Feed the work.
Nothing wasted.

What a calorie is

• A calorie is a unit of energy — the energy needed to raise 1 g of water by 1°C. What everyone calls a calorie is really a kilocalorie (kcal), a thousand of them. UK labels also give kilojoules (kJ): 1 kcal ≈ 4.184 kJ.
• Energy comes from four things and only four things. Everything else in food — vitamins, minerals, fibre, water — supplies none.

Energy balance

• Energy in = energy out → weight stable. In > out → surplus, weight gain. In < out → deficit, weight loss. This is thermodynamics, and it is not optional — but it says nothing about what you gain or lose, or how easy it is to sustain.
• "Energy out" is not just exercise. It has four parts, and the one people focus on is usually the smallest.

Estimating how much someone needs

• Every equation is an estimate with real error bars — commonly ±10–20% for any individual. Use one as a starting point, then adjust from what actually happens to body mass over two to three weeks. That feedback loop beats any formula.
• A quick, defensible method: estimate BMR, then multiply by an activity factor to get TDEE.

What it is and what it does

• The body's preferred fuel, and the only one that can support genuinely high-intensity work. Broken down to glucose and stored as glycogen in muscle and liver — roughly 400–500 g in total, worth about 60–90 minutes of hard exercise.
• Muscle glycogen fuels the muscle it sits in and cannot be shared. Liver glycogen maintains blood glucose — which is what the brain runs on, and why running low makes you foggy and irritable long before your legs give out.
• Carbohydrate is not an essential nutrient in the strict sense — the body can make glucose from other substrates. It is, however, the limiting factor for performance in almost every sport.

Types

Glycaemic index and glycaemic load

• Glycaemic index (GI) ranks a carbohydrate food 0–100 by how quickly it raises blood glucose against a reference. Low ≤55 · medium 56–69 · high ≥70.
• Glycaemic load (GL) = GI × grams of carbohydrate per portion ÷ 100. It is the more useful number, because it accounts for how much you actually eat. Watermelon has a high GI and a low GL — there is very little carbohydrate in a slice.
• Practical use: lower GI most of the time for steadier energy and appetite; higher GI immediately after hard training, when fast glycogen replacement is the goal. GI is also affected by ripeness, cooking, processing and what else is on the plate — fat, protein and fibre all slow it down.

Fibre

• 🇬🇧 30 g a day (AOAC method). 🇺🇸 about 14 g per 1,000 kcal, working out around 25 g for women and 38 g for men. Actual intake falls well short in both — around 19–20 g in the UK and about 16 g in the US.
• Increase it gradually and with more fluid, or you get bloating and wind. And time it away from competition: a very high-fibre meal before a race is a common, avoidable mistake.

How much

What it is

• Chains of amino acids — 20 of them. Nine are essential: the body cannot make them, so they have to come from food. The rest it can synthesise.
• Protein's job is structure and function, not fuel: muscle, bone matrix, tendon, skin, hair, enzymes, hormones, antibodies, transport molecules like haemoglobin. It contributes meaningfully to energy only when carbohydrate is depleted or intake is inadequate.
• There is no storage depot for protein. Excess is either used, converted to glucose, or stored as fat — which is why intake needs to be spread across the day rather than banked.

Quality

• Complementary proteins do not need to be eaten in the same meal — the body maintains a pool of amino acids across the day. A varied plant-based diet with adequate total protein covers it comfortably.
• Leucine is the amino acid that triggers muscle protein synthesis. Roughly 2.5–3 g of leucine per meal — about 20–40 g of a complete protein — is what flips the switch. Most plant proteins are lower in leucine, so plant-based clients generally need somewhat more total protein and a wider variety of sources.

How much

Timing and distribution

• Total daily intake matters most. Distribution is second, timing a distant third — the "anabolic window" is hours wide, not thirty minutes.
• Per meal: roughly 0.25–0.4 g/kg, or about 20–40 g, of a complete protein. Beyond ~40 g the extra does not add further to muscle protein synthesis in a single sitting, though it is not wasted.
• Spread it: three to five such doses across the day beats one large hit. A protein-containing meal before bed is a reasonable, evidence-supported habit for trainees.
• Very high intakes are not harmful to healthy kidneys — that claim has not held up. But anyone with existing kidney disease needs medical advice, not a protein target from a personal trainer.

