I love spicy food. Many spices like garlic and onions affect the breath. In the digestive system the by-products of these spices are able to enter into the bloodstream. From there they enter the breath by being excreted from the lungs. This may actually be caused by the juices in the stomach.
Dieters also burn stored fat which gives off acetone.
These odors enter the breath via the lungs. Remember alcohol tends to dry out the oral tissues. Alcohol is also excreted into the breath via the lungs. Smoking encourages periodontal disease, decreases salivary flow and causes a tongue condition which can trap food debris and tobacco odor. It is also true that since most denture wearers are older their salivary flow seems to be less.