What should be avoided for 12 hours prior to an oral glucose tolerance test?

For an oral glucose tolerance test (OGTT), avoiding caffeine and smoking for 12 hours prior to the test is crucial because both substances can affect metabolic processes and influence insulin sensitivity. Caffeine can stimulate the central nervous system, leading to increased heart rate and altered glucose metabolism, which may skew test results. Similarly, smoking has known effects on glucose levels and insulin response, potentially compromising the reliability of the test.

Other options, while important in different contexts, do not have the same level of impact on the results of the OGTT. For example, high carbohydrate foods can actually affect the glucose levels if consumed too close to the test but are typically not a primary concern for the 12-hour fast prior to the test. Alcohol can also interfere with glucose metabolism but it is more about its effects in combination with fasting and is less emphasized than caffeine and smoking. Exercise may impact transient glucose levels but individuals are generally encouraged to maintain their regular routine unless specified otherwise by a healthcare provider.

By avoiding caffeine and smoking, the integrity of the glucose levels measured during the test is more likely to reflect the individual's true glucose metabolism, leading to more accurate diagnosis and management of any potential glucose-related disorders.