The Science of Flexible Dieting

In this article we’ll talk about flexible dieting, also known as IIFYM. By the time you’ve finished reading, you’ll know what flexible dieting is and how to apply it.

Where did flexible dieting come from?

Flexible dieting is not a new concept at all. Bodybuilders have done this for decades, but it has been receiving a lot of attention lately. The whole thing started in a bodybuilding forum a while back when a powerlifter and former bodybuilder, tired of new lifters asking if they could eat this or couldn’t eat that, said, “if it fits your macros, eat that sh*t”.

What is flexible dieting?

The most important thing to remember is that flexible dieting is not a diet (as strange as that may sound). Flexible dieting is simply the scientific approach to dieting. You can eat whatever you want as long as you count and manage the food you eat in order to hit your daily requirements.

Requirements? What requirements?

The “requirements” are your macronutrient and micronutrient goals. Macronutrients is what is supplying energy for your body. Macronutrients include carbohydrates, proteins and fats (there’s also other macronutrientes such as fiber or alcohol, but that’s beyond the point of this article). Each macronutrient has energy value: for example, each gram of fat has 9 calories, each gram of carbohydrates and protein have 4 calories.

Micronutrients are vitamins and minerals. They are labeled as micronutrients because the body only requires them in very small amounts. They don’t have any calories and don’t supply your body with energy.

Is IIFYM right for me?

Flexible dieting is a great way of dieting for bodybuilders. If you just want to get fit or lose some fat on your belly, IIFYM is probably a waste of time and energy, but if you’re serious about your goals and want optimal results, you must count your macros and make sure you meet your requirements every day.

Also, it’s way less stressful since you’re allowing yourself to enjoy your favorite foods and treats in moderation without the accompanying feelings of remorse or guilt because you know that it won’t impact your progress.

So I can eat junk food all day and get ripped?

The reason why IIFYM has such a bad reputation is because people don’t know it’s concept. Flexible dieting tells you that you can eat whatever you want, as long as you hit your daily needs. If you eat only junk food, you don’t get a considerable amount of micro-nutrients, and even hitting your macro-nutrients gets pretty hard, since most fast-food or processed foods are pretty high in fat.

A general guideline is to eat 80% nutrient-dense food so you can hit all your micros, and then eat whatever you want (junk food or not, it’s entirely your choice), as long as you still are abiding by your macro-nutrient needs. So if you’re eating 3000 calories per day, you can save 600 calories to eat your favorite foods and treats.

But I thought junk food makes you fat?

A caloric surplus makes you fat. People need to forget this idea that health and fitness are the same thing. I wish that was true (so I can convince people to eat healthier) but it’s not. The type of food you eat has no impact on your body composition. This has been proven over and over again. It’s all about numbers: calories in, calories out.

How do I start?

The only thing you need to successfully practice flexible dieting is a weight scale food scale. You must track every single piece of food that goes in your mouth (and supplements, if they have calories). But tracking isn’t enough. The whole point of flexible dieting is to hit your daily nutritional requirements.

Back in the day this used to be really boring and time-wasting, but today there’s several websites to help you track your food such as, or You must also weight yourself every single day (before eating anything and after going to the bathroom, to get has accurate as possible).

The calculators aren’t 100% accurate, if the calculator tells you that 2400 calories is a caloric deficit for you, but you don’t lose weight, it means the calculator was wrong and therefore you must adjust your macros. Plus, you must re-calculate your numbers as you go on, since your caloric needs change with your weight.

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  1. Alan
    • F&P Admin

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