What Is Postprandial Blood Sugar, And Why Is It Important?

Measurement of your blood glucose levels after a meal can provide unique insights into your metabolic health.

What is postprandial blood sugar? Postprandial blood sugar is a measurement of the glucose concentration in your bloodstream in the period up to four hours after eating a meal. Abnormally high glucose levels during this time interval, called postprandial hyperglycemia, represents one of the earliest abnormalities associated with type 2 diabetes (TD2) and is a hallmark of type 1 diabetes.

Controlling post-meal glucose surges is a critical element of the overall glycemic management undertaken with these individuals in order to prevent microvascular complications as well as cardiovascular disease (CVD). Therefore, these individuals with diabetes, and possibly even those either at risk for or currently diagnosed with prediabetes, might benefit from keener assessment of postprandial glucose (PPG) as a complement to analysis of other glucose parameters, as it might lead your medical team to propose new, individualized diet, exercise and medication management strategies to improve your health. 

Metabolic health and the glycemic control component 

According to a 2019 study, only 12% of American adults are considered metabolically healthy. In our report, What Is Metabolic Health?, we delved into the five markers — blood sugar, waist circumference, blood pressure, cholesterol and triglycerides — that doctors and scientists analyze to determine if you are metabolically “healthy” or not. If you’re outside of the healthy limits for any one of the five key markers, you are at higher risk for metabolic syndrome, which increases your chance of developing type 2 diabetes (T2D), heart disease, or stroke. Out of bounds on three or more of the five categories? Research has shown that your risk of developing these chronic diseases goes even higher. 

This report focuses on postprandial glucose, which is but one component, or biomarker, of glycemic health — the first of the five metabolic health markers.

Learn more about glycemic health:
What Is Glucose?
What Is Insulin Resistance?
Blood Sugar, Diabetes and Inflammation
The Link Between Blood Sugar and Diabetes
7 Simple Ways To Control Blood Sugar Spikes

Keep in mind that glycemic control — with postprandial glucose (PPG) being but one parameter of it — is just one part of the more complex metabolic equation that involves triglycerides, insulin, tissue inflammation and gut disturbances, as was aptly voiced in a 2020 clinical study.

Measuring glucose levels, and where the postprandial glucose interval fits in

If your healthcare provider thinks you may be at risk for or could have prediabetes or T2D, they will conduct an assessment of risk factors (which may be performed with an assessment tool, such as the ADA’s risk test, diabetes.org/socrisktest). The provider may then go on to perform certain tests, and some of these same tests are also used regularly if you’ve already received a diabetes diagnosis: 

  • The most common tool, historically, for measuring your blood glucose has been the fasting plasma glucose (FPG) test, key for determining threshold glucose levels. Typically, this blood test is performed after at least 8 hours of fasting. 

  • The hemoglobin A1c (HbA1c, or A1c for short) measures nonreversible glycosylation of the hemoglobin molecule (expressed as a percentage of total hemoglobin), which is directly related to blood glucose concentrations. This test is the gold standard for assessing glucose homeostasis as it reflects mean blood glucose values, both fasting and postprandial, during a 2- to 3-month period and can be used as a predictor of a patient’s risk of microvascular complications.

  • A glucose tolerance test measures how your body responds to a glucose-heavy drink after a night of fasting. Blood glucose levels are measured before drinking the glucose solution (fasting blood glucose level) and at hourly intervals after consuming the drink.

    • The oral glucose tolerance test (OGTT) is the gold standard for measuring postprandial glucose (PPG). In a medical setting, a person is required to drink an intensely flavored beverage that contains 75g of glucose. (The test is done after a period of fasting, so previous meals don’t influence results.) A blood sample is typically taken at 30 minutes, 1 hour, and 2 hours after eating and then plasma glucose is analyzed. A reading of <140 mg/dL after 2 hours indicates normal glucose response; over 140 mg/dL after 2 hours would indicate impaired glucose tolerance or prediabetes. Postprandial glucose values above 200 mg/dL meet the criteria for type 2 diabetes.

  • Continuous glucose monitoring (CGM) has emerged as a strategy to enhance glucose control in individuals diagnosed with diabetes, and research has also begun to emerge showing its promise in monitoring non-insulin-treated T2D individuals as well as those with prediabetes and potentially even healthy individuals. A CGM measures interstitial fluid (where your glucose moves after it has been through your blood vessels and capillaries) and is helpful when you want to understand a more detailed picture of what’s impacting (whether it be food or exercise or sleep) your blood glucose levels throughout the day and night.
  • A CGM can provide insights about postprandial glucose by measuring the “glucose area under the curve,” or AUC, which is considered an index of “whole glucose excursion after glucose loading.” Emerging research suggests that AUC provides a more complete look at PPG levels, and has been shown in some cases to be a more sensitive predictor of glucose tolerance and diabetes risk.
  • A random blood glucose test measures your blood glucose at any given time, without the need for fasting or drinking a glucose mixture.

