Total calories decide whether you lose or gain weight. Macros — protein, carbs, fat — decide what you lose (fat vs muscle), how you feel during the deficit, and whether the diet survives long-term.
Ignoring macros and only watching calories is why many people "lose weight" but end up frail, exhausted and with loose skin. This guide explains how to compute the right split for your goal.
The three macros and their energy density
| Macro | kcal per gram | Main role |
|---|---|---|
| Protein | 4 kcal/g | Build and preserve lean mass, satiety |
| Carbs | 4 kcal/g | Fast energy, glycogen recovery, performance |
| Fats | 9 kcal/g | Hormonal balance, fat-soluble vitamins, satiety |
| (Alcohol) | 7 kcal/g | Nothing useful — empty calories |
Notice the density: fats have more than double the calories per gram of protein and carbs. That's not a reason to avoid them (they're essential), but it explains why one extra tablespoon of olive oil per meal moves the needle.
Protein: the absolute priority in a deficit
When you're in a caloric deficit, the body looks for energy. If you don't give it enough protein, it raids your muscle. For anyone trying to lose fat while keeping decent body composition, protein is the macro that matters most.
How many grams per day?
The sports nutrition literature is mostly aligned:
- Sedentary: 0.8 g/kg of bodyweight (RDA — survival, not optimization).
- Active in a deficit: 1.6–2.2 g/kg (Helms et al., JISSN 2014).
- Bodybuilders in extreme cuts: up to 2.5–2.7 g/kg.
For Julia (65 kg / 143 lb): between 104 and 143 g of protein per day. A solid middle target is 130 g.
Where to get it
100 g cooked chicken = ~30 g protein. 100 g tuna = ~25 g. One egg = ~6 g. 200 g 0% Greek yogurt = ~20 g. 100 g cooked lentils = ~9 g. One whey scoop = ~25 g.
Translation: hitting 130 g requires at least 4 protein sources a day. If you only have two (meat at lunch, cheese at dinner), you'll cap at 70-80 g — not enough.
Fat: the non-negotiable minimum
Fats often get cut first in DIY diets because they're more calorie-dense. Mistake. Fats are required for:
- Production of steroid hormones (testosterone, estrogen, cortisol).
- Absorption of vitamins A, D, E, K.
- Cell membrane and nervous-system health.
How much fat?
The physiological floor is 0.6 g/kg of bodyweight (Helms et al.). For Julia: ~40 g/day minimum. Most guidelines target 20-35% of total kcal from fat.
Below 0.5 g/kg chronically — especially in women — you'll see drops in libido, irregular cycles, persistent feeling cold, hair shedding. Not worth it.
Carbs: the filler (and the fuel)
Once protein and fat are set, carbs fill the calorie gap. They're the preferred fuel for high-intensity training and replenishing muscle glycogen. Cutting them below 100 g/day during intense training tanks performance and recovery.
Full worked example
Julia, 65 kg, TDEE 2,100 kcal, 20% deficit → target 1,700 kcal/day.
Step 1 — Protein: 2 g/kg × 65 = 130 g = 520 kcal. Step 2 — Fat: 30% of kcal = 1700 × 0.30 = 510 kcal = 57 g. Step 3 — Carbs: remaining kcal = 1700 − 520 − 510 = 670 kcal = 167 g.
Julia's final split: 130 g P / 167 g C / 57 g F, roughly 30% P / 40% C / 30% F in percent terms.
Alternative splits: when they make sense
The 30/40/30 split works for most. But there are valid alternatives for specific cases.
Keto / very-low-carb (5–10% carbs)
Example: 130 g P / 25 g C / 130 g F for Julia.
Use when: insulin resistance, certain forms of epilepsy, documented personal preference for very satiating meals. Fat-loss results equal to a standard deficit when calories are matched (Hall et al., AJCN 2016).
Don't use when: you do explosive sports, team sports, or high-volume strength work.
Balanced / Mediterranean (30/40/30)
The default split shown above. Sustainable, flexible, supports sport. Best default for most.
High-protein / "lean cut" (40/30/30)
Example: 170 g P / 130 g C / 57 g F for Julia.
Use when: dropping the last 5-8% of body fat (athletes pre-show), people who struggle with hunger, recomposition phases.
Don't use when: sustained high-intensity training (you won't have the carbs to recover).
Common mistakes
- Ignoring protein. It's the difference between losing "weight" and losing "fat". Add a protein source to every meal, no exceptions.
- Cutting fat to zero. Below 0.5 g/kg chronically you tank hormonal health, especially women.
- Chasing the perfect split instead of the total. Hitting protein and total calories — even with carbs and fats swinging 10% — gets you 90% of the result. Obsessing over 32/41/27 to the gram is counterproductive perfectionism.
- Not adjusting over time. If at 8 weeks the mirror hasn't moved, "more broccoli" isn't the fix. Revisit the deficit, the protein target, the activity level.
Calculate your split
If you want to skip the manual math, our macro calculator gives you exact grams once you input weight, activity and goal. No email, 30 seconds.
And if you want to stop doing mental math at every meal, dyllo computes macros automatically when you describe out loud or in writing what you ate. "Pasta with pesto, 100 grams" → the app understands, calculates, logs. Done.
