Negative Calorie Nonsense
I got a message this morning from a trainer buddy of mine. Here’s what he wrote:
“Hey Elissa,
I’m in a debate about negative calorie foods. I think you wrote an article about it but couldn’t find it on the forum.
I know Celery is claimed to be negative calorie but is the cost of digestion really 146 calories to it’s 5 calorie content?!?”
146 calories to digest a stalk of celery????
Intrigued, I did a bit of digging to see where this little factoid came from, and I think I found it here (or at least one version of it):
Consider the facts:
- A piece of dessert consisting of 400 Calories (actually 400 kilocalories) may only require 150 Calorie (actually 150 kilocalories) to digest by our body, resulting in a net gain of 250 calories which is added to our body fat !
- On the other hand, a 5 calorie piece of celery may require 150 calorie to digest, but resulting in a net loss of 145 calories from our body fat !! It implies that the more you eat, the more you lose weight!!!
Whoa! For starters, that 150 calorie figure is impossibly high…it’s 37.5% of the total calories. There is such a thing as the “thermic effect of food” – but, while it varies for different macronutrients, a general estimate is 10%. Even protein, the most thermogenic macronutrient, has a TEF of “only” 30%. Our hypothetical (presumably high carb and/or fat) dessert wouldn’t have a thermogenic effect that high, let alone a piece of celery.
Which brings up a related point: you can’t equate the two, anyway. The body “sees” a piece of celery rather differently than it “sees” the dessert.
Why is that? Here’s a clue…
…Typical postprandial responses can be initiated in experimental situations by infusion of meal nutrients (carbohydrate, lipid, and protein or amino acids) into the distal and proximal small intestine and the cecum and the colon. The existence of these feedback and feedforward responses implies the existence of “sensors” that can detect the presence of nutrients. There is good evidence that these sensors are located in the gut wall, but they may also exist at extraintestinal sites such as lymph vessels, portal veins, liver, pancreas, and the central nervous system.
Much of the work to characterize the sensors that are activated by nutrients has involved functional analysis that uses inhibition of gastric motility or acid secretion as a measure of activation of sensors. This approach has yielded useful information about the nature of the mechanisms by which nutrients are sensed by the intestinal wall. It is clear that nutrients act separately from any osmotic or mechanical effects, that all macronutrient groups alter gastric secretomotor function and food intake (suggesting the effect is not secondary to detection of caloric content), and that each macronutrient group acts via activation of separate and distinct mechanisms and pathways.
Emphasis mine.
In other words, your digestive system isn’t some dumb tube, running from your esophagus to your anus, that responds the same way, no matter what’s pushed through it. It’s a complex, highly sensitive system that can sense the nutrient density of the incoming foods, and respond accordingly. And beyond that, there’s a cascade of events that flow from the digestion and absorption of certain nutrients that require energy (in addition to producing/storing it). The digestion/absorption of complex, nutrient and energy-dense foods will trigger responses that simple, low-nutrient/energy foods won’t (or won’t to the same degree).
And “very simple, low nutrient/energy food” is a perfect description for celery. It’s mostly water and some cellulose. There really isn’t that much for the body to respond to. Thus, it’s not reasonable to expect that the celery will “cost” the same as the dessert in terms of the energy needed to digest/absorb/eliminate it.
But beyond the physiology and biochemistry, it makes little sense. As I put it to my bud, if it were true that eating celery “wastes” 146 calories a stalk, then…
“…all anyone would need to do to lose oodles of weight would be to snack on celery all day. Sure, s/he might accidentally reduce his/her calorie intake, if the celery replaced their daily allotment of candy bars and croissants, but the size of the main meals could be increased to compensate.
Just imagine: if a small stalk of celery could induce that sort of deficit, then you could use it to truly “eat all you want and still lose weight!”
Awesome, eh? You’d think that bodybuilders and fitness models would be all over this one – after all, people who need to be extra lean for a living have a few more tricks up their sleeves than your average joe. Yet this isn’t one they seem to employ…I wonder why?
Because it’s total bullshit…that’s why. I don’t know of a single study that’s ever validated the “negative calorie” concept, let alone looked at the specific thermic effect of celery (and that is what we’re talking about here – a “kcal” is the amount of energy required to increase the temperature of a kg of water by 1 (Centigrade) degree). If I had to guess, I’d say it’s true, but the deficit is almost certainly irrelevant compared to other ways of reducing cals (i.e., reduced food intake and increased energy expenditure).”
As it turns out, a lot of mainstream folks agree with that last sentence. Click here, here and here.
In other words, the concept of “negative calorie foods” may be valid in a technical sense, but not in a practical one.
Nonetheless, high fiber foods like celery do serve a practical purpose in a weight loss program…they fill you up for comparatively few calories, and take a while to eat – which gives your brain a chance to process the “I’m full” signal. Thus, they make it easier to manage on reduced calories without feeling hungry. They also contain valuable vitamins, minerals and phytonutrients, so – even if they don’t have any profound, “negative calorie” effects, it’s still worthwhile to add them to your diet.