  • Self-monitoring blood glucose (SMBG) involves the use of over-the-counter  glucometer devices that allow you to measure glucose at home via a small blood sample from a finger prick. 

Here are the 2022 testing guidelines (American Diabetes Association) for determining adult prediabetes or diabetes:

PrediabetesDiabetes
A1C 5.7–6.4% (39–47 mmol/mol)* ≥6.5% (48 mmol/mol) 
Fasting plasma glucose 100–125 mg/dL (5.6–6.9 mmol/L)* ≥126 mg/dL (7.0 mmol/L) 
2-hour plasma glucose during 75-g OGTT 140–199 mg/dL (7.8–11.0 mmol/L)* ≥200 mg/dL (11.1 mmol/L) 
Random plasma glucose — ≥200 mg/dL (11.1 mmol/L) 

Adapted from Tables 2.2 and 2.5 in the complete 2022 Standards of Care.
* For all three tests, risk is continuous, extending below the lower limit of the range and becoming disproportionately greater at the higher end of the range.
In the absence of unequivocal hyperglycemia, diagnosis requires two abnormal test results from the same sample or in two separate samples.
Only diagnostic in a patient with classic symptoms of hyperglycemia or hyperglycemic crisis.

The four most common glucose measurement times

Current guidelines recommend that patients with diabetes self-monitor their glucose at least three times per day, or four if they take insulin. (Historically, non-insulin-using T2D individuals typically self-monitored blood glucose only once/day, with glucose testing rotated at different times of the day over a 4-day period to get a broader picture of the glucose fluctuations over daytime. However, the advent of CGMs has paved the way for multiple relevant readings throughout the day and night, preprandial and postprandial included.)

These testing intervals are typically described as:

Fasted: This is your pre-breakfast glucose, when your body produces glucose through non-carbohydrate sources, such as lactate, through a process known as gluconeogenesis. 

Postprandial: This is the period 2-4 hours after eating or drinking, and if the goal is four glucose readings/day, one of these readings is usually taken mid-morning and another during the 2-hour post-lunch interval. At both times, complex carbohydrates and simple sugars are absorbed into the bloodstream and lead to an increase in blood glucose. Blood glucose begins rising within a few minutes of eating and tends to peak within 1-2 hours, but can stay partially elevated for as many as four hours.

Postabsorptive: This period occurs about four to eight hours after the postprandial period, when the liver breaks down glycogen (the stored form of glucose) to keep blood sugar levels relatively stable.

Postprandial blood sugar readings: Why they’ve gained favor

There are several, interrelated reasons why it is now believed that analyzing postprandial glucose (PPG) can confer important, additive medical insights. They all relate to the fact that what happens to your blood glucose after a meal gives you a vital glimpse into your metabolic health, and most people are predominantly in the postprandial state during waking hours. Here are some of the important research findings and clinical conclusions:

  • Definitively, postprandial blood sugar monitoring has been shown to improve outcomes if you are pregnant and have gestational diabetes
  • PPG is not only an independent risk factor for non-communicable disorders such as diabetes, but also for obesity. What’s particularly fascinating is the more recent understanding that genes are not as responsible for obesity as is a lifetime of high glucose-stimulated insulin secretion. The time of day your insulin is put to its biggest test is after a meal — the postprandial period, when people with insulin resistance have difficulty processing carbohydrates.

