If It Fits Your Macros (IIFYM): Your Guide to Flexible Dieting

What Is Flexible Dieting?

Weight loss is far simpler than it's made out to be. Through a method called "If It Fits Your Macros" (IIFYM or flexible dieting), you can lose weight safely, learn to keep it off, and change your life. Unlike other dieting fads, no magic is required to make it work—only science. In fact, all diets rely on the same principles that make IIFYM work.

What Is Flexible Dieting?

Flexible dieting is a weight-loss method that requires you to track your total macronutrients (protein, fat, and carbs) and keep your calories beneath a certain threshold. This threshold is regularly adjusted throughout your diet and varies from person to person. Flexible dieting is generally more sustainable than other diets because progress is gradual, and you can satisfy your cravings for your favorite foods in moderation.

How IIFYM Works

When it comes to weight gain and weight loss, everything boils down to a simple equation:

Calories Ingested – Calories Expended = Daily Gain or Loss

If you eat 2,000 calories in a day, but only burn 1,800 calories throughout the day, then you're left with +200 calories. If you did this every day, you could expect to weigh more in the long-term.

The two primary elements that make up your “Calories Expended” category include:

  1. Your Metabolism: The number of calories your body naturally burns in order to function.
  2. Your Daily Activities: Calories burned from work, fitness, doing chores, etc.

How Many Pounds Can You Lose in a Week?

Unless you're morbidly obese, you should not lose more than 2 pounds per week. Doing so will result in muscle atrophy (muscle and strength loss). Similarly, gaining weight too quickly will result in the addition of mostly fat and water weight.

How to Do IIFYM

Let’s assume your goal is to lose 5 pounds. Let’s also assume that your metabolism naturally burns about 1,400 calories per day, and your workout plus daily activities burn another 600 calories.

Calories Ingested – 2,000 Calories = Daily Gain or Loss

To keep yourself at a safe rate of weight loss, and for simplicity, we want your "Daily Loss" to be roughly 100 calories.

Calories Ingested – 2,000 Calories = -100 Calories

Calories Ingested = 1,900 Calories

Obviously, some trial and error is needed. The best way to find your "Calories Expended" is to:

  1. Weigh yourself in the morning
  2. Track the number of calories you eat that day
  3. Weigh yourself the next morning under the same conditions
  4. See if you went up or down in weight
  5. Adjust your calories until you're the same weight as the day before

Ideally, you'll operate off of an average weight over several days to avoid making drastic (and unwarranted) changes.

Now let’s assume you continue at -100 calories per day as your "Daily Loss" (this translated to a rough average of -0.2 lbs per day for me).

After about a week, your metabolism will slow down in order to adjust to your caloric deficit (this is a basic survival mechanism).

This means that you'll need to eat less or do additional exercise if you want to keep losing weight. For example, you could drop your "Calories Ingested" by 100 calories and see how your body reacts. You'll need to continue this trend until you reach your desired weight. You can also use these principles to speed up your metabolism and gain weight.

What Are Macronutrients (Macros)?

    Macronutrients are the nutrients we need in relatively large amounts for our growth and health. They consist of protein, fat, and carbohydrates. These three macros can be broken down on a calorie-per-gram level as follows:

    • Protein = 4 calories/gram
    • Fat = 9 calories/gram
    • Carbs = 4 calories/gram

    How to Count Macros

    Counting your macros is as simple as multiplying the calorie density of each macro by the grams you have of each, then adding the totals. Let’s say you have grilled chicken with BBQ sauce. We will assume it’s 25 grams of protein, 1 gram of fat, and 8 grams of carbs:

    • Protein = 25 x 4 = 100 calories
    • Fat = 1 x 9 = 9 calories
    • Carbs = 8 x 4 = 32 calories
    • Total = 141 calories
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    Quantity of Protein, Fat, and Carbs per Day

    The amount of each macronutrient you need to eat per day will vary for each individual, and especially between men and women. Of the three macros, you technically only need protein and fat to live, but each serves a purpose in your diet.

    Grams of Protein per Day

    Unless you take performance-enhancing drugs, there's a natural limit to how much protein you will benefit from in a day. Generally speaking:

    • For women, multiply your bodyweight by between 0.6 and 0.8
    • For men, multiply your bodyweight by between 0.8 and 1.2

    Men and women require different amounts of protein because of the differences in our lean body mass. Because men have a greater proportion of lean body mass, they need more protein per pound of bodyweight to avoid muscle atrophy.

    Grams of Fat per Day

    Fat is necessary in order to maintain healthy body functions and hormonal balances, so you should play it safe when hitting your minimums.

    Women generally need more fat than men, but anything over 45 grams per day should be safe. Men can make do with around 25 grams per day.

    Some people like to use a percentage of their total calories consumed to track fat intake, typically between 20% to 35%.

    Grams of Carbs per Day

    Carbohydrates are not necessary to live; however, they're a great energy source and taste delicious. After you hit your required protein and fat consumption, feel free to fill the remaining calories in your diet with carbs. Many health agencies state you should eat around 25g of fiber per day, as well.

    Benefits of Flexible Dieting

    When utilized correctly, flexible dieting forces you to create healthier eating habits while still enjoying your favorite foods. You can eat what you want as long as you hit your macros. This makes it a sustainable diet for most people.

    Downsides of Flexible Dieting

    Some people abuse flexible dieting by eating large amounts of low-quality foods that hurt their performance. For example, you can eat 300g of processed sugar and still lose weight, but you'll feel worse than you would had you chosen a balanced approach. It can also be cumbersome and unrealistic to weigh out all of your food, but you can still make progress by eyeballing your macros after you've learned them.

    My Favorite Resource for Nutrition

    For more on nutrition, I recommend www.biolayne.com. Layne Norton is a tremendous resource for nutrition and exercise science, and stays up to date on related scientific literature.

    Overall, IIFYM is a great tool to implement in your daily life. It will help you maintain your desired body image and limit cravings that tend to develop when specific foods are purposely (and unnecessarily) avoided.


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