What it does

• The body's largest energy store — effectively unlimited, and the dominant fuel at rest and low intensity. But fat has jobs beyond fuel, which is why very low-fat diets cause problems.
• Insulation and protection of organs · cell membranes are built from it · it carries the fat-soluble vitamins A, D, E and K · it is the raw material for steroid hormones including testosterone and oestrogen · and it makes food palatable, which matters for adherence.
• Two fatty acids are essential — the body cannot make them: linoleic acid (an omega-6) and alpha-linolenic acid (an omega-3).

The types

Omega-3 and omega-6

• Omega-3 — ALA from flaxseed, walnuts and rapeseed oil; EPA and DHA from oily fish. The body converts ALA to EPA and DHA only poorly (a few per cent), so oily fish, or an algae-based supplement for vegans, is the reliable route. Anti-inflammatory; supports heart and brain health.
• Omega-6 — mainly linoleic acid from vegetable oils, nuts and seeds. Also essential. Western diets supply it in abundance; the practical issue is usually getting enough omega-3, not avoiding omega-6.
• 🇬🇧 Two portions of fish a week, one of them oily (2 × 140 g). 🇺🇸 similar — around 8 oz of seafood a week.

Cholesterol

• Cholesterol is not a fat — it is a sterol, needed for cell membranes, vitamin D and steroid hormones. The liver makes most of it; dietary cholesterol has far less effect on blood cholesterol than saturated and trans fat intake does.
• LDL carries cholesterol to the tissues and deposits it in artery walls — the "bad" one. HDL carries it back to the liver — the "good" one. Hook: L for Lousy and Lodges in arteries, H for Healthy and Heads home.
• What actually improves the picture: less saturated and trans fat, more unsaturated fat and soluble fibre, regular aerobic exercise, not smoking, and a healthy body weight.

How much

The one distinction that organises the whole topic

The fat-soluble four

The water-soluble group

• Does exercise increase vitamin needs? Slightly, for the B vitamins involved in energy metabolism — but because active people eat more food, they usually get more of them automatically. A varied diet covers it for the overwhelming majority.
• The real supplementation cases are specific and evidence-based, not general: vitamin D in winter, B12 for vegans, folic acid before and in early pregnancy, and iron or others where a blood test has shown a deficiency.

Macro and trace

• Macrominerals are needed in milligram quantities or more: calcium, phosphorus, magnesium, sodium, potassium, chloride, sulphur. Trace elements are needed in microgram to small milligram amounts: iron, zinc, iodine, selenium, copper, manganese, fluoride, chromium.
• Unlike vitamins, minerals are elements — they can't be destroyed by cooking, but water-soluble ones do leach into cooking water.

The ones that get examined

Absorption — the part people miss

Who actually runs short

What water does

• 50–60% of body mass — higher in lean and younger people, lower in older and fatter ones — and closer to 75% of muscle. It transports nutrients and waste, is the medium for every chemical reaction in the body, lubricates joints, and — the one that matters during exercise — regulates temperature through sweat.
• You lose it through urine, sweat, breathing and faeces. In hard exercise, sweat rates of 0.5–2.0 litres per hour are normal, and can go higher in heat.

Dehydration

How much

What to drink

• Timing is third on the list, behind total energy and total macronutrients. It matters most when sessions are long, hard, or close together — and barely at all for someone training three times a week with a day between.

Before

• Never try anything new on competition day. Rehearse race-morning food in training. Gut tolerance is trainable and highly individual.
• Training fasted is fine for easy, low-intensity work and some people prefer it. It does not burn more fat overall once the day is accounted for, and it compromises quality in hard sessions.

During

After

• Carbohydrate: 1–1.2 g/kg/hour for the first 4 hours if another demanding session is coming within about 8 hours. Otherwise, normal meals across the day do the job.
• Protein: 0.25–0.4 g/kg, or about 20–40 g of a complete protein, within a couple of hours. The window is far wider than supplement marketing suggests.
• Fluid: 1.25–1.5 litres per kilogram of body mass lost, with sodium.
• The "3 Rs" of recovery: Refuel, Repair, Rehydrate. Milk-based drinks happen to deliver all three, which is why chocolate milk keeps showing up in the research.

The figures in this topic are population numbers for exam study — worked examples, not targets for any individual.

The arithmetic, and its limits

• Weight change is driven by energy balance. Roughly 7,700 kcal ≈ 1 kg of body fat (3,500 kcal per pound). A 500 kcal daily deficit is therefore about 0.45 kg a week.
• But the body is not a spreadsheet. As you lose weight, BMR falls (there is less of you), NEAT falls (you move less without noticing), and appetite hormones push back. This is adaptive thermogenesis, and it is why loss slows before the maths says it should.
• Early rapid loss is largely glycogen and its associated water — each gram of glycogen holds around 3 g of water. That is why low-carbohydrate diets show dramatic first-week results and why the scale jumps back when carbohydrate returns.

