Which is more important when trying to get a healthy, lean body; diet, or exercise?
Here's my honest overall take on this; every time I hear the saying that being or looking fit is "80 percent diet and 20 percent exercise", I cringe. Is diet incredibly important to fat loss, weight loss, and/or a healthy body? Yes. Is working out essential to fat loss, weight loss, and a healthy body? Yes; completely. Both are absolutely necessary for a strong, healthy, good-looking body; there's no reason to diminish the immensely important role of exercise in order to highlight the value of nutrition.
In our collective personal opinions, the minimization of the value of workouts is an over simplified, overly dramatic response to the incorrect assumption that you can out-exercise a bad diet.
To minimize the importance of exercise in the equation is to completely ignore the fact that working out has the capacity to strengthen your heart and your immune system, increase bone density, ward diabetes, cancer and heart disease, increase your lung capacity, and more. For this reason, we think it's irresponsible to downplay the role of exercise in both weight loss and health.
There is a big difference in weight loss via diet, and weight loss via diet and exercise; the method that uses both is significantly more healthy, and leads to a body that is capable, and strong. Lose weight from diet alone and you're going to be frail, and your health will suffer.
It's true that it's much easier (and some would argue it's also more fun) to devour a significant number of calories that would be very difficult or maybe even possible to burn off through exercise. For example, let's take a hypothetical huge holiday cheat for example, where a person has consumed upwards of 7000 calories. How likely is it that they have the endurance or the time (or will) to burn off that many calories? This even rings true on a much less dramatic, day-by-day example, if you eat lousily and over your maintenance calories by 400 calories a day, for example. Eventually, it adds up to weight gain.
Without exercise, a person will be forced to maintain a very low calorie diet, which is not particularly pleasant, reasonable, or healthy. Additionally, unless a person is being 100% on point with their food choices, it also lessens the likelihood that a person is easily able to get all of the vitamins and nutrients that they need.
For anyone who's still standing by the idea of diet being so much more important, remember that weight loss, bodyweight, and/or "having abs" (I hate that saying, too - everyone has abs) is not the end-all sign of a healthy body.
Diet-dominate weight loss also puts the focus on deprivation from food, instead of the growth and increase in strength and endurance that comes with exercise. Exercise increases self efficacy and confidence, which in turn can increase the likelihood that a person makes smart food choices.
Regarding the "abs are made in the kitchen" saying, I still disagree. Abs are made in the gym; the fat the covers them is burnt off via strength training, cardio, and maintaining a healthy diet that includes an appropriate amount of caloric intake.
In closing, we definitely, 100% believe that diet is enormously important to fitness, weight loss, and health. However, we don't see why the value of exercise needs to be dragged through the mud to prove this point. Both are important, it's not one or the other and what percentage each counts towards your end goal is a moot point. This is our opinion; you're welcome to disagree.