Every fact in the three food and nutrients lessons is listed here with where it comes from. The numbers in [brackets] on the lesson pages link to this list.
How we rate sources
High: space agencies (NASA), peer-reviewed open textbooks (OpenStax, Rice University) and professional scientific societies (American Physical Society).
Medium-high: reputable science news reporting directly on a primary document.
Medium: single-author essays and popular history sites. We only use these for history details, and never on their own: each one is paired with a second source.
Wikipedia was not used as a source. Numbers are rounded (for example 9.8 m/s² for Earth's gravity). The text was drafted with help from AI (Claude) and then checked against these sources. Corrections: hello@echoesof.science.
Where the facts are simplified or less certain: the food-group proportions, portion sizes, sugar and fibre amounts come from UK (NHS) guidance [1, 2, 3, 4]; other countries use slightly different plates and numbers, and the WHO limits [5] are written mainly for adults. The 4–4–9 rule (kcal per gram of carbohydrate, protein and fat) [6] is a rounded average, so energy worked out from a label rarely matches the printed figure exactly. The traffic-light limits per 100 g [8, 3] are UK front-of-pack guidance; the NHS writes 'more than 22.5 g' and the BHF '22.5 g or more' for high sugars. Daily energy figures (about 2,000 kcal for women and 2,500 kcal for men) are averages; children need different amounts depending on age and activity [1, 8]. Links between fibre and lower disease risk are associations from studies [4]. These lessons are general education, not medical or dietary advice: anyone with allergies or special dietary needs should talk to a doctor, a registered dietitian or the school nurse.
All sources
[1] The Eatwell Guide
NHS (UK National Health Service) · Reliability: High
Type: National health service
Aim for balance over a day or a week. Fruit and vegetables just over a third of what we eat (at least 5 portions a day; fresh, frozen, tinned, dried and juiced count; juice and smoothies max 150 ml a day); starchy foods (potatoes, bread, rice, pasta) just over a third, a main source of energy, choose wholegrain; protein foods: beans, pulses, fish, eggs, meat; dairy and alternatives, a key source of calcium; small amounts of unsaturated oils and spreads, all fats are high in energy. Foods high in fat, salt or sugar (chocolate, cakes, biscuits, sugary drinks) less often and in small amounts. 6 to 8 cups or glasses of fluid a day. Around 2,000 kcal (8,400 kJ) for women and 2,500 kcal (10,500 kJ) for men. Applies from age 2.
NHS (UK National Health Service) · Reliability: High
Type: National health service
80 g of fresh, frozen or tinned fruit or vegetables counts as one adult portion; 30 g of dried fruit counts as one portion; juice and smoothies count as one portion at most (max 150 ml a day); beans and pulses count only once a day; potatoes do not count because they are a starchy food, but sweet potatoes, parsnips, swedes and turnips do.
NHS (UK National Health Service) · Reliability: High
Type: National health service
Maximum free sugars a day: adults 30 g (about 7 sugar cubes), ages 7 to 10 24 g (6 cubes), ages 4 to 6 19 g (5 cubes). Free sugars = sugars added to food and drinks plus sugars in honey, syrups and fruit juices and smoothies; sugars naturally in milk, fruit and vegetables do not count as free sugars. Sugar is one of the main causes of tooth decay; sugars inside whole fruit are less likely to cause decay. Labels: high sugar = more than 22.5 g per 100 g, low = 5 g or less.
NHS (UK National Health Service) · Reliability: High
Type: National health service
Fibre helps digestion and can prevent constipation; eating plenty of fibre is linked to a lower risk of heart disease, stroke, type 2 diabetes and bowel cancer. Adults should have 30 g a day but most average about 20 g; children aged 2 to 5 about 15 g, 5 to 11 about 20 g, 11 to 16 about 25 g. Sources: wholegrain bread and cereals, porridge oats, brown rice, potatoes with skins, beans, lentils, chickpeas, fruit and vegetables, nuts and seeds.
World Health Organization (WHO) · Reliability: High
Type: International health agency
Healthy diets protect against malnutrition in all its forms and reduce the risk of diseases such as diabetes, heart disease, stroke and cancer. Everyone older than 10 should aim for at least 400 g of fruit and vegetables a day. Free sugars below 10% of total energy intake, with further benefits below 5%. Salt below 5 g a day for adults. Total fat 30% or less of energy, saturated fat no more than 10%, trans fat no more than 1%.
Merck Manual Consumer Version (Merck & Co.) · Reliability: Medium-high
Type: Medical reference written by doctors
Macronutrients are needed daily in large quantities. 4 calories in a gram of carbohydrate or protein, 9 in a gram of fat. Proteins are made of amino acids; the body cannot make 9 of the 20, so they must come from the diet; the body needs protein to maintain and replace tissues and to grow; muscle, connective tissue and skin are built of protein. Sugars such as fructose (fruit sugar) and sucrose (table sugar) are simple carbohydrates; complex carbohydrates (starches and fibres) are long strings of simple ones; glycogen can be quickly turned into energy. The body needs fats for growth and energy and stores excess energy as fat.
[7] Anatomy and Physiology, 24.7 Nutrition and Diet
OpenStax, Rice University · Reliability: High
Type: Peer-reviewed open textbook
The nutritional Calorie is the heat needed to raise 1 kg of water by 1 °C. Vitamins are organic compounds needed for the body's chemical reactions; minerals are inorganic and cannot be made in the body. Fat-soluble vitamins (A, D, E, K) can build up in the body; water-soluble vitamins (B vitamins and C) are lost in urine, so overload is rare except with supplements. Vitamin C (citrus fruits, peppers) is needed for collagen and wound healing; vitamin D helps calcium absorption; calcium (dairy, dark green leafy vegetables) for bones, nerves and muscles; iron (meat, fish, legumes) carries oxygen in the blood.
British Heart Foundation (BHF) · Reliability: Medium-high
Type: Medical research charity
Traffic-light thresholds per 100 g: fat low 3 g or less, high 17.5 g or more; saturates low 1.5 g or less, high 5 g or more; sugars low 5 g or less, high 22.5 g or more; salt low 0.3 g or less, high 1.5 g or more. Energy is given in kcal and kJ. About 2,000 kcal a day for women and 2,500 kcal for men as a guide; children's needs vary.