Sensible rates

Measuring what actually changed

Why diets fail — and what to do instead

Coaching the change — the part the exam calls "applying the principles"

• The unit isn't only science — it assesses the process: gather information, analyse it against guidance, agree goals, support the change, review. Miss the process marks and the science can't save you.
• Gathering intake: a 3-day food diary including one weekend day is the working standard — recorded at the time, not from memory, with drinks, oils, sauces and portions in. A 24-hour recall is quicker and cruder; and remember from topic 01 that people under-report by 20–30%, so diaries are conversation starters, not evidence.
• Analyse against national guidance — the Eatwell Guide or the Dietary Guidelines — never against a coach's personal diet. Look for patterns before nutrients: meals skipped, drinks, weekends, the habits that make up most of the picture.
• Stages of change (the transtheoretical model): precontemplation → contemplation → preparation → action → maintenance — with relapse built in as part of the model, not a failure. Match the approach to the stage: information for contemplators, plans for preparers, troubleshooting and reviews for actors. Handing a meal plan to a precontemplator is the classic exam-scenario error.
• Goals are SMART and behavioural: "two vegetables at dinner on five nights" beats "eat better" — and beats "lose 5 kg", because behaviour is in the client's control and outcomes follow. Review on a schedule; adjust rather than judge.
• Barriers are practical before they are motivational: time, cost, cooking skills, family meals, shift work. The answer is usually planning — batch cooking, shopping lists, default breakfasts — not more willpower. Ask with open questions ("what gets in the way?") rather than assuming.

• The hierarchy again: total energy → macronutrients → food quality → timing → supplements. Supplements sit at the bottom for a reason. For most clients the honest answer to "what should I take?" is "nothing, yet".

The ones with good evidence

Useful, but food in a packet

• Protein powder — convenient and cost-effective, and nothing more. It has no advantage over the same protein from food. Useful when appetite, schedule or travel makes real food impractical.
• Sports drinks, gels and bars — genuinely useful during sessions over an hour, and largely unnecessary below that. A gym client doing 45 minutes does not need a gel.
• Multivitamins — often described as low-cost insurance for someone with a poor or restricted diet. They do not improve performance in someone who is already well fed, and they do not compensate for a bad diet.

The ones to be sceptical about

Contamination, regulation and the law

• Recommending supplements is close to the edge of a Level 3 or CPT scope. You can explain the evidence and point at national guidance. Prescribing a protocol to an individual, particularly one with a health condition or on medication, is not yours to do — supplements interact with drugs.
• Neither country permits a food or supplement to claim it prevents, treats or cures a disease. UK and EU health claims must come from an authorised list; US labels carry a disclaimer that the FDA has not evaluated the claim. A label making a medical promise is telling you about the seller.

Where your scope ends

Plant-based diets

• A well-planned vegetarian or vegan diet supports every stage of life and every level of training. "Well-planned" is doing real work in that sentence.
• The nutrients to watch: vitamin B12 (the one gap both countries' guidance says vegans must cover, with fortified foods or a supplement) · iron (non-haem, less well absorbed — pair with vitamin C) · calcium (fortified plant milks, tofu, greens) · iodine (scarce in plant foods; seaweed is wildly variable) · omega-3 EPA/DHA (algae oil) · zinc · and protein — generally 10–20% more total, from a wider variety, because plant proteins are lower in leucine and less digestible.
• Vitamin D matters for everyone, but check the form: D3 is often lambswool-derived, though lichen-derived vegan D3 exists.

Across the lifespan

Under-fuelling and RED-S

• RED-S — Relative Energy Deficiency in Sport — is what happens when energy intake does not cover training plus basic physiology. It replaced and broadened the older "female athlete triad", because it affects both sexes.
• Consequences: disrupted or absent menstrual cycles, reduced testosterone, lost bone density and stress fractures, suppressed immunity, poor recovery, impaired growth in young athletes, low mood, and — the irony — worse performance.
• Watch for: unexplained fatigue, recurrent illness or injury, stalled performance in someone training hard, missed periods, obsessive food or training rules, rapid weight loss.
• Your job is to notice and refer — to a GP and a sports dietitian. Not to diagnose, and not to fix it with a meal plan.