Drinks

What you drink often has a bigger impact on your calorie balance than dessert – because liquid calories hardly fill you up at all. A glass of fizzy drink (250 millilitres) contains around 25 grams of sugar and 100 kcal, a glass of apple juice about the same, and an iced tea or energy drink often even more. Your body barely registers this energy, so you don't eat any less at your next meal.

The German Nutrition Society (DGE) recommends around 1.5 litres of fluid a day for adults, more in hot weather and when exercising; children need about 0.8 to 1.3 litres, depending on their age. Ideal choices are water (tap or bottled), unsweetened herbal or fruit tea and, for adults, coffee and black or green tea in moderation. Milk is more a food than a thirst quencher – nutritious, but it does contain calories.

Juice is not fruit: pressing leaves the fibre behind, and according to WHO its sugar counts as free sugar. Mixed 1:3 with water as a spritzer, it makes a good compromise – for children and athletes alike. Diet drinks with sweeteners have hardly any calories, but they keep you used to very sweet tastes; they're fine as a stepping stone, but not really as a long-term solution.

If you switch from one glass of fizzy drink a day to water, you'll save around 36,000 kcal a year on paper – roughly equivalent to 5 kilograms of body fat, even if your body adjusts its energy use somewhat over time. Few changes are this simple and this effective.

Tips for families: put water on the table where everyone can see it, give each child their own water bottle, liven up water with slices of lemon, cucumber or mint, and don't stock up on sugary drinks – save them for special occasions. Children drink what they see – and that includes what their parents drink.