  • In patients with T2D, clinical trials have shown the importance of maintaining blood glucose levels after meals within the normal range to prevent the potential complications and mortality associated with this disease. Accordingly, for individuals with diabetes who achieve their premeal glucose targets, but whose overall glycemic control as determined by A1c is still inappropriately high, PPG monitoring and therapy to minimize PPG surges can improve outcomes.
  • Postprandial hyperglycemia raises risk of cardiovascular disease (CVD), coronary heart disease (CHD) and cardiovascular mortality, even in individuals with normal fasting glucose. It is now well known that in diabetic patients, 2 h plasma glucose is a better risk predictor for coronary heart disease than fasting plasma glucose. 
  • In individuals with type 1 or type 2 diabetes who are treated with glucose-lowering agents expected primarily to reduce PPG, monitoring may be useful in titrating these treatments or in confirming that patients have responded to the intervention. It is also possible that PPG monitoring may be beneficial to evaluate the effect of changes in nutrition or exercise patterns.
  • Even if your fasting glucose is normal, individuals with higher levels of 2 h plasma glucose have a higher risk of developing diabetes. A landmark 2006 study demonstrated that healthy individuals can be stratified for risk of progression to type 2 diabetes based on the relationship between their fasting glucose (FPG) concentration and their postprandial (OGTT) plasma glucose concentration. Subjects whose postload plasma glucose concentration returned to baseline (i.e., FPG level) more quickly had greater insulin sensitivity, a higher insulinogenic index, and a lower risk of developing type 2 diabetes after 8 years of follow-up compared with subjects whose postload glucose concentration returned to baseline more slowly.
  • While A1c and fasting plasma glucose (FPG) levels are commonly recognized as diagnostic indices for diabetes and glucose intolerance, they are not sufficient for clear detection of glucose intolerance in the early stage unless an oral glucose tolerance test (OGTT) is performed, particularly to measure postprandial blood sugar. CGMs are increasingly proving valuable as well, especially because they provide a way to analyze “whole glucose excursion” (see below) during the postprandial period and relate it to health interventions, including dietary changes.

PPG as a complementary, not competing, glycemic marker

It is critical to reiterate that, while analysis of postprandial blood sugar has both established and emerging merit, all of the existing glycemic (and other) tests and time intervals retain an important place in the medical diagnosis and management of metabolic health. These different tests complement each other in many important respects; and the relative usefulness of each depends upon many factors, including where a particular individual is on the spectrum of glycemic control. Just as an example, a recent study concluded that postprandial glucose was not as informative as fasting glucose at predicting 10-year atherosclerotic cardiovascular disease (ASCVD) risk — but adding a PPG AUC curve analysis to the fasting glucose measurement resulted in better disease predictability. Similarly, another study cautions that while PPG measurements prove very useful for individuals that have A1c levels below 7.5%, for those individuals with higher A1c levels, fasting glucose tests still prove very informative.

Much research remains to be done on the practicality and usefulness of using postprandial blood sugar analysis as a screening tool for healthy individuals. As one study notes, A1c and fasting glucose levels are often only affected by short-term meal-based interventions in healthy or nondiabetic obese subjects, possibly because the markers just aren’t sensitive enough. This represents one of the challenges that further CGM research hopes to better tackle: it is difficult to monitor peak glucose levels after a meal in daily practice, because the peak glucose time is strongly dependent on diet and glucose tolerance. AUC analysis via a CGM, because it includes the whole postprandial glucose and peak glucose levels, represents an opportunity to predict peak glucose levels, in a minimally invasive manner, without consideration of the timing of measurement. As a 2016 study suggested, preliminary research hints at the promise that such testing could become a useful glucose intolerance screening tool. But further research needs to be completed. 

What can impact your postprandial blood sugar levels?

With the helpful information that glucose testing provides, PPG levels can often be improved by a combination of dietary choices, meal timing, exercise, sleep and (when and if indicated by your provider) medications.

Diet: Caloric restriction PLUS choosing better carbohydrates

PPG levels are greatly influenced by an individual’s ability to process carbohydrates, and to a lesser extent fats and protein. Monitoring PPG levels while also assessing concurrent lifestyle factors (such as dietary choices and exercise/activity) is promising because scientists now know that there is a high between-person variability in response to foods and weight-loss diets, demanding development of more personalized approaches rather than just population-wide recommendations. When it comes to weight loss, what this means is that certain individuals will respond well to a certain type of low-carbohydrate diet, and others may not.

However, it still appears likely that both (1) overall caloric restriction together with (2) choosing higher quality carbohydrate foods benefits glycemic control, and measuring PPG can provide insights into how a particular individual fares with those particular carbohydrate choices. 

As summed up in a 2016 study, balancing meals with protein, vegetables, fiber and healthy fat decreases the glycemic load of the meal and offers lower glucose peaks. Breaking it down further, a 2020 clinical review concludes that “high-quality carbohydrates such as whole grains (especially oats and barley), pulses, or fruit; low glycemic index and load; or high fiber (especially viscous fiber) sources decrease intermediate cardiometabolic risk factors in randomized trials and are associated with weight loss and decreased incidence of diabetes, cardiovascular disease, and cardiovascular mortality in prospective cohort studies.”

