If you've heard people talking about "hitting their macros" but had no idea what that means — you're not alone. Macro tracking sounds complicated, but the core idea is simple. This guide breaks it down from scratch.
What Are Macronutrients?
Macronutrients — "macros" for short — are the three main categories of nutrients your body uses for energy:
- Protein — builds and repairs muscle tissue. 4 calories per gram.
- Carbohydrates — your body's primary fuel source. 4 calories per gram.
- Fat — supports hormones, brain function, and absorbing vitamins. 9 calories per gram.
These caloric values have been established by the Atwater General Factor System and are the standard used by the USDA and the FDA in food labeling.¹
Every food you eat is made up of some combination of these three. A chicken breast is mostly protein and fat. Rice is mostly carbohydrates. Peanut butter is a mix of all three, leaning fat and protein.
Why Track Macros Instead of Just Calories?
Calories tell you how much you're eating. Macros tell you what you're eating.
Two people can eat the same number of calories and get wildly different results. A 2019 study published in Obesity Reviews found that higher protein intake during a caloric deficit significantly preserved lean muscle mass compared to standard protein intake — even at identical calorie levels.² This means the composition of your diet matters as much as the total energy.
Macro tracking gives you control over:
- How much muscle you hold onto (or build) while losing fat
- Your energy levels throughout the day
- How full and satisfied you feel after meals
- Performance in the gym or on the trail
The Three Macros and What They Do
Protein
Protein is the most critical macro if body composition is your goal. It supports muscle protein synthesis — the process by which your body repairs and builds muscle tissue. It's also the most satiating macro, meaning it keeps you fuller longer than carbs or fat at equivalent calorie levels.³
The International Society of Sports Nutrition (ISSN) recommends 1.4–2.0g of protein per kilogram of bodyweight (0.64–0.9g per pound) per day for active individuals, with some evidence supporting up to 2.2g/kg for those in a caloric deficit trying to preserve muscle.⁴
A 180lb (82kg) person doing regular training might target 130–165g of protein per day. For a full breakdown by goal and bodyweight, see how much protein per day you actually need.
Carbohydrates
Carbohydrates are your body's preferred energy source for high-intensity activity. Your muscles store carbohydrates as glycogen, which fuels intense training. Research consistently shows that low carbohydrate availability impairs performance in strength and endurance exercise.⁵
Carbs get a bad reputation, but they're not the problem. Total caloric intake and food quality matter far more than carbohydrate content for most people.
Fat
Dietary fat is essential — not optional. It supports the production of hormones including testosterone and estrogen, facilitates absorption of fat-soluble vitamins (A, D, E, K), and contributes to brain function. The Dietary Guidelines for Americans recommend fat comprise 20–35% of total daily calories.⁶
A practical floor for most active people is around 0.5–0.6g of fat per kilogram of bodyweight (0.22–0.27g per pound) per day as a minimum.
How Do You Set Your Macro Targets?
The standard process:
Step 1: Calculate your Total Daily Energy Expenditure (TDEE)
Your TDEE is your calorie maintenance level — the number of calories your body burns per day based on your stats and activity. If you want a deeper breakdown of how TDEE is calculated and used, see this guide to TDEE and fat loss. The most clinically validated equation for estimating this is the Mifflin-St Jeor equation, which calculates your Basal Metabolic Rate (BMR) and then applies an activity multiplier.⁷
- Men: BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age) + 5
- Women: BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age) − 161
If you know your body fat percentage, the Katch-McArdle formula (which calculates BMR from lean body mass) is more accurate for athletic individuals.⁸
FuelLog's "Calculate My Macros" feature runs either Mifflin-St Jeor or Katch-McArdle depending on whether you've entered your body fat percentage — the same clinically recognized equations used by registered dietitians.
Step 2: Set your calorie target relative to your goal
- Fat loss: TDEE − 300 to 500 calories
- Muscle gain: TDEE + 200 to 300 calories
- Maintain: TDEE ± 100 calories
Step 3: Set protein first
Use the ISSN guidelines above as your starting point.
Step 4: Set a fat floor
Aim for at least 20–25% of total calories from fat to maintain hormonal function.
Step 5: Fill the rest with carbohydrates
Whatever calories remain after protein and fat are accounted for go to carbohydrates.
Example — 175lb (79kg) active male targeting 2,300 calories for muscle gain:
| Macro | Target | Calories |
|---|---|---|
| Protein | 160g | 640 |
| Fat | 70g | 630 |
| Carbs | 258g | 1,030 |
| Total | 2,300 |
These numbers are a starting point. You adjust based on how you feel, how you perform, and how your body responds over several weeks.
Do You Have to Be Exact?
No. Research suggests that hitting your targets within 10% is sufficient for meaningful progress.⁹ The goal is consistency over weeks, not perfection on any single day.
Most people who quit macro tracking do so because they set the bar too high. Aim for your targets, log consistently, and course-correct over time.
How FuelLog Calculates Your Targets
FuelLog's Goals tab walks you through entering your stats — age, height, weight, sex, activity level, and optionally body fat percentage — and calculates your macro targets using the same Mifflin-St Jeor or Katch-McArdle equations referenced above.
Once your targets are set, logging what you ate is as simple as describing your meal in plain language. For tips on making tracking actually stick, see the easiest way to track macros. FuelLog's AI cross-references your description against USDA nutritional data and published restaurant nutrition data to estimate the macros — no food database browsing required.
Quick Reference
| Macro | Calories per gram | Primary role |
|---|---|---|
| Protein | 4 | Muscle building and repair |
| Carbohydrates | 4 | Energy and performance |
| Fat | 9 | Hormones, brain function, satiety |
References
- Merrill AL, Watt BK. Energy Value of Foods: Basis and Derivation. USDA Agriculture Handbook No. 74. 1973.
- Frestedt JL, et al. "A whey-protein supplement increases fat loss and spares lean muscle in obese subjects." Nutrition & Metabolism. 2008. (See also: Helms ER, et al. "A systematic review of dietary protein during caloric restriction in resistance trained lean athletes." JSCR. 2014.)
- Leidy HJ, et al. "The role of protein in weight loss and maintenance." American Journal of Clinical Nutrition. 2015;101(6):1320S–1329S.
- Stokes T, et al. "Recent Perspectives Regarding the Role of Dietary Protein for the Promotion of Muscle Hypertrophy." Nutrients. 2018;10(2):180. International Society of Sports Nutrition Position Stand: protein and exercise. Journal of the International Society of Sports Nutrition. 2017.
- Burke LM, et al. "Carbohydrates for training and competition." Journal of Sports Sciences. 2011;29(S1):S17–S27.
- U.S. Department of Agriculture and U.S. Department of Health and Human Services. Dietary Guidelines for Americans, 2020–2025. 9th Edition.
- Mifflin MD, et al. "A new predictive equation for resting energy expenditure in healthy individuals." American Journal of Clinical Nutrition. 1990;51(2):241–247.
- Katch VL, McArdle WD. Introduction to Nutrition, Exercise, and Health. 4th ed. Lea & Febiger, 1993.
- Helms ER, Aragon AA, Fitschen PJ. "Evidence-based recommendations for natural bodybuilding contest preparation." Journal of the International Society of Sports Nutrition. 2014;11:20.