If you’ve ever Googled, “Is diet or exercise more important for weight loss?” you’ve probably come across this seemingly arbitrary formula for dropping pounds: It’s 80 percent diet and 20 percent exercise. But where did that 80/20 ratio come from? And what does it really mean?
The key to weight loss is achieving a negative energy balance or taking in fewer calories than you burn. To shed a single pound, you need to achieve a 3,500 calorie deficit. So if you’re following the 80/20 ratio, you’d want to burn approximately 750 calories through exercise and cut an additional 3,000 calories through dieting. That’s a total deficit of 3,750 calories for the week.
You don’t need to hit an exact 80/20 ratio to shed pounds, but it is important for people to focus primarily on a diet when they’re trying to lose weight. You can lose weight without exercise, but you cannot lose weight if your nutrition counteracts your energy expenditure through exercise. 
The principle behind the 80/20 rule is simple: Eat nutritious foods 80 percent of the time and allow yourself to indulge a little the other 20 percent of the time. Proponents of the diet disagree on how to determine the 20 percent when you eat less healthy foods, however. The 20 percent portion of less healthy eating should occur once per week, and not consume 20 percent of what you eat each day. Healthy eating on the 80/20 diet includes eating mainly whole, unprocessed or minimally processed foods, including fruits, vegetables, lean protein and whole unprocessed grains, as well as plenty of water. Fruits, vegetables and other foods high in water and fiber are low in energy density or calories per gram. This means you can eat large portions of them to help you fill up without eating too many calories at meals. It’s possible, however, to eat too many calories while still eating nutritious foods like those recommended for the 80 percent of the time you’re eating healthily. Listen to your body’s hunger cues and avoid eating when you are not truly hungry.
Exercise is still very important! Staying active is important to keeping your well-oiled machine running at an optimum level. Make sure that if you exercise (and if you don’t you should) that you keep mixing up your workouts. You do not want to continue repeating the same workouts as your body will adapt to a routine. Keep your body guessing and you will see increased benefits. Diet and exercise complement each other. Feed your engine with good food and it will perform at a high level. Throw in exercise and your body will be at another level. .