The Urban Trainer Blog - UK

The theory of negative calories is not a new one. Some very fibrous vegetables, like celery and lettuce, are very low calorie and it is claimed by some that the energy cost of actually chewing, digesting and then absorbing these foods, is higher than the actual amount of energy they provide. So, following this theory, the net result would actually be negative calories thus helping to lose weight.

However, this theory is flawed, and here’s why. We all have the so called ‘good’ bacterial flora living in our gut, which live in symbiosis with us, i.e. we help them and they help us. The term dietary fibre refers to all the polysaccharides, i.e. complex carbohydrates, which humans are unable to digest as we do not have the correct enzymes to do so (the only natural polysaccharide we can digest is starch). Some of these gut bacteria living in our small intestine can actually digest and process some of the polysaccharide fibre into mono- and disaccharides (simple carb) which we are then able to absorb, metabolise and use for energy.

Obviously this is only a tiny amount of energy produced, but it is roughly equal to the amount of calories which we use in the digestion fibrous foods. So the cost of digesting celery and lettuce would be about equal to that which the gut flora produce from fibre foods, leaving the real energy value being the actual amount that it does provide in calories. Obviously this is an approximation as calorie counting has a huge variance anyway, and factors like how much you chew your food would be significant with these small values.

Not that I want to put you off your fibrous salad veg though! Far from it. I’m just explaining the flaws with the ‘negative calorie’ theory. Remember, there are huge health benefits from consuming veg like celery, especially as the calorie value is very low anyway and they are useful ‘fill up’ foods to stop you getting hungry and snacking. So enjoy your veg!