What is the prediabetes range, and what should I do if I’m borderline?

Dr. Rich Joseph discusses how to keep your blood sugar from creeping into prediabetic or diabetic levels.


Our bodies generally do a great job of keeping blood sugar tightly controlled. But over time, that process can get thrown off balance for various reasons.

This glycemic dysfunction happens when a person develops insulin resistance, and some of their cells slowly stop responding to the hormone (insulin) that helps them convert sugar into energy. As excess sugar builds up in the blood, the pancreas pumps out more and more insulin until it eventually can’t produce enough. Without insulin working as it should, blood sugar can increase to diabetic levels.

Prediabetes means you’re in the danger zone—you have a higher-than-normal blood sugar but not high enough to be considered Type 2 diabetes. However, even without progressing to Type 2, prediabetes carries health risks on its own. To keep your blood sugar in the healthy range, you may wish to consider your lifestyle and risk factors.

What are prediabetic blood glucose levels?

A few blood tests can diagnose prediabetes. Most require a visit to a doctor’s office or lab-testing site.

Fasting blood sugar: This test can be part of a standard annual exam. Before the test, you fast—no food or drink, except water—for up to 12 hours. A fasting blood sugar of 99 mg/dL or lower is normal, 100 to 125 mg/dL indicates prediabetes, and 126 mg/dL or higher suggests diabetes.

Glycated hemoglobin (A1C) test: This test measures the percentage of hemoglobin proteins in your red blood cells coated with sugar—in other words, how much glucose is stuck to your cells. The result represents average blood sugar levels over the past three months, which can be more useful for diagnosis than the single point-in-time snapshot you get from other tests. An A1C below 5.7 percent is normal, 5.7 to 6.4 percent may mean prediabetes, and 6.5 percent or higher indicates diabetes. However, we look at movement as well: a rising A1c (say from 4.5-> 4.8-> 5.2) over a few months or years can indicate creeping insulin resistance even though the level is still technically below 5.7

Glucose tolerance test: This test is less common than the other two, except during pregnancy. After fasting for at least eight hours, you drink 8 ounces of a sugary drink and have your blood sugar tested every 30 to 60 minutes for 2-3 hours. Less than 140 mg/dL is normal, 140 mg/dL to 199 mg/dL is consistent with prediabetes, and 200 mg/dL or higher suggests diabetes.

What if your blood sugar is on the high end of “normal”?

If your test results fall into the normal range, that means you likely don’t have prediabetes or diabetes. However, if you’re just over the line on both tests—even by a little—you have prediabetes.

However, there may be better strategies than fixating on a particular line. Blood sugar control, from normal to prediabetes to diabetes, exists along a continuum. Over time, blood sugar can progress down that continuum, particularly if you have risk factors and an unhealthy lifestyle.

Some research suggests that people with high-normal fasting blood sugar (90 to 99 mg/dL) are more likely than those on the lower end to develop diabetes over the next decade. Meanwhile, people with prediabetes have a much higher risk of developing Type 2 diabetes.

But blood sugar is only one part of the picture. It’s important to pay attention to risk factors, too.

Additionally, some ethnic groups have a higher risk. These include African Americans, Pacific Islanders and Asians, Hispanics and Latino Americans, Native Americans, and Alaskan Natives.

A quick and easy way to find out if you’re at high risk of developing prediabetes is to take the Centers for Disease Control and Prevention’s prediabetes risk test here. If you find that your prediabetes risk is high, there are a few things you can do.

What can you do if you’re at risk for prediabetes?

Research suggests that lifestyle changes, including exercise and healthy eating patterns, are associated with a lower risk for prediabetes and diabetes.

Long-term studies funded by the National Institutes of Health (NIH) show that people with prediabetes who make healthy diet changes and increase their physical activity lower their risk of developing Type 2 diabetes by 58 percent. This research has led to the development of a national lifestyle change program available in person and online nationwide. If you’re overweight and have prediabetes, have previously had gestational diabetes, or receive a high-risk result on the prediabetes risk test mentioned above, you may be eligible to join this program, which connects you with a lifestyle coach and lasts for a year. The program’s cost varies, though it may be covered by insurance or even free.

