First three days: what the body feels

Not necessarily, and it cannot be promised.\n\nThe words about three days acknowledge that the beginning is genuinely difficult; they are not a guarantee of the duration. Initial headaches and weakness ease within the first or second week for many people, but for some they last longer.\n\nThere is no rigid calendar. Expecting a turning point on a specific day is a sure way to be disappointed.

Eat normally. The most common mistake during the first days is undereating: familiar foods have been removed, but an equivalent amount of other food has not replaced them.\n\nDrink about two liters of fluid per day and keep salt at around 3-5 g. Do not combine the start with a severe calorie deficit. Do not add strenuous workouts.\n\nIf your diet used to be low in fat, start with half or one-third of the recommended fat portions and increase them as tolerated.

Marked deterioration should not be dismissed as adjustment. Fainting or near-fainting, confusion, unusual weakness, repeated vomiting or an inability to drink, symptoms of hypoglycemia, or severe or increasing abdominal pain are reasons to stop and seek help.

You must not start on your own during pregnancy or breastfeeding, with type 1 diabetes, or with type 2 diabetes if you use insulin or medications that carry a risk of hypoglycemia.\n\nChronic kidney disease, an absent gallbladder, eating disorders, and adolescence should be discussed separately with a doctor.

Because starting conditions differ.\n\nIf your day used to revolve around fast carbohydrates—pastries, sweet coffee, snacks every two hours—the adjustment feels stronger. If you already ate little sweet food, the first days may pass unnoticed.\n\nIt also matters how abruptly the transition is made, how much a person sleeps, and whether they have combined a new diet with a new training routine in the same week. Three changes at once almost guarantee difficult days.

No exact figure can be given—it depends on how much glycogen was stored.\n\nIt is more important to understand the mechanics: each gram of glycogen holds water with it, and when the store is used up, that water leaves. This explains the rapid drop on the scales during the first week, which has little to do with fat.\n\nThere is one practical conclusion: do not build expectations around this figure. The second week almost always looks less dramatic, and that is when people most often quit.

You can, but it is better not to start during a week with a project defense or a move.\n\nFor some people, concentration decreases on the second or third day, which is noticeable at work requiring attention. Planning the transition for a calm period is not weakness but sensible calculation.\n\nIf there is no choice: eat normally, keep water and salt at around the recommended levels, and do not add anything new on top during these days.