In terms of exercise, “fat burning” is the most commonly sought after type of training. The majority of people are looking to drop some weight and this title is exactly what we’re after. But how many times is the term “fat burning” actually explained to us? …Exactly. Well, I’m going to let the cat out the bag!
The simplest answer is, it is a matter of FUEL
Our bodies run on energy. Stores of energy, which are replenished by eating and drinking healthy foods like complex carbohydrates and fruit & veg. The energy is stored up either in your liver and muscles in the form of Glycogen, or as adipose tissue underneath the skin – more commonly known as fat.
Now, when you start doing a cardiovascular exercise such as running, stepping, cycling etc, the first place your body is going to look for energy is in those stores of Glycogen. Therefore the liver and muscles will instantly be raided for this source of fuel. And it works, brilliantly… while it lasts. After about 20 minutes the Glycogen stores are depleted and your poor tired body needs to look somewhere else for a new source of fuel.
Introducing – FAT
The next place to get energy for exercise after Glycogen is fat. It’s the next best thing. Your body will be able to do the same exercise for almost the same exertion running on fat. Any exercise you are doing after the initial 20 minutes will be eating into your fat stores until you rest up and replenish the Glycogen stores.
Which begs another interesting question: “Would it not be better to exercise on an empty stomach so there are fewer carbohydrates working their way through the digestive system?” And this is where it gets slightly more complicated.
Fat burning is not just about what fuel your body is using to complete your workout. It is also about total calorie expenditure. This means that you need to actually be working hard enough to use up a good chunk of your weekly calorie deficit. A good session should burn 500 – 750 calories in 45 – 60 minutes.
A weekly deficit of 3500 calories will equate to roughly 1lb of fat burnt off. In order to work hard enough to achieve this in a few workouts (and eating properly!), you will need a decent blood sugar level to get you started; otherwise you simply won’t have the initial start-up energy to complete such a workout. So eating something sensible such as fruit, oatmeal or energy bars will put your best foot forward before setting off.
Also, if you start getting hungry while working out, chances are you won’t go as hard or as long compared to if you eat something beforehand. Always remember to allow for digestion though! A light snack of 100 – 200 calories needs roughly 40 minutes before you start to train.
Jim Norfolk is a Personal Trainer in Milton Keynes