Weight loss occurs when energy output is greater that energy input.
Ie... weight loss occurs when the amount of calories burnt is greater than the amount of calories consumed.
Reducing dietary intake (eating less) certainly provides a simple and effective method in decreasing body mass. However, a decrease in body mass, through restricting the amount of food you eat alone, can result in a loss of muscle tissue. So although total weight may decrease, not all of the weight lost will come from body fat.
When it comes to losing weight, for most people, the first port of call is the dreaded treadmill. Cardiovascular exercise has several benefits such as enhanced mood, improvements in cardiovascular fitness, reduced risk of stroke, heart attack and several cancers along with the bonus of burning calories at the same time.
However its efficiency as a weight loss tool may be greatly overestimated.
What is the best way to approach decreasing body fat?
A research study conducted by Dr Jeff Volek and colleagues looked at 3 different ways to decrease body fat over a 12 week period:
- Dietary Calorie restriction
- Dietary Calorie restriction combined with Cardio Exercise
- Dietary Calorie restriction combined with Cardio exercise and Weight training
Table 1 - Effects of different intervention on the total decrease in body mass, total mass lost as fat and total mass lost as muscle tissue over a 12 week period.
As the table suggests, despite all three interventions losing a similar amount of total body mass, the quality of weight lost is not the same. When a programme is taken up combining a change in diet with cardiovascular and weight training, almost all of the amount of total weight lost comes directly from body fat as opposed to muscle tissue.
This is because weight training preserves muscle mass, therefore the body has no other option than to use body fat as its fuel when in a calorie deficit as opposed to breaking down muscle tissue.
So how much fat do I actually burn during exercise?
Results from the FASTER study conducted by Dr Volek in 2013 ,showed that when a high fat diet is followed, the body's ability to burn fat as a fuel is significantly enhanced (see figure 1).
Figure 1 - The comparison of overall amount of fat burnt per minute during exercise between a diet High in Carbohydrate and Low in Fat vs a diet High in Fat and Low in Carbohydrate (Volek et al, 2013).
However, when you look at the results closer, even when a high-fat diet is followed and fat burning is at its maximum, using more than twice as much fat as fuel during exercise than a low-fat diet, this amount is still only at 1.5 grams of body fat per minute.
To put this into perspective, if your goal was to lose 1kg in body fat, burning 1.5g of fat per minute, you would have to run for over 11 hours to shift that kilo of body fat. And remember this would be if you were following a perfectly formulated ketogenic (high fat diet).
If a low-fat diet option was adopted, burning 0.6 grams of fat per minute, you would have to run for 28 hours to burn off 1kg of body fat.
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