If It Fits Your Macros (IIFYM), or Flexible Dieting, is a diet trend that allows you to eat anything you want whenever you want it and still reach your weight goals! The catch? You have to eat exactly the right amount of carbohydrates, protein and fat, down to the gram.

IIFYM supporters say that "clean eating burns fat by accident" because it nixes high calorie desserts, snacks and fast food, which causes a natural calorie deficit. However, "clean" diets tend to be restrictive, boring and difficult to sustain. IIFYM is not meant to be a starvation plan and claims that a 15-20 percent reduction in calories is "all that is needed to make your body a fat burning furnace." Basically, if you reach your macro goals, you automatically hit your caloric goals.

Where did it come from?
This trend seems to have originated from bodybuilders who wanted some more variety in their training diets. The boredom associated with eating only "clean" foods (chicken breast, broccoli, brown rice) made it hard for athletes to stick to their meal plan.

What are "Macros"?
"Macros" is short for macronutrients, and there are three – carbohydrates, protein and fat. These nutrients provide calories needed for energy, growth, repair and just plain old survival.

  • Carbs – the ultimate fuel. Carbs are your body's preferred source of energy. Fruits, veggies, dairy and foods with added sugar all have carbs.
  • Protein – the muscle maker. Protein builds and repairs muscles and is found in every cell, tissue and organ in your body. Eating enough carbs allows protein to focus on muscle growth and strength.
  • Fat – the energy powerhouse. Fat is more chock full of energy than the other macronutrients. It helps to store and absorb important vitamins, aids in insulation and protects our vital organs.

How do I know what to eat?
An online calculator determines your calorie goal and then breaks down how many grams of each macronutrient you should get. This free online Macro Calculator asks for sex, age, height, weight, daily activity level and frequency, duration and intensity of exercise. It then allows for customization based on weight goals.

What do the numbers look like? For a 30 year old woman who is 5'4, 140 pounds, with a light level of daily activity and 60 minutes a day of moderate intensity exercise most days, here's how it breaks down:

To maintain weight:

  • Total calories: 2056
  • Protein Grams: 112 (22% total calories)
  • Fat Grams: 56 (25% total calories)
  • Carbs Grams: 276 (54% total calories)
  • Fiber Grams: 21 – 28

With a 15% calorie cut (for fat loss):

  • Total calories: 1748
  • Protein Grams: 112 (26% total calories)
  • Fat Grams: 56 (29% total calories)
  • Carbs Grams: 199 (46% total calories)
  • Fiber Grams: 21 – 28

With a 10% calorie addition (to bulk up):

  • Total calories: 2262
  • Protein Grams: 112 (20% total calories)
  • Fat Grams: 56 (22% total calories)
  • Carbs Grams: 328 (58% total calories)
  • Fiber Grams: 21 – 28

How does this compare to other recommendations?
The Food and Nutrition Board of the Institute of Medicine (IOM) recommends that adults get 45-65% of their calories from carbohydrates, 10-35% of their calories from protein and 20-35% of their calories from fat. Men should aim for 38 grams of fiber each day and women should shoot for 25 grams. IIFYM recommendations for all weight goals fall within the recommended range. The only major variable seems to be carbohydrate allowance – protein and fat stayed relatively the same whether goal was weight gain, loss or maintenance.

Pros:
Rather than offering a quick fix, like so many fad diets, IIFYM teaches an all-inclusive, balanced style of eating. All foods can be included as long as macronutrient goals are met. Once you hit your number for protein and fiber, fat and carb allowances can be flexed within calorie allowance for a little indulgence. Bottom line, all food comes from these three macronutrients, so whether it's an apple and almond butter or a brownie sundae, both options have protein, carbs and fat. This method can help dieters get away from the "good food/bad food" mentality. With the macronutrient and fiber requirements, it would be hard to NOT eat nutrient-dense foods. Theoretically, IIFYM could be considered a diet education boot camp - once you get the hang of what a balanced diet looks like, you could potentially ease up on counting and transition smoothly into a less rigid eating style.

Cons:
This diet requires a serious level of commitment. You have to be meticulous and number-focused. You need a digital scale to weigh foods and a food log to track your intake of each macronutrient. It may be hard to eat out at restaurants if you don't know the exact recipe of what you're eating. Tracking intake at this level of intensity may become obsessive and exhausting. If you're the kind of person who struggles with self-control around certain foods (ice cream, pizza, cookies, chips, etc.), including these foods may increase your risk of bingeing.

The bottom line.
The IIFYM recommendations fall in line with the general recommendations for a healthy diet according to the IOM and can be customized based on individual goals and activity levels. However, weighing, measuring and tracking all food is unrealistic in the long term. There's also no new magic to these recommendations. They will not lead to "spectacular" results or faster fat loss as compared to regular healthful eating according to those IOM recommendations.

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