1000 calories a day: what it means for the body and what the risks are

The query "1000 calories a day" looks like a precise figure, but behind it there is usually a diet that is two or three times lower than the reference values for an adult. Below: what is measured in kilocalories, where daily norms come from, and at what point low calorie intake stops being harmless arithmetic.

What calories and kilocalories are

A calorie is a non-SI unit of quantity of heat: the energy needed to heat 1 gram of water by 1 degree Celsius. There are three varieties in use — the international (4.1868 J), the thermochemical (4.1840 J) and the 15-degree (about 4.1855 J); they differ by less than 0.07%, so for kitchen arithmetic this is not the scale worth arguing over. The energy value of food is stated in kilocalories (kcal), and the prefix "kilo" is often dropped in dietetics: "1000 calories" on a package and in conversation almost always means 1000 kcal, that is, 1,000,000 cal. The body needs energy to function: if more comes in than is expended, the excess is stored as fat; if less, the body takes energy from fat stores.

How many calories a person needs per day

Reference values for adults: on average, a man needs 2500 kcal a day and a woman 2000 kcal. The figure is individual and depends on age, weight, height and level of physical activity. Expenditure also changes: brisk walking burns more energy than walking at a calm pace. The general recommendation for adults is 150 minutes of physical activity per week, and this volume can be divided into short episodes throughout the day. Any downward deviation from the reference value means an energy deficit, and the body covers it from stores.

What 1000 and 1200 calories a day mean

1000 kcal a day is half the reference value for a woman (2000 kcal) and 40% of the reference value for a man (2500 kcal). 1200 kcal a day is 60% and 48%, respectively. Formally, the mechanism is the same as described above: energy intake is below expenditure, and weight decreases through fat stores. The verdict: 1000–1200 kcal is not "the norm, only smaller" but a pronounced deficit, which is not something to prescribe for yourself based on an article.

A diet of 500–900 kcal: how it differs from the norm

500 kcal a day is 25% of the reference value for a woman and 20% for a man; 600, 700, 800 and 900 kcal give roughly 24% to 45% of the reference value. Converted against the norm, such a diet is 2.2–5 times below it. The difference from 1000–1200 kcal lies in the degree of restriction. Weight loss follows the same path — through the use of fat stores.

Health risks of very low calorie intake

There is no single list of symptoms for a diet of 1000 kcal or less: the response to an energy deficit depends on baseline weight, age, activity and concomitant conditions. Weight is regulated not only by calories: it is influenced by sleep, emotions, medications (for example, steroids and some antidepressants) and chronic conditions, including Cushing's syndrome and polycystic ovary syndrome.

Low-calorie nutrition in itself is not a reason to call an ambulance; 103/112 are needed if signs of life-threatening conditions appear — for example, stroke or myocardial infarction.

When to see a doctor or dietitian

Before starting any weight-loss program or restrictive diet, a doctor's consultation is needed: the doctor will name the healthy weight specifically for you, help with goals and advise on how to achieve them. At the appointment, body mass index (the ratio of weight to height), weight dynamics and factors that may interfere are assessed:

• body mass index as a reference for the healthy weight range;
• age, height, weight and level of physical activity;
• medications that can affect weight — steroids, some antidepressants;
• chronic conditions that affect weight — Cushing's syndrome, polycystic ovary syndrome.

A separate reason for discussion is a diet of 500–900 kcal: it is better to discuss it with a doctor. This material is for reference: it does not replace a doctor's consultation, and calorie intake should not be selected based on an article.

This content is for reference and does not replace a doctor's consultation. Medical disclaimer