What Is Insulin Resistance? Signs, Causes, and How to Improve It

How does insulin resistance work?

Insulin resistance works by making cells respond sluggishly to insulin, so the pancreas has to release more of it to clear the same sugar from the blood. After a meal heavy in refined carbohydrate, blood sugar rises; the pancreas releases insulin; insulin signals cells to take that sugar in for energy or storage. In a healthy person, a small amount of insulin is enough to clear the meal.

In an insulin-resistant person, the same meal triggers a much larger insulin release because the cells respond sluggishly. Over years of this pattern, two things happen: insulin stays chronically elevated (high insulin slows the release of stored fat, per Jensen et al., Diabetes 1989), and the pancreas can slowly lose capacity to keep up. What starts the cycle is still being worked out; one line of mostly cell and animal research, reviewed by Dr. Benjamin Bikman and Scott Summers, points to ceramides, fats that build up under cellular stress and shift cell metabolism in ways relevant to diabetes (Bikman and Summers, 2011).

We argue this may help explain a pattern many people describe: weight gain that begins gradually, then accelerates, and stops responding to the habits that worked in their twenties. The calorie arithmetic is the same as it was; the hormonal picture may not be.

What are the early signs of insulin resistance?

Insulin resistance usually has no symptoms, according to the U.S. National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), so the clearest signs come from blood tests and, for some people, a skin change.

• Blood tests, not symptoms. NIDDK says prediabetes is diagnosed with an A1C of 5.7% to 6.4% or a fasting blood sugar of 100 to 125 mg/dL. Health professionals may not test for insulin resistance itself, because that test is mainly used in research.
• Acanthosis nigricans. Dark, velvety patches at the neck or armpits are a skin sign associated with insulin resistance, and a 2004 dermatology review (Hermanns-Lê et al., American Journal of Clinical Dermatology) describes them together with skin tags and excess weight.
• Common experiences, not signs. Weight gain around the middle, sleepiness after meals and cravings soon after eating are widely reported, but they have many causes, such as sleep, stress and meal composition, so none of them can tell you whether you are insulin resistant.

No single sign is diagnostic. If you have risk factors or any of the signs above, ask your doctor which tests make sense for you, such as an A1C or fasting blood sugar test.

How can insulin resistance be improved?

The strategy in outline is to eat in ways that send blood sugar up less and call in less insulin across the day, and sensitivity may improve. These levers all aim at that, and the lifestyle changes tested in the Diabetes Prevention Program overlap with them:

1. Choose less refined carbohydrate. Refined bread and pasta, juice, sweetened drinks and ultra-processed snacks tend to carry the highest estimated insulin impact.
2. Build meals around protein and whole foods. Protein slows gastric emptying, which tends to ease the post-meal rise in blood sugar.
3. Add fibre. Vegetables, legumes, and intact whole grains physically slow how fast sugar is absorbed.
4. A long gap between dinner and breakfast is an option. Some people choose 12 to 16 hours; if you take medication that affects blood sugar, talk to your doctor first.
5. Move after meals. In a crossover trial of 41 adults with type 2 diabetes, advice to walk for 10 minutes after each main meal lowered the post-meal blood sugar rise (the 3-hour area under the blood sugar curve) by about 12% compared with advice to walk for 30 minutes once a day (Reynolds et al., Diabetologia 2016).

For a food-by-food list scored for insulin impact, see our guide to eating with insulin resistance. If you want an app to time an overnight fast, see our comparison of fasting apps.

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Insulin resistance and PCOS

Polycystic ovary syndrome (PCOS) affects about 10 to 13% of women, according to the 2023 international guideline, and is one of the most common reasons women experience unexplained weight gain despite eating carefully. Insulin resistance is common in PCOS, but the 2023 international guideline says routinely available insulin tests are of limited clinical relevance and are not recommended in routine care, so there is no routine number to chase. A review in Endocrine Reviews (Diamanti-Kandarakis and Dunaif, 2012) describes a two-way loop in which insulin influences ovarian hormone production and androgens in turn contribute to insulin resistance.

Mainstream guidelines describe insulin resistance as one factor in PCOS rather than the whole story, and no single eating pattern has been proven best. An insulin-first pattern of food choices fits within the healthy eating principles those guidelines recommend. The Weight Impact Score can help you spot which of your usual meals have the highest estimated insulin impact so you can find easy swaps, but it is a modelled estimate, not a medical measurement or a PCOS treatment. The PCOS guide covers what the evidence does and does not show, and your doctor can advise on what is right for you.

Where RealFoods fits in

Knowing the levers is one thing; applying them at every meal, every day, is another. In RealFoods each meal gets a Weight Impact Score from 1 to 10, a modelled estimate of how strongly it is likely to raise blood sugar and call in insulin, where lower is better, with a suggested daily average below 5 as a simple feedback target. Over a week, the pattern shows which meals are the biggest levers. It is a feedback tool, not a medical measurement or a treatment.

Common questions

What does insulin resistance actually mean?

Insulin resistance describes a state in which the body's cells respond more weakly to insulin than they should. The pancreas compensates by releasing more insulin, which keeps blood sugar in range temporarily but also keeps insulin levels elevated. High insulin slows the release of stored fat (Jensen et al., Diabetes 1989), and over time the extra demand can strain the pancreas.

What are the early signs of insulin resistance?

Insulin resistance usually causes no symptoms, according to the U.S. National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), so it is often found through blood tests for prediabetes: an A1C of 5.7% to 6.4% or a fasting blood sugar of 100 to 125 mg/dL. One visible skin sign linked to insulin resistance is acanthosis nigricans, dark velvety patches at the neck or armpits, which a 2004 dermatology review describes alongside skin tags and excess weight. Tiredness after meals, cravings and weight gain around the middle are common experiences with many causes, so they are not reliable signs on their own.

Can insulin resistance be improved?

Often, yes, though results vary. The CDC says physical activity, weight loss if you have overweight, and balanced eating make your cells more sensitive to insulin. In the U.S. Diabetes Prevention Program (Knowler et al., NEJM 2002), a program of eating changes, weight loss and exercise cut progression to type 2 diabetes by 58% over an average of 2.8 years among 3,234 adults without diabetes who had elevated blood sugar. Eating less refined carbohydrate, adding fibre, building meals around protein and whole foods, and moving regularly overlap with that program, and your doctor should guide testing and treatment.

Is insulin resistance the same as diabetes?

No, but it is a common precursor. Insulin resistance can persist for years before fasting blood sugar rises into the prediabetes or type 2 diabetes range. Catching it early and acting on it is the standard public-health rationale for screening and lifestyle intervention.

Continue reading: blood sugar and weight gain, foods linked to weight gain, or weight loss without calorie counting.