Understanding The Glycemic Index And Glycemic Load And Their Practical Applications

We have introduced the study of synthesis pathways using two experiments: 1-the determination of the glycemic index (GI) of some foods and the effects of fiber and fat on the GI; 2-the determination of blood glucose levels after the ingestion of meals with high and low glycemic loads (GL). After a practice assembly, when the foods and meals that were eaten by the students were tallied, the students were divided into groups. At the next class, three members of each group, who had fasted for 8 hr, ingested 50 g of carbohydrate in food or a meal. After ingestion, the blood glucose was measured with a portable device every 30 min for a period of 2 hr. Discussion of the data obtained in experiment 1 allowed the students to understand the mechanism of action of insulin and to understand how the GI, as presented in the literature, is determined. The students also concluded that the addition of fiber to food reduces the glycemic response even with high GI foods, and these results could be a useful strategy for diet prescription. Discussion of experiment 2 allowed the students to understand that the amount of food intake is a determining factor for the glycemic response and subsequent release of insulin. These experimental observations allowed the students to transfer theoretical knowledge to their daily lives very easily. The students approved the classes and felt encouraged to study the synthesis pathways and metabolic integration in the fed state. © 2009 by The International Union of Biochemistry and Molecular Biology.375296300Jenkins, D.J., Wolever, T.M., Taylor, R.H., Barker, H., Fielden, H., Baldwin, J.M., Bowling, A.C., Goff, D.V., Glycemic index of foods: A physiological basis for carbohydrate exchange (1981) Am. J. Clin. Nutr., 34, pp. 362-366Wolever, T.M., Jenkins, D.J., Jenkins, A.L., Josse, R.G., The glycemic index: Methodology and clinical implications (1991) Am. J. Clin. Nutr., 54, pp. 846-854Ostman, E.M., Liljeberg Elmstahl, H.G.M., Inconsistency between glycemic index and insulinemic responses to regular and fermented milk products (2001) Am. J. Clin. Nutr., 74, pp. 96-100Salmeron, J., Manson, J.E., Stampfer, M.J., Colditz, G.A., Wing, A.L., Willett, W.C., Dietary fiber, glycemic load, and risk of non-insulindependent diabetes mellitus in women (1997) JAMA, 277, pp. 472-477(2006) Tabela brasileira de composic ̧a ̃o de alimentos, T113 Versa ̃o II, p. 113. , NEPA-UNICAMP, 2nd ed., NEPA-UNICAMP, Campinas, SPFoster-Powell, K., Holt, S.H.A., Brand-Miller, J.C., International table of glycemic index and glycemic loadvalues: 2002 (2002) Am. J. Clin. Nutr., 76, pp. 5-56Stevenson, E., Williams, C., Biscoe, H., The metabolic responses to high carbohydrate meals with different glycemic indices consumed during recovery from prolonged strenuous (2005) Exerc. Int. J. Sp. Nutr. Exerc. Metab., 15, pp. 291-307Wallis, G.A., Dawson, R., Achten, J., Webber, J., Jeukendrup, A.J., Metabolic response to carbohydrate ingestion during exercise in males and females (2006) Am. J. Physiol. Endocrinol. Metab., 290, pp. E708-E715Tsintzas, K., Williams, C., Human muscle glycogen metabolism during exercise: Effect of carbohydrate supplementation (1998) Sports Med, 25, pp. 7-23Sacks, F.A., Bray, G.A., Carey, V.J., Smith, S.R., Steven, D.H., Anton, S., McManus, K., Williamson, D.A., Comparison of weight-loss diets with different compositions of fat, protein and carbohydrates (2009) N. Engl. J. Med., 360, pp. 859-873(2004) Report of a Join FAO/WHO Expert Consulation. Diet, nutrition and prevention of chronic disease, 916, pp. 1-333. , World Health Organization, World Health Organization, GenevaRiccardi, G., Rivellese, A.A., Giacco, R., Role of glycemic index and glycemic load in the healthy state, in prediabetes, and in diabetes (2008) Am. J. Clin. Nutr., 87, pp. 269S-274SVolp, A.C.P., Alfenas, R.C.G., Glycemic index, glycemic load and cardiovascular diseases (2006) Rev. Bras. Nutr. Clin., 21, pp. 302-30

Lactate production retards, not causes, acidosis: a practical approach for physical education students.

