Feeding a fat-containing diet to the exercising horse is a facile way to increase energy density without risking the complications associated with hydrolyzable carbohydrates. Fat adaptation may also result in increases in the utilization of free fatty acids for fuel during exercise and sparing of muscle glycogen. Phosphatidylcholine, the main component of lecithins, can influence muscle contraction and improve endurance capacity during exercise. When it is combined with corn oil in a total mixed ration, soy lecithin is both highly digestible and palatable to horses. Our objectives in this study were to compare the effects of incremental exercise and isocaloric control (CON), corn oil (CO), and a soy lecithin/corn oil (LE) diets on plasma free fatty acids (FFA), cholesterol, glycerol, triglyceride (TG), lactate, and glucose. Also three different statistical models were compared for goodness of fit to the lactate curve. Plasma lactate and glucose both increased slowly early in the incremental exercise test (IET), then increased rapidly as the work intensity increased. Both decreased during recovery. No effects of IET or diet were found for either of these variables. Plasma TG was unchanged during exercise, but increased rapidly during recovery. Plasma FFA decreased from resting early in the IET then remained steady throughout the remainder of exercise. During recovery a rapid increase was exhibited. Plasma glycerol was constant during exercise, but increased during recovery. Plasma cholesterol did not change during exercise or recovery. Diet affected plasma FFA. Plasma FFA were lower for the CO and LE diets than the CON diet during the IET. Plasma glycerol was lower for the CO diet than the CON diet during the IET, with the LE diet intermediate between the two. Plasma cholesterol was higher for the CO and LE diets than the CON diet during the IET. A segmented model and an exponential model were found to have a good fit to the lactate curve. A point of inflection for a rapid increase in plasma lactate during incremental exercise was discovered. When this model was applied to diet, no differences in lactate threshold were found between the diets. Some criteria for fat adaptation were met, namely diet affected plasma FFA, glycerol, and cholesterol. However diet did not affect plasma TG, lactate, or glucose. This indicates that the rate of fatty acid oxidation was increased following fat adaptation, but it did not affect the rate of glucose oxidation and glycolysis during exercise. A lactate threshold for the equine can be obtained using a broken line model. Further studies using this approach are needed to establish its correlation with performance. / Master of Science

Syfte och frågeställningar Syftet med denna litteraturstudie är att undersöka om det finns stöd i nuvarande forskning för att en fettrik kost är mer effektiv som nutritionsstrategi vid uthållighetsprestationer jämfört med en kolhydratrik kost. Studiens frågeställningar är: Förbättras uthållighetsprestationen av en fettrik kost jämfört med en kolhydratrik kost? Hur påverkas kolhydrat- och fettmetabolismen av en högfett- och lågkolhydratkost? Metod Litteratursökningen genomfördes i databaserna Ebsco, Pubmed och Cinahl. Totalt inkluderades 16 artiklar, 11 artiklar från litteratursökningen i databaserna och 5 artiklar från valda referenslistor. Studierna kvalitetsgranskades med hjälp av SBU:s granskningsmall för randomiserade kontrollerade studier. Resultat I 3 av 16 studier förbättrades uthållighetprestationen vid intag av högfett- och lågkolhydratkost, i 4 av 16 studier försämrades prestationen och i resterande 9 studier sågs ingen signifikant skillnad i prestationen mellan kostinterventionerna. Majoriteten av studierna fick en förhöjd fettoxidation som resultat av en högfett- och lågkolhydratkost men ingen signifikant skillnad gällande blodglukos-, blodinsulin- eller blodlaktatvärde mellan kostinterventionerna. Slutsats Trots en förhöjd fettoxidation och välfyllda glykogenlager finns inte tillräcklig evidens för att påvisa en generell prestationshöjning vid uthållighetsprestationer av en högfettkost jämfört med en högkolhydratkost. Detta troligtvis på grund av nedsatt förmåga hos musklerna att använda glykogen. Resultaten från de studier som ingick i denna systematiska litteraturstudie visar konsekvent en försämrad prestation efter intag av högfett- och lågkolhydratkost vid arbetsintensiteter över 80% av VO2max. Vid arbetsintensiteter omkring 60-70% av VO2max kan prestationen eventuellt förbättras efter intag av högfettkost bestående av 60-70% fett och mindre än 15% kolhydrater. / Aim The purpose of this study is to investigate whether there is scientific evidence that a high fat diet is more effective as a nutrition strategy for endurance performance than a high carbohydrate diet is. The objectives of the study are: Does endurance performance improve by a high fat diet compared by a high carbohydrate diet? How is the metabolism of fat and carbohydrate affected by a high fat and low carbohydrate diet? Method The literature search was conducted in the databases Ebsco, Pubmed and Cinahl. A total of 16 studies was included, 11 studies from the literature search and 5 studies from selected reference lists. The studies quality was audited by SBU: s questionnaire for randomized controlled studies. Results Endurance performance was enhanced after ingesting a high fat- and low carbohydrate diet in 3 of 16 studies and was decreased in 4 of 16 studies. In the remaining 9 studies there was no significant difference in performance between the two trials. A high fat- and low carbohydrate diet resulted in an increased fat oxidation in the majority of the studies but there was no significant difference in bloodglucose-, blodinsulin- or blodlactatelevels between the two trials. Conclusions Despite increased fat oxidation and well-filled glycogen levels there is not sufficient evidence to prove that endurance performance will be enhanced by a high fat diet compared to a high carbohydrate diet. This is probably because of a lower ability of the muscles to use glycogen. The results from this systematic review consequently shows a decreased performance after a high fat- and low carbohydrate diet at work intensities over 80% of VO2max. At intensities around 60-70% of VO2max, the performance can possibly be enhanced after a high fat diet consisting 60-70% of fat and 15% or lower of carbohydrate.