One of the biggest nutritional myths is completely inaccurate
Summer is upon us and last-minute holiday diets are everywhere, but does eating ‘negative calorie’ foods such as celery, actually help to increase weight loss?
A calorie is a unit of energy, usually expressed as kilocalories (kcal) for the energy content in food. It is commonly believed that in the act of eating celery you are actually burning off more calories than you are consuming.
In reality, even the lowest calorie foods, such as celery, contain more calories than it takes to break down and absorb them in the body.
Our energy needs are made up of three components:
- The energy needed to maintain a body at rest, which is the energy needed for our body to carry out its basic processes, so we can live.
- The thermic effect of eating, which is the increase in metabolic rate after eating, while food is digested and absorbed.
- Additional energy needed for activity and exercise.
Of these, the thermic effect uses the fewest calories – about 10% of the energy we take in. In other words, about a tenth of the calories we eat are used to process our food – this includes chewing our food, moving it through the digestive system, absorbing nutrients and storing excess energy.
Foods such as celery, grapefruit, broccoli, tomatoes and cucumber have all been touted as negative calorie foods, but there is no scientific evidence to support this idea. Although they are very low-calorie foods, with seven to 30 kcal per 100g, it still takes less energy than this to process them. This is because they contain large amounts of water and fibre, which have a very low energy cost.
Don’t be too disappointed though…
These foods are very useful for people who are trying to lose weight, as they contain a low number of calories. By replacing the food in your diet with some of these – for example, replacing a side portion of chips with a side salad – it is possible to lower your calorie intake considerably. As an extra boost, they are full of nutrients, such as vitamins and minerals, and also contain a lot of fibre, which also has many benefits for your health.
In order to lose weight, people need to use up more energy than the energy (calories) they eat and drink, but this is difficult. Research has shown that people tend to underestimate the calorie content of the food they consume, and they underestimate it by more if they are obese rather than normal weight.