The content of numerous  textbooks  of exercise physiology, biochemistry and even many papers  in the current  literature explain  acidosis  during  intense  exercise by the  production of lactic  acid,  causing the  release  of a proton  with  lactate as the  final product.   However,  lactate  production retards not cause acidosis.  To understand better the importance of training schedules features  and to do a correct interpretation of blood lactate measurements during different kinds of exercise, the goal of this work is to present a practical  approach  carried out with physical education  students that allows the discussion of these concepts with real datas,  breaking  the myth  involving this subject.  Firstly,  the students were conduct to plan different exercise protocols  (continuous versus intermittent) where the average speed and blood lactate were measured.  After the exercise protocols done, the students did some correlation among blood lactate, fatigue index and performance  datas.  The results  show that there  is not a clear relationship between blood lactate and fatigue, independently of exercise type that is being considered. By this way, it is possible to build with the students a new view of this polemic subject (blood lactate and fatigue) through  a simple practical  approach, helping the students to understand better metabolic aspects  involved with physical exercises

Lactate production retards, not causes, acidosis: a theoretical approach for physical education students.

The  widespread  belief that intense  exercise causes the  production  of lactic  acid that contributes to acidose is erroneous.  This belief, carried  out by physical  education  and other  professionals,  interferes on methods of training and raise the opinion that muscle lactate is the vilain of exercise fatigue.  For a theorical  approach  we show a structural illustration of all the glycolysis reactions  with enphasis  to phosphoglycerate kinase reaction  wich envolves a simple phosphate transfer  from the  first carbon  of1,3 bisphosphoglycerate to  ADP,  forming  ATP.  The  carboxyl  group  of 3 phosphoglycerate remains unprotonated for the remaining  intermediates of glycolisis. From this biochemical fact it is impossible the production of acid lactic causing the release of a proton.  Actually,  glycolysis releases 2 protons  and lactate formation  consumes 2 protons.  After this biochemical explanation we present three  illustrated exercises situations: low intensity, anaerobic threshold  and high intensity exercise. From this point the students can understand that the protons  came mainly  from the ATP  hydrolysis  and when the ATP demand  for muscle contraction is met by mithocondrial respiration, there  is no proton  accumulation in the  cell as protons  are  used  by mithocondria to  maintain the  proton  gradient in the  intermem- branous  space.  When the ATP  hydrolysis exceeds mithocondria buffering capacity  and ATP  demand is supplied  by nonmithocondrial sources,  protons  increase  inside  the  cell causing  acidoses.   Lactate production  increases  under  these  cellular  conditions  to  prevent  pyruvate accumulation and  supply the  NAD+  for glycolysis.  Lactate also retards the acidoses by the  symport with protons  (from ATP hydrolysys  not  from lactate production) mediated  by Lactate Transporters (MCT).  Thus,  increased blood  lactate detection  is the  effect  not  the  cause  of acidosis.   The  students  must  understand that if muscles do not  produce  lactate, acidoses and fatigue  would accour faster,  impairing  high intensity exercise performance.  This information must be considered  in their  training schedules

