The 80/20 rule is a sustainability framework: roughly 80% of the time you eat nutrient-dense whole foods, and about 20% you allow flexibility for enjoyment and social life. It is not strict math; it is behavioral strategy. Long-term outcomes come from consistent habits, and planned flexibility can improve adherence rather than derail it. Keep the “80” anchored in protein, fiber, vegetables, legumes/whole grains, healthy fats, and hydration. Use the “20” for treats or dining out with portion awareness. When combined with IF, don’t let the eating window expand the “20” into the majority. For diabetes or lipid issues, choose the flexible foods more strategically.