Fatty food and long-term weight gain

Behind the Headlines

Wednesday August 25 2010

Fast food is high in saturated fat

“A moment on the lips really does mean a lifetime on the hips,” says the Daily Mail. The newspaper suggests that even short periods of overeating “could cause the waistline to bulge years later”.

This story is based on a study that asked 18 young adults of normal weight to reduce their physical activity and increase their calorie intake by 70% by eating fast food for four weeks. During this period, a further 18 volunteers maintained their normal diet and activity levels. Two-and-a-half years after the study finished, the overeating group weighed about 3kg more than they had at the start of the study, while the other group’s weight had not changed.

This study has a number of flaws, primarily that the small study groups may have led different lifestyles outside of the study period, which could be the true cause of the long-term weight changes observed. Overall, this study’s limitations mean that it cannot reliably inform us about the long-term effects of just a few weeks of unhealthy living. However, being overweight or obese is associated with numerous adverse effects on health, and therefore overeating and inactivity are best avoided.


Where did the story come from?

The study was carried out by researchers from Linköping University in Sweden and was funded by Linköping University Hospital, Linköping university, the Gamla Tjänarinnor Foundation, the Medical Research Council of Southeast Sweden and the Diabetes Research Centre (Linköping university). It was published in the peer-reviewed journal Nutrition & Metabolism.

The Daily Mail, BBC News, and the Daily Express report the findings accurately. The Daily Mail includes quotes from a study author about the possibility that longer-term eating habits and attitude to weight gain may have differed between the groups of participants. However, there are further, unreported limitations to the study that could discount the results.


What kind of research was this?

This was a non-randomised controlled study looking at the long-term effects of a short period of overeating and reduced physical activity. It compared two groups of volunteers that were asked to either follow their normal lifestyle or to overeat and limit their physical activity.

The regimen followed by each participant was selected rather than randomly allocated, which means that there may be differences between the groups that account for the long-term weight changes seen. In particular, participants who were placed into the overeating group had to agree to follow an unhealthy diet and reduce their activity, and this may mean they were less concerned about their weight than the control group, who did not overeat. This means that we cannot be sure that any long-term weight differences seen were due to the study’s designated period of overeating and inactivity.


What did the research involve?

The researchers enrolled 18 healthy young adult volunteers whose weight was normal (body mass index <25) and who were willing to put on weight during the study. They were instructed to double the amount of calories they consumed and to walk no more than 5,000 steps a day for a four-week period. The researchers also enrolled an age- and gender-matched control group who were asked to maintain their normal eating and physical activity habits during the four-week period. The researchers then looked how weight changed in the overeating group and in the control group, and how body fat changed in the overeating group.

At the start of the study, the overeating group had their diet and activity assessed using a three-day food diary and pedometer recordings. During the intervention period, they were told to aim for no more than 5,000 steps a day and to double their calorie intake by eating at least two fast-food meals a day (or foods high in protein and saturated fat). Participants reported on their eating during the dietary intervention period and provided receipts for food eaten. The overeating group ate on average 5,753 kilocalories a day during the intervention, a 70% increase in their usual calorie intake. Most of the extra calories they ate came from fast food.

The researchers measured the groups’ weights before and after the four-week period, and then six months, one year and two-and-a-half years later. They also measured body fat in the overeating group.


What were the basic results?

The researchers found that after the four-week intervention period the group who overate and reduced their activity increased their weight by an average of 6.4kg. Six months after returning to their normal diet and activity levels, they had lost most of this weight but were still an average of 1.6kg heavier than at the start of the study. One year later, the overeating participants still weighed an average of 1.5kg more than they did at the start of the study. This change in weight was almost entirely due to an increase in body fat (1.4kg increase). Two-and-a-half years later, they weighed an average of 3.1kg more than they did at the start of the study.

The control group’s weight did not change between the start of the study and two-and-a-half years later.


How did the researchers interpret the results?

The researchers say that a short-term intervention period of increased calorie consumption and reduced physical activity was associated with an increased body fat mass a year later. They say that this raises the issue of whether a short period of overeating leads to long-term increases in fat mass.



This study has a number of limitations, such as its small size and the fact that the groups were not randomly assigned. Participants who were in the overeating group had to be happy to gain weight in the study, and they may have been less concerned about their weight than individuals in the control group. Ideally, the researchers should have enrolled only people who would be happy to gain weight and then randomly assigned them to either follow a healthy lifestyle or the high-fat, low-exercise regime for four weeks.

Additionally, the researchers only compared the groups’ eating and exercise habits at the time of intervention but not before or after the four-week study period. This means these important factors may have differed between the groups. Overall, these limitations mean that we cannot be sure that any differences in long-term weight and body fat were solely due to the four-week period of overeating and inactivity.

Other limitations include the fact that the results may not apply to older and less healthy individuals, as only young, healthy adults participated.

Despite the fact that this study cannot tell us what the long-term effects of this intervention are, being overweight or obese is associated with numerous adverse effects on health. Overeating foods high in saturated fat and remaining sedentary, as tested in this study, is not recommended for anyone.

Analysis by Bazian

Edited by NHS Choices


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