Study probes weight gain after diets
“Trying to lose weight alters your brain and hormones so you’re doomed to pile it on again,” the Daily Mail reported.
Many people struggle to maintain their new weight after a diet, and this news is based on a small study that investigated the biological reasons for this. Researchers monitored the hormone levels of 50 volunteers who were given very low calorie diets, of around 500 calories a day, for 10 weeks alongside weight loss advice, a recommended exercise programme and supervision from a dietitian. Comparing levels of several dietary hormones before, during and after the weight loss programme, researchers found that many of the hormonal changes experienced during the diet persisted a year after the diets ended, when participants were trying to maintain their new lower weight. Researchers suggest that this means the body has a hormonal “backlash” against the lack of calories during a diet, and will instruct the body to replace lost weight in the future.
This study provides some useful evidence about hormone levels and appetite in obese people following a weight loss programme. However, to make firm conclusions, larger studies are needed to compare dieting participants with people not attempting the diet. People who want to lose weight should not be alarmed by this study’s findings or feel “doomed”. It is well known that keeping off weight lost through dieting is difficult. Instead, they should see a dietitian or their GP if they are struggling to maintain or reach a healthy weight.
Where did the story come from?
The study was carried out by researchers from the University of Melbourne and La Trobe University, both in Australia. It was funded by Australia’s National Health and Medical Research Council, the Sir Edward Dunlop Medical Research Foundation and grants from the Endocrine Society of Australia and the Royal Australasian College of Physicians. The study was published in the peer-reviewed New England Journal of Medicine.
During weight loss diets, people experience changes in the levels of various appetite-regulating hormones in the body. The researchers behind this new study say it is not yet known whether these changes are sustained when people try to maintain their new lower weight.
The story was reported accurately by the Daily Mail. However, the newspaper’s announcement that people trying to lose weight are “doomed” to put it back on again seems overly negative and does not represent the findings of this small study.
What kind of research was this?
This research looked at 50 obese men and women who took part in a 10-week weight loss programme. Measurements of their weight, hormone levels and appetite were recorded before, during and one year after the programme.
The research was a case series. This is a type of descriptive study of a group of people who have something in common. For instance, they may have the same condition or are using the same treatment. This type of study describes characteristics or outcomes in a single group, but does not compare them with people who are offered a different treatment or who do not have the condition.
The researchers say that many people experience initial weight loss during a diet, but that most obese people fail to maintain their reduced weight. Understanding the biological barriers that stop people keeping off lost weight, and the hormones involved, is crucial for designing ways to prevent weight gain, they argue.
What did the research involve?
Researchers recruited 50 obese adult volunteers through a newspaper advert (34 post-menopausal women and 16 men) to undertake a 10-week weight loss programme. This programme featured a very low energy diet, which provided 500–550 calories a day. This is around a quarter of the normal intake for a woman.
A healthy body mass index is considered to be between 18.5 and 25kg/m2. In this study, the researchers recruited people with a body mass index between 27 and 40. Smokers, people with significant illness (including diabetes) and those taking medications known to affect body weight were excluded from the study.
At the end of the 10-week programme, participants received individual counselling and written advice from a dietitian on a recommended dietary intake to maintain weight loss. They were also encouraged to perform 30 minutes of moderately intense physical activity on most days of the week. Over the following year, participants visited the hospital every two months and were contacted by telephone between visits for continued counselling.
Patients were assessed for circulating levels of a variety of hormones at the start of the study, at week 10 and after the study at week 62. Subjective ratings of appetite were also measured. Measured hormones included:
- leptin – a hormone produced by fat cells and an indicator of energy stores
- peptide YY, glucagon-like peptide 1, amylin, pancreatic polypeptide, cholecystokinin and insulin – hormones released from the gastrointestinal tract and pancreas in response to food (they reduce food intake)
- ghrelin – a hormone also released in response to food, which stimulates hunger
- gastric inhibitory polypeptide – a hormone that may promote energy storage
Researchers used two types of analysis to report their findings:
- an “intention to treat” analysis that included all participants who started the study, even if they did not complete it
- a secondary analysis that included only those who completed the trial (34 participants)
The intention to treat analysis is the preferred analysis, as including only participants who completed the trial will bias the results. By including everyone who started a study, an intention to treat analysis also reveals other factors, such as the potential dropout rate for a treatment if it were used in clinical practice.
