Flexible Dieting (IIFYM)

Flexible dieting, popularly "IIFYM (If It Fits Your Macros)," sets daily targets for calories and the three macronutrients (protein, carbohydrate, fat — see macronutrient-distribution) and lets the person fill them with whatever foods they prefer, as long as the totals are met. It is less a diet than a framework built directly on energy balance (see caloric-balance) and protein adequacy (see protein).

Pros: No foods are forbidden, which improves adherence and reduces the all-or-nothing rebound common with restrictive diets (see diet-adherence-principle). It teaches portion and macro awareness, fits social eating, and works for fat loss, maintenance, or gain by adjusting the calorie target (see calorie-targets).

Cons / considerations: It requires tracking (a food log or app — see calorie-logging), at least until intuition develops, which not everyone enjoys or sustains. Hitting macros says nothing about micronutrients, fiber, or food quality, so a sensible practice is the "80/20" guideline — roughly 80% nutrient-dense whole foods, up to 20% discretionary — to cover health, satiety, and fiber while keeping flexibility. Obsessive tracking can be unhealthy for some; it is not advised for those with disordered-eating tendencies.

• Set calorie + macro (protein/carb/fat) targets; food choice is flexible.
• Built on energy balance and protein adequacy.
• High adherence: no banned foods, fits social life.
• Requires food tracking until habits form.
• Use ~80/20 (mostly whole foods) to cover micronutrients and fiber.

• macronutrient-distribution — the targets being tracked.
• caloric-balance — the underlying mechanism.
• diet-adherence-principle — why flexibility aids long-term success.
• calorie-logging — the tracking it depends on.