“You can’t out-run a bad diet”
Vs
If the furnace is hot enough you’ll burn anything”
What’s more important for health: physical activity or diet?
These questions are hotly debated in health and fitness forums, blogs and articles around the web. It’s baffling how this can be such an emotive and polarising topic. Some hold their opinions with religious-like unwavering fervour. Both sides have robust science on their side.
For Exercise:
Trying to cast my own bias aside, exercise has some pretty compelling arguments.
1. NOTHING has a greater influence on ALL-CAUSE morbidity and mortality (including cancer and mental health) than switching from a sedentary lifestyle to at least 30mins of daily activity. There is no more effective health intervention than that.
2. The exercise argument has another advantage over diet. You can’t super-optimise diet ie there is a limit to just how healthy you can get from dietary adjustments alone. Once you have achieved an optimal diet, it can’t be further improved upon. Nothing is limitless but the limits of human adaptation to exercise have not, and probably will not, ever be realised.
3. Diet can’t influence fitness the way that fitness can influence diet. What does that mean? Well, you can’t improve your cardiovascular fitness through changing your diet but you can change your dietary caloric requirements by exercising. Exercise will help to forgive a calorie excess by burning it off.
4. Exercise has less side-effects when you get the dosage wrong. In general terms (and with a few minor exceptions) more exercise = more health benefit. Many elements of diet are not so forgiving. Just this week I’ve seen a patient diagnosed with nerve damage due to B6 toxicity from dietary supplements and good intentions.
For Diet:
The catch-phrase of this argument is that “you can’t out-train a bad diet”. Coca Cola have invested heavily in research supporting exercise as it helps them push the message that it’s ok to consume their drinks as long as you exercise. However, evidence suggests that it DOES matter where the calories come from. A large econometric analysis of worldwide sugar availability, revealed that for every excess 150 calories of sugar, there was an 11-fold increase in the prevalence of type 2 diabetes, in comparison to an identical 150 calories obtained from fat or protein. And this was independent of the person's weight and physical activity level.
Although you can’t super-optimise health through diet, you can certainly speed up disease with a bad diet faster than a sedentary lifestyle will. If we look at the extreme end of the spectrum a bad diet can, literally, be poisonous. A sedentary lifestyle will kill you slowly but if your diet is bad enough, you can kill yourself in days to weeks by causes as diverse as acute alcohol toxicity to scurvy. No amount of exercise will save you from that.
The Verdict:
Diet and exercise are extremely hard to compare. It depends on how low we set the bar.
A self-destructive diet can harm you quicker than being a couch potato but regular exercise can improve your health to a far greater extent than just eating right. Both complement each other, neither can out-run the ill-effects of completely neglecting the other.
If we set the bar above the level of dangerous neglect then exercise has a far greater effect on overall health outcomes than diet but, as my dietician friend has just pointed out to me only 4% of Australians are getting there 2 fruit and 5 veg daily whereas 33% of Australians are getting their 150mins of activity a week.
