🔬 Digestion and nutrition science

Once you swallow food, it travels down to your stomach, where powerful acid and churning muscles break it down into a thick liquid, before it moves into your small intestine to be broken down even further. There, your body absorbs the nutrients it needs, sugars, proteins, fats, vitamins and minerals, passing them into your bloodstream to be carried to cells all over your body. Whatever your body cannot use gets passed along to your large intestine, where water gets reabsorbed before the leftover waste eventually leaves your body.

These three, often called macronutrients, each play a different main role, carbohydrates give your body quick, ready energy, protein supplies the building blocks used to grow and repair muscles and other tissue, and fat stores longer lasting energy while also protecting organs and helping absorb certain vitamins. Your body actually needs a mix of all three every day, not just one, since none of them can fully do the other's job. The right balance between them can shift depending on age, activity level and overall health, which is part of why nutrition advice is not exactly the same for everyone.

Vitamins and minerals are needed only in tiny amounts, but they act like essential helpers behind the scenes, enabling countless processes your body relies on, from healing a cut to keeping bones strong to letting your nerves send signals properly. Unlike protein, carbohydrates and fat, your body cannot use vitamins and minerals for energy at all, they work more like tools than fuel. Because your body cannot make most vitamins and minerals on its own, or can only make a few, eating a wide variety of different foods is really the main way to get a full, steady supply of them.

How much energy your body needs depends on several things at once, your size, age, how active you are, and even how your individual body processes food, which is why two people who look similar can genuinely need quite different amounts. A growing child or teenager going through a growth spurt can burn through remarkably more energy than the same person just a year earlier, simply because their body is busy building new tissue. Because these needs shift so much between individuals, and even change over time within one person, general nutrition guidelines are always closer to a helpful average than an exact rule that applies perfectly to everyone.