Protein, fat and carbs, in plain language

Open any food tracker and you get four numbers: calories, protein, fat, carbohydrate. The last three are the macronutrients, "macro" because you eat them in grams rather than milligrams. Here is what each one is for, without the supplement-industry framing.

Protein

Protein is the body's building material. Muscle, enzymes, hormones, the structure of skin and hair are all protein. Unlike fat and carbohydrate, the body has no real storage depot for it, which is why intake spread across the day matters more here than for the others.

It is also the most filling of the three per calorie. If you find yourself hungry an hour after eating, the composition of that meal is often a better thing to look at than its size.

Fat

Fat is the densest energy source at roughly nine calories per gram, against four for protein and carbohydrate. It is also structural: cell membranes are built from it, and vitamins A, D, E and K need it present to be absorbed at all.

The useful distinction is not fat versus no fat, it is which fat. Saturated fat is the one health guidance singles out, which is why Senumi tracks it separately rather than folding it into one total.

Carbohydrate

Carbohydrate is the body's most accessible fuel. Starches and sugars both break down to glucose; the difference is speed. A bowl of oats and a glass of juice can carry similar carbohydrate, and behave very differently once eaten.

The carbohydrate in an apple arrives with fibre and water attached; the carbohydrate in a soft drink does not. Senumi tracks total sugar rather than separating out added sugar, so that distinction is one you still have to make yourself.

The two numbers most people should actually watch

Calories are the headline, but for most people two others are more actionable:

1. Protein. Because under-eating it is common, easy to fix, and the fix makes you less hungry rather than more disciplined.
2. Saturated fat and sugar. Because these are the two where health guidance is most specific, and where small habitual changes compound. Senumi gives each its own line on the daily target.

Senumi shows all of these on the daily target, not just the calorie ring. Sugar, saturated fat, dietary cholesterol and trans fat each get their own line, because a day can hit its calorie target and still be a bad day on three of them.

A word on precision

Targets are population averages adjusted for your height, weight, age and activity. They are a starting point, not a prescription. If you have a condition that makes any of this clinically relevant, such as diabetes, kidney disease or a lipid disorder, the numbers that matter for you come from someone who has seen your results, not from an app.