If It Fits Your Macros Is BS

You've probably heard some version of the “If It Fits Your Macros” (IIFYM) pitch: hit your protein, carbs, and fat targets for the day and it doesn't matter where those calories come from. A Pop-Tart and a sweet potato have the same carbs, right? A Jimmy Dean sausage and grilled chicken both have protein, so they are both fine. So eat whatever fits the numbers and trust the math.

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It's a compelling idea, but it’s wrong because food quality matters. And if you care about muscle quality and not just a number on the scale, this is very important. 

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Here's what the research shows...

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The same calories do different things depending on where they come from.

In 2019, the NIH ran the first randomized controlled trial comparing ultra-processed versus whole-food diets. Researchers matched the two diets for total calories, protein, fat, carbohydrates, sugar, fiber, and sodium. The macros were identical. Then they let participants eat as much or as little as they wanted.

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On the ultra-processed diet, people spontaneously consumed an average of 508 extra calories per day. They gained about 2 pounds over two weeks. The whole-food group lost about 2 pounds over the same period. In a nutshell, the same macros were consumed on paper, but there were wildly different outcomes in the body.

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The whole-food group also saw increases in peptide YY (the hormone that tells you to stop eating) and drops in ghrelin, the hunger hormone. Processed food disrupts those signals. So you eat more, you're less satisfied, and your body handles the calories differently.

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Processed food doesn't just affect body fat, it gets inside your muscles.

A 2024 UCSF study used MRI scans to look at 666 adults and measured the relationship between ultra-processed food intake and intramuscular fat (fat deposited inside the thigh muscles). Think of it like marbling in a cheap cut of meat.

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The finding: the more ultra-processed foods people consumed, the more intramuscular fat was found in their thigh muscles, regardless of total calorie intake, BMI, physical activity level, or sociodemographic factors.

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That last part matters. You can be at the gym four days a week and still be accumulating fat inside your muscle tissue if your diet is built around processed food. A calorie from a frozen breakfast sandwich and a calorie from eggs are doing fundamentally different things to your muscle composition.

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Elevated intramuscular fat is linked to reduced strength, impaired function, type 2 diabetes, metabolic syndrome, and accelerated aging.

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Processing changes how your body handles food.

A study in Food and Nutrition Research found that a meal made with whole foods required nearly twice the metabolic energy to digest compared to a meal with identical macros made from processed ingredients. The calorie count was the same. The net calories retained were different.

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On top of that, ultra-processed foods drive chronic low-grade inflammation through their effect on gut bacteria. Your gut contains trillions of microorganisms, and the composition of your microbiome (which directly affects hormone regulation, immune function, and recovery) shifts based on what you feed it. Processed ingredients, synthetic additives, and refined seed oils tip the ecosystem toward bacteria associated with metabolic disease and inflammation. You can't out-train a diet that's keeping your body in a low-grade inflammatory state.

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So what does this mean?

IIFYM isn't entirely wrong. Calories and macros matter. But using macros as the only lens and not worrying about food quality misses most of what determines long-term body composition, muscle health, and how you feel and function over time.

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The question isn't whether your calories fit your goals, it's what those calories are actually doing once they're inside you. For anyone training to build or maintain muscle, especially as they get older, food quality isn't just a consideration…it’s crucial. 

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Eat food that looks like food. Your muscles will show the difference.