5 Ways Intermittent Fasting Affects Glucose Levels

Intermittent fasting (IF) is the intentional restriction of our mealtimes to maximize health. Media coverage tends to paint IF as a trend, but it isn’t a diet plan. IF existed long before it became trendy, and it can be unique in that it lacks some of the bizarre or arbitrary rules of other diets.

Intermittent fasting really isn’t a “diet.” Think of IF like the dietary cousin to restricting kids’ screen time. Limiting computer time keeps our kids from gorging on YouTube and helps their developing brains. Intermittent fasting may help some people feel and function better.

How Intermittent Fasting Affects Glucose Levels

When it comes to IF and glucose, the results are so much more than just calories and weight loss. IF is a boon for numerous bodily systems. It lowers glucose. It increases our bodies’ sensitivity to insulin. It reduces inflammation. It makes our digestive and metabolic processes more adaptable, and it can even change when and how our bodies make glucose.

1) Lower Insulin Levels

While our body does produce some insulin throughout the day, the majority of insulin release happens when we eat. Counting meals and snacks, the typical adult eats six or seven times a day.

This means our insulin levels spike six or seven times a day. IF, by reducing the frequency of eating and snacking, lessens our insulin spikes and reduces our body’s overall insulin levels. So, why is this good?

Well, in addition to its role in regulating our glucose levels, insulin plays a part in cell growth and both DNA and RNA synthesis. Dangerous increases in insulin levels not only impact our glucose but can also hinder cell growth and bodily regeneration.

2) Increased Insulin Sensitivity

IF’s increased insulin sensitivity goes hand-in-hand with reduced insulin levels. The more our insulin spikes, the more our body becomes accustomed to insulin (like needing more coffee in the morning, the longer you drink it). So the next time we eat, our body needs to spike even more insulin to get the job done.

Additionally, reductions in adiposity (the scientific term for losing body fat) increase our sensitivity to insulin. And wouldn’t you know? One of the benefits of IF is that the weight we lose tends to be fat. This reduces our “adiposity” and increases our insulin sensitivity.

Even with no weight loss, with no reduction in our body fat, science suggests intermittent fasting still increases our bodies’ sensitivity to insulin. The bodily changes triggered by IF tend to “reprogram” our metabolism. In this scenario, our bodies are like a computer on the fritz - turning it off and back on again usually fixes the problem.

IF is like a power switch, resetting how our bodies respond to insulin. Increased insulin sensitivity means our bodies require less insulin to lower our glucose.

3) Lower Inflammation

Our bodies become inflamed as a response to stressors. We often think of stressors as germs or viruses, but the process of metabolizing food is an energy-intensive process that puts oxidative stress on our bodies.

Too much oxidative stress makes it difficult for our bodies to detoxify; it’s why so many products and supplements tout themselves as “antioxidants.” Fasting patterns may influence markers of oxidative stress in some studies.

Because those who practice IF intentionally limit when they eat, they also, by extension, limit the oxidative stress of metabolism. Limiting this kind of stress is key; a number of diseases-Alzheimer's, Parkinson’s, and, most pertinently, diabetes - are thought to arise from excess inflammation and oxidative stress.

Lowering inflammation through IF can reduce our susceptibility to these diseases and lessen our symptoms if we already have them.

4) Improved Metabolic Flexibility

As we talked about above, humans aren’t really designed for “three square meals a day.” We evolved over hundreds of thousands of years to subsist through cycles of feast and famine. Our ancestors couldn’t just call for fast-food delivery when they got the munchies.

The food they did get wasn’t always nutritionally sound, either, meaning the body jealously stored whatever nutrients it could find. IF simulates our evolutionary feast and famine cycles, but on a much smaller scale. It trains our bodies to smartly use their metabolic resources.

For example, if your stomach is empty and your body needs energy, IF trains it to metabolize fat reserves as nature intended. This may support steadier glucose trends for some people. This kind of metabolic flexibility also reduces the side effects of hunger, meaning we won’t get “hangry” if we’re a few minutes late for dinner.

5) Early Time Restricted Eating

One of the hidden superpowers of IF is how it boosts our natural circadian rhythms. Deep within everyone’s brain is a master clock that, taking into account external data such as sunlight, nudges our bodies toward certain activities.

This circadian rhythm, as it's called, is like having a smartphone pre-set with a whole day’s worth of alarms - wake up, eat lunch, etc. - but much less annoying. Our circadian rhythm includes a glucose/insulin timer. Sensitivity to insulin actually decreases as the day wears on.

It takes our bodies longer to process a piece of toast at 9 PM than it does at noon. Those who practice early time-restricted feeding IF, (sticking with a 16:8 pattern but eating only between 10 AM and 6 PM, say) boost insulin’s circadian effectiveness.

Overall, insulin sensitivity rises. Mean glucose levels fall. By shifting our eating window earlier in the day, we are aligning our food intake with when our body is naturally most insulin sensitive, reducing spikes in insulin and glucose.

That "Must-Eat-Breakfast" Feeling

You finish your morning workout and glance at the clock. It’s 10 a.m. In the past, you would have eaten breakfast hours ago, convinced you needed it for energy. 

Now, you feel clear-headed and ready for the day, easily waiting until noon to break your 16-hour fast. You’re letting your body rest and reset, rather than constantly processing food. 

As one member shares: “I feel more confident and I think I'm healthier and I understand how glucose works in my body.”

Why has intermittent fasting become popular?

Let's have a look at a few of the different reasons that intermittent fasting has become a popular dieting method.

It's Simple

The secret to IF’s appeal is its simplicity. You merely don’t eat for a certain number of hours per day (or days per week). Those who practice 16/8 IF, for example, fast for 16 hours and then allow themselves food for eight hours.

