Insulin resistance: what to eat, what to limit and whether it can be reversed

What insulin resistance is and why it almost never causes symptoms

Insulin is the hormone that lets glucose move from the blood into your cells. With insulin resistance, cells respond less well to that signal, and the pancreas has to make more insulin to keep blood glucose in check. While it manages to do so, glucose can stay normal; when it can no longer compensate, glucose rises and prediabetes appears, and over time type 2 diabetes. According to the NIDDK (NIH), insulin resistance and prediabetes usually cause no symptoms, and the test that directly measures insulin resistance is mainly used in research studies. The usual route is to detect prediabetes with a blood test: glycated haemoglobin (A1C), fasting plasma glucose or an oral glucose tolerance test. The NIDDK also links it with high blood pressure, unhealthy cholesterol and triglyceride levels, metabolic syndrome and fatty liver, and lists PCOS among the risk factors. If your glucose is already high, see the guide on what to eat with diabetes and prediabetes.

What to eat and what to limit: the table by food group

With insulin resistance there is no list of forbidden foods and no list of miracle foods either. What the evidence supports is changing the base of your meals. This table sums up what to prioritise and what to limit in each group, and what the evidence says. Keep in mind that almost all the data on specific foods come from observational studies, which show an association and do not prove cause and effect.

What has the strongest evidence: losing some weight and moving more

The two landmark trials were run in people whose blood glucose was already abnormal. In the Diabetes Prevention Program (3,234 people), the lifestyle programme had two goals: losing at least 7% of body weight and doing at least 150 minutes of physical activity a week. Over almost three years it cut the onset of type 2 diabetes by 58% compared with placebo; metformin cut it by 31%. In the Finnish study (522 people with overweight), individual advice to lose weight, reduce total and saturated fat, eat more fibre and move more also reduced the risk by 58%. You do not need to reach an "ideal weight": in a controlled trial, losing 5% of body weight already improved insulin sensitivity in the liver, the muscle and fat tissue, and further weight loss improved muscle insulin sensitivity even more.

• A realistic goal: start with 5% of your body weight. Work out your pace with the weight loss calculator.
• A moderate deficit you can sustain, not an extreme diet: estimate your needs with the calorie calculator.
• Activity: the goal in the Diabetes Prevention Program was 150 minutes a week, for example 30 minutes on five days.
• Changes you can keep up for years: both trials worked with lifestyle programmes, not with diets that last a few weeks.

Exercise: it improves insulin sensitivity even without weight loss

Working muscle uses glucose, and studies show that exercise helps in its own right, not only through weight. In 18 sedentary adults, six months of walking improved insulin sensitivity with no change in BMI or waist size. A meta-analysis of 27 studies in adults with overweight or obesity without diabetes found that strength training lowered fasting insulin and HOMA-IR, an index of insulin resistance. And in one-day trials, breaking up sitting time with short, light walks lowered blood glucose and insulin after meals, more than staying seated or simply standing up.

Can insulin resistance be reversed?

It can be improved a great deal, especially in the early stages, and the CDC notes that prediabetes can be reversed with lifestyle changes. What trials have shown is this: losing 5% of body weight improves insulin sensitivity, and lifestyle change reduces the onset of diabetes in people with prediabetes. But it should not be sold as a cure for life. In the 15-year follow-up of the Diabetes Prevention Program, the lifestyle group still had 27% less diabetes than the placebo group, but the gap narrowed over time (everyone was later offered the lifestyle programme). In plain terms: improving is realistic, but it is long-term work, with whatever check-ups your doctor recommends.

What about intermittent fasting?

It can be a way to organise your eating if it suits you, but the trials do not place it above cutting calories every day. In a one-year trial of 100 adults with obesity, alternate-day fasting achieved the same weight loss as daily calorie restriction, with no differences in fasting glucose, fasting insulin or insulin resistance, and with more dropouts (38% vs 29%). In another 12-month trial of 139 people with obesity, eating only between 8 a.m. and 4 p.m. on top of cutting calories was no better than cutting calories alone for weight, body fat or metabolic risk factors. In 107 women with overweight, cutting calories sharply on two days a week and cutting them moderately every day gave the same weight loss; the drop in fasting insulin was modest in both groups and slightly larger with the intermittent version. Bottom line: choose the method you can keep up.

Before you start

Insulin resistance is a medical matter: it is assessed with blood tests, can come with other conditions (PCOS, fatty liver, high blood pressure) and sometimes needs drug treatment, which is your doctor's decision. Use this guide to understand how what you eat plays a part, but make the changes together with your doctor or a registered dietitian, especially if you take glucose-lowering medication. If you also have PCOS, see what to eat with PCOS, and if your liver is a concern, fatty liver: what to eat and avoid.