Practical approach for the study of metabolic regulation

First year students in Physical Education must understand metabolic regulation to comprehend thewhole integration of biochemical pathways in attempt to establish the relation with exercise. Thiswhole view is not easy to learn and the task becomes even harder with the lack of time at theend of course, when normally the students think about metabolic integration. Trying to get thestudents attention to this important issue, we developed practical works beginning in the middle ofthe course, in parallel with theory classes. Blood and urine were collected for metabolite analysis ineach practice. The students were divided in groups (10 students) and they created the protocols in formthat they only have been guided and directed by the teacher and monitors. The practical activitiesand biochemical analysis were: six 30m sprints with dierent recovery times (blood lactate and meanvelocities), lactate removal from muscle to blood after high intensity exercise (blood lactate), anaerobicthreshold (blood lactate and heart rate), the eect of glycogen depletion after high and moderateintensity exercises (plasma glucose and urea concentrations) and low carbohydrate diet vs. normaldiet (plasma glucose and urine ketone bodies). After data collection, discussion and interpretation, thestudents presented orally each work in the same order above. Each presentation had the focus on themetabolic pathways involved in each practice. Group 1: phosphocreatine utilization and resynthesis.Group 2: anaerobic glycolysis, lactate production and removal. Group 3: transition between anaerobicglycolysis and oxidative metabolism. In attempt to promote the integration between muscle and liver-Group 4: protein catabolism after high intensity exercise with low muscular glycogen concentration(transamination, Cori Cycle and gluconeogenesis). Group 5: liver ketogenesis in low carbohydratediet. This sequence was intended to promote the comprehension of integrated metabolism. As a nalactivity, the students showed their results in the form of poster. All activities were part of disciplineevaluation. All students approved this practical approach

USING SUCROSE FOR THE GLUCOSE TOLERANCE TEST DETERMINATION IN BIOCHEMISTRY CLASSES

The development of enzymatic, portable, non-expensive kits for glucose dosage allowed this test to beconducted outside the laboratory. Besides, the increasing number of diabetic patients making use ofthese kits turn their prices quite aordable, nowadays. In a previous work we have reported the use ofglucose kits inside the classroom, for the Glucose Tolerance Tests determination, in association withaerobic exercises, as a starting point to teach metabolism (Alves, A.A. et al., Annals of the XXIXSBBq Meeting, 2000). That experience has been successfully employed in the last ve years withstudents from careers such as Biology, Physical Education, Nursing and Medicine, at Unicamp. Wenow extend those observations to the use of sucrose, instead of glucose, as the sugar given in overchargeat the beginning of the experiment (1.15 and 2.3 g/kg weight for glucose and sucrose, respectively).Portable reectance meters provided accurate enzymatic measurement of glucose with a drop of blood.Since the enzyme (glucose oxydase) is specic for glucose (and not for fructose, for instance), the plotsobtained after sucrose intake are very similar to those with glucose. The advantages in using sucroseare: it is cheaper than glucose and suitable for the use outside the lab (easy to nd) and it does notinduce the characteristic unsettled stomach/nausea caused by glucose. Besides, the use of sucrosedoes not invalidate the classical use of the test, since sucrose is cleaved by invertase (giving rise toglucose and fructose) in the duodenum, where glucose units can be absorbed, giving rise the bloodprole evaluated in the tolerance test

Building the glycolisis and Krebs cycle as a puzzle: a strategy to learning metabolic pathways.

First year physical  education  students must  understand metabolic  pathways to know how our body produces  energy  during  exercise  of different intensities and  rest.   However,  in a  first contact they usually complain about the difficulty to understand and visualize all the process such as the sequence of reactions,  the structure of the molecules and mainly what is changing in the molecule.  In an attempt to make easier the comprehension  of the metabolic  pathways we make a puzzle in a classroom where the  students have to build  the  glicolysis and  Krebs cycle through some clues given to guide them  to organize  the  sequence  of reactions.   For  this,  the  students were divided  in groups  of four and  each one received figures with  the  structural formula  of the  molecules and  their  names.  The  groups  that were changing  in the  structure were colored.  The  clues included  information such as the  compound that begins the pathway and its final product, number  and kind of enzymes involved, number  of ATPs produced,  reactions  with negative energy variation and number of compounds rich in energy produced. The students have no difficulty to visualize the structures or building these pathways. After that, they have some questions  to answer to see if they understand and learned the pathway. They reported that is easier  to  understand what  is changing  and  why,  making  the  comprehension  of what  is occurring during  exercise easier and have no difficulties to discuss and answer the questionnaire