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Flexible Dieting (IIFYM): What It Is and How to Do It Right

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IIFYM means 'if it fits your macros, you can eat it.' It works when you prioritize food quality as your base and save flexibility for the extras.

IIFYM (If It Fits Your Macros), also called flexible dieting, says any food can fit your diet if it matches your daily macros and calories. It's the opposite of elimination diets.

What the evidence says

Helms et al. 2014 and later studies compare flexible dieting with rigid diets. Key findings: equal or better adherence, same fat loss with the same protein and calories, and a lower risk of eating disorders tied to rigid rules.

How to do it right

  1. Quality base: 80-85% of your intake from minimally processed foods.
  2. Flexibility: 15-20% can be anything that fits your macros.
  3. Priority order: calories > protein > fiber > micronutrients > the rest.
  4. Aim for at least 25-35 g of fiber per day.

When IIFYM is a bad idea

  • If you have a history of eating disorders: the rigidity of tracking can be as harmful as a restrictive diet.
  • If counting macros leads you to eat 70% ultra-processed foods: that's not flexible dieting, it's poor nutrition.
  • If it kills enjoyment and your social life: invisible costs matter as much as results.
Flexible dieting isn't 'eat whatever you want.' It's 'you don't need to cut out whole food groups.' Quality still matters.

About this guide

Last reviewed
. We review content at least once a year, and sooner if relevant literature comes out. Update policy.
How it is verified
We prioritize meta-analyses, systematic reviews and official positions (ISSN, ACSM, EFSA, WHO, Cochrane). Full methodology · topic: Nutrición y calorías.
Conflicts of interest
Some product links are affiliate links from Amazon España and earn us a small commission at no extra cost to you. How we fund the project.
Medical disclaimer
Educational content. Does not replace consultation with a healthcare professional. More detail.

Spotted an error in a formula or recommendation? Email us at jesus.narvaez.tames@hotmail.com. Corrections are published as an updated note on the guide.

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