs high intensity) the high intensity session would lead to a larger energy expenditure (larger energy deficit) and be more effective. In conclusion both low and high intensity training work. The question is which one is more effective?
Comparing low vs high intensity training
Reviews including studies that compared low vs. high-intensity endurance training for weight loss have confirmed that there is no difference between low vs. high-intensity endurance training in terms of weight loss (Keating et al., Sultana et al.)
From a practical point of view, this means that individuals can choose the form of training that they enjoy best and that suits their needs and lifestyle. Both forms of exercise have their advantages and disadvantages. Low-intensity cardio for instance is very time consuming whereas HIIT is time efficient but much tougher to do.
Another important (slightly unexpected) conclusion from the studies is that training alone (without any diet modification) is pretty ineffective for weight loss. The resulting weight loss was often exceedingly small regardless of exercise intensity.
The reason why endurance training alone leads to a smaller weight loss than one might expect is attributed to compensatory mechanisms. Some of these compensatory mechanisms are behavioral (eating more, moving less) or metabolic (increased metabolic efficiency).
Why diet is key when it comes to weight loss
For weight loss to occur it is necessary to achieve a state of energy deficit. This forces the body to tap on its stores. A state of energy deficit can be achieved by increasing the amount of physical activity (i.e., “moving more”) or reducing energy intake (i.e., “eating less) or a combination of both strategies. This sounds easy in theory but it’s hard to implement for most people.
“You can’t out exercise a bad diet”
Expending energy trough exercise is time consuming and physically/mentally demanding. Overconsuming calorie rich food on the other hand is quite easy to do.
As an example, it would take man weighing 80 kg approximately 60 minutes of running to “burn” 1000 kilo calories. It would take the same man 5 minutes to consume 1000 kilo calories by eating a pizza.
This shows us that it takes a lot of effort to “burn” calories by training, but it is extremely easy to offset that training effect with a bad diet. To put it in other words: “you can’t out exercise a bad diet”.
Limiting energy intake by watching what you eat is therefore the most important part if the goal is to achieve weight loss.
Finally, it should be said that even if endurance training is not essential for weight loss (since an energy deficit can be achieved without it) it shouldn’t be considered as a waste of time. There are still many positive health benefits attributed to endurance training and it could serve as a support in achieving a state of energy deficit and therefore weight loss.
References
Keating, S, Johnson, N., Mielke, G., et al (2017). A systematic review and meta-analysis of interval training versus moderate-intensity continuous training on body adiposity. Obesity Reviews, 18 (8), 943-964
Sultana RN, Sabag A, Keating S., et al. (2019). The Effect of Low-Volume High-Intensity Interval Training on Body Composition and Cardiorespiratory Fitness: A Systematic Review and Meta-Analysis. Sports Med. 49(11):1687-1721.
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