What were the basic results?
Of the 50 participants who began the study, only 34 completed it (68%). Although there were no significant differences between those who completed the study and those who did not, there was a trend towards younger participants not completing the study, which may have had some effect on the results.
At the end of the 10-week programme, the average (mean) weight loss was 13.5kg, and participants had a significant increase in subjective measures of appetite (p<0.001). Significant reductions were seen in levels of the hormones leptin, cholecystokinin, insulin and the appetite-suppressing peptide YY (P<0.001). There were also increases in levels of the appetite-stimulating hormone ghrelin (P<0.001).
One year after the end of the programme, mean weight loss since the start of the study was 7.9kg. This means that participants had put back on some of the weight initially lost, but had maintained an overall weight loss. A year after the end of the weight loss programme, there were still significant differences in the mean levels of appetite-suppressing peptide YY and the appetite-stimulating hormone ghrelin (p<0.001) compared with at the start of the study. Participant-reported hunger had also risen (p<0.001).
How did the researchers interpret the results?
The researchers concluded that after initial weight reduction in obese people, circulating levels of hormones thought to encourage post-diet weight regain do not revert to the levels seen before weight loss. One of the researchers described this as a “co-ordinated defence mechanism” with multiple components all directed towards making us put on weight. In other words, the body mounts a backlash against dieting and the reduced intake of food and energy it brings.
The researchers also said that long-term strategies to counteract this change may be needed to prevent “obesity relapse”.
This small study found that after obese adults completed an intense weight loss programme, the levels of several dietary hormones did not revert to their pre-diet state. Instead, during this long-term maintenance phase, certain hormone levels thought to affect appetite and weight gain remained as they were during the intense weight loss phase. This may affect a person’s ability to maintain the weigh loss benefits from their very low calorie diet plan.
The study had limitations, some of which the authors noted:
- The study featured a very low calorie diet (500–550 calories a day), recommended exercise and supervision from a dietitian. The levels of support, motivation and weight loss seen in this study may not be typical of those seen in everyday diets. In particular, this diet may not reflect the type of dieting in people hoping to lose a moderate amount of weight.
- The study recruited people with a minimum BMI of 27 and an average BMI of 35 (healthy BMI range is 18.5 to 25). Very low calorie diets are generally not considered to be suitable for people who are only slightly overweight or with a BMI just above 25. Therefore, participants in this study may not represent the types of people who would normally use these diets.
- This study did not have a control group of people who did not participate in the weight loss programme. Using a control group, though not essential for this type of study, would have allowed the researchers to make allowances for the natural fluctuations in many hormones.
- The dropout rates were high, with only 34 people completing the study out of the original 50 who started it. This is typical for weight loss studies. The researchers say that there were no significant differences between those who did and did not complete the study, though there was a trend for younger participants to drop out. Therefore, the findings of this study may not be useful for a younger obese population.
- The authors mainly analysed results for only the people who completed the study. It is not known whether changes in hormone levels and appetite were seen in the 16 people who did not complete the study.
- This was a small study of only 50 people. To draw more accurate conclusions about the effects of dieting in obese people, larger studies are needed. The results of this study may help in designing these.
People who want to lose weight should not be alarmed by this study’s findings or assume that dieting is futile or will damage their hormone balance. Instead, they can see a dietitian or their GP if they are struggling to lose weight or maintain a healthy weight.
- Sumithran P, Prendergast LA, Delbridge E et al. Long-Term Persistence of Hormonal Adaptations to Weight Loss. N Engl J Med 2011; 2011.365:1597-1604