Sometimes, diabetes can be a cause of body odor. When untreated, this disease can cause a condition called diabetic ketoacidosis. Without enough insulin to regulate the metabolism, the body starts to break down fat for fuel. This causes a sickeningly sweet aroma comparable to decomposing apples. It's most obvious on a person's breath, but it's also given off by the body as well [source: Liddell].
That's why when a patient seeks treatment for body odor, physicians may order blood or urine tests to determine if there is an underlying medical condition such as diabetes [source: Mayo Clinic].