We hear about calories all the time. How many calories are in this cookie? How many are burned by 100 jumping jacks, or long distance running, or fidgeting? But what is a calorie, really, and how many of them do we actually need? Calories are a way of keeping track of the body's energy budget. A healthy balance occurs when we put in about as much energy as we lose. If we consistently put more energy into our bodies than we burn, the excess will gradually be stored as fat in our cells, and we'll gain weight. If we burn off more energy than we replenish, we'll lose weight. So we have to be able to measure the energy we consume and use, and we do so with a unit called the calorie. One calorie, the kind we measure in food, also called a large calorie, is defined as the amount of energy it would take to raise the temperature of one kilogram of water by one degree Celsius. Everything we consume has a calorie count, a measure of how much energy the item stores in its chemical bonds. The average pizza slice has 272 calories, there are about 78 in a piece of bread, and an apple has about 52. That energy is released during digestion, and stored in other molecules that can be broken down to provide energy when the body needs it. It's used in three ways: about 10% enables digestion, about 20% fuels physical activity, and the biggest chunk, around 70%, supports the basic functions of our organs and tissues. That third usage corresponds to your basal metabolic rate, a number of calories you would need to survive if you weren't eating or moving around. Add in some physical activity and digestion, and you arrive at the official guidelines for how many calories the average person requires each day: 2000 for women and 2500 for men. Those estimates are based on factors like average weight, physical activity and muscle mass. So does that mean everyone should shoot for around 2000 calories? Not necessarily. If you're doing an energy guzzling activity, like cycling the Tour de France, your body could use up to 9000 calories per day. Pregnancy requires slightly more calories than usual, and elderly people typically have a slower metabolic rate, energy is burned more gradually, so less is needed. Here's something else you should know before you start counting calories. The calorie counts on nutrition labels measure how much energy the food contains, not how much energy you can actually get out of it. Fibrous foods like celery and whole wheat take more energy to digest, so you'd actually wind up with less energy from a 100 calorie serving of celery than a 100 calorie serving of potato chips. Not to mention the fact that some foods offer nutrients like protein and vitamins, while others provide far less nutritional value. Eating too many of those foods could leave you overweight and malnourished. And even with the exact same food, different people might not get the same number of calories. Variations in things like enzyme levels, gut bacteria, and even intestine length, means that every individual's ability to extract energy from food is a little different. So a calorie is a useful energy measure, but to work out exactly how many of them each of us requires we need to factor in things like exercise, food type, and our body's ability to process energy. Good luck finding all of that on a nutrition label.
Stalno slušamo o kalorijama. Koliko kalorija ima u ovom kolačiću? Koliko se njih sagori u 100 skokova, ili trčanjem na duge relacije ili vrpoljenjem? Ali šta je zapravo kalorija i koliko ih nam je zapravo potrebno? Kalorije su način praćenja energetskog budžeta tela. Zdrava ravnoteža postiže se kada unesemo onoliko energije koliko izgubimo. Ako stalno u naša tela unosimo više energije nego što je sagorevamo, višak će se postepeno slagati u našim masnim ćelijama i ugojićemo se. Ako sagorevamo više energije nego što unosimo, smršaćemo. Moramo da imamo mogućnost merenja energije koju unosimo i koristimo, a to radimo sa jedinicom koja se zove kalorija. Jedna kalorija, kao ona u hrani, takođe se naziva i velikom kalorijom i definiše se kao količina energije koja bi bila potrebna da se podigne temperatura jednog kilograma vode za jedan stepen Celzijusa. Sve što unosimo ima kalorijsku vrednost, meru toga koliko energije taj proizvod skladišti u svojim hemijskim jedinjenjima. Prosečno parče pice ima 272 kalorije, u parčetu hleba ih ima oko 78, a jabuka ih ima oko 52. Ta energija oslobađa se tokom varenja i skladišti u drugim molekulima koji se mogu razbiti da se pruži energija kada je potrebna telu. Koristi se na tri načina: oko 10% omogućava varenje, oko 20% napaja fizičke aktivnosti, a najveći deo, oko 70%, održava osnovne funkcije naših organa i tkiva. Ta treća funkcija odgovara vašoj osnovnoj stopi metabolizma, što je broj kalorija koji bi vam bio potreban da preživite ukoliko ne biste jeli ili se kretali. Dodajte fizičku aktivnost i varenje i dolazite do zvaničnih uputstava za to koliko je kalorija potrebno prosečnoj osobi svakog dana: 2000 za žene i 2500 za muškarce. Ove procene zasnovane su na faktorima poput prosečne težine, fizičke aktivnosti i mišićne mase. Da li to znači da svako treba da teži ka 2000 kalorija? Ne mora da znači. Ukoliko se bavite aktivnošću koja zahteva puno energije, poput učešća na Tur de fransu, vaše telo može da koristi i do 9000 kalorija dnevno. U trudnoći je potrebno neznatno više kalorija nego inače i stariji ljudi obično imaju sporiji metabolizam, energija se postpenije sagoreva, tako da je potrebno manje. Evo još nečega što treba da znate pre nego što počnete s brojanjem kalorija. Broj kalorija na etiketama kod hrane označava koliko energije hrana sadrži, a ne koliko energije zapravo možete iz nje dobiti. Vlaknastoj hrani poput celera i žitarica potrebno je više energije za varenje tako biste zapravo dobili manje energije od porcije celera od 100 kalorija nego od porcije čipsa od 100 kalorija. Ne zaboravimo i činjenicu da neka hrana nudi hranljive sastojke, poput proteina i vitamina dok druga nudi dosta manje hranljive vrednosti. Ukoliko jedete previše takve hrane, možete postati gojazni i neuhranjeni. Čak i sa potpuno istom hranom, različiti ljudi mogu da dobiju različit broj kalorija. Varijacije u stvarima poput nivoa enzima, crevnih bakterija i čak i dužine creva znače da je sposobnost svakog čoveka da dobije energiju iz hrane pomalo drugačije. Kalorija je dakle korisna jedinica mere energije, ali kako bismo otkrili tačno koliko ih je potrebno svakom od nas, potrebno je uračunati i stvari poput vežbe, vrste hrane, kao i sposobnosti našeg tela da preradi hranu. Srećno vam bilo da sve to nađete na etiketi proizvoda.