Exercise can improve the insulin sensitivity of people with non-alcoholic fatty liver disease

The insulin sensitivity of patients with non-alcoholic fatty liver disease (NAFLD) is just as poor as that of patients with type 2 diabetes. Exercise, however, can help the patients to improve their insulin sensitivity, reduce the amount of fat in the liver and, effectively, pre-empt the development of type 2 diabetes. This was the conclusion Bram Brouwers reached in his doctoral thesis ‘Exercise in relation to NAFLD and insulin resistance: A physiological approach in humans.’ Brouwers advocates first-line treatment of people with NAFLD to prevent type 2 diabetes.

Brouwers used two research methods to investigate whether exercise could reduce the level of fat in the liver in people with obesity, NAFLD and type 2 diabetes. In addition, he studied the insulin sensitivity of test subjects and whether exercise might improve insulin sensitivity in the liver of these people.

An MRI scanner was used to determine the levels of fat in the liver. Insulin sensitivity was determined by administering a fixed amount of insulin to the test subjects using an intravenous drip in the left arm. A variable quantity of glucose was administered through an intravenous drip in the test subject’s right arm. This was to ensure the test subject’s blood sugar levels would remain constant. If much glucose was required to maintain a constant blood sugar level this indicated insulin sensitivity. A small glucose requirement indicated insulin resistance. 

The key conclusions of Brouwers’ research were:

The insulin sensitivity of the liver and of the muscles in NAFLD patients was significantly lower and comparable to that of patients with type 2 diabetes.

The 12-week exercise period lowered the levels of fat in the livers of NAFLD patients, but did not lower the levels of fat in healthy, overweight people and obese patients and patients with type 2 diabetes.

The 12-week exercise period improved the insulin sensitivity of the muscles, but not of the liver, in patients with NAFLD. 

Bram Brouwers: ‘I compared three groups of people in my research. This procedure deviates from previous studies in which only one group was studied. The research shows that a 12-week exercise programme improves insulin sensitivity and moreover results in a significant reduction in the levels of fat in the liver. As such, I recommend people with NAFLD receive first-line treatment to prevent type 2 diabetes.’

Following the measurement of the levels of fat in the liver and the insulin sensitivity of the liver and muscles, test subjects were subjected to a supervised exercise regime. They were made to cycle on an ergometer two times a week for 40 minutes at an individually predetermined intensity. They would subsequently participate in one strength training session a week, consisting of eight exercises. The levels of fat in the liver and the insulin sensitivity of the liver and of the muscles were subsequently reassessed.

The research was carried out among three different groups of people. The first group (the control group) consisted of 11 healthy, overweight or obese, males. The second group consisted of 11 overweight or obese males who had elevated liver fat levels but were generally healthy. This group was unaware of having elevated levels of liver fat and did not otherwise differ from the healthy control group. The third group of test subjects consisted of 13 overweight or obese males with type 2 diabetes, who had been in treatment at their GP for at least six months prior to taking part in this study.

NAFLD, non-alcoholic fatty liver disease, is a key risk factor that may cause type 2 diabetes. At present there is no medical treatment for this condition. People who suffer from NAFLD have significantly lower insulin sensitivity comparable to people suffering from type 2 diabetes.

NAFLD is defined as a liver in which more than 5% of the total weight of the organ is made up of fat, in the absence of excessive alcohol consumption. People with NAFLD have a significantly higher risk of developing type 2 diabetes. NAFLD often occurs in people who are overweight, obese or insulin resistant. In these people, the lipids present in foodstuffs are no longer stored in the fatty tissue alone, but also flow to the liver due to the fatty tissue having reached its maximum fat storage capacity.

The research was carried out in the research group of Prof. Patrick Schrauwen and Prof. Matthijs Hesselink (Diabetes and Metabolism Research Group), and NUTRIM (School of Nutrition and Translational Research in Metabolism).

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