What Are Macronutrients? Protein, Carbs and Fat Explained

Food gets its energy from a small number of nutrients. The three that supply it in large amounts are protein, carbohydrate and fat, and they are called macronutrients ("macro" means large). Vitamins and minerals matter too, but they are needed in small quantities and are not counted for energy. When someone says they are tracking macros, they mean they log grams of these three, alongside the calorie total.

The calorie number on a food label is not a separate thing from the macros. It is built from them, which is why the two always travel together.

From grams to calories

Each macro carries a fixed amount of energy per gram. CalorTracker's macro calculator uses the standard conversion factors:

USDA FoodData Central, the database behind our food pages, also publishes energy values calculated from fixed energy per gram (the Atwater values), so the idea is the same one. The consequence is easy to remember: fat packs more than twice the energy of the other two in the same weight, which is one reason foods rich in it tend to be calorie-dense.

How a percentage split becomes grams

The macro calculator starts from a daily calorie target and a split in percentages. It gives each macro its share of the calories, then divides by the calories per gram to get grams. The default split is 30 percent protein, 40 percent carbohydrate and 30 percent fat. It is a preset, not a finding that this split is best, and you can change it.

Worked example

Take the target for the man on the TDEE page, 2,759 kcal, and apply the default split. The macro calculator gives:

Each row is the share of 2,759 kcal divided by the calories per gram: protein and carbohydrate by 4, fat by 9, rounded to whole grams. The three calorie columns add back up to the target within rounding, which is a useful check on any macro plan.

Counting macros in practice

Macros are read straight from food data. Every food page lists protein, carbohydrate and fat per 100 grams from USDA, so a portion's macros are a straight proportion of those values. When you log a meal by photo, voice or text in the app, the macros are an estimate that you can correct.

Two details are worth knowing. Fiber is part of the carbohydrate figure, which is why net carbs subtracts it. And the calorie total on a label is rounded, so adding up rounded macros will not always match it exactly.

What macros do not tell you

A macro split describes quantities, not quality. Two meals with identical grams can differ in fiber, vitamins and how filling they are. The method for the calculator is written out on how we calculate, and the protein part of the split is covered in protein intake. As with any target here, it is general information, and anyone managing a health condition should plan with a clinician.