Metabolic Health

7 Surprising Reasons Your Blood Sugar Is High

8 minutes read

Keeping your blood sugar levels within healthy ranges has a number of benefits, both in the short and long term. Maintaining blood sugar stability can help with everything from your day-to-day energy levels to future health outcomes and overall sense of well-being as the years go by. 

Ultimately, being proactive is essential when it comes to blood sugar balance, which is why we’re covering the basics of non-diabetic hyperglycemia, symptoms of high blood sugar, and some surprising causes of blood sugar rises in non-diabetics.

What is non-diabetic hyperglycemia?

Hyperglycemia is when your blood sugar levels are higher than normal. While it’s often associated with diabetes, non-diabetics can experience it too.

If you’re a healthy individual, you’ll want to keep your fasting blood sugar between 70 and 100 mg/dL [1]. Current guidelines indicate that if your fasting blood glucose levels are above 100 mg/dL (5.6 mmol/L), you may have insulin resistance [2].

At the same time, you’ll want to pay attention to how much your glucose levels rise after eating, also known as postprandial glucose. While it’s hard to provide clear-cut standards regarding your postprandial glucose levels, it’s reasonable to aim to keep your glucose rise under 40 mg/dL (<2.5 mmol/L), and ideally <30 mg/dL (<1.7 mmol/L). Two hours after eating, your glucose levels should be below 140 mg/dL (7.8 mmol/L) [12]. The goal is to minimize your glucose variability, or how drastically your glucose rises and falls. In a 2019 study published in the journal Medicine, researchers found that the risk of cardiovascular disease and mortality in a general non-diabetic population was greater in subjects with higher glycemic variability [3]. This underscores the importance of minimizing glucose fluctuations, even in healthy, non-diabetic individuals.

What are the symptoms of high blood sugar in people without diabetes?

If you don’t have a CGM just yet and are curious about the main symptoms of high blood sugar in non-diabetics, you’ll want to pay attention to the following [4]:

  • increased thirst/hunger
  • frequent urination
  • headaches
  • fatigue
  • blurred vision

However, symptoms aren’t always apparent and instead can take months or even years to manifest — which emphasizes how important personalized insights from a CGM and regular check-ins with your doctor are to stay on top of your metabolic health.

What causes blood sugar to rise in non-diabetics?

Here’s a closer look at seven key causes of blood sugar rises in non-diabetics.

1. An unhealthy diet

Some foods are more likely to spike your blood sugar even if you’re metabolically healthy, such as refined carbs, processed foods, sodas, and items that contain added sugar.

If you have a sweet tooth or carb cravings that tend to veer you off course from an otherwise healthy diet, you’ll want to be extra cautious of sudden rises in blood sugar, which over time can lead to insulin resistance, i.e., how responsive your cells are to insulin, the hormone that regulates the amount of glucose in your blood and “unlocks” cells so they can turn glucose into energy.

As you’re grocery shopping or putting together your meals for the week, try to prioritize whole foods that are low on the glycemic index (GI).

Foods that are high in added refined sugars or flours tend to have a higher GI, whereas foods that contain fats and/or fiber (which slow the absorption of carbohydrates) tend to have a lower GI. Aim to keep GI under 55.

But GI isn’t the whole picture. Glycemic load (GL) is a more complete indicator of actual blood sugar impact. It takes the glycemic index and multiplies it by the number of carbohydrates per serving of that food (and then divides by 100 for simplicity’s sake) [6]. So a food with a glycemic index of 55 and 10 grams of carbs per serving would have a glycemic load of 5.5. 

Whole fruit is a great example of why this is helpful. Many fruits rank high on the glycemic index but actually have a low GL, since a single serving of fruit doesn’t actually have a significant amount of carbohydrates per serving, thanks to fiber and water.

Some overarching tips on diet:

  • Eat whole, minimally processed foods that are free from refined sugar and flour. Go for colorful vegetables and fruits, which are rich in phytonutrients.
  • Eat a metabolically balanced plate that consists of vegetables, whole grains, lean proteins, and healthy fats.Look at both GI and GL, and try to keep the numbers under 55 and 10, respectively.
  • Fiber can help slow the absorption of carbs and keep blood sugar levels stable, so eat plenty of leafy greens and opt for whole fruits and smoothies over fruit-based juices (even fresh-pressed or -squeezed). Even better if you consume them with a healthy fat.

2. Dehydration

Staying hydrated is one of the best things you can do to promote overall well-being — and that includes promoting metabolic health. According to a 2017 entry in Nutrition Research, research demonstrates that consistently low water intake is associated with an increased diagnosis of non-diabetic hyperglycemia [7]. (Less water means less blood volume — which in turn results in a higher concentration of glucose in your blood.)

