Our two-week guide aims to teach you everything you need to know about food labelling. This week, we tell you what your body needs to maintain your present weight, and what it needs to lose weight. Next week, we help you to understand label jargon. Want to know why reduced-fat taramasalata is still a high-fat food? Or why a no-added-sugar food can still contain a fair whack of sugar? We interpret the label-speak so that you can really get to grips with what you are eating.

WHAT YOU NEED EVERY DAY

There is no point poring over the figures for calories, fat, protein, sugar, salt and fibre on a label if you do not know how much of these you ought to be consuming each day. Use the tables below to work out what you should be aiming for.

For example, if you are a woman hoping to lose a few pounds, you should aim to consume about 1,200 calories a day. If you scoff 390 in a chocolate croissant and cappuccino for breakfast, 350 in a slice of banana cake at elevenses, and 500 in a tuna-mayo baguette at lunch, then you know you have already blown it — with nothing left for dinner. The same goes for fat. On a 1,200-calorie diet, your goal is 40g a day, so if you consume two slices of a meat-feast deep-pan pizza, that is double your recommended fat intake in one fell swoop. The figures on the labels are meaningless without knowing what you require every day.

So, now you know what your daily intake should be, but what if you go over the recommended amounts? Here are the answers in black and white.

CALORIES AND KILOJOULES

All food provides energy. Just as electrical energy is measured in watts, the energy we get from the food and drink used to power every activity of cell maintenance and growth is measured in kilocalories. Better known as kcals or simply calories, just to confuse us, labels also carry the metric version for measuring energy in foods known as kilojoules or kJ. There’s nothing like accidentally misreading kilojoules for calories to give you sudden palpitations, since there are 4.2 kilojoules in every calorie. A virtuous-sounding Cadbury’s Highlights chocolate drink has 170kJ, but that is only 40 calories.

The total number of calories in a food depends on how much protein, fat and carbohydrate it contains. For every gram of fat in a type of food, you get 9 calories. For every gram of protein or carbohydrate, you get just 4 calories. It makes sense, then, that foods containing a lot of fat tend to be high in calories. For example, 100g of Anchor Spreadable has 82g of fat and 741 calories, whereas half-fat Anchor contains 40g of fat and 363 calories.

The average woman, trying to maintain her weight, should aim for a total of about 1,900 calories each day, and the average man 2,500 calories. However, these figures are only a guide. Genetics, lifestyle, height, weight, how much of your weight is muscle and how much of it is fat, plus your age, all play a role in the exact number you as an individual require. Nevertheless, they are handy benchmarks.

Eat too many calories for your needs, and I need hardly tell you the result: your body will turn them into fat stores. For every 3,500 excess calories you eat, 1lb of body fat is stored. Eat 3,500 calories less than you need and 1lb of fat is burned. Most of us can lose 2lb of fat each week by dropping our calorie intake to about 1,200 a day in the case of women and 1,500 a day for men.

Always check the calories a food supplies per serving, not per 100g. While a Marks & Spencer Bacon and Blue Cheese Pasta meal supplies just 160 calories per 100g, the 400g pack, which is designed as one serving, provides a total of 640 calories.

PROTEIN

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