What macros actually do
"Macros" — protein, carbohydrates, and fat — are the three calorie-bearing nutrients in your diet. Calories decide whether you lose, maintain, or gain weight. Macros decide what kind of weight that is (muscle vs. fat) and how you feel doing it.
A useful way to think about it:
- Protein protects muscle and drives satiety.
- Fat supports hormones and absorbs fat-soluble vitamins.
- Carbs fuel hard training and brain function.
Get protein and fat to a sane minimum, then carbs do the rest.
The 3-step macro framework
Step 1: Set protein first
The single most evidence-supported macro target during fat loss in trained adults is 0.7–1.0 g/lb of bodyweight (Source: Helms et al., A systematic review of dietary protein during caloric restriction in resistance trained lean athletes, Int J Sport Nutr Exerc Metab, 2014). For untrained or recreational lifters, 0.7 g/lb is plenty; for serious lifters cutting hard, push to 1.0 g/lb.
Examples:
- 150 lb adult, fat loss → 105–150 g protein/day
- 200 lb adult, fat loss → 140–200 g protein/day
For maintenance or muscle gain, 0.6–0.8 g/lb works well for most people.
Step 2: Set a fat floor
Fat is essential for hormones (especially in women) and vitamin absorption. The minimum useful target is 0.3 g/lb of bodyweight, with most people landing in 0.35–0.5 g/lb (Source: Mountjoy et al., IOC consensus statement on Relative Energy Deficiency in Sport (RED-S), Br J Sports Med, 2014).
Examples:
- 150 lb adult → 45–75 g fat/day
- 200 lb adult → 60–100 g fat/day
Going below the floor for extended periods is associated with hormonal disruption, especially during energy deficits.
Step 3: Carbs fill the rest
After protein and fat are set, divide remaining calories by 4 to get carb grams (carbs and protein = 4 kcal/g, fat = 9 kcal/g).
Worked example. 180-lb adult, 2,200 kcal target for fat loss:
| Macro | g/lb | Grams | Calories |
|---|---|---|---|
| Protein | 0.9 | 162 | 648 |
| Fat | 0.4 | 72 | 648 |
| Carbs | — | 226 | 904 |
| Total | 2,200 |
The calculator below runs this math automatically.
How macros change with goal
| Goal | Protein | Fat | Carbs |
|---|---|---|---|
| Fat loss | 0.8–1.0 g/lb | 0.35 g/lb floor | Fill remainder |
| Maintenance | 0.7–0.8 g/lb | 0.4–0.5 g/lb | Fill remainder |
| Muscle gain | 0.7–0.9 g/lb | 0.4 g/lb floor | Fill remainder (intentionally high) |
Notice protein doesn't drop dramatically when you stop dieting — it stays moderately high because it supports recovery and satiety year-round.
Common mistakes
- Chasing a "perfect" ratio — 40/30/30, 50/30/20, etc. These are starting heuristics, not laws. Hit your protein and fat floors and you're 90% of the way there.
- Treating fat as the enemy. Going under 0.3 g/lb fat for months tanks hormones and adherence.
- Treating carbs as the enemy. Carbs aren't fattening; calories are. Low-carb works for some people because protein and fat are filling, but a moderate-carb plan is generally easier to train hard on.
- Not counting drinks and sauces. Olive oil, dressing, alcohol, and cream are the most-missed calories in tracking.
- Ignoring fiber. Aim for 14 g per 1,000 kcal (Source: Dietary Guidelines for Americans, 2020-2025). Fiber is the satiety lever most people skip.
What about IIFYM (If It Fits Your Macros)?
IIFYM is the popular shorthand for "as long as you hit your macros, food choice is yours." It's directionally correct: you don't need to eat clean to lose weight, only to be in a deficit with enough protein. But there's a catch: micronutrients and fiber are not free. A diet that hits macros entirely from candy and protein powder will leave you under-nourished and hungry. Use IIFYM as a permission structure for treats inside an otherwise whole-food diet — not as a license to skip vegetables.
How Fitly removes the math
Setting macros is the easy part. Hitting them every day is what breaks people. Fitly:
- Tracks every meal, with a barcode scanner and 5,500+ exercise database for full-day energy balance.
- Smart Coach adjusts your macros automatically when goals change or the scale stalls.
- Daily target rings show how close you are without doing arithmetic.
Open the macro calculator Get the macro cheatsheet