A Mixed Meal Tolerance Test for Clinical Trials

The Mixed Meal Tolerance Test (MMTT) evaluates how well the beta cells, which are produced in the pancreas and produce insulin, are functioning. It involves drinking a liquid meal replacement containing protein, carbohydrates, and fat, after which blood samples are drawn every 30 minutes for two hours. The samples are sent to a lab for evaluation.

The MMTT is regarded as the gold standard of beta cell reserve function, but healthcare providers rarely use it as part of diabetes care because it's time-consuming and invasive. Instead, the MMTT is used most often as a measurement tool in research settings, such as clinical research trials. When the MMTT is used in clinical settings, it is most often performed on people who have type 1 diabetes.

the beverage causes blood sugar to rise and, as a result, the pancreas releases just enough insulin to normalize blood sugar.

Close up nurse demonstrating insulin pen on finger
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The primary reason a healthcare provider would order an MMTT for someone with diabetes is to determine how effectively their pancreas can produce insulin—a hormone that normalizes blood sugar levels after food is eaten. Test results can show whether the pancreas is under-producing insulin, over-producing insulin, or not producing insulin at all

Again, the MMTT is largely reserved for clinical trials, but there are some circumstances in which it might be used in a clinical setting:

  • For a very young child who has been diagnosed with type 1 diabetes to determine how much insulin their pancreas is still making.
  • For a person who does not have diabetes but who experiences low blood sugar two-to-three hours after eating, a medical condition called reactive hypoglycemia. The MMTT can determine if the person's pancrease is releasing excess insulin in response to food.
  • For someone who has episodes of post-meal hypoglycemia after having gastric bypass surgery.
  • For a person with a suspected insulinoma (a tumor of the pancreas) who has recurrent episodes of hypoglycemia.

When used in a clinical trial, the MMTT can provide a comprehensive physiological stimulus to insulin since the beta cells of the pancreas are responsive to certain amino acids and fatty acids in addition to glucose. For example, research trials may use MMTT tests in drug development, assessing the effectiveness of certain types of therapies such as insulin pumps, glucagon-like peptide (GLP-1) agonists, and continuous glucose monitors.

What to Expect Before the Test

Before an MMTT test, you will be required to fast for at least eight house beforehand. This means ingesting nothing besides water. Even a breath mint or chewing gum that contains sugar can throw off the results. If you accidentally eat, drink, or chew anything besides water, you'll need to reschedule the test.

You also may be asked to limit strenuous exercise, alcohol, caffeine, and tobacco use the day before the test as these activities may influence insulin sensitivity.

Plan to wear comfortable clothing, as you'll be sitting in one place for a couple of hours. For much of that time you'll be free to do whatever you like, so you may want to bring along something to read, needlework, or your laptop.

If your child is the one having the test and seems anxious about it, they can bring a special blanket, stuffed toy, or other comfort object with them, as well as plenty of portable activities to keep them occupied.

What to Expect During the Test

Set aside several hours for an MMTT. The test itself typically takes a minimum of two hours and there is some preparation involved as well. To make sure you clear enough time on your calendar, ask your healthcare provider to confirm how long you'll need to be at the test.

There are multiple steps involved in an MMTT:

  • When you arrive for your appointment, there may be some paperwork to complete, after which a nurse will measure your height and weigh you.
  • Next, you'll be escorted to a room where an intravenous (IV) catheter will be placed. It will be used to draw blood samples. Having an IV needle inserted can be briefly unpleasant—for example, you may feel a pinch is it goes in—but once it's in place there should be no pain or other discomfort.
  • With the IV in place, you'll drink a liquid meal beverage. This beverage tastes similar to a milkshake and comes in a variety of flavors.
  • Afterwards, blood will be drawn from the IV every 30 minutes over the course of two hours.
  • While you're waiting, you may read, work on your laptop, phone, or tablet, watch television, or simply relax or nap.

It may be interesting to note that there has been some research to determine the efficacy of shortening the MMTT test to 90 minutes and to limit the number of blood draws to one.

What to Expect After the Test

After the test, the blood samples will be sent to a lab. It will likely take a few weeks before the results are in; your healthcare provider will notify you when that happens.

You should not experience any side effects after having an MMTT. After the IV needle is withdrawn, a bandage will be placed over the area, which you can remove whenever you'd like. Sometimes after an IV there is slight bruising.

You can break your fast and eat or drink whatever you'd like.

Different From the Oral Glucose Tolerance Test

You may be wondering—is the MMTT the same as the Oral Glucose Tolerance Test (OGTT)? These tests have similarities, but if you've had the OGTT in the past you know they're not exactly the same.

The OGTT is a good indicator of glucose tolerance and is used in conjunction with other tests, such as Fasting Blood Glucose (FBG) and Hemoglobin A1C to diagnose prediabetes, diabetes, and to screen for gestational diabetes.

Similarly to the MMTT, you must take this test when fasting for at least eight hours. However, as opposed to drinking a mixed meal, during an OGTT a person is asked to ingest a glucose load only, equivalent to 75 grams of glucose (sugar) dissolved in water.

The results of the OGTT can help clinicians determine impaired fasting glucose (IFG) and impaired glucose intolerance (IGT). IFG and IGT cannot be diagnosed using the MMTT since the latter provides a non-standardized oral glucose challenge.

Not Used to Diagnose Type 1 Diabetes

The MMTT can assist in detecting the earliest stages of glucose intolerance, but it is not used to diagnose type 1 diabetes. Instead, in symptomatic patients, the American Diabetes Association recommends that blood glucose should be used to diagnose the acute onset of type 1 diabetes. In conjunction, a c-peptide test or autoantibodies test (both are blood tests) can confirm a diagnosis of type 1 diabetes.

Screening for Type 1 Diabetes Can Determine Diabetes Risk

Type 1 diabetes typically is not diagnosed until the disease has progressed. With advances in medicine, we now have the ability to screen for type 1 diabetes in the setting of a research trial, in first-degree family members, or a proband with type 1 diabetes. The screening consists of testing for a panel of autoantibodies. In diabetes, it is these autoantibodies, that indicate the activation of the body's attack on insulin-producing beta cells in the pancreas, thus eventually causing the beta cells to die. The American Diabetes Association states the following:

"[It] is now clear from studies of first-degree relatives of patients with type 1 diabetes that the persistent presence of two or more autoantibodies is an almost certain predictor of clinical hyperglycemia and diabetes. The rate of progression is dependent on the age at first detection of antibody, number of antibodies, antibody specificity, and antibody titer." (Titer is the concentration of antibodies found in blood.)

Using autoantibodies to help determine diabetes risk can reduce the rate of diabetic ketoacidosis, assist researchers in designing prevention studies, potentially delay disease progression, and help people understand and better prepare for the disease.

It's important to note that just because you have autoantibodies doesn't necessarily mean you have full-blown insulin-dependent type 1 diabetes; rather it may mean that the chances of you developing it are increased. If you'd like more information on the staging process you can access the American Diabetes Standards of Care.

A Word From Verywell

Remember, also, that this test is not used to diagnose any type of diabetes. And as always, if you suspect you or someone you love may have diabetes because of suspicious symptoms, such as increased thirst, increased urination, fatigue, excessive hunger, weight loss, etc. contact your healthcare team right away.

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6 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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