While a 16-hour fast sounds extreme, remember, you’ll probably be asleep for eight of those hours. And, really, we shouldn’t be eating late at night anyway, right? Paired with a sensible meal plan, IF can be a powerful tool for controlling glucose levels.

Fad diets fail because they ask us to juggle a thousand different rules. Is this vegetable Keto-approved? Are these burgers Paleo? IF replaces the maze of rules with one simple code: only eat during a set window of time.

It's Evolutionarily Normal

The way most Americans eat - breakfast when we wake, lunch near noon, and dinner near sunset - is a new-ish invention. Three meals just happened to fit the Industrial Revolution workday. Even in modern times, “three square meals'' isn't universal.

Non-diabetics with hypoglycemia, for example, often eat many smaller meals a day to regulate glucose. Many farming cultures eat five or six meals a day. The Greeks and Spanish are infamous for their 11 pm “dinners.”

For most of human history, we ate what we could when we could. We have body fat for a reason, after all. When our ancestors failed to hunt Mammoths, fat kept them alive. When they found a walnut grove, our ancestors gorged to build up fat reserves. Simply put, our forebears lived in a perpetual state of intermittent fasting.

Ages of hunter-gathering shaped our bodies. From an evolutionary standpoint, intermittent fasting is more “normal” than breakfast-lunch-dinner. Add in issues brought on by our modern processed foods, ultra-rich and sugar-heavy, and it becomes clear that maybe IF, biologically speaking, is the way to go.

It May Support Weight Loss

This is the hook for most people to try IF. Systematic studies show a strong correlation between IF and weight loss. Across multiple trials, intermittent fasting and continuous energy restriction can reduce body weight compared to ad-libitum intake. That’s an astounding result.

The asterisk here (there’s always an asterisk, right?) is that the study of intermittent fasting is a relatively nascent field. Established science generally stretches back decades and centuries. Scientists need much more data before definitely linking IF and weight loss.

Still, participants losing weight in these IF trials is a very promising start.

It May Increase Longevity

The other interesting aspect of IF is its potential to extend human lifespan. Obviously, weight loss lowers our risk for a whole host of diseases. Less disease means longer lives. IF offers more than that, though. Emerging science suggests that intermittent fasting affects our bodies on a cellular level, improving health and increasing lifespans.

Autophagy is the process by which our cells break down old materials. Think of it as cellular recycling. Enzymes break down cellular waste and use the product to build fresh new cells. Science suggests intermittent fasting increases autophagy, making our cells more efficient recyclers. This makes us, on a cellular level, “younger.”

IF also increases mitochondrial efficiency. Those who still remember their paper plate/jelly bean cell projects from middle school will proudly tell you the mitochondria are “the powerhouse of the cell.” Mitochondria produce the chemical energy our cells rely on.

As we age, our mitochondria become less efficient. Studies show, however, that IF reverses cellular aging, giving us the mitochondria of a (relative) teenager.

How to pair intermittent fasting with 24/7 glucose trends

Pair your fasting schedule with a glucose biosensor and the Nutrisense app to see how your window, first meal, and activity map onto your daily curves. The sensor reports glucose measured in interstitial fluid, then the app displays those trends so you can fine-tune timing and meal composition. See “What is a CGM?” for how the system works and what you can track.

Use these practical steps to make IF sustainable and your data easier to interpret.

• Keep one eating window for 7 to 10 days before changing it. Tag fast length and first meal time in your logs to compare trend lines over time.
• Break the fast with a lower glycemic, balanced plate. Build it around protein, non-starchy vegetables, healthy fats, and a portion of whole food carbohydrates if desired.
• Hydrate during the fast. Favor water, mineral water, or broth. Include electrolytes such as sodium, potassium, and magnesium from foods like leafy greens, avocado, nuts, and seeds.
• Manage hunger with small tactics like a short walk, unsweetened tea or coffee if tolerated, or by shifting your window earlier.
• If you use medications that can lower glucose, set guardrails with your clinician and carry fast-acting options such as glucose tablets or gels. If a reading does not match how you feel, remember interstitial readings can lag during rapid change. Follow your clinician’s guidance if symptoms are concerning.
• For sensor adhesion during workouts or swimming, apply to clean, dry skin and consider a cover.

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Who should avoid intermittent fasting?

Though the benefits of IF are alluring, it must be said that this kind of deliberate restriction isn’t for everyone. Here are a few types of people who may want to consult their doctor before beginning this type of diet.

1) People Who Are Underweight or Suffer From Eating Disorders

Twitter co-founder Jack Dorsey claims eating one meal a day (OMAD) gives him a laser-like focus. If Dorsey were a woman, though, especially a young woman, would we call his habits “intermittent fasting” or would we call them an “eating disorder?”

The line can be blurry. And for those who have suffered past eating disorders or are chronically underweight, it’s a line best avoided.

2) Pregnant And Breastfeeding People

IF probably isn’t a great idea for pregnant and breastfeeding women. IF’s caloric restriction can negatively impact fetal development. And because breastmilk nutrition is largely informed by what the mother eats, restricting diet during breastfeeding can produce less nutritious milk.

3) People With Chronic Fatigue or Burnout

The “warning label” on almost every scientific study of IF is how it interplays with stress. Deliberately restricting our caloric intake puts stress on our bodies. For most, this low-level stress is beneficial. It does, after all, help us lose weight and revitalize our cells.

However, for those who already live under a high degree of bodily stress, or those who pair IF with other activities such as cold therapy or lots of high-intensity training, extended IF can overload our body’s stress tolerance and cause negative effects.

4) People Taking Insulin Therapy or Hypoglycemic Medications

Because IF directly affects our body’s production of glucose, those on insulin therapy or medications that cause hypoglycemia should contact their doctor before beginning an IF regimen.