A Mini Primer on Nutrition
September 2026
A note to my future self, so I stop googling the same things. If it helps you too, good.
Why I wrote this
I wanted to burn some fat. I gained over 20 kg in three years, and not because of adolescence: I stopped playing sports, studies got more stressful and time-consuming, and I started cooking my own food. Then studying got even more stressful, which pushed me to the gym, which got me interested in nutrition. De fil en aiguille, Instagram's algorithm caught on, my feed filled up with nutrition reels, and I started trying to eat better. Still not there, but getting there, slowly but surely.
P.S. I am writing this while eating a French tacos at 6:30 pm.
My takeaways
This might sound super didactic, and I hate it, but I think it's true.
- 1.
Protein and fiber at every meal. They do most of the work keeping you full on fewer calories. Everything else follows from this.
- 2.
Don't get to the evening hungry. Hunger at 7pm plus the pull of immediate gratification is how sweets and guilty food win. Real meals during the day are the only actual defense.
- 3.
Walk and run when the occasion is there. 10,000 steps a day compounds faster than an extra gym session and doesn't make you hungry the way hard training does. Make it structural — live in a way where moving is the default.
- 4.
Mix gym and runs — and let them keep your diet honest. When you put real effort into building a better body, two things happen: you develop a genuine desire to feed it well, and eating nonsense starts to feel like throwing the effort away. The training and the diet reinforce each other in a way that pure willpower never does.
- 5.
On sweets: reduce exposure, build the streak. It's easier not to start than to stop. Take it one day at a time and build proof that you can resist — not eating them today raises your discipline capital tomorrow. Optimize intertemporally.
How this is organised
The first tab is the reference material: what each nutrient is and what it does. The second tab is the part that actually matters for fat loss: how these pieces fit together, and why knowing them changes what you eat without you having to white-knuckle it. The third tab is food.
Every nutrient uses the same card:
Numbers are for a healthy adult and are approximations from EFSA (European Food Safety Authority), WHO, and the US NIH Office of Dietary Supplements. Country recommendations differ slightly. When in doubt, check EFSA's Dietary Reference Values.
1. Energy (Calories)
What it is. A kilocalorie (kcal) is a unit of energy. Food energy comes from four sources:
| Source | kcal per gram |
|---|---|
| Carbohydrate | 4 |
| Protein | 4 |
| Fat | 9 |
| Alcohol | 7 |
Fat is more than twice as energy-dense as carbs or protein. That is the single most useful number in this document.
What it does. Runs everything. Your body spends energy on (a) keeping you alive at rest — basal metabolic rate, ~60–70% of the total — (b) digesting food (~10%), (c) deliberate exercise, and (d) everything else you do while moving around (NEAT: non-exercise activity thermogenesis). Exercise is usually the smallest of the four. NEAT is the one you can most easily change.
How much. Depends on size, sex, age, and activity. Typical adult range: 1,800–2,800 kcal/day. Online TDEE calculators give a starting estimate; adjust based on what the scale does over 2–3 weeks. A deficit of ~300–500 kcal/day below maintenance is a sustainable fat-loss pace (~0.3–0.5 kg/week).
Common pitfall. Treating the calculator number as truth. It's a guess; your weight trend is the data.
My case
188 cm, 87 kg, male, 26 y. BMI 24.6 — upper end of normal, so the goal is composition, not a big number on the scale. Mifflin-St Jeor BMR ≈ 1,920 kcal. Two scenarios depending on how life is going:
| Scenario A — low | Scenario B — active | |
|---|---|---|
| Steps/day | ~3,000 | ~10,000 |
| Training | 1–2 lifting sessions/week | 2 lifting + 3 × 5 km runs/week |
| Estimated maintenance | ~2,450 kcal | ~3,000 kcal |
| Cut (−500/day, ~0.5 kg/week) | ~1,950 kcal | ~2,500 kcal |
| Gentle cut (−300/day, ~0.3 kg/week) | ~2,150 kcal | ~2,700 kcal |
The gap between A and B is ~550 kcal/day — the same size as the deficit itself. In Scenario B I can eat at Scenario A's maintenance and still lose ~0.5 kg/week. That's why NEAT matters more than any food rule.
Start at the cut number. Weigh 3–4 times a week, take the weekly average. If it hasn't moved after 2–3 weeks, drop 150–200 kcal. If losing faster than 0.7 kg/week for more than two weeks, add some back — that pace costs muscle.
2. Macronutrients
2.1 Protein
What it is. Chains of amino acids. Nine are "essential" (your body can't make them). Animal proteins and soy contain all nine in good proportions ("complete"); most plant proteins are lower in one or two, which stops mattering if you eat a variety across the day.
What it does. Builds and repairs tissue (muscle included), makes enzymes and hormones, supports immune function. In a calorie deficit, adequate protein is what keeps you losing fat rather than muscle. It's also the most filling macronutrient per calorie.
How much. EFSA's minimum is 0.83 g/kg bodyweight/day — the floor, not the target. For someone training and trying to lose fat, 1.6–2.2 g/kg is the well-supported range. For an 85 kg person, that's roughly 135–185 g/day.
