Blood glucose levels normally rise after a high-carbohydrate meal and drop back to normal levels within a few hours. But if your glucose levels rise higher than normal and recover more slowly, you might have diabetes. Your doctor can administer tests that measure your blood glucose levels immediately before you consume a high-carbohydrate meal and for several hours afterward. If you already have diabetes, your doctor might want you to check your blood glucose levels after meals, to make sure you're keeping your glucose within the expected range.
Normal Levels After Eating
Healthy, non-diabetic people normally have blood glucose levels of less than 120 milligrams per deciliter two hours after a normal meal, rarely exceeding 140 mg/dL, according to the American Diabetes Association. Levels return to normal within two to three hours. When you undergo a glucose tolerance test, you consume a high-carbohydrate drink or snack containing 75 grams of carbohydrate.
At one hour, your test falls into the normal, non-diabetic range if your blood glucose remains below 200 mg/dL. Two hours after your meal, blood glucose should remain below 140 mg/dL.
A level of over 200 mg/dL at two hours post-prandial -- which means after a meal -- indicates diabetes. Levels between 140 and 200 mg/dL indicate pre-diabetes, a condition with a strong risk of developing diabetes in the future.
Expected Results in Diabetics
Diabetics experience larger spikes in blood glucose that take longer to return to baseline. For diabetics, blood glucose an hour after eating should remain below 180 mg/dL or no more than 80 mg/dL over your pre-meal levels. The highest spikes in blood glucose levels often occur after breakfast. If you experience hypoglycemia, or low blood glucose levels before a meal, you might experience a higher-than-normal spike over baseline levels; this doesn't necessarily indicate an abnormal rise.
Keeping Your Levels in Range
If you have diabetes, keeping your blood glucose within normal range after a high-carbohydrate meal can be difficult. The type of carbohydrates you choose can make a difference in your blood sugar. Complex carbohydrates, which must be broken down into simple sugars before your body can absorb them, slow the absorption process and help stabilize your blood sugars. The glycemic index defines carbohydrates by their absorption rate. Carbohydrates with a low glycemic index, less than 45, cause a slow steady rise in blood glucose. Whole grains such as oats, wheat, barley, brown rice and lesser known grains such as quinoa help keep your levels within range. Foods high in fiber, such as whole grains, fruits and vegetables, also slow digestion and help stabilize blood glucose after meals. Exercise can also help slow digestion and stabilize peaks in glucose.
Risks of High Readings
If you experience spikes in blood glucose after you eat high-carbohydrate meals, your levels will be higher than normal for as much as six to nine hours out of each day. High blood glucose damages blood vessels, which leads to complications such as diabetic retinopathy and neuropathy, or nerve damage. High blood glucose levels after meals also increases your risk of developing atherosclerosis, a build-up of plaque in the arteries that can cause heart attack or stroke.
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