| Abstract | SDA ili termogeni učinak hrane je metabolički odgovor uslijed probave i asimilacije hrane. Ona je definirana kao sva potrošena energija (tj. sva proizvedena toplina) koja se događa radi uzimanja, probave, apsorpcije i asimilacije hrane. SDA najviše ovisi o veličini i tipu hrane, a povećava se zajedno sa energijom obroka. Toplina se proizvodi kao nusproizvod katabolizma hrane. Katabolizmom slobođena energija u tijelu se može pretvoriti u tri oblika: energiju za kemijsku pohranu, energiju za vanjski rad i metaboličku toplinu. Glavni izvor povećanja topline tijela je jetra i njen metabolizam. Kod mjerenja i izračunavanja SDA kod egzoterma, prvo treba ustanoviti SMR („standard metabolic rate“), što je minimalna metabolička razina jedinke nakon absorpcije hrane u mirovanju u svom neaktivnom periodu. BMR („basal metabolic rate“) se uzima za endoterme, i ona je minimalna razina metabolizma inaktivne jedinke nakon absorpcije koja je u svojoj termoneutralnoj zoni u neaktivnom periodu. Mnoge životinje neće ostati neaktivne nakon hranjenja, što otežava mjerenje temeljne razine. Razina metabolizma je mjera sveukupne energije koje tijelo iskoristi u jedinici vremena. Osoba koja miruje i nalazi se u svojoj termoneutralnoj zoni skoro svu energiju pretvara u toplinu, a tjelesna temperatura se održava tako da se jednaka količina topline otpusti kao što se i proizvede. SDA se mjeri izravnom ili neizravnom kalorimetrijom. Izravna kalorimetrija je skuplja i nespretnija, a mjeri potrošnju energije iz količine topline koju jedinka proizvede u izoliranoj komori (kalorimetar). Neizravna kalorimetrija je jeftinija i samo malo manje točna od izravne, a mjeri potrošenu energiju mjerenjem izmjene plinova u jedinici vremena. SDA se računa iz zbroja potrošenog O2 ili proizvedenog CO2, iznad crte osnovnog metabolizma i pretvorenog u energiju. Mnoge stvari utječu na SDA, ali najbitniji čimbenici su kompozicija obroka, tip obroka, veličina obroka, temperatura obroka, veličina i sastav tijela, temperatura okoline, koncentracija plinova, salinitet, spol i dob. Uz te čimbenike postoje i druge stvari koje utječu na SDA, a to su preabsorptivni i postabsorptivni procesi. Preabsorptivni procesi su hranjenje, gutanje, želučana probava, crijevna peristaltika i absorpcija. Postabsorptivni procesi su katabolizam supstrata i biosinteza tjelesnih komponenata. Danas imamo puno radova o termogenom učinku hrane, ali još mnogo toga nije dovoljno istraženo i mišljenja mnogih znanstvenika su podvojena oko toga koji čimbenik najviše utječe na SDA i utječe li uopće na razinu metabolizma. |
| Abstract (english) | SDA or thermogenic effect of food is a metabolic response to digestion and assimilation of a meal. SDA is defined as all energy that has been spent (or heat produced) due to ingestion, digestion, absorption and assimilation of food. SDA mostly depends on size and tipe of food consumed, and it increases with meal energy. Heat is produced as a nusproduct of food catabolism. The energy released by catabolism inside the body can be converted to 3 other forms: energy for chemical storage, energy for external work, and metabolic heat. The main source of increased body heat is the liver and its metabolism. When you are measuring and calculating SDA for ectotherms, first you need to establish SMR („standard metabolic rate“) which is the minimum metabolic rate of an individual after absorption of food during rest in their inactive period. BMR („basal metabolic rate“) is measured for endotherms, and is the minimal metabolic rate of an inactive individual, in its thermoneutral zone and in its inactive period, after absorption. Metabolic rates are a measurment of all energy that a body spends in a known period of time. An individual that is in rest and is in its thermoneutral zone, converts almost all of its energy to heat. Body temperature is maintained by releasing an amount of heat into the environment that is the same amount produced. SDA is measured by direct and indirect calorimetry. Direct calorimetry is more expensive and can be difficult to perform. It measures the amount of heat that an individual releases inside an isolated chamber (calorimeter). Indirect calorimetry measures the amount of energy spent from the amount of gas exchange inside a known period of time. SDA is calculated from a sum of spent O2 or produced CO2, above the baseline and converted into energy (calories, Watt, Jull). Most common measured parameters are SMR or BMR, peak metabolism, factorial scope, response duration time, SDA and SDA coefficient. A lot of factors influence SDA, but the most important are meal composition, meal tipe, meal size, meal temperature, body size, body composition, sex, age, ambient temperature, gas concentrations and salinity. Except these factors there are others that influence SDA, and those are preabsorptive and postabsorptive processes. Preabsorptive processes are eating, swallowing, gastric breakdown, intestinal peristalsis and absorption. Postabsorptive processes are substrate catabolism and biosynthesis of body constituents. Today we have a lot of published papers about thermogenic effect of food, but there is still a lot that is insufficiently explored and there are many different opinions among scientists as to what factors influence SDA the most and do these factors have any impact whatsoever on metabolic rates. |
