Athletes from an array of sports and military personnel often desire weight gain, ideally as lean body mass (LBM), to improve performance in sport or military operations. These athletic individuals are commonly encouraged to increase energy intake by ~500 kcal/day with an emphasis on adequate protein and carbohydrate (CHO) and judicious inclusion of healthy fat-containing energy-dense foods (including nuts/nut butters), along with rigorous resistance training (RT). These guidelines target gains of ~0.23 kg/wk (0.5 lb/wk). However, little is known about the efficacy of such regimens, particularly in female athletes. Purpose: 1) to evaluate the outcomes of a 10-wk diet and exercise regimen designed to promote healthy weight gain with excess energy from protein- or CHO-dominant foods, 2) to determine the predictors of weight gain under these conditions, and 3) to survey the methods that athletes currently use to achieve weight gain for athletic purposes. Methods: Two projects included 19 male and 13 female athletes (from a variety of athletic backgrounds with previous RT experience; mean age 25±6 years) who were randomly assigned to receive 500 additional kcal/day above weight maintenance diet through provision of either peanut-based whole foods/snacks (PNT group) or a similar, high-CHO, peanut-free snack (CHO group) along with a supervised RT regimen (60 to 120 min, 3 day/wk targeting major muscle groups). Body composition (via dual-energy x-ray absorptiometry), basic anthropometric measurements, resting metabolic rate, hormonal profile, muscular strength, aerobic fitness (VO2max), and food intake records were assessed at baseline (BSL) and post-intervention with some measurements also assessed at weeks 3 and 7. Predictors of weight gain were determined following the intervention. A third project included an online survey with targeted questions regarding athletes' habits for promoting weight gain. Results: 1) Total body mass (TBM) increased 2.2±1.3 kg with 1.5±1.1 kg as LBM after week 10. The PNT group (n=16; 10 men, 6 women) gained less TBM than the CHO group (n=16; 9 men, 7 women) (1.6±1.1 kg vs 2.7±1.2 kg, respectively, P=0.007) with no differences in LBM (1.2±1.1 kg vs 1.9±1.0 kg, P=0.136). 2) 15 (47% women) of 32 participants gained at least 2.27 kg after 10 weeks with 70% as LBM. Over time, from linear mixed effects models, increased free thyroxine (T4) and increased blood urea nitrogen concentration (as a marker of protein intake) predicted TBM and LBM gains. From general linear models, the CHO energy surplus was a significant predictor of TBM and LBM gains, while the female sex alone was significant for LBM gains at study completion. 3) 168 athletic participants (mean age 24±5 years; 29% female, 71% male) completed the survey and were actively attempting or had attempted weight gain in the last 12 months to gain muscle mass (87.5%), for aesthetic reasons (66.1%), or to improve athletic performance (63.7%). The most prevalent dietary strategies reported to help promote weight gain were consuming more energy than usual (88.0%) from mainly protein foods (83.9%) and using protein powders (67.3). 9.6% of participants reported using anabolic hormones. The main exercise change was increased RT (81.5%). Conclusions: 1) These results suggest that the addition of 500 kcal/day from whole foods/snacks in combination with a rigorous RT program promotes a similar weight gain of ~0.22 kg/week, primarily as LBM, over 10 weeks in both male and female athletes. However, snack macronutrient content may impact the effectiveness of this regimen. 2) Factors that predict ability to gain body weight as expected under these circumstances are incorporating a CHO-dominant energy surplus, consuming overall adequate protein (~1.6 g/kg/day), and free T4 status. Furthermore, athletic women are able to gain LBM as effectively as athletic men. 3) Results confirm that both male and female athletic individuals intentionally attempt to gain weight. Nutrition and exercise professionals may use the findings to be aware of these common dietary and exercise strategies and to better educate their athletic clients on appropriate methods that are evidence-based and not detrimental to health. / Doctor of Philosophy / Athletes from different sports, including military members, often want to gain weight, mainly as muscle, to improve their athletic performance (for example, strength and power) or to match the opposing team's size. Current sports nutrition recommendations include eating ~500 kcal more each day from carbohydrate (CHO), protein, and healthy fats in combination with hard weightlifting. These recommendations support a slow weight gain of about 0.5 lb to 1 lb per week, which should mostly be muscle. However, these recommendations have not been well studied, particularly in female athletes. Purpose: 1) to study purposeful overfeeding with weightlifting for 10 weeks to promote healthy weight gain with extra calories from either high-protein or high-CHO foods, 2) to figure out what factors are responsible for healthy weight gain under these conditions, and 3) to survey the methods that athletes currently use to achieve weight gain for athletic purposes. Methods: Two projects included 19 male and 13 female athletes (from a variety of athletic backgrounds with previous weightlifting experience; mean age 25±6 years) who overate 500 additional kcal/day from either peanut-based whole foods/snacks (PNT group) or a similar, high-CHO, peanut-free snack (CHO group) along with a supervised weightlifting regimen (60 to 120 min, 3 day/wk targeting major muscle groups). Body composition, metabolism, blood analyses, muscular strength, cardio fitness, and food intake records were done at the beginning and end with some measurements also done at weeks 3 and 7. Predictors of weight gain were studied later. A third project included an online survey with questions about athletes' habits for promoting weight gain. Results: 1) In all 32 participants, weight increased 4.8 lb (3.3 lb as muscle) after week 10. The PNT group (n=16; 10 men, 6 women) gained less weight than the CHO group (n=16; 9 men, 7 women) (3.5 lb vs 5.9 lb, respectively) with no differences in muscle (2.6 lb vs 4.2 lb). 2) An increased thyroid hormone (thyroxine) and increased blood urea nitrogen (as a marker of protein intake) predicted overall weight and muscle gains. From the beginning of the study, the CHO energy surplus was a significant predictor of weight and muscle gains, while the female sex alone was significant for muscle gains by the end of the study. 3) 168 athletic participants (mean age 24±5 years; 29% female, 71% male) completed the survey and were actively attempting or had attempted weight gain in the last 12 months to gain muscle (87.5%), to look better (66.1%), or to improve athletic performance (63.7%). The main dietary ways reported to help promote weight gain were eating more than usual (88.0%) from mainly protein-rich foods (83.9%) and using protein powders (67.3%). 9.6% of participants reported using anabolic hormones. The main exercise change was increased weightlifting (81.5%). Conclusions: 1) These results suggest that an extra 500 kcal/day from whole foods/snacks in combination with hard weightlifting promotes a similar weight gain of ~0.5 lb/week, mainly as muscle, over 10 weeks in both male and female athletes. 2) What affects healthy weight gain may be eating a CHO-dominant energy surplus, eating enough protein in general, and thyroid status. Furthermore, athletic women are able to gain muscle as effectively as athletic men. 3) Results confirm that both male and female athletic individuals try to gain weight. Nutrition and exercise experts may use these findings to be aware of these common nutrition and exercise strategies and to better educate their athletic clients on appropriate methods that are based on scientific experiments and not bad for health.

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Nous avons étudié les mécanismes adaptatifs induits par une surnutrition hyperlipidique (+757 kcal/j) de 56 jours sur le métabolisme énergétique et le muscle squelettique chez des sujets sains. En parallèle, nous avons étudié les mécanismes adaptatifs induits par une surnutrition en fructose de 7 jours sur le métabolisme énergétique et le muscle squelettique chez des sujets apparentés diabétiques de type 2 et nous avons réalisé des études in vitro sur myotubes humains afin d'identifier le médiateur contribuant aux effets du fructose. Ces deux surnutritions contribuent à augmenter le poids corporel. Ces modifications sont accompagnées par l'oxydation préférentielle des glucides au détriment des lipides. La surnutrition hyperlipidique induit, au niveau musculaire, une diminution de l'expression de PDK4 qui pourrait être la conséquence de la diminution de la concentration en NAD+ associée à la baisse de l'activité de SIRT1 comme supportée par l'hyperacétylation de PGC1alpha. Bien que l'activation de la voie SIRT1/PGC1alpha semble réduite, la surnutrition hyperlipidique est associée à une augmentation de l'expression des gènes liés à la mitochondrie. La surnutrition riche en fructose induit quant à elle, au niveau musculaire, une baisse de l'expression de nombreux gènes liés à l'oxydation des lipides et à la mitochondrie comme CPT1 et MLYCD. Les études in vitro suggèrent que le fructose agit de manière indirecte sur le muscle squelettique. Ce travail de thèse met en lumière les conséquences d'une balance énergétique positive induite par la surconsommation de lipides ou de fructose sur le métabolisme énergétique et l'expression génique du muscle squelettique / We studied the effects of a high-fat overfeeding (+757 kcal/d) during 56 days on energy metabolism and skeletal muscle of healthy subjects. ln parallel, we studied the effects of high fructose overfeeding during 7 days on energy metabolism and skeletal muscle of first-degree relatives of type 2 diabetic patients and we performed in vitro studies with human myotubes to identify the mediator contributing to the fructose effects. High-fat and high-fructose overfeeding both contribute to increase body. These changes are associated with a preferential oxidation of carbohydrates instead of lipid. High-fat overfeeding induces in skeletal muscle, a decrease in PDK4 expression that could be the consequences of decreased NAD+ concentration associated with a decreased SlRT1 activity as supported by the hyperacetylation of PGC1alpha. Although this reduction of the SlRT1/PGC-1alpha pathway appears, the high-fat overfeeding is associated with increased mitochondrial gene expression. The high-fructose overfeeding induces in skeletal muscle a decrease in many genes expression related to lipid oxidation and mitochondria as CPT1 and MLYCD. ln vitro experiments suggest an indirect action of fructose in skeletal muscle. This thesis highlights the consequences of a positive energy balance induced by over- consumption of lipid or fructose, which we can find in the general population, on energy metabolism and skeletal muscle gene expression