What is a mixed meal glucose tolerance test (MMTT)?

From the Guidelines

A mixed meal glucose tolerance test (MMTT) is not explicitly defined in the provided evidence, but based on general medical knowledge, it is a diagnostic procedure used to assess insulin secretion and glucose metabolism. To perform this test, the patient typically consumes a standardized meal containing carbohydrates, proteins, and fats, after which blood glucose and insulin levels are measured at specific intervals.

• The test is used to evaluate glucose handling and insulin secretory capacity in various conditions, such as diabetes, pancreatitis, or after bariatric surgery.
• The test provides a more physiological assessment of glucose metabolism than the standard glucose tolerance test because it includes multiple nutrients that trigger various metabolic pathways and incretin responses.
• Patients should fast for 8-12 hours before the test and avoid medications that affect glucose metabolism on the test day unless specifically instructed otherwise, as certain medications, such as glucocorticoids, thiazide diuretics, and atypical antipsychotics, may increase the risk for diabetes 1.
• The test is generally well-tolerated but may cause nausea in some patients.
• Glycemic control is assessed by patient self-monitoring of blood glucose (SMBG) and hemoglobin A1c (HbA1c) levels, and the MMTT can be a useful adjunct to SMBG in selected patients on intensive insulin regimens 1.

From the Research

Definition and Purpose of Mixed Meal Glucose Tolerance Test (MMTT)

• A mixed meal glucose tolerance test (MMTT) is a test used to evaluate the body's ability to regulate blood glucose levels after consuming a meal that contains a mix of carbohydrates, proteins, and fats 2, 3, 4, 5, 6.
• The test is used to assess insulin secretion and glucose metabolism in individuals with diabetes or those at risk of developing diabetes 2, 3, 4, 5, 6.

Comparison with Oral Glucose Tolerance Test (OGTT)

• The MMTT is often compared to the oral glucose tolerance test (OGTT), which involves consuming a sugary drink to assess glucose metabolism 2, 3, 6.
• Studies have shown that the MMTT may be a more physiological test than the OGTT, as it reflects real-life eating habits and provides a more complete nutrient challenge 2, 3.
• The MMTT has been found to induce a greater insulin response than the OGTT in some studies, particularly in models of insulin resistance 3.

Reproducibility and Determinants of MMTT Responses

• The reproducibility of MMTT responses has been found to vary depending on factors such as glucose status, time, and subtraction of fasting values 5.
• Insulin secretion and action have been found to explain approximately 20% of MMTT responses, highlighting the complexity of glucose metabolism 5.

Clinical Applications and Limitations

• The MMTT has been used to assess endogenous insulin secretion and glucose metabolism in individuals with diabetes or those at risk of developing diabetes 2, 3, 4, 5, 6.
• However, the test has limitations, including the need for insulin omission prior to the test, which can result in marked hyperglycemia 4.
• Fasting serum C-peptide has been proposed as a practical alternative to the MMTT in insulin-treated patients, with a high correlation between fasting C-peptide and 90-min serum C-peptide during the test 4.