Where to get it. Chicken, turkey, fish, eggs, Greek yogurt, skyr, fromage blanc, cottage cheese, lean beef, tofu, tempeh, lentils, chickpeas, beans, whey.
Common pitfall. Getting most of it at dinner. Spreading protein across 3–4 meals (~30–40 g each) is better for both satiety and muscle.
My case
87 kg × 1.8–2.0 g/kg ≈ 160–175 g/day while cutting. Same in both scenarios — protein is set by bodyweight and the deficit, not by activity. Over four eating occasions that's ~40 g per meal, or 3 × 45 g + a 25 g snack. Below ~140 g I'm giving muscle away for nothing.
Where I get it right now: Greek yogurt / cottage cheese, wholegrain toast, a pack of almonds. Honest audit: cottage cheese is the only dense source (~12 g per 100 g). Toast is ~4 g a slice; 30 g almonds is ~6 g for 175 kcal — a fat source with protein attached, not a protein source. This setup probably lands at 80–100 g/day. The fix isn't more of the same; it's one real protein anchor at lunch and dinner (chicken, fish, eggs, tofu, lentils) and, if that's not enough, a whey shake.
2.2 Carbohydrates
What it is. Sugars, starches, and fibre. Starches and sugars break down into glucose; fibre mostly doesn't.
What it does. Primary fuel for the brain and for high-intensity exercise. Stored as glycogen in muscle and liver.
How much. No strict requirement; the body can make glucose. Practically, carbs fill whatever's left after protein and fat are set. If you train, more carbs help performance. If you're sedentary, you need fewer.
Common pitfall. Treating all carbs as equivalent. 400 kcal of potatoes and 400 kcal of croissant are the same energy but very different in fibre, volume, and how full you'll feel an hour later.
My case
Carbs are the leftover after protein (~165 g) and fat are set. On a −500 cut: Scenario A ≈ 200 g/day; Scenario B ≈ 300 g/day. The extra 100 g in B fuels the runs — put most of it in the meal before and after training. On a rest day in B, drift toward 250 g.
2.2a Fibre
What it is. Plant carbohydrate that your small intestine can't digest. Two types: soluble (forms a gel — oats, legumes, fruit) and insoluble (adds bulk — wholegrains, vegetable skins).
What it does. Slows digestion and glucose absorption, feeds gut bacteria, keeps you regular, and makes you feel full for longer on fewer calories. Higher fibre intake is associated with lower cardiovascular disease and colorectal cancer risk.
How much. EFSA: 25 g/day. Most people in Western countries eat 15–20 g. Aim for 25–35 g.
Where to get it. Legumes (lentils, chickpeas, beans: 7–8 g per 100 g cooked), oats, wholegrain bread, berries, pears, apples with skin, broccoli, carrots, nuts, seeds (chia, flax).
Common pitfall. Jumping from 15 g to 35 g overnight. Increase gradually and drink water, or you'll be bloated for a week.
My case
30–35 g/day, both scenarios. Easiest route: legumes at one meal (~10 g), oats or wholegrain bread at breakfast (~6–8 g), fruit ×2 (~6 g), vegetables at two meals (~8 g). That's 30 g without trying.
Where I get it right now: wholegrain toast (~2–3 g a slice), flaxseed (~3 g per tablespoon), fruit and vegetables. Probably 18–22 g/day. The missing 10 g is legumes. Flax note: whole seeds deliver the fibre but the shell keeps the omega-3 locked in; grind them to get both.
2.2b Sugar
What it is. Simple carbohydrates. "Free" or "added" sugars are added during processing or present in juices, honey, syrups. Sugars in whole fruit and milk come packaged with fibre, water, or protein — a different matter.
What it does. Fast energy. In excess: easy way to over-consume calories with zero satiety, plus dental caries.
How much. WHO: keep free sugars under 10% of total energy, ideally under 5%. At 2,200 kcal, that's under 55 g (ideally under ~28 g). One 330 ml can of regular soda is ~35 g.
Common pitfall. Drinks. Soda, juice, flavoured coffee, sweet alcohol. Liquid sugar doesn't register as food; you drink 300 kcal and eat the same lunch anyway.
My case
10% ceiling: ~50 g free sugar in Scenario A, ~62 g in B; 5% target: ~25 g / ~31 g. In practice: one sweet thing a day, not a can of soda plus a pastry plus a sweetened yogurt.
Diet soda. I drink Coke Zero to dodge the liquid-sugar trap. Randomised trials that swap sugary drinks for zero-calorie ones show modest weight loss. The scary observational headlines have cause and effect reversed — people who are already heavier drink more diet soda. WHO's 2023 advice against sweeteners for weight control was explicitly graded low-certainty. Two real downsides: the acid erodes enamel (rinse with water, don't sip all day), and for some people the sweet taste keeps sweet cravings alive. Neither is a reason to switch back to sugar.
2.3 Fat
What it is. Fatty acids, grouped by chemistry. Unsaturated (mono- and poly-): olive oil, nuts, avocado, oily fish, seeds — generally beneficial. Saturated: butter, cheese, fatty meat, coconut oil — neutral-to-harmful in excess; limit, don't eliminate. Trans: industrially hardened fats — harmful; largely regulated out of the EU food supply. Omega-3 (EPA/DHA): a subtype of polyunsaturated fat with specific cardiovascular and anti-inflammatory benefits.
