Not everyone runs on empty. But some groups do it often: people on repeated diets, young women who restrict, endurance athletes. When energy intake stays too low for the demands, the body down-regulates – hormones, menstrual cycle, sleep, mood and concentration can all suffer .

Why weighing helps. 100 g of boiled potatoes contain roughly 15–20 g of carbohydrate; 100 g of rolled oats about 60 g . A plate of potatoes that looks generous may deliver less than 30 g. Reaching 100 g of carbohydrate from potatoes alone takes around half a kilo or more.

Evidence: whole fruit, fruit juice and diabetes risk ; ketones as brain fuel during fasting .

Your glycogen stores hold around 600 g of carbohydrate – about 500 g in muscle and 80 g in the liver on average . Each gram is stored with at least 3 g of water . Refilling stores that have been running low can therefore add around 1–2 kg within days: stored fuel and water, not fat. Fat gain follows only a sustained energy surplus – which is why this plan raises carbohydrate without adding extra fat on top.

Adequate intake is about 300 mg a day for women and 350 mg for men . In an open-label trial, 248 mg of magnesium a day for six weeks improved mild-to-moderate depression scores . For supplements, more is not better: tolerable upper levels are 250 mg a day in the EU and 350 mg in the US – above that, diarrhoea is common. Taking it with a meal is gentler on the stomach. The same principle applies to iron, vitamin B12 and vitamin D: have levels checked before you supplement.