Improving Insulin Action

Is changing your diet or exercising better for insulin action?

Sheri Colberg-OchsBy Sheri Colberg-Ochs, PhD

December 2013 — How well your insulin works (that is, your insulin action) is affected by many different factors, but the one that may have the biggest impact on your blood glucose control is how many carbohydrates you already have stored in your body as muscle glycogen. When you eat carbs, any of them that your body can't use immediately must go into storage. Unfortunately, unlike with fat, your body's storage capacity for carbs is very limited: only about 400 grams in your muscles, depending on how much muscle you have (plus 100 grams in your liver). To give you some perspective, the average person eating about 2,000 calories a day usually consumes at least half of those as carbs, or a minimum of 250 grams of carbs daily (at four calories per gram).

If you're sedentary and eat a carb-rich diet, your carb stores will already be full when you eat more of them and your body will have to store any additional carbs past what you need (which is only about 130 grams a day that serves as fuel for your brain and nervous system) as fat. You can store fat in various tissues around the body, including in fat cells, muscle, liver, and more. The bottom line is that when your carb "storage tanks" are full, you're invariably more insulin resistant and will have a harder time keeping your blood glucose in check when you eat carbs.

So, is it better to eat fewer or different types of carbs, exercise more, or do both to improve how well your insulin works? Several studies have addressed this question. For example, when obese subjects ate a carb-reduced and energy-restricted diet for two weeks, their insulin action improved. About half of them also did high-intensity interval training, which consisted of doing four-minute bouts of intense exercise up to 10 times three times a week. After two weeks of eating a carb-reduced diet, their insulin action had improved, but adding the interval training didn't make the effect any greater (although it did make them fitter).

Changing the types of carbs that people eat has also been studied as an alternative to simply lowering carbohydrate intake. In another study, older, obese adults ate either a low-glycemic index (about 40 on the GI scale) diet or a more usual high GI (80) one and exercised daily for a week. The exercise was more moderate and 60 minutes per day. They found that either GI diet equally improved insulin action in this case, which suggests that the exercise training had a bigger impact than the GI of the diet—but this is only likely true when exercising regularly, or else the GI may matter more.

Finally, the liver fat content in obese, older adults was studied since both obesity and aging increase fat storage in the liver, which can lead to nonalcoholic fatty liver disease and insulin resistance. Fat is usually only stored in the liver when blood levels rise too high and has to be converted into fat to store it somewhere. In that study, six months of dieting or dieting plus aerobic exercise caused older adults to have a similar decrease in liver fat and comparable improvements in insulin action. Dieting with or without exercising resulted in the same positive outcome (although the exercisers got more fit).

What is the best advice for you then? First and foremost, it's clear that cutting back on your total carb intake will help to improve how well your insulin works — regardless of the GI of the carbs. Exercise also has a short-term effect on insulin action that lasts only two to 72 hours, so you must be physically active on a regular basis to see the benefit. Not surprisingly, doing a combination of both cutting back on carbs and exercising more has the best all-around benefit on insulin action. Keep the carb storage tanks in your muscles from getting and staying full by moderating your carb intake and staying active!

Read Sheri's bio here.

Read more of Sheri Colberg-Och's columns.

NOTE: The information is not intended to be a replacement or substitute for consultation with a qualified medical professional or for professional medical advice related to diabetes or another medical condition. Please contact your physician or medical professional with any questions and concerns about your medical condition.

Last Modified Date: January 06, 2014

All content on is created and reviewed in compliance with our editorial policy.
  1. Sartor F, de Morree HM, Matschke V, Marcora SM, Milousis A, Thom JM, Kubis HP. High-intensity exercise and carbohydrate-reduced energy-restricted diet in obese individuals. Eur J Appl Physiol. 2010;110(5):893-903.
  2. Shah K, Stufflebam A, Hilton TN, Sinacore DR, Klein S, Villareal DT. Diet and exercise interventions reduce intrahepatic fat content and improve insulin sensitivity in obese older adults. Obesity (Silver Spring). 2009;17(12):2162-8.
  3. Solomon TP, Haus JM, Kelly KR, Cook MD, Riccardi M, Rocco M, Kashyap SR, Barkoukis H, Kirwan JP. Randomized trial on the effects of a 7-d low-glycemic diet and exercise intervention on insulin resistance in older obese humans. Am J Clin Nutr. 2009;90(5):1222-9.

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