A common approach to eating is to eat 80% “clean” food and 20% treats/sweets/not-so-healthy foods. It makes sense initially that this would be a less strict way of eating that could increase your long-term compliance to your diet. But upon further exploration, it turns out that it might not be the best fit for you. Let me explain.
To quantify in calories (kcal) what 80% and 20% of your daily calorie intake might look like, let’s assume that you were eating 2000kcal/day. This is a reasonable estimate for someone who is around 150-175 lbs, who exercises moderately 3-5 times a week, and who is trying to eat at a maintenance level (neither lose nor gain weight). Using this nice round number as an assumption also makes the math really easy. If you want to calculate your personal energy requirements, this “How To Calculate Your Macros” video will show you how.
Setting aside any judgement of what defines a food as “dirty” or “junky” or “clean”, I am choosing to use the words “clean” and “junk food” solely for ease-of-reading. So if you were going to eat 80% clean foods, you would be eating 1600 kcal of clean food. And since 20% of 2000 is 400, so you would be eating 400 kcal or junk food on a 2000 calorie diet. Further, we can assume that the 400 kcal is most likely going to be coming from carbohydrates (carbs) (and perhaps partially from fats) since no one is going to choose boiled chicken breast as their junk food. Since there are 4kcal/g for carbohydrates, choosing junk food such as chips, cookies, cupcakes, and sugary crackers translates to about 100g carbohydrates. (The calculation is slightly different if you were to choose ice cream or fried-foods that were more fat-laden than carb-laden.)
Now for a lot of people, 100g carbs is likely more-than-half of their daily carb totals! You can watch the above linked video that explains how to calculate your daily nutrition needs in terms of quantities of proteins, carbs, and fats if you want a refresher. So if you are trying to eat towards your goals, and you eat half of your carbs in one sitting on a big junk food snack, you are going to be left with the unfortunate struggle of trying to pack in a lot of protein into your day with very little carbs to go with it.
On top of that, for many people, eating 100g carbs at once feels pretty terrible! Your blood sugar spikes up, your body signals insulin to rush in to mitigate that sugar rush, and then since such a big dose of insulin was rushed in, you end up with low blood sugar, which can cause headaches, dizziness, wooziness, and other uncomfortable sensations.
I think a better approach is to shoot for about 10% of your daily calories coming from junk food. 10% of 2000 kcal/day is 200 kcal, and that is plenty to fit in a small cupcake, muffin, cookie, sweetened yogurt, or a small serving of ice cream. If you know that you can fit one thing like this into your diet everyday, you are less likely to binge eat everything in sight when the stress of attempting perfection for too long backfires. Try it out and let me know what you think.