“You Cant Outrun Your Fork”
You’ve heard that one before, haven’t you? It’s one of my favourite quotes although I have no idea who said it (and neither does the Internet, it seems).
Some people think that if you eat 2 slices of pizza and then head outside for a run, you’ll burn off the calories you just ate. Or if you burn 300 calories going out for a run, that you can indulge in that 300-calorie hot fudge ice cream dessert you were anticipating eating all through that run. But is that what is really happening?
Let’s start with the obvious. Your stomach is outside your body. Wait, that might not be so obvious unless you’ve studied physiology. It’s true though. Specifically, the surface of your stomach that faces the inside is outside your body while the surface that’s on the outside of your stomach faces the inside of your body. Did you get that? It forms a barrier. Just like your skin.
It’s not just your stomach but your entire digestive tract from your mouth through to your anus that is considered to be outside your body. And just like your skin, the purpose of your digestive tract is to provide a barrier between the outside world and the inside of your body. Why am I telling you this? It’s to help you understand what happens when you eat.
Your digestive system extracts the nutrients your body needs from the food you eat. And not just the calories in the form of fat, protein, and carbs But a host of vitamins and minerals essential to the running of literally hundreds of bodily functions.
We think of eating as putting food into our bodies. That’s kind of true. The food you just ate is inside your digestive tract but it’s not inside your body. Not until your small intestines begin to absorb it does the food enter your body – or more precisely, the metabolized components of the food you ate. It can take 2 to 5 hours for the food to get from your plate to your small intestines where the absorption actually happens. And then several more hours for the whole metabolism process to finish. The whole trip, mouth to ass, can take several days.
When you go out for a run you draw on your stored energy reserves – most commonly glycogen stored in your muscles and liver and also triglycerides stored in your adipose cells (fat cells). Those stored energy reserves are the endpoints of metabolizing the food you eat.
So there you have it. The point where eating 300 calories and burning 300 calories meet is in your muscle tissues, your liver and your adipose tissues (your fat). The locations where your body stores energy. So while you can’t actually run off the 300 calories doughnut you just ate, you can run off the one you ate yesterday, or at least you will run off the accumulated food you stored yesterday.
Here’s the thing. Glycogen capacity is limited. The average male might be able to store 500 g of glycogen in the liver and muscle tissues. Triglyceride capacity on the other hand is almost unlimited as demonstrated by the extreme level of obesity that some humans have managed to acquire. That means that if you eat that 300 calorie doughnut when glycogen stores are full, then your body will store the energy as fat. On the other hand, your preferred source of energy when you exercise is the glycogen in your muscles. It’s readily available and quick to turn into energy. Only when glycogen stores become depleted does your body start recruiting fat for energy.
What does that mean? Well, in both cases it is your body that decides in what form to store the energy you’ve eaten – fat or muscle – and from what source to recruit the energy for your run.
Back to the question at hand; If your run and the doughnut you eat have no connection, then it doesn’t really matter whether you run and have dessert or skip both the run and dessert.
And now we bump into precisely why many people get so frustrated when they start to exercise and find that the weight does not come off. They’re eating to boost fat stores and running to deplete glycogen stores. Yes, some eating goes into glycogen stores and some running recruits from fat stores; But it’s not a simple calories in versus calories out game. And because of that, you have to think about more than just calories. What you eat and how much matters. So does what sorts of exercise you engage in and how much.
The bottom line is that the processes involved in digesting food in order to store fuel in your muscles, liver and fat cells are completely separate from the processes involved in burning that stored fuel.
Your body is an amazing machine and the processes of metabolizing food and burning energy are some of the most astonishingly complex processes that happen inside your body. But you don’t have to understand those processes to relish the joy of burning your stored fuel; Just go out and have a fun run in the sun or play a game of pickleball with your family. And you don’t have to understand to relish the joy of storing fuel by sitting down with a knife and fork to a gastronomic delight. That’s what life is all about. Storing and burning fuel.