When it comes to diet, we try. We know the rules: Fill up on fresh fruits and vegetables, whole grains and lean protein; avoid saturated and trans-fats and processed foods. As well-known author and nutritional guru Michael Pollan sums up, Eat food. Not too much. Mostly plants.

Yet being ‘good’ all the time is a tough proposition in a world of restaurant meals, convenience foods and sweet temptations. “There is no such thing as perfect, and people should not set themselves up for failure,” says dietitian Emily Bailey, director of nutrition at NutriFormance and Athletic Republic. “If you set out a goal, it should always be measurable but, most important, attainable.”

This is where the ‘80/20 rule’ can come in handy. Also known as ‘Pareto’s principle’ after Vilfredo Pareto, who coined the term in the early 20th century, the rule was originally applied to economics, stating that 20 percent of the people owned 80 percent of the wealth. Since then, the 80/20 split has been used to exemplify a variety of business and lifestyle principles. In nutrition, it has become a way of expressing the need for moderation and recognizing that an allor- nothing mindset often leads to failure.

“The 80/20 rule is a principle that is based on maintaining positive behaviors 80 percent of the time and including less desirable behaviors the other 20 percent of the time,” says Julie Pozzoli, a registered dietitian at St. Luke’s Hospital Nutrition Wellness Center. “Allowing yourself the green light to indulge once in a while may help you remain on track with your health goals.”

Amy Moore, a nutrition and dietetics instructor at Saint Louis University, notes that “the tried and true focuses on variety and moderation. If you’re eating a variety of foods then you’re better able to get the vitamins and minerals that your body needs. And we don’t want people to deprive themselves so much that it becomes an obsession.”

Another dietary take on the 80/20 rule is to stop eating when you’re 80 percent full. But how do you know when you’ve reached the 80 percent mark? “I like to use the word ‘satisfied’ versus ‘full,’ ” Bailey says. “On a scale of zero to 10, with zero being starving to the point of physical low blood sugar symptoms and 10 being full to the point of food coma, need-to-unbutton-my-pants, Thanksgiving-full, we should try to gauge seven being a level of ‘satisfied’ and eight as a level of ‘full.’

Since it takes 20 minutes for the brain to register satiety, and the average meal is consumed in only 12 minutes, many people continue eating past satisfaction and only realize they’re stuffed when their plate is empty. Enter another 80/20 rule variation: eat only 80 percent of a regular serving and pause for a few minutes to gauge your true level of satiety.

“There are many variations to the 80/20 rule,” Pozzoli says. “For meal planning, a person may choose to eat healthfully during the week but not during the weekend, or maybe drink water 80 percent of the time versus other caloric beverages.”

However, she urges caution. “If you need to maintain certain restrictions for medical reasons, those 20 percent indiscretions can have an unhealthy impact on your life or make achieving your specific health goals take longer.”

Consider your goals and then strive to eat a healthy, balanced diet. Don’t sweat an occasional indulgence, and you can learn to love healthy eating.