Is Your Fuel Right?

Is your fuel right?
Is your fuel right?

Originally published here on 25-Jan-2014 at
Note: I no longer believe that we need to consume carbohydrates in order to burn fat

The F-word

I live in Mumbai for part of the year, where now there are recreational distance running races on almost every other weekend. Invariably, I receive calls from runners, in the days running up to the longer races, asking questions about energy drinks for the race.  There was even the one time that I received a frantic phone call from a lady flying out to a half marathon in another part of the country.  She was desperate to buy energy gels for her race on her way to the airport. Wholly unnecessary!  Why?  Read on…

Many of us are unaware of how much energy our bodies store.  This chat with you now is to help you get a handle on that in an easy way.  Once you understand that better, you will also understand why we tend to put on excess fat and struggle to get rid of it. At the end of the two minutes you take to read this, you will easily remember the units of measure of fuel, what they mean, how much we store, where we should ideally get our fuel from, and how much we need.

In my previous article I spoke to you about the various nutrient groups that provide fuel – fat, carbohydrates and protein.  In order that we do not burn protein (our tissue rebuilding material) we need to ensure that we consume sufficient quantities of the other two types of fuel (carbohydrates and fat).

Understanding food fuel measures

Visualizing Calories In and Out
Visualizing Calories In and Out

You hear talk about calories and often you may not quite appreciate what 1 calorie or 100 calories or 1000 calories really means.  To grasp it is actually quite simple. In terms of input, you can think of 100 calories as a banana!  Think about an apple or an egg – about 80 calories each.
In term of output, measuring your weight in kilograms, if you run 1km, you are likely to burn the same number in calories as your weight in kilograms.  So if you are 70kg, you will burn 70 calories if you run 1km.  If you are 50kg, you will burn 50 calories.

Can you now visualize the measure of the energy from a typical fuel source (bananas!) and the way it maps into energy for a simple human activity (running)?

Why can’t you endlessly burn your huge stores of fat?

You might eagerly ask, “Can I then not just stop eating and just burn all my body fat to lose weight?”. Why does that not work? Besides all the various chemical changes that occur in your body that will make such an act of starvation harmful, quite simply, you cannot burn fat without also burning carbohydrates in parallel.
“Big deal, so what’s the problem?  I shall burn my body’s carbohydrates too” you might then say. Well, therein lies the problem. If you are an average sized adult, whether skinny, muscular or with, perhaps, 10kg of excess fat that you would like to burn, did you know that the most you are ever likely to store as fuel in the form of carbohydrates is 500 grams? This form of what I call “premium fuel” is what we need when we sprint for the public bus to work, or lift our bags off the luggage carousel at the airport.

Limited stores of Carbohydrates are your premium fuel that are also required in parallel when burning fat!

Limited stores of Carbohydrates are your premium fuel that are also required in parallel when burning fat!

What limits our ability to burn fuel is our store of this premium fuel, carbohydrate.  Very approximately and theoretically, with that 10kg of excess fat as his sole source of fuel a 70kg adult might run 1,285km (London to Edinburgh and back! Or, almost the distance from Mumbai to Delhi!). But the most he could run with his body tanked up on carbohydrates is only 29km. Note, this is also the reason why a recreational runner who ate and drank sensibly until race day will not need a mid-race carbohydrate drink or snack for a half marathon, whereas she will definitely need it for a full marathon. So, it is carbohydrates not fat that set the limits of human endurance from a fuel perspective.
(Note that post race hydration and the immediate consumption of carbohydrates is extremely important, whether running a 100m sprint or a 100km ultramarathon.  More on this in a later blog.)

How much of each fuel type then?

The natural question that you might then follow up with is – “how much of each fuel type should I be consuming?”
The answer will vary based on your individual specific requirement but splitting hairs at this level is what makes most of us also lose interest in the topic.  Instead, make it is easier to remember by simply noting that, for a physically active adult, about half of your energy intake should be from carbohydrates, with the remaining half being split equally between fat and protein.

Input for a healthy active adult

Food (calorie) input for a healthy active adult

How much fuel should you put into your tank today?

The final question then is, “how much fuel in total?” A simple but very approximate answer would be to simply use one of the many free calorie requirement calculators available on the internet.  For instance, here or here or here.  What is more important is to appreciate the situation that you find yourself in and then being mindful of where you need to go.  For instance, assuming you are otherwise free of metabolic diseases, here are some example situations:

  •  if you think you are overweight, you are probably consuming too much fat and carbohydrates and, therefore, too many calories per day – reduce daily intake of both fat and carbohydrates to a safer level (remember “the power of miniscule change“)
  • if you recently took up recreational running a few miles a week but don’t seem to be losing much weight, you are probably consuming more calories than you used to before you started running and many more than you are burning through running – reassess your fuel intake
  • if you took up weight training a few months ago and seem to be gaining weight instead of losing it, you could check even visibly that the gain is lean muscle and there has been fat lost – stick with your routine
  • if you are very active and struggle to put on weight or are often tired – eat and drink more fuel but in the right proportions to avoid eating too much fat or burning protein as fuel

Your specific situation may need more carbohydrates (e.g. you are exercising a lot more than the average person).  Or you may need to reduce your carbohydrate intake and cut your fat intake (if you have a sedentary lifestyle and are obese).  An experienced nutritionist ought to be able to advise you more specifically about safe ways to reduce your fuel intake given your lifestyle.  But, in the end, it is up to you to be mindful of your situation and mindful of all the steps you take to ensure that your fuel is right!



Dr Purnendu Nath spends his waking hours focusing on helping individuals and organizations reach their goals, to make the world a better place. He speaks, writes and advises on topics such as finance, investment management, discipline, education, self-improvement, exercise, nutrition, health and fitness, leadership and parenting.


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