Estimate protein in grams a day for your goal, and roughly what that means per meal. In a deficit it is the single macronutrient that decides how much of the weight you lose comes off as fat rather than as muscle.
A general guideline for healthy adults. If you have kidney disease, are pregnant, or are managing a medical condition, set your protein target with a clinician rather than a calculator.
Protein is the macronutrient that decides what kind of weight you lose. In a deficit the body will take energy from wherever it can reach, and without enough protein — and enough resistance training to give it a reason — a meaningful share of that comes out of muscle rather than fat.
The target is set per kilogram of your goal weight rather than your current weight, so the figure does not inflate with fat mass you intend to lose. The ranges used here are the ones that recur across the sports-nutrition literature: roughly 1.2 to 1.6 grams per kilogram to maintain, 1.6 to 2.4 in a deficit, and 1.6 to 2.2 when building muscle. Activity level nudges the whole range upward, and the figure is trimmed slightly for women, who typically carry a lower proportion of lean mass at the same body weight.
Muscle protein synthesis responds to a dose, not a daily total. Somewhere between 25 and 40 grams in a sitting is enough to produce a full response in most adults, which is why the per-meal figure above divides the daily target across four eating occasions rather than leaving you to make it up at dinner.
For people with healthy kidneys, intakes in this range have not been shown to cause harm. The practical ceiling is appetite and displacement: past a point, protein crowds out the carbohydrate that fuels training and the fibre your gut needs. If you have kidney disease, or are pregnant, set your target with a clinician rather than a calculator.
Because the right figure depends on things this form cannot see — how much of your weight is lean mass, how hard you actually trained this week, how deep the deficit is running today. A range is the honest output of a formula. A measurement is what narrows it.
Every calculator on this page works the same way: it takes your height, your weight, your age and a guess about how much you move, and returns the average answer for people who look like that on paper. It is a reasonable place to start. It is not a reading of you, and it cannot change when you do.
Rysflo measures instead. One sixty-second exhale each morning reads three molecules in your breath, and the day’s protein, carbohydrate, fat and fibre come out in grams — against the goal you set, from what your metabolism is actually doing rather than from a formula on your dimensions.