There are countless causes — some of which may be surprising — that can contribute to dehydration, which naturally includes not drinking enough H2O but also:

  • sweating excessively
  • high altitudes (at which your respiration rate and urine output increase)
  • low-carb diets (carb-rich foods tend to have more water and electrolytes; additionally, when your body uses up its glucose stores, it has a diuretic effect)
  • diarrhea
  • aging (your body naturally contains less water the older you get)
  • breastfeeding
  • not eating enough water-rich foods such as cucumbers, celery, and watermelon

3. Meal timing

A key component of stabilizing your blood sugar isn’t just paying attention to what you eat, but also when. As it turns out, your body’s insulin sensitivity isn’t static — it fluctuates throughout the day. As studies have noted, there is an intrinsic “circadian rhythm in insulin sensitivity,” with reduced sensitivity/higher blood sugar levels at night (which means it’s best to space out your carb intake throughout the day and avoid saving it up for dinners or evenings) [8]. If you’re curious about how to create a meal timing schedule, consider practicing time-restricted feeding or intermittent fasting, where you consume all of your meals within a set window and fast until your first meal the following day.

Ever wonder why your blood sugar is higher in the morning? The “dawn phenomenon” — in which the liver revs up glucose production, prompting your body to rise and shine — can cause high blood sugar levels especially if insulin can’t keep it in check [9].

4. Genetics

If metabolic dysfunction runs in your family, you may be at greater risk of developing non-diabetic hyperglycemia [10].

However, the good news is that a family history of diabetes doesn’t guarantee that you’re destined to struggle with metabolic issues. By eating the right foods (which includes knowing and limiting the ones that cause your blood sugar to rise; a CGM comes in handy for this very purpose) and practicing healthy lifestyle habits, you’ll have a better chance of maintaining healthy glucose levels.


Polycystic ovarian syndrome (PCOS) is a common hormonal disorder amongst women of reproductive age that can negatively impact metabolic health. According to a medical review in Reproductive Health, as many as 50 percent of women with PCOS are insulin resistant [11].

Insulin is necessary to maintain steady blood sugar levels; an excess of it and/or resistance to it permits glucose to build up in the blood, resulting in high blood sugar levels.

6. Exercise

Research has shown that exercise is one of the best ways to improve insulin sensitivity, which can help you stabilize your glucose levels and reverse insulin resistance. But if you use a CGM, you may have noticed that your glucose levels actually increase after exercising. This happens because your liver, a glucose storehouse, releases glucose into the bloodstream so your muscles have enough energy to complete a workout, which registers as a spike. This is particularly true of demanding exercises like HIIT. These types of spikes are completely normal and temporary, so don’t worry about them too much.

7. Illness

When you’re sick, your body produces more cytokines, small proteins that signal the immune system to act. However, cytokines make your cells temporarily insulin-resistant. As a result, your muscles and liver can’t use up all the extra glucose circulating in your bloodstream, leading to higher-than-usual levels. The sicker you are, the more likely you’ll see a spike in your glucose levels, but they’ll go back down once your body recovers and reduces its production of cytokines.

What can you do to stabilize your glucose levels?

If you’re non-diabetic yet have high fasting blood sugar, you’ll want to take care to address any underlying causes of blood sugar rises before it evolves into more serious health issues. While your family history and certain health conditions such as PCOS may heighten your risk of non-diabetic hyperglycemia, we hope you’ll be empowered by the fact that you can mitigate your risk through healthy dietary and lifestyle habits.

Of course, limiting your intake of certain foods and being mindful of eating patterns that can cause high blood sugar is key. But it’s just as important to keep your body moving, get enough sleep, and manage stress on a consistent basis to avoid insulin resistance and ultimately normalize blood sugar levels.

Key takeaways

  • Hyperglycemia is when your blood sugar levels are higher than normal. It can affect both diabetics and non-diabetics.
  • Symptoms aren’t always noticeable, but they can include increased thirst/hunger, frequent urination, headaches, fatigue, and blurred vision.
  • An unhealthy diet, dehydration, meal timing, genetics, PCOS, exercise, and illness can all lead to hyperglycemia, but it doesn’t always mean something is wrong with your health.
  • Stabilizing your glucose levels boils down to making healthy lifestyle choices when it comes to diet, exercise, sleep, and stress management.



Written by: Michele Ross
Reviewed by: Emily Johnson, MSc RD

Table of Contents

  • What is non-diabetic hyperglycemia?
  • What are the symptoms of high blood sugar in people without diabetes?
  • What causes blood sugar to rise in non-diabetics?
  • What can you do to stabilize your glucose levels?
  • Key takeaways


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