Exercise: Don’t Sweat It
“Why don’t fat people just go for a jog?”
This is one very popular response to a lot of the discussion on food, particularly when we start talking about taxing unhealthy food. We have already looked at the fallacies of calling obese people lazy gluttons in another blog. However, the role of exercise deserves a separate mention.
The idea that exercise can purge all our dietary sins is an appealing one, but it is wrong.
Let’s start by looking at the numbers. Ministry of Health estimates suggest that poor diet costs Kiwis about 110,000 years of life every year. By contrast lack of exercise costs about 40,000. That means that in terms of lifestyle, exercise is ¼ of the problem. Food is the real issue.
This result is borne out by diet studies. Most people who successfully control their weight get some exercise almost every day, but while exercise may be necessary for health, it is not sufficient in itself. Weight control first and foremost requires you to control your food intake.
How can this be? We all know that weight control is a simple matter of balancing energy in and energy out. So surely exercise plays a role. The food we eat is the source of energy for our bodies, but the amount of exercise we do is one determinant of how much energy our bodies actually need. If you exercise more, you can eat more. Woohoo! However, there are several reasons why focussing on exercise doesn’t mean you can eat whatever you like.
Firstly, while exercise adds to your energy needs, the difference it makes is surprisingly little: a 40-minute run for most people only adds around a quarter to the daily food energy you need. This may seem strange, until you understand that you actually burn most of your energy just by going about normal daily life. For most people just keeping your body working (even lying down) takes up between half and two thirds of the energy you release. For example, your brain only makes up 2% of your body weight but it burns about 18% of the energy you eat. You can see why our forefathers developed a taste for sugary and fatty foods in order to feed their growing, energy hungry brains.
Thanks to the energy packed into modern fake food, all this hard work can be wiped out in an instant with a little indulgence. Some examples:
- As we pointed out in our infographic, it takes a 60 minutes of walking to burn off a bottle of Coke or a solitary muffin.
- Drinking a ‘sports drink’ to ‘rehydrate’ after a run wipes out 20 minutes worth of jogging.
- It takes a person 20 minutes to sip away a glass of chardonnay or pinot noir, but 30 minutes of walking to work it off
You start to see how easy it is to fill your internal warehouse faster than it’s emptied by energy requests, and to snack or sip your way to obesity. Unless you have the time to train like a competitive triathlete, most of us can’t expect to exercise enough to allow us to eat or drink what we want. Dietary control (restricting the shipments of energy into your warehouse) is by far the most potent weapon in the battle of the bulge.[i] And yes, that includes alcohol, which is often overlooked as a source of calories.
Another issue for proponents of exercise is that they assume exercise has no impact on your appetite. It doesn’t take a genius to realise this is a complete fallacy. The body naturally compensates for exercise by eating more or exercising less over the rest of their day, which can render any sweaty exertions in the gym futile.
In fact it seems the best way to ‘fool’ your body into exercising without compensating for it is by making exercise part of your day to day lives. Having a job where you are on your feet is a great help. Walking or cycling to work, or even getting off the bus early and walking the last stretch to work are great ways to get your heart rate up. Of course, whether or not people can do that depends how safe and easy those options are. But they are worth doing, because those of us locked into a sedentary lifestyle are even more vulnerable to the damage wrought by indulgent diet.
We are not bagging exercise at all, simply identifying its limitations. Exercise is really important and has benefits far beyond helping to balance out your food intake: including building muscles and bones, heart health, and even making you happier. And if you exercise to work up an appetite, then fill up on decent tucker rather than fake food, you will benefit from the extra nutrients. But exercise isn’t a magic charm that can absolve you from the ill effects of eating whatever you like.
[i] Thompson, W.G. et al (2007) Treatment of Obesity in Mayo Clinic Proceedings January 2007 vol. 82 no. 1 93-102