What they are#
Three things food energy is made of, at fixed conversion factors:
| Macronutrient | Energy | What it mostly does |
|---|---|---|
| Protein | 4 kcal per gram | tissue repair; the one that matters most in a deficit |
| Carbohydrate | 4 kcal per gram | the body’s easiest fuel |
| Fat | 9 kcal per gram | hormones, absorption of some vitamins, energy |
A calorie target says how much. A macro split says what it is made of.
The rule that keeps it honest#
The three must add back up to the budget. Protein grams × 4, plus carbohydrate grams × 4, plus fat grams × 9, should equal your calorie target.
That sounds obvious and it is routinely broken by apps that let you edit each target independently. The result is a screen showing two different daily numbers with no indication of which one is real.
In SmartCrunch it is an invariant rather than a convention — the split is derived from the budget and always sums back to it. The macro calculator shows the sum for exactly this reason: so you can check it rather than trust it.
Setting a split#
The order that works for most people:
- Protein first. In a deficit this is the one with the clearest evidence behind it, because it is what preserves lean tissue while you lose weight. Common targets land somewhere around 1.6–2.2 g per kilogram of body weight, with the higher end more relevant the leaner and more trained you are.
- Fat second, with a floor. There is a level below which people feel bad and hormones are affected; around 0.6–0.8 g per kilogram is a commonly used minimum.
- Carbohydrate gets the rest. It is the flexible one. More if you train hard, less if you prefer.
As percentages, that usually lands somewhere between 30/40/30 and 40/30/30 (protein/carbs/fat). Neither is magic, and the app offers presets rather than prescriptions — what to eat is deliberately outside what it has an opinion on.
How much precision is useful#
Less than people assume.
- Protein: worth hitting. Being 30 g short every day is a real difference over months.
- Fat and carbohydrate: worth a range. Trading 20 g of carbohydrate for 9 g of fat is the same calories and, for most purposes, the same day.
- Daily versus weekly: a week that averages correctly beats four perfect days and three abandoned ones.
If you are new to this, track calories alone for a fortnight and add macros after. Two targets from a standing start is how people quit in week three.
The bit trackers get wrong#
Carbohydrate is the one to watch when comparing apps. Some show net carbs — total minus fibre and some sugar alcohols — and some show total. The same meal therefore reads differently in two apps and neither is lying.
SmartCrunch counts total carbohydrate and does not compute net carbs at all. If you need them, that is a genuine reason to use something else, and the comparison pages say which.
What macros do not tell you#
Nothing about food quality, timing, or whether a meal was a good idea. Two days can hit identical macros and be completely different diets. The split is a constraint that keeps a budget from being met entirely with one thing; it is not a nutrition plan, and no app that shows you three numbers is giving you one.
Read next
- How to count calories without it taking over your life Weigh things, log before you eat, accept that you are under-recording. Precision on the parts that matter beats precision everywhere.
- Maintenance calories, explained Maintenance is the intake at which your weight holds. Every calculator predicts it from a population; your own logged weeks can measure it instead.