Exercise vs. Diet: Which Is More Important for Weight Loss? Your Answer Will Affect The Result

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Being healthy is simple, right? “Eat less, move more.” That’s easy to say, but practicality is one of the most important things when it comes to health and fitness. Recommendations like this are blanket statements that don’t address practicality—so when it comes down to it, which is more important? Diet, or exercise?

Yes, we should all eat healthier. Yes, we should exercise every day. There are infinite things we could do in order to be healthier, like sit less, eat more vegetables, eat less processed food, or drink less alcohol. But they don’t take into account the reality of life: we are all constrained by a finite amount of resources such as time, energy, willpower, and money. Recommendations that don’t take this into account can easily make us feel like we are failing our fitness and health goals.

To give you a sense of the importance of practicality, consider this recent meta-study (i.e. a study of studies), published in the Journal of the American Medical Association, which sought to figure out “which diet works best?” by looking at the results of 59 individual studies. These studies included various nutritional recommendations, such as low-fat, low-carb, and so on. Which of these recommendations reigned king? None. There were no major differences between the diets, and success was completely dependent on what the individual could adhere to. In other words, practicality reigned king.

Similarly, one of the most frequent questions that’s asked by aspiring fitness enthusiasts is “Which is more important: diet or exercise?” With practicality in mind, we decided to take a look at the evidence.

A Primer on Calories

At a physiological level, weight loss and weight gain revolve around caloric consumption and expenditure*. Because of this, it’s important to understand the basics of calories. Put simply: we lose weight when we eat less calories than we expend. Conversely, we gain weight when we eat more calories than we expend. In order to lose one pound of fat, we must create a 3,500 calorie deficit, which can be achieved either through exercise or diet.

*As an aside, it’s worth noting that some argue that carbohydrates and insulin are the culprits behind weight loss and weight gain in what is called “the insulin hypothesis of obesity.” While controlling both carbohydrates and insulin may be important for some individuals, this hypothesis has been thoroughly debunked.

Let’s say that a 200 pound man wants to lose one pound in a week. Through exercise alone, he needs to run about 3.5 miles per day (or 24.5 miles total), assuming his diet stays the same. Through dieting alone, he needs to cut back 500 calories/day (the equivalent of two Starbucks Frappuccinos), given his exercise regime stays the same. Theoretically, the two should achieve the same results.

But in the world of fitness theory and reality are not the same thing, because theory does not account for adherence. We don’t live in a magical house that contains a gym, a Whole Foods, and a personal staff of nutritionists and trainers. Instead, we’re left about our own devices in everyday life. What happens then?

What the Research Says

Dr. John Briffa, who runs an excellent health blog, analyzed a study examining weight loss without dietary intervention here. He explains:

In this study, 320 post-menopausal women whose weight ranged from normal to obese were randomised to either an additional exercise or no additional exercise group (the control group). Those in the exercise group were instructed to take 45 minutes worth of moderate-vigorous aerobic exercise, 5 times a week for a year. Both groups (the additional exercise and the control group) were instructed not to change their diets.

At the end of the year, it was found that the exercise group, compared to the control group, lost an average of 2 kg (4.4 lbs) of fat. I’d say that quite a lot of us would be glad to drop a couple of kgs of fat. But now I’d also like to focus on what these women had to do to achieve this loss.

While the exercise group were instructed to exercise 5 times a week for 45 minutes, what they actually did was exercise for an average of 3.6 days each week. Total exercise time averaged 178.5 mins per week. We can multiply this by 52 to get the total number of minutes exercise over the course of the year, and divide this by 60 to convert it into hours. Doing this, we get a total of just under 155 hours. That’s about 77 hours of exercise for each kg of fat lost.

Most people would balk at the idea of exercising for 77 hours to lose 1 kg of fat. (Or equivalently 35 hours to lose 1 pound, for us American folk.)

But what about simultaneously exercising and accounting for dietary intake?

One study, published in the International Journal of Obesity and Related Metabolic Disorders, took trained subjects and had them track dietary intake along with energy expenditure. On paper, there was an overall caloric deficit created by the subjects. However, when researchers examined empirical changes, no weight was actually lost. As it turns out, subjects were simultaneously underestimating caloric intake and overestimating caloric expenditure.

Compare the studies above to the hilarious self-experiment by a nutritionist who went on the “Twinkie Diet” and subsequently lost 27 pound in 10 weeks. (Pro tip: Don’t try this at home.)

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