Prediabetes affects over 38 million adults in the US alone, and the vast majority of them have no idea they have it. No symptoms. No warning. Just blood sugar quietly creeping up year after year until one day a doctor says your numbers are too high.
So what actually causes it? The short answer is insulin resistance. But understanding why that happens, and what drives it, is where things get really useful.
What is the number one cause of prediabetes?
Insulin resistance is the number one cause of prediabetes. Here is what that actually means.
When you eat carbohydrates, your body breaks them down into glucose and puts that glucose into your blood. Your pancreas then releases a hormone called insulin, and insulin acts like a key that unlocks your muscle, liver, and fat cells so they can pull that glucose in and use it for energy.
When your cells stop responding properly to insulin, that key stops working as well as it should. Your pancreas responds by pumping out even more insulin to try to force the door open. For a while, this works and blood sugar stays relatively normal. But over time, your pancreas gets tired of producing so much insulin, it starts to fall behind, and blood sugar begins to rise. That rise into the prediabetic range, between 5.7 and 6.4% on an HbA1c test, is the direct result of this breakdown.
A 2021 review published in the journal Nutrients confirmed that insulin resistance precedes prediabetes by years, often developing silently for a decade before blood sugar ever shows up as abnormal on a test.
What actually causes insulin resistance in the first place?
This is the deeper question, and it has a few solid answers backed by research.
1. Too much body fat, especially around the belly
Visceral fat, the fat stored deep in your abdomen around your organs, releases inflammatory signals that directly interfere with how insulin works at the cellular level. Research published in Cell Metabolism showed that visceral fat produces proteins called cytokines that block insulin receptors on muscle cells, reducing their ability to absorb glucose.
You do not need to be obese for this to be a problem. A person at a normal body weight can still carry too much visceral fat, which researchers call being “skinny fat” or having a high body fat percentage despite a healthy BMI.
2. Chronic inactivity
Muscle is the biggest consumer of glucose in your body. When your muscles contract during movement, they pull glucose in without even needing insulin. Regular movement, especially resistance training and walking, makes your muscle cells more sensitive to insulin by increasing something called GLUT4 transporters, which are the proteins that physically move glucose into cells.
A 2020 study in Diabetes Care found that people who walked at least 7,500 steps per day had significantly lower insulin resistance than sedentary people, even after controlling for body weight.
3. Poor sleep
This one surprises most people. Getting fewer than 6 hours of sleep per night raises cortisol levels, which directly raises blood sugar and reduces insulin sensitivity. A study from the University of Chicago found that just one week of sleeping 4.5 hours per night reduced insulin sensitivity by 25% in healthy young adults. That is a dramatic drop in a very short time.
4. Chronic stress
Cortisol, the stress hormone, tells your liver to dump glucose into your blood as an emergency fuel supply. This made sense when stress meant a lion was chasing you. It does not make sense when stress means work emails and traffic. Ongoing high cortisol from daily life stress keeps blood sugar elevated and chips away at insulin sensitivity over time.
5. Ultra-processed food and excess refined carbohydrates
Diets high in refined carbohydrates, added sugars, and ultra-processed foods spike blood sugar rapidly and repeatedly, forcing the pancreas to constantly pump out large amounts of insulin. Over time, cells adapt by becoming less sensitive to insulin’s signal, a process similar to how you stop noticing a loud noise after a while because your brain tunes it out.
A large 2019 study in JAMA Internal Medicine found that every 10% increase in ultra-processed food intake was associated with a 15% higher risk of developing type 2 diabetes.
What’s the worst thing for prediabetes?
Doing nothing. That is the worst thing.
Without any changes, around 37% of people with prediabetes will develop type 2 diabetes within 10 years, according to the CDC. Some research puts the figure higher depending on other risk factors.
But beyond inaction, here are the specific habits that accelerate the problem fastest.
- Drinking sugary drinks daily. Liquid sugar bypasses satiety signals completely. A 600ml bottle of regular soft drink contains around 64 grams of sugar, hits your bloodstream fast, and trains your cells toward insulin resistance faster than almost anything else.
- Sitting for long unbroken stretches. Studies show that sitting for more than 8 continuous hours raises blood sugar markers even in people who exercise regularly. Breaking up sitting every 30 minutes with even a 2-minute walk significantly reduces the blood sugar spike after meals.
- Ignoring sleep. Poor sleep may be the most underrated driver of prediabetes progression and it is the one most people never address.
- Crash dieting and then regaining weight. Yo-yo dieting increases visceral fat over time even when total body weight stays the same, making insulin resistance worse with each cycle.
Can a prediabetic become normal again?
Yes. Absolutely yes.
Prediabetes is reversible, and the evidence on this is strong. The CDC-recognized National Diabetes Prevention Program showed that people who made modest lifestyle changes, losing 5 to 7% of body weight and adding 150 minutes of walking per week, reduced their risk of progressing to type 2 diabetes by 58%. For people over 60, the reduction was 71%.
Blood sugar returning to the normal range, below 5.7% on HbA1c, is a realistic outcome for a large percentage of people with prediabetes who make consistent changes. A 2020 systematic review in BMJ Open Diabetes Research and Care found that around 50% of participants who made structured lifestyle changes returned to normal blood sugar levels within one to three years.
