What Is IIFYM?
IIFYM (If It Fits Your Macros) is a dietary framework based on one principle: total daily macronutrient intake determines body composition outcomes, not the specific foods eaten to reach those targets.
The three macronutrients each carry a caloric value:
| Macronutrient | Calories per gram | Primary role |
|---|---|---|
| Protein | 4 kcal/g | Muscle protein synthesis, satiety |
| Carbohydrates | 4 kcal/g | Primary energy substrate, glycogen |
| Fat | 9 kcal/g | Hormonal function, fat-soluble vitamins |
By tracking grams of each macronutrient rather than adhering to a fixed food list, IIFYM allows dietary flexibility within a structured caloric framework.
How to Set Your Macros
Step 1: Calculate Your TDEE
Your TDEE is the calorie total that maintains your current weight. See our complete TDEE guide for the full calculation methodology.
Step 2: Set a Calorie Target
| Goal | Adjustment |
|---|---|
| Fat loss | TDEE − 300 to −500 kcal |
| Maintenance | TDEE |
| Muscle gain (lean bulk) | TDEE + 200 to +300 kcal |
Step 3: Set Protein
Protein is the highest-priority macro because of its role in muscle protein synthesis and satiety.
Target: 1.6–2.2g per kg of bodyweight (or 0.7–1.0g per lb)
Research by Morton et al. (2018) in the British Journal of Sports Medicine found that protein intakes above 2.2g/kg/day do not produce additional lean mass gains in resistance-trained individuals. Lower-bound 1.6g/kg is sufficient for most.
Step 4: Set Fat
Fat is critical for testosterone production, cell membrane integrity, and absorption of fat-soluble vitamins (A, D, E, K).
Minimum: 0.5g/kg bodyweight; Typical range: 0.8–1.2g/kg
Step 5: Fill Remaining Calories with Carbohydrates
Carbohydrates are calculated from the remaining calories after protein and fat are allocated:
Formula: Carb grams = (Total kcal − [Protein kcal] − [Fat kcal]) ÷ 4
Macro Targets by Goal: Reference Table
| Goal | Protein | Fat | Carbs |
|---|---|---|---|
| Fat loss (80kg) | 160–176g | 60–80g | Remainder |
| Maintenance (80kg) | 144–160g | 70–90g | Remainder |
| Lean bulk (80kg) | 160–176g | 80–100g | Remainder |
Common IIFYM Mistakes
Mistake 1: Ignoring Micronutrient Quality
Hitting 160g protein via protein shakes and 300g carbs via sugar is nutritionally incomplete. Apply these minimums regardless of food choices:
- Fibre: ≥14g per 1,000 kcal consumed
- Vegetables: ≥5 servings per day
- Whole food protein: ≥50% of protein target from whole sources
Mistake 2: Incorrect TDEE Calculation
IIFYM is only as accurate as the TDEE it is built on. Validate your TDEE with 2 weeks of consistent intake and weight tracking before adjusting macros.
Mistake 3: Inconsistent Tracking
Studies on food tracking accuracy show that self-reported intake underestimates actual consumption by 12–40% on average (Dhurandhar et al., IJOB, 2015). Weigh foods with a digital scale rather than estimating volumes, especially for calorie-dense foods (oils, nuts, nut butters).
How Does IIFYM Compare to Other Diet Approaches?
Is IIFYM better than clean eating?
For body composition outcomes, research shows no significant difference when calories and protein are matched. The key advantage of IIFYM is adherence: a 2011 review by Westenhoefer et al. found that flexible dietary restraint was associated with lower BMI, lower reported food intake, and less disordered eating than rigid restraint, over a 12-month period.
Can IIFYM be combined with intermittent fasting?
Yes. IIFYM governs what you eat; intermittent fasting governs when you eat. Both can be used simultaneously. The research on their combined use shows no synergistic or antagonistic effect on body composition vs either approach alone when calories are equated.