What it does. Hormone production, absorption of vitamins A, D, E, K, cell membranes, brain tissue. Also flavour and satiety — very-low-fat diets are hard to stick to.
How much. Roughly 20–35% of energy. Saturated fat below ~10% of energy. Omega-3: ~250 mg/day EPA+DHA, roughly two portions of oily fish a week.
Where to get it. Olive oil, nuts, seeds, avocado, salmon, sardines, mackerel, eggs.
Common pitfall. Forgetting fat is 9 kcal/g. Two tablespoons of olive oil on a salad is ~240 kcal. That's fine. Just know it.
My case
~25% of intake: Scenario A ≈ 55 g/day; Scenario B ≈ 70 g/day. Saturated under ~20 g. That's roughly: 1 tbsp olive oil for cooking, a handful of nuts, and whatever comes with eggs/fish/meat. Cheese and butter eat this budget fast — in A especially, they're the first thing to cut when calories are tight.
2.4 Water and Alcohol
Water. ~2–2.5 L/day total including food; more when hot or training. Thirst and pale-yellow urine are adequate guides. Hunger and mild dehydration feel similar — drink first.
Alcohol. 7 kcal/g, no nutrients. What it does to a fat-loss effort, in order of importance:
- Calories. Pint of beer ~200 kcal; 15 cl wine ~120–150; 4 cl spirit ~90 (plus whatever it's mixed with: a rum-and-Coke is ~200, a rum-and-Coke-Zero is ~90).
- It jumps the queue. The body can't store alcohol, so it burns it first and pauses fat oxidation until it's cleared — roughly one drink per hour.
- Disinhibition. Two drinks in, the plan is negotiable. Most of alcohol's damage to a diet is the kebab, not the beer.
- Sleep and recovery. Even moderate amounts fragment deep sleep and blunt the muscle-repair response after training. Next-day hunger is higher and workouts worse.
Current consensus (WHO, Canadian 2023 guidance): risk starts at the first drink and rises from there. Under ~2 drinks a week is considered low risk. The older idea that a glass of red wine is protective has not survived better studies.
My case
Water: ~2.5 L/day in A; ~3 L on run days in B, plus a pinch of salt or an electrolyte tab if a run is longer than 45 min in summer.
Alcohol: in Scenario A, three pints is 30% of the day's calories, plus a paused fat-burn for three hours, plus whatever I eat at 1 am. Budget it as a full meal or skip it.
3. Micronutrients (the ones people actually run short on)
Vitamins and minerals are needed in tiny amounts but you can't make them. A varied diet covers almost all of them. These are the exceptions worth knowing.
| Nutrient | What it does | Daily target | Good sources | Who falls short |
|---|---|---|---|---|
| Vitamin D | Bone, immune, muscle function | 15 µg (600 IU); many take 1,000–2,000 IU Oct–Mar | Sunlight, oily fish, eggs, fortified foods | Almost everyone north of ~40°N in winter |
| Vitamin B12 | Nerves, red blood cells | 4 µg | Meat, fish, eggs, dairy; fortified foods/supplement | Vegans (must supplement), older adults |
| Iron | Oxygen transport; deficiency = fatigue | 11 mg men / 16 mg menstruating women | Red meat, lentils, spinach, fortified cereals (pair plant iron with vitamin C) | Menstruating women, vegetarians, endurance athletes |
| Calcium | Bone, muscle contraction | ~950–1,000 mg | Dairy, fortified plant milks, sardines, tofu, kale | People avoiding dairy |
| Magnesium | 300+ enzyme reactions, muscle relaxation, sleep quality | 300–350 mg | Nuts, seeds, legumes, wholegrains, dark chocolate, leafy greens | Anyone on a low-wholegrain, low-legume diet |
| Potassium | Blood pressure, counterbalances sodium | ~3,500 mg | Potatoes, bananas, legumes, leafy greens, yogurt | Most people; low fruit/veg intake |
| Folate (B9) | Cell division; critical pre-/early pregnancy | 330 µg | Leafy greens, legumes, fortified grains | Women who may become pregnant |
| Iodine | Thyroid | 150 µg | Iodised salt, dairy, fish, seaweed | People using only non-iodised sea/fancy salt |
Common pitfall: buying a multivitamin instead of eating legumes and vegetables. Supplements fix specific, identified gaps (vitamin D in winter, B12 for vegans). They don't fix a diet.
4. Salt (Sodium)
What it is. Table salt is sodium chloride; sodium is the active part. 1 g sodium ≈ 2.5 g salt.
What it does. Fluid balance, nerve signalling. In excess, raises blood pressure over time — the main modifiable risk factor for stroke.
How much. WHO: under 5 g salt/day (2 g sodium). Average European intake is 8–11 g. Roughly 75% of that comes from processed and restaurant food, not the shaker.
Common pitfall. Bread, cheese, cured meat, sauces, ready meals. A French tacos is likely 3–4 g of salt on its own.