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1.
The phrase If It Fits Your Macros (often abbreviated to IIFYM) refers to meeting the individual macronutrient needs relevant to one’s goals and then filling the remaining calories with foods of personal preference. Meaning, eat whatever you want as long as it fits your macros.

What “eat whatever you want as long as it fits your macros” means is basically, eat right, but don’t get all caught up in the whole ‘clean vs dirty’ food debate that seems to still go on. If you want to eat whole grain bread, oats, brown rice, etc. etc. Then do it. If you want to eat white bread, white rice, and pop tarts, as long as it fits in with your other macronutrients and your goals in terms of caloric intake then it isn’t going to make much of a difference in the long run. It all comes down to personal preference.
IIFYM is achieved by following a structured diet similar to the below:
- 200lb man at 20% body fat wants to lose weight
- Maintenance Calories: 3000
- Calories to cut: 2400 - this is a 20% caloric deficit
- 1.5g protein per lb/LBM: (1.5 * 160) 240g
- 0.45g fat per lb/BW: (200 * 0.45) 90g
- Calories from fats + protein minimums: (240 * 4) + (90 * 9) = 1770
- Calories from reaching minimums taken from calories to cut: (2400 - 1770) 630
- He has 630 kcal left to fill with whatever foods he chooses (pop-tarts, pizza, cake, ice cream) and still lose weight as a result of remaining in a calorie deficit.
by tsw March 07, 2012
 
2.
If It Fits Your Macros (Refers to diet, google macros if you don't know what they are.) Usually used in Forums
OP: So I can eat pop tarts and still get ripped??

Reply: IIFYM.
by DaddyD June 15, 2012