Macronutrients
Macronutrients and micronutrients are the two big pillars of nutrition. Macronutrients are the nutrients your body needs in the largest amounts: they're your main source of energy, they build and repair your body's structure, and they keep you growing and running. There are three of them: carbohydrates, protein, and fats. Despite what the internet might tell you, none of them is the enemy, and none is more important than the others. They each do a job the other two can't, making them all equally important.
Fats
Fats have spent decades being unfairly villainized. In reality, they give you long-lasting energy (not the quick spike-and-crash of sugar), help you absorb vitamins A, D, E, and K, build your cell membranes, cushion and insulate your organs, keep your hormones balanced, support your brain, and help control inflammation. That's a serious resume, Harvard is calling.
There are three main types, and this is where "healthy fat" versus "less healthy fat" actually comes from:
Unsaturated fats
The all-stars, comparable to the rating we'd give the movie Ratatouille (a 10/10). Usually liquid at room temperature, unsaturated fats support heart health when eaten in reasonable amounts. Find them in olive oil, nuts, seeds, avocado, fish, and spreads like peanut butter. "Unsaturated" is an umbrella term covering two subtypes:
Polyunsaturated fats deliver omega-3 and omega-6 fatty acids, nutrients your body can't make itself, found in fatty fish, walnuts, flaxseed, and more. A recent study reveals that omega-3 induced supplements may not produce measurable improvements in cognition or memory: a positive effect that has often been linked with omega-3. This is important to note, because in this case it is likely better to eat omega-3 straight from the source, rather than relying on a supplement.
Monounsaturated fats provide oleic acid, which supports heart health, found in olive oil, nuts, and some fish.
Saturated fats
Usually solid at room temperature: think butter, cheese, and fatty cuts of meat. They're fine in moderation, but too much can raise your LDL ("bad") cholesterol, so they're a "some, not a lot" food.
Trans fats
The one type genuinely worth avoiding. The artificial kind (made through a process called partial hydrogenation) has actually been banned from the U.S. food supply since 2018 because it's so strongly linked to heart disease. Tiny natural amounts still show up in some meat and dairy, and a product can legally say "0g trans fat" if it has under 0.5g per serving, so if you spot "partially hydrogenated oil" in an ingredient list, that's your cue to skip it. Trans fats are uniquely bad because they raise your "bad" LDL cholesterol and lower your "good" HDL cholesterol at the same time, a double whammy few other foods pull off.
FATS IN REAL LIFE
Don't fear fat, just choose the right kinds most of the time. Make unsaturated fats (olive oil, nuts, avocado, fish) your default, enjoy saturated fats (cheese, butter, red meat) in moderation, and dodge artificial trans fats when you can. A drizzle of olive oil, a small handful of nuts, or a few slices of avocado are easy ways to work healthy fats into a meal. Fat is calorie-dense, so a little goes a long way, but it also keeps you full and satisfied, which is a good thing.
Protein
Protein builds, repairs, and maintains your body's tissues: muscle, skin, hair, organs, all of it. It also forms enzymes and hormones, supports your immune system, helps transport nutrients, and keeps you feeling full (that's called satiety).
Protein is made of 20 different building blocks called amino acids, each with its own role, that link together to form the protein your body uses.
Your body can make 11 of those 20 amino acids on its own. The other 9, called essential amino acids, have to come from food.
Complete proteins contain all 9 essential amino acids in one package. These include eggs, milk, meat, fish, quinoa, and soy.
Incomplete proteins only have some of the 9. These include most beans, nuts, and vegetables. The good news? You can combine two incomplete proteins to make a complete one, the classic combo being rice and beans. You don't even have to eat them in the same bite; getting a variety across the day does the trick.
PROTEIN IN REAL LIFE
A rough daily guide for most people is about 0.8 grams of protein per kilogram of body weight (roughly your weight in pounds, divided by 2, gives you a ballpark in grams). Teens who are growing or very active need a bit more. In practice, aim to include a protein source at every meal, a palm-sized portion is an easy visual, and you'll almost certainly meet your needs. If you eat mostly plant-based, just mix up your sources (beans, tofu, nuts, whole grains) across the day and you'll get all your amino acids covered.
EXTRA NOTE
In the media and in general, there is an extreme emphasis on protein right now. Please keep in mind that protein is very important, but it is also equally important to get the other two kinds of macronutrients (fats and carbohydrates).
Carbohydrates
Carbs are your body's favorite fuel, full stop. Your body breaks them down into glucose (blood sugar), which powers your cells, your brain, your nervous system, your muscles during exercise, and basically every tissue and organ you have. When people say they feel foggy or sluggish on a super-low-carb diet, this is why.
There are two main kinds: