I've been doing some long bike rides (50+ miles) on routes which include long (several miles) of low to moderate grades, or short distances of 3 to 8% grades. I've experience what smelled like ammonia or amines while exhaling through my nostrils, or while drinking and breathing heavily. I've been searching for information on the matter, but most often, the commentary is found on various sites related to health and fitness, and the respondents may not be licensed physicians, or folks with medical degrees. So, I'm looking for reliable sources on the subject. As far as I can tell, at some point, I'm metabolizing protein, whereby my body is converting protein to sugar. One response on a website indicated: I think this is probably correct, but I need to verify with reliable sources. Another respondent indicated ketones, e.g., acetone, but as I recall, there is a fruity smell to ketones, and the smell was more like ammonia, although it did have a metallic taste. Apparently folks on high protein, low carbohydrate diet can experience similar symptoms, and apparently the resolution is to increase the carbohydrates and reduce protein, although consuming whey protein after such exertion may be indicated. Catabolism refers to processes in which large molecules into smaller units to release energy, so that applies to breaking polysaccharides into simpler sugars, or proteins into sugars, and so on. Gluconeogenesis is a metabolic pathway that results in the generation of glucose from non-carbohydrate compounds such as pyruvate, lactate, glycerol, and glucogenic amino acids. It is the metabolism of proteins rather than carbohydrates that is of particular interest to me. I clearly have to consume more carbohydrates or sugar before or during the ride. The other affect is that during heavy exertion, I've been told that the digestive process shuts down, so it would not be helpful to eat just before strenuously exercising. I would appreciate any articles in medical or sports medicine journals on the subject. My goal is to do 100+ mile rides, and preferably with an average speed above 15 mph. So far on my 50+ miles rides, I can do 15 mph or better, even with the hills.