Adding on exercise does not equate to losing body fat. In a 16-week study, untrained women (ages 18 to 34) built up to 40 minutes of hard cardio or weight lifting three days a week. They were told to not change their diet, and they saw no changes in body fatness.
Creating a calorie deficit by eating less food seems to be more effective than simply adding on exercise to try to lose weight.
More: 100 Ways to Cut 100 Calories From Your Diet
Runners who complain they "eat like a bird" but fail to lose body fat may simply be under-reporting their food intake. A survey of female marathoners indicated the fatter runners under-reported their food intake more than the leaner ones. Were they oblivious to how much they actually consumed? Or were they too sedentary in the non-exercise hours of their day?
Myth: If you train for a marathon or triathlon, surely your body fat will melt away.
Wishful thinking. If you are an endurance athlete who complains, "For all the exercise I do, I should be pencil-thin" take a look at your 24-hour energy expenditure.
Do you put most of your energy into exercising, but then tend to be quite sedentary the rest of the day as you recover from your tough workouts? Male endurance athletes who reported a seemingly low calorie intake did less spontaneous activity than their peers in the non-exercise parts of their day.
You need to keep taking the stairs instead of the elevators, no matter how much you train. Again, you should eat according to your whole day's activity level, not according only to how hard you trained that day.
More: What to Eat for Peak Marathon Performance
Myth: The more miles you run, the more fat you will lose.
Often, the more miles you run, the hungrier you get and (1) the more you will eat, or (2) the more you believe you "deserve" to eat for having survived the killer workout.
Unfortunately, rewarding yourself with a 600-calorie cinnamon roll can quickly erase in a few minutes the 600-calorie deficit you generated during your workout.
The effects of exercise on weight loss are complex and unclear—and depend on the 24-hour picture. We know among people (ages 56 to 78) who participated in a vigorous walking program, that their daily energy needs remained about the same despite adding an hour of exercise.
How could that be? The participants napped more and were 62 percent less active the rest of their day. Be sure to pay attention to your whole day's activity level. One hour of running does not compensate for a sedentary lifestyle.