You can also work to develop healthy habits in your lifestyle on your own to help curb prediabetes risk. Here are some backed by solid evidence:

1. Aerobic exercise

Participants in the NIH study engaged in moderate physical activity, such as brisk walking, for 150 minutes a week (something like 30 minutes a day, five days a week). “Moderate” physical activity means you’re working hard enough to raise your heart rate. Think bicycling on flat terrain or playing pickleball.

Research also suggests that the timing of exercise can make a difference. A 2022 study of middle-aged, slightly overweight adults (average BMI 26) found that those who exercised in the afternoon or evening were up to 25 percent less likely to have insulin resistance. The authors surmise that our body’s muscular and oxidative systems peak in the late afternoon, so “being most active during this period may elicit greater metabolic responses than earlier in the day.”

2. Strength training

Building and maintaining muscle mass is crucial for metabolic health and insulin sensitivity. Muscles suck up a lot of glucose, so if you have less muscle, you hinder your body’s ability to clear glucose from the bloodstream.

Here are some tips if you’re just getting started:

  • Focus on your lower body. This is where many of your biggest muscles are: the glutes, quadriceps, and hamstrings. Focusing your efforts here may provide the greatest return on investment. Squats, lunges, deadlifts, and glute bridges are great options for targeting these muscles. However, this doesn’t mean skipping other muscle groups—all-around strength is crucial for fitness.
  • Take advantage of machines. Weight machines guide your movement, making you less likely to be injured using bad form.
  • Grab something heavy and move. You can still do a lot at home if you don’t have gym access. Grab some weights—or a couple of gallon milk jugs, paint cans, books, or anything heavy—and climb stairs at home or a local football stadium.
  • Hit the pool. If you have joint pain, water can provide resistance while reducing the impact on joints. You can swim laps or do pretty much any strength move you’d do on land in shallow water.
  • Use resistance bands. Resistance bands are affordable, portable, and versatile. A few kinds are available. Exercise tubing with handles can help you work back muscles (anchor the band to a door and do rows or lat pulldowns). Mini bands, which look like oversized rubber bands, are great for adding resistance to lower-body moves like squats and glute bridges—loop one around your legs just above the knee.
  • Invest in a trainer. A few sessions with a qualified personal trainer can help you understand proper movement patterns and good form.

3. Diet

Most people can improve their metabolic health by cutting back on refined carbs. Fewer carbs means your body doesn’t need to pump out as much insulin, easing the burden on the pancreas and lowering insulin resistance.

That generally means eating plenty of protein and healthy fats and avoiding refined grains and added sugars (found in foods like bread, pasta, cookies, and soda).

That doesn’t mean you have to go full keto. A very low-carb diet may not be sustainable for everyone. Try this: Plan your carb intake earlier in the day and around your workouts. But try to cut out all refined carbs at dinner. Glucose tolerance tends to be diminished in the evening, even for healthy people. So a small change like this could make a big difference.

4. Weight loss

Excess weight contributes to insulin resistance, and losing weight is helpful for most people’s metabolic health. According to the NIH study, even losing as little as 5 percent of your body weight can significantly reduce your risk of Type 2 diabetes.

Still, it’s essential to focus on body composition, not just body weight. A healthy body composition means less fat and more muscle—key factors that aren’t reflected in body weight alone.

And don’t get discouraged if the number on the scale just won’t budge. Know that exercise and diet changes benefit your metabolic health in ways you can’t see unless you get lab work done.

How soon can you expect to see changes in metabolic markers?

Research shows that lifestyle changes can positively affect blood pressure, triglycerides, waist circumference, and fasting blood sugar within as little as six months or even sooner.

Still, maintaining these improvements is vital to long-term success. The NIH study found that the most significant improvements in glycemic changes occurred in the first year of lifestyle intervention.

So, don’t think of these changes as a short-term intervention. You want to find lasting ways to incorporate them into your life. One way to stay motivated is to envision your future self and remind yourself of the benefits you’ll receive from these changes.

As long as you maintain a healthy, active lifestyle and stay on top of regular diabetes screenings—although CDC guidelines are every three years beginning at age 35 for those who test in the normal range, I advocate that everyone do them yearly—you should be in good shape. Future you will thank you someday.


Rich Joseph, MD, is a Stanford-trained physician and the chief medical officer of Restore Hyper Wellness.


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