The internet is full of tips for losing weight fast. A popular suggestion is to eat “negative calorie” foods such as celery, as you burn more energy by eating & digesting celery than you absorb.
Is it true that eating certain foods causes you to lose calories instead of increasing them, and does eating these foods help you lose weight? We asked 3 experts in nutrition & physiology: “Do negative calorie foods exist? here is what we found.
What are calories & what are they for?
Louise Dunford, a nutrition & physiology expert at Montfort University in the UK, explains that “a calorie is an energy unit, which is generally expressed as kilocalories (KCAL) for the energy content in food.”
Most food packaging comes with labels describing how many calories this product contains. We consume calories by eating & we use them up by burning energy.
Dunford says, “Our energy needs are made up of 3 components:
- The energy needed to keep a body at rest, that is, the energy that our body needs to carry out its basic processes so that we can live.
- The thermal effect of eating, which is increase in metabolic rate after eating, as food is digested & absorbed.
- Extra energy needed for activity & exercise.
What are “negative calorie” foods?
“The theory behind negative calorie foods is that some foods contain fewer calories (energy) than the amount of energy needed to digest & absorb the food in the body,” says Dunford.
“It sounds plausible, in theory. But in reality, even the lowest calorie foods, like celery, contain more calories than needed to break them down & absorb them into the body.
Some foods labeled “negative calories” include celery, grapefruit, tomatoes, cucumbers, broccoli, lettuce, & carrots.
What is the evidence for “negative calorie” foods exist?
2 of 3 experts stated that there was no evidence that there are negative foods exist.
“Even humble stalk of celery, despite being about 95% water, still contains a small number of kilojoules from carbohydrate (65 kJ to be exact),” says Tim Crowe, nutrition expert from Thinking Nutrition. .
“Although there is an energy cost to your body in digestion of food, called the thermic effect of food, but this is equivalent to about 10% of the energy contained in food. So, celery also adds a few kilojoules to your diet. And while it’s a small number, it sure isn’t a negative number.
Although it is not a food, cold water has been considered negative calories. Cornelie Nienaber Rousseau, Nutrition Expert at North West University in South Africa, says: “Water does not contain energy & when you drink water outside of body temperature ranges will expend energy to maintain the body’s internal-temperature, this is called the water-induced thermogenesis effect.
Several studies have tried to investigate the question of whether this effect could be advantageous for weight loss, but most have found no or minimal expenditure of calorie after drinking cold water.
Chewing gum, while something we might not think of as food, has also been rated as “negative calorie”.
Again, however, its effect is minimal, explains Nienaber Rousseau: “Chewing only burns 11 kcal (46.2 kJ) per hour & therefore can hardly be considered real exercise. Since a rubber stick contains about 10 kcal (42.0 kJ), it will take one or more hours to chew to burn off the energy provided by the gum.
Do So-called “negative Calorie Foods” offer any benefits?
If celery, grapefruit & cucumber do not lose calories, how are they often in effective weight loss schemes?
“Diets based on so-called negative-calorie foods, or to use the more acceptable term ‘free food’, don’t work because they cause an energy deficit, but rather because these foods satisfy hunger by filling stomach with food that is not energy dense & coupled with exercise can lead to burning more fuel than what has been ingested to create an overall energy deficit, ”explains Nienaber Rousseau.
Or, as Crowe puts it, “The way foods like celery, lettuce, & broccoli can help you lose weight is if your mouth is full of celery, there’s no room for burgers.” & fries.
Eating so-called “negative calorie” foods can therefore help you lose weight by making you feel full. However, it’s important not to just add them to your diet.
“It is important to replace the highest caloric items on a plate rather than adding these fruits & vegetables to meals, as simply by adding healthy items you increases overall calorie content. Example, a cheeseburger plus a salad contains more calories than a cheeseburger alone, Dunford said.
Interestingly, this can be psychologically difficult to do – notes Nienaber Rousseau “Studies indicate that people would underestimate the energy content of a food / meal when a healthy food is present as free food – this phenomenon as the ‘negative calorie illusion’ ”.
“Unfortunately negative calorie foods are a myth and there is no easy way to lose weight & keep it off in long haul,” Dunford sums up.
“Permanently changing food & drink options to healthier foods is more likely to lead to sustained long-term weight loss than short-term dieting alone.