The key word is consistent. One good week does not undo years of insulin resistance. But six months of steady changes absolutely can.
What is the fastest way to reverse prediabetes?
Four strategies have the strongest evidence behind them, and they work even better when combined.
1. Cut dietary fat in the right places to reduce calories quickly
Fat contains 9 calories per gram, more than double what protein and carbs contain at 4 calories per gram. Cutting one or two high-fat foods in half, think cheese, butter, cream, fatty meats, immediately creates a calorie deficit without stripping your diet of everything enjoyable. This is not about going fat-free. Your body needs at least 35 to 50 grams of fat per day for hormonal health. It is about being strategic with where the big calorie loads are hiding.
2. Walk more, every single day
Walking is underrated for blood sugar specifically because it uses muscle glucose uptake without triggering a stress response in the body. A 30-minute walk after dinner reduces post-meal blood sugar by up to 22% according to research published in Diabetologia. Aim for 7,000 to 10,000 steps per day. If you are currently at 2,000, just doubling that is a meaningful start.
3. Add resistance training twice a week
Building muscle increases insulin sensitivity because more muscle means more cells available to absorb glucose. Even bodyweight exercises, squats, lunges, push-ups, have been shown to improve insulin sensitivity within 8 weeks in people with prediabetes.
4. Prioritise sleep and stress management
Getting 7 to 9 hours of sleep per night is not optional if you are trying to reverse prediabetes. Neither is finding some way to reduce chronic stress, whether that is exercise, time outside, reducing workload, or building in proper rest. These are not soft lifestyle suggestions, they are direct interventions that shift cortisol and insulin sensitivity in measurable ways.
Does sugar directly cause prediabetes?
Sugar does not cause prediabetes on its own. Total calorie excess, physical inactivity, and the resulting body fat accumulation are the main drivers. But added sugar, especially in liquid form, is one of the fastest ways to push calories over your budget and cause repeated blood sugar spikes that accelerate insulin resistance.
The distinction matters because people who avoid sugar but still eat too many total calories and sit all day will still develop insulin resistance. And people who eat small amounts of sugar within an otherwise healthy diet with regular movement are generally fine.
That said, cutting added sugar and sugary drinks is one of the highest-impact single changes you can make because the calorie savings are significant and the blood sugar benefits are immediate.
How long does it take to see results after making changes?
Most people see measurable improvements in blood sugar and insulin sensitivity within 8 to 12 weeks of consistent changes. Full reversal, meaning HbA1c returning to the normal range, typically takes 3 to 12 months depending on starting point, how much weight is lost, and how consistently the habits are maintained.
An important note: do not wait until your blood sugar is fully normal to feel encouraged. Insulin sensitivity often improves before HbA1c moves, which means your body is responding even before the test numbers confirm it.
Frequently Asked Questions
Is prediabetes genetic?
Genetics increase your risk but they do not cause prediabetes on their own. Family history of type 2 diabetes raises your likelihood of developing insulin resistance, but the lifestyle factors above are still the main drivers. People with a strong family history just need to be more proactive earlier.
Do I need medication for prediabetes?
Most guidelines, including those from the American Diabetes Association, recommend lifestyle changes as the first treatment for prediabetes. Medication like metformin is sometimes used for high-risk cases, but research consistently shows lifestyle changes outperform medication for reversing prediabetes. The 58% risk reduction from the National Diabetes Prevention Program beats the 31% reduction seen with metformin alone.
Can thin people get prediabetes?
Yes. Around 10 to 15% of people with prediabetes have a normal BMI. The main risk factors for lean individuals are high visceral fat, low muscle mass, poor sleep, chronic stress, and a diet high in ultra-processed foods. Body weight is one indicator but not the only one.
What foods should I focus on eating more of?
Foods high in fiber and resistant starch, like oats, legumes, potatoes that have been cooked and cooled, and most vegetables, slow glucose absorption and feed gut bacteria that improve insulin sensitivity. Lean proteins like chicken, fish, eggs, and Greek yogurt help preserve muscle and have a high thermic effect, meaning your body burns more calories just digesting them.
Is intermittent fasting good for prediabetes?
Some research supports intermittent fasting as a tool for improving insulin sensitivity, particularly because it lowers overall calorie intake and gives the pancreas extended rest periods between meals. A 2022 study in Nature Medicine found that time-restricted eating improved insulin sensitivity in people with metabolic syndrome. It works for some people but is not required. Consistent calorie control and daily movement achieve the same outcome for most people.
The bottom line
Insulin resistance is the root cause of prediabetes, and insulin resistance develops from a combination of excess body fat, too little movement, poor sleep, chronic stress, and a diet heavy in ultra-processed foods. None of these work in isolation, and none of them require a perfect response.
Pick one strategy and start this week. Add a 20-minute walk after dinner. Swap one sugary drink for water. Go to bed 45 minutes earlier. The research is clear that small, consistent changes compound into real results, and prediabetes reversal is a realistic outcome for the majority of people who take it seriously.