Low-quality carbs, for most individuals, include (in this order of “evidence of harm”): (1) sugar-sweetened beverages; (2) starchy carbs that are low in fiber (including many cereals, white bread, corn, refined pasta and white rice); and (3) the vast array of processed and ultra-processed foods containing gobs of added sugars and fats (everything from candy and cookies to ketchup, potato chips, hot dogs). 

Learn more about the most nutritious high-fiber carbohydrates:
Confused About Carbohydrates?
What Is Fiber? 

Diet: Balanced consumption of protein and healthy fats

While carbohydrates are the macronutrients that impact glucose levels the most, and PPG levels especially, the way you “tolerate” carbohydrates can be influenced by the ingestion of protein and lipid nutrients (through the activation of neural reflexes, hormonal responses and gradients of plasma substrates that modulate gastric emptying, insulin secretion and insulin clearance). Protein ingestion has been shown to improve glucose tolerance to a threefold greater extent than fat in healthy participants, and a 2015 study showed that “pre-loading” with certain proteins and fats was able improve postprandial blood sugar levels, seemingly from delayed glucose absorption (in all participants) and improvements in insulin secretion and clearance, which led to a large improvement in beta cell glucose sensitivity in T2D individuals.

Learn more about your protein choices and your best sources of healthy fats.

Diet: Meal timing

Much research is underway to determine what impact changes in meal timing can have on glycemic control and other metabolic markers. Intermittent fasting (IF) has been shown to positively influence glucose and lipid homeostasis in the short-to-medium term, but study authors cautioned that more long-term safety studies are required. Time restricted eating (TRE) is also gaining interest; a 2019 review concluded that “confining all caloric intake to within a defined time interval that is a few hours separated from the daily sleep interval has multiple health benefits.” However, only a few studies have been published that used time restricted eating as a health intervention, most notably a controlled study on a small cohort that has shown that time restricted eating of 6 hours for 5 weeks did not lead to weight loss, but did increase β-cell function and insulin sensitivity and decreased postprandial insulin, oxidative stress, blood pressure, and appetite. Learn more in our report, Is Time Restricted Eating or Intermittent Fasting Good For You?

Stay active

Regular physical activity (the ADA recommends at least 150 minutes per week) can help with blood glucose control, and this benefit seems even more pronounced in the postprandial interval. Studies featuring moderate exercise after meals consistently show glucose levels going down. It is possible to blunt the post-meal glucose surge substantially by starting the physical activity about 30 minutes post-meal and continuing it for up to 60 minutes, and hypoglycemia (low blood sugar) is not a significant concern during this period. Learn more: Exercise and Blood Sugar: What You Need To Know and What Should You Eat Before A Workout?.

Mind your sleep hygiene

The quality and duration of your sleep impacts your metabolic health, including your glycemic control. In a 2018 study, researchers found a compelling connection between lack of sleep and insulin resistance, which put subjects at greater risk for glucose intolerance and diabetes. Learn more about the best sleep duration (7 hours) and what high-quality sleeping looks like in our report, Why Sleep Matters For Your Metabolic Health.

Medications

Clearly, pharmacologic therapy can impact postprandial glucose levels. Determining whether any pharmacologic therapy is warranted, and what kind, is between a patient and medical provider team. Considerations include whether the patient is insulin-deficient, insulin-resistant, or both. Treatment options are divided into noninsulin therapies — insulin sensitizers, secretagogues, alpha-glucosidase inhibitors, incretins, pramlintide, bromocriptine, and sodium-glucose cotransporter 2 (SGLT-2) inhibitors — and insulin therapies (insulin and insulin analogues). This Cleveland Clinic guide lists treatment options, but talk with your medical team to learn how they pertain to you and your health. 

Key takeaways

Postprandial blood sugar (PPG) is but one component, or biomarker, of glycemic health… and glycemic health is one of five markers (blood sugar, waist circumference, blood pressure, cholesterol and triglycerides) that doctors analyze to determine if you are metabolically “healthy” or not. If you are at risk for or currently diagnosed with diabetes, along with other tests (such as the gold standard A1c test), your provider might suggest the oral glucose tolerance test (OGTT) to measure your postprandial glucose levels, providing insights into how your body reacts to a glucose challenge following a meal. The A1c test and continuous glucose monitors (CGMs) also provide postprandial glucose insights that can prove helpful in tailoring your diet, exercise, and medication management strategies in order to prevent diabetes complications from developing. For healthy individuals, the utility of  obtaining PPG levels is less clear, but preliminary research shows some promising applications, especially with CGMs. Meanwhile, dietary and exercise modifications clearly can beneficially impact your postprandial blood sugar levels, whether you have diabetes or not. 

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