麻豆传媒

IN OUR world of constant information bombardment, there are so many conflicting claims about food out there that it can often be hard to sift fact from fiction. Sometimes you hear an idea being proclaimed as incontrovertible truth almost as often as you hear the exact same one being resoundingly debunked by scientists.

Yet when it comes to a topic as complex as diet, could this often be because both claims have some merit depending on the context? I think looking at one long-enduring dieting belief 鈥� that you burn more calories digesting celery than it contains 鈥� is a useful way of answering this question.

This is a piece of received wisdom that I have been hearing since I was a kid. Indeed, it is intuitively plausible given the extremely small number of calories that celery contains and how much chewing is involved to crack open its fibre-lined cells and access their contents.

So I was fascinated to learn that the idea that celery was a 鈥渘egative-calorie鈥� food had been scientifically investigated by a team at Oxford Brookes University in the UK back in 2012. The researchers served a group of women a typical 100-gram portion of the fresh stems, then closely measured their calorie expenditure at specific intervals using an ingenious 鈥渧entilated hood鈥� system that calculated their bodies鈥� energy usage by .

Crunching the numbers, the team found that although digesting, assimilating and storing the energy from the veg did, on average, burn more than 85 per cent of the calories that the celery contained, there was indeed a small surplus.

How much is a 15 per cent surplus from 100 grams of celery? A ridiculously tiny amount: just 2 whole calories. However, it is still technically a surplus. Case closed, right?

Well, here鈥檚 the thing: in reality, humans don鈥檛 live off celery alone. We don鈥檛 even tend to eat it on its own, but as part of meals containing all sorts of other ingredients. We also know that foods with a low calorie density, particularly those that contain loads of water and fibre, can measurably increase satiety.

鈥淗umans tend to eat a similar weight of food each day, irrespective of the number of calories it contains鈥�

So, in the context of wider diet, could foods like celery fill us up faster, resulting in a reduction in our consumption of more calorie-dense food, cutting overall calorie intake? Well, looking at the evidence so far, the answer seems to be: probably.

According to a study published in the , for example, serving up a large starter salad to a group of volunteers saw them eat significantly smaller portions when presented with a massive, all-you-can-eat buffet of pasta. How much smaller? Well, there was as much as a 12 per cent reduction in calories consumed, even when those contained in the salad were factored in.

On average, this clocked in a saving of up to 100 calories in a single meal. Although extrapolating too much from the limited data is fraught with difficulty, if this sort of calorie cut could be replicated, it would constitute a significant 300-calorie saving per day.

This isn鈥檛 just the findings of a single study either. One experiment at the University of Pennsylvania found that eating a single apple before lunch could . That is an impressive reduction of an average of 187 calories, more than is found in a can of soft drink.

It is fair to say that both of these trials were short term and included only a limited number of participants, but similar results have been echoed by a number of other studies investigating foods with low-calorie densities, like vegetable soup and pears, suggesting a consistent pattern.

This points to a curious phenomenon surrounding appetite regulation and our eating behaviour. Humans tend to eat a similar weight of food each day, irrespective of the number of calories it contains. To me, this is a fascinating quirk of how our bodies regulate our appetite, one that may offer key insights into weight management.

In the concluding words of by researchers at Pennsylvania State University: 鈥淭his approach may facilitate weight loss because it emphasizes positive messages rather than negative, restrictive messages.鈥�

So, while even extremely low-calorie, high-fibre foods like celery don鈥檛 contain magical negative calories when tested in isolation, when viewed in the more accurate, real-world context of how we actually eat, it seems that this could indeed be a reasonable label. So could the difference between fact and fiction in simple scientific measures sometimes just be the frame of reference used in the definition? I think so.