Ammonia smelling sweat - is it a useful indicator?

It probably means you are not fueling/hydrating properly while training. If you are training to lose weight once you define your daily calorie needs based on BMR, activities, etc and set a lower goal so you are on deficit, then shoot for that but make sure to fuel properly when training.

During sessions is not a good time to limit your calorie intake and for sure hydrate properly, after training you can consume a bit less of the grams of carbs you would normaly consume to recover faster, that will help you lose some weight without jeopirdizing the quality of your training.

First off, congratulations on deciding to get healthier.

You use muscles to make your self go (exercise) not fat.  What you are doing is exhausting your muscles.  For an overweight and out of shape person, that can come rather quick at first.

To lose weight or in other words, get your energy from your stored fat is to have a deficit in calories eat to the caloric needs of your daily activities.  You also do not want to exceed a 1000 calorie deficit.

***Dumb question alert----- So when I workout I am not burning the fat stores per se, Im burning the fuel in my system and then muscle because it is easier to get to than the fat? 

I will starting fueling better before the workout and that will solve the problem, thanks for providing the additional information guidance, much appreciated.

You aren't "burning muscle" in the sense that you are losing your muscle. You are burning the glycogen that is stored there. It's stored there so it's available for exercise. So burning it is part of the process. Then, over time (usually overnight), your body replaces the glycogen so you can do it again and that's when you burn the fat. (If you are operating at a calorie deficit, of course.)When I was losing weight, I sometimes got that ammonia smell and it usually meant I wasn't hydrating well enough. I increased my fluid intake, both during the day and during exercise, and the smell went away.It can be a lack of carbs too but, in my case, the carbs weren't the issue. Hydration was.

I notice this same smell about 30% of the time after a hard run.  Biking and swimming do not seem to contribute to this condition.

I have had this ammonia smell as well on several occaisions when I was exercising for long periods of time...marathon runs, and long bike rides over 100 miles. I have been searching the web trying to find answers. In the instances when I smelled the ammonia smell it was very hot and I was likely under hydrated. There is some stuff on the web speaking of ammonia build up in the blood due to the breakdown of proteins and I believe this is triggered by low blood glucose.....although I am not sure about this. I am very curious about this also.

How weird! I always get that smell when I do long runs outside and never at any other time. I noticed it, but never gave it any more thought.

I can't believe it actually means something.....

The ammonia smell is coming from waste products being excreted from sweat glands rather than getting filtered through the kidneys.  You might need to be better hydrated (which is easier on the bike; and obviously in the swim the waste gets washed right off).

As for burning fat or muscle, like someone posted above, your body "burns" the glycogen first.  It uses the muscles to the point of exhaustion.  You don't really catabolize the muscle except as a last resort.  Carbohydrates in the diet restock the glycogen, and simple carbs provide ready "fuel" for burning in the bloodstream (which is why you "crash" a couple hours after eating them, even without engaging in exercise). It takes a little while for your body to convert the fat into glucose and other more readily available forms of sugars for use.  That's why "fat burning" HR is lower - you are really just managing the exercise at a level that is sustainable for a longer period of time, allowing this shift to occur.

The clue that your body is in a catabolic state is a fruity smell to your breath (from being in a ketotic state).

Your body will burn muscle glycogen first, then turn to fat conversion. Anything over approximately 45 seconds, and your body is using aerobic pathways to get power. Those aerobic pathways use methods such as glycogen release from storage in the liver, fat breakdown, recycling waste products, etc. to provide the muscles with fuel.

You will NOT "burn muscle" unless you get to a severe starvation kind of situation, and if you are that far gone, you're either stranded in the desert or about to be hospitalized.

The "burning muscle" myth comes from people that have a misunderstanding of physiology. Someone lifts a ton, gets really large muscles, but a lot of fat covering it. They lay off the lifting, start increasing endurance, and they lose the fat, but they also lose muscle mass. The muscle mass loss is only because you are not stressing the muscles in the same way, so they change size/shape to adapt to the new activity.

Just remember, it's a very simple calculation. If calories out > calories in, you will lose weight. At first, it'll be easy, once you start plateauing, then it's time to start tracking. You want to aim for around 2-500 calorie deficit per day, that'll give you about 1, maybe 2 lbs a week of sustainable weight loss.

John