Tuesday December 2 2014
A gastric band essentially shrinks the size of the stomach
"Weight loss surgery isn't just a quick fix to becoming healthy – you have to exercise too," the Mail Online reports.
Weight loss surgery, such as fitting a gastric band, usually results in significant weight loss.
But this weight loss doesn't automatically lead to improvements in important markers for metabolic health, such as insulin sensitivity. A low level of insulin sensitivity is a major risk factor for type 2 diabetes.
In a new study, 128 adults were randomised into two groups. One group received a six-month moderate exercise programme, while the other received a six-month health education programme.
After six months, those that followed the exercise programme had better insulin sensitivity than those following the educational programme.
But the picture was not completely clear. Quite a few people dropped out of the study or did not adhere to the six-month exercise programme fully.
This could mean the programme as a whole would not yield any significantly better improvements at a population level. This balance of cost and benefit influences whether a supervised exercise plan would (or should) be funded on the NHS.
Where did the story come from?
The study was carried out by researchers from the University of Pittsburgh, East Carolina University and Florida Hospital in the US.
It was funded by the US National Institutes of Health.
The study was published in The Journal of Clinical Investigation, a peer-reviewed medical journal, on an open access basis, so it is free to read online or download as a PDF.
The Mail Online's coverage of the science was generally accurate, although they did not discuss the issues around compliance to the exercise programme.
What kind of research was this?
This was a single-blinded, prospective, randomised clinical trial (RCT) to find out whether, after weight loss surgery, an exercise programme improved insulin sensitivity, compared with a health education programme.
A single-blinded RCT means the researchers analysing the data at the end of the trial did not know what programme each individual was assigned to.
The study reports weight loss surgery can result in dramatic weight loss and helps partially cure type 2 diabetes in a large percentage of obese patients.
However, it seems their insulin sensitivity does not return to healthy levels, despite significant weight loss.
Insulin helps lower blood glucose levels. How sensitive the body is to insulin (insulin sensitivity) varies from person to person.
People with type 2 diabetes are not very sensitive to insulin (insulin resistant), meaning they need more insulin to lower their blood sugar levels than someone who is more insulin sensitive.
Insulin sensitivity is often used as an indicator of how well the body is regulating blood glucose levels and can be a sign of diabetes.
The researchers thought exercise might help insulin sensitivity in patients after weight loss surgery, so they designed the trial to test this theory.
What did the research involve?
The researchers randomised 128 mainly female adult volunteers who had recently undergone weight loss surgery into two groups.
One group was assigned a six-month semi-supervised moderate exercise programme (66 people), while the other group was assigned a health education programme over a similar period to act as a control group (62 people).
After six months, the researchers compared the two groups for insulin sensitivity, fitness and body composition.
All participants had a Roux-en-Y gastric bypass within one to three months of the study's start date. This procedure involves creating a small pouch at the top of the stomach.
This pouch is then connected directly to a section of the small intestine, bypassing the rest of the stomach and bowel, so it takes less food for a person to feel full.
The Roux-en-Y gastric bypass was described in the research as the most commonly performed weight loss surgery in the US.
Participants had to be aged between 21 and 60 to be included in the study. They were excluded if they had a diagnosis of diabetes, hypertension, anaemia, hypothyroidism, elevated liver enzymes, current malignancy or a history of cancer within the past five years.
They were also excluded if they had had a stent placement within the past three years, or if they had a history of myocardial infarction, angioplasty, angina, liver disease or neuromuscular disease.
The exercise intervention was three to five exercise sessions per week, with at least one directly supervised session a week to ensure that target exercise intensity and duration was achieved.
Participants used a heart rate monitor and recorded detailed logs of their exercise sessions, including the type of exercise, duration and average heart rate.
Exercise was built up gradually, but they were aiming to achieve a minimum of 120 minutes of exercise a week for the last three months of the intervention.
The health education control group was asked to attend six health education sessions. The sessions were held once a month, and involved lectures, discussions and demonstrations providing up-to-date information on topics such as medication use, nutrition and upper body stretching.
The participants in the exercise group also received the same health education sessions, including advice on nutrition (six sessions, one every month).
As well as insulin sensitivity, the team measured glucose effectiveness, which was worked out from an intravenous glucose tolerance test.
Data was analysed to assess whether the exercise programme worked better than the education programme for:
- all participants using intention-to-treat (ITT) calculations
- participants who completed the exercise and education interventions using a per protocol (PP) approach
What were the basic results?
A total of 128 participants were randomised at the start of the trial, and 100 completed the six-month interventions as planned, giving an overall completion rate of 78%.
This breaks down into 67% completing the exercise intervention and 90% completing the educational intervention.
There was a similar and significant decrease in body weight, waist circumference and fat mass for both groups following surgery and the interventions. Insulin sensitivity also significantly improved in both groups post-surgery.
The main finding was that exercise intervention led to a greater improvement in insulin sensitivity than the education intervention.
But this was only true (statistically significant) using the per protocol data. This means the people who completed the exercise intervention from start to finish benefited more than the education group.
However, not everyone assigned to the exercise intervention completed it. When these "non-completers" were included in the analysis (ITT analysis), the improvement for each group was the same.
The fact that a relatively large minority dropped out of the exercise programme has wider implications when considering whether such a programme would be effective and efficient if it was rolled out to larger populations.
Additional ITT analysis showed exercise improved cardiorespiratory fitness compared with the education group.
How did the researchers interpret the results?
The authors interpreted their results as meaning that, "Moderate exercise following RYGB [Roux-en-Y gastric bypass] surgery provides additional improvements in SI, SG, [insulin sensitivity and blood glucose control] and cardiorespiratory fitness compared with a sedentary [non-active] lifestyle during similar weight loss."
This study provides some tentative evidence that adding a six-month exercise programme shortly after people have weight loss surgery might lead to more improvements in insulin sensitivity compared with a six-month-long educational programme.
However, the picture is muddied by the fact quite a few people dropped out or did not adhere to the exercise programme fully. It seemed that if people were able to stick to the exercise programme, it was more beneficial than no exercise.
This might seem obvious, but if this programme was introduced more widely, you might expect a similar proportion of people not to complete it. This could mean the programme as a whole would not yield any significant improvements at a population level.
Indeed, when all participants in each group were included in the analyses, there was little difference between the groups.
The authors reported high completion rates for both exercise and educational interventions – both over 90%. However, our calculations put this at a significantly lower 67% and 90% respectively.
Irrespective of the exact figures, those that did not complete the intervention did influence the results. This suggests the exercise intervention may be more effective than an education-only programme, but there is an important group who failed to adhere to it.
If the reasons for this non-compliance are not explored, they have the potential to widen health inequalities.
The study also mostly recruited adult women who were free from many additional diseases, such as cancer. This group might not be representative of the wider UK population undergoing weight loss surgery. Further trials involving more representative groups would give more generally applicable results.
In sum, for those who completed the trial as planned, exercise improved their insulin sensitivity, but there were adherence issues that call into question whether it would be effective at a population level.
If you want to gain the maximum benefit from weight loss surgery, it is important to adhere to any post-surgical advice, such as recommendations on diet and exercise.
Failure to do so could lead to a worsening of your health and possibly regaining some of the weight you previously lost.
Analysis by Bazian. Edited by NHS Choices. Follow Behind the Headlines on Twitter. Join the Healthy Evidence forum.