Diet or Exercise?

There is no easy answer. It all depends on what your goal is in the end. Do you want to lose weight, or be able to get through the day without having to take a mid afternoon nap? In some cases it'll be a bigger benefit to cut down on calories, whereas in some you'll see a bigger effect by simply exercising.

Here are a few scenarios in which one of the two trumps the other...

Goal - Losing Weight...
...diet! It's easier to cut a few hundred calories than to burn a few hundred calories at the gym. Lowering your calorie consumption does not mean dieting by any means though. It just means finding healthier alternatives to the items you currently indulge on.

Goal - Energy...
...exercise! Coffee can only do so much for us. Of course caffeine and a good night sleep are two major contributors, but exercising stimulates invigorating neurotransmitters in the brain that'll leave you feeling much more energized.

Goal - Prevent/Fight Diabetes...
...exercise! Many think that diabetes can only be controlled or prevented through your diet, but regular exercise is the main contributor (only by a bit). Activated muscles use glucose for fuel, and this helps to keep your blood-sugar levels stable.

Goal - Mood...
...exercise! Did you know that working out for 20 minutes can leave you feeling upbeat for up to 12 hours? Exercising regularly for a longer period of time can also lead to changes in your brain that'll improve your response to stress.

Bottom line is...both eating well and exercising a few times a week will greatly help in all scenarios. It's not just eating less that allows you to lose weight. It's the combination of a healthy diet and fitness...just for people that don't have time to work on both, it's a better idea to start with adjusting your diet in that specific case.

Enjoy!
R