New studies by McMaster University researchers, published in CMAJ Open, have confirmed that people of all ages find it difficult to prevent weight gain; that it is terrifically difficult to get rid of it later and to keep it off once lost. However, even small weight losses can mean better health.
The McMaster Evidence Review and Synthesis Centre reviewed hundreds of recent studies about overweight and obesity published in the past decade. 

“This is an important area to investigate, as we know that overweight and obesity are public health problems impacting a growing proportion of the Canadian population, and that this is related to many health problems,” said Leslea Peirson, lead author and study co-ordinator.

The reports reviewed studies about the prevention and treatment of overweight and obesity among children; the prevention and treatment of overweight and obesity among adults and about keeping lost weight off.

• Regarding prevention of overweight/obesity among children and youth, a review of 90 studies found:
o There were small improvements in weight outcomes. The programs that work best targeted school-aged children and youth, were delivered in educational settings, included both diet and exercise and lasted 12 weeks to a year.

• Regarding treating overweight/obesity among children and youth, a review of 31 studies found:
o Evidence showed that enrolment in a program that focuses on changes in diet, exercise and lifestyle can help reduce weight and, more importantly, enrolment in such a program also improves health and quality of life in children and adolescents. However, the permanence of this weight loss has not been well studied.

• Regarding prevention of overweight/obesity among adults, a search of more than two decades of research literature found:
o Almost no trials have been conducted to investigate programs that help normal-weight adults maintain their normal weight. A single small study conducted in the U.S. in the 1980s showed benefits from a 12-month education and incentive-based program.

• Regarding treating overweight/obesity among adults, a review of 68 studies found:
o Doing some activity is better than doing nothing. Adults who took part in some form of treatment had, on average, a three kilogram (or seven pound) greater weight loss than adults who did not. Weight loss results did not differ whether treatments involved diet, exercise, lifestyle changes or drugs (orlistat or metformin), but the drugs had side effects that the other strategies did not.
o A clinically meaningful weight loss of five to 10 per cent of body weight, which was found in this review, can positively impact the health of adults who lose weight.

• Regarding keeping that weight off once lost, a review of eight studies since 2011 found:
o Doing something to keep that weight off, either through diet, exercise, lifestyle changes or even drugs, can help, at least in the short term. There just weren’t any studies addressing the long-term sustainability of weight maintenance strategies.
o Use of drugs along with behavioural changes may help maintain a loss of five percent body weight, but this combined strategy did not make a difference in maintaining a loss of 10 per cent of body weight.
“We know that more research is needed that looks at programs designed to prevent weight gain in normal weight adults, youth and children,” said Peirson. “Future research should look at the longevity of weight loss and study the health consequences of repeated cycling of weight loss and gain.”