Credit: Jim Henderson, CC-BY-SA 3.0
Banning sodas from school vending machines, building walking paths and playgrounds, adding supermarkets to food deserts and requiring nutritional labels on restaurant menus: Such changes to the environments where people live and work are among the growing number of solutions that have been proposed and attempted in efforts to stem the rising obesity epidemic with viable, population-based solutions. But which of these changes actually make an impact?
To answer that question, many public health researchers take advantage of "natural experiments"—looking at people's calorie consumption or physical activity levels, either comparing before and after a policy or environmental change, or comparing against a similar group of people not affected by that change. But not all natural experiments are created equal.
"Rigorous science is needed to evaluate these natural or quasi-experiments," said Amy Auchincloss, PhD, an associate professor at the Drexel University School of Public Health who was a member of a research team that authored a new study published online ahead of print in Obesity Reviews: "Impact of policy and built environment changes on obesity-related outcomes: a systematic review of naturally occurring experiments." The review was led by Stephanie Mayne, a doctoral student supervised by Auchincloss, and also co-authored by Yvonne Michael, ScD, an associate professor and associate dean for academic and faculty affairs in the Drexel University School of Public Health.
The Drexel team reviewed the state of the science on this topic, evaluating the results and methods of all previous such studies published in the medical literature, in particular:
- Which policies and built environment changes have been evaluated via natural- or quasi-experiments and what are the results from these studies?
- Are there issues of concern with the studies' design, including methods of assessment?
- What are the limitations of these studies and areas where additional science is needed?
This is the first review that has examined the use of natural- or quasi-experiments to evaluate the efficacy of policy and built environment changes on obesity-related outcomes (body mass index, diet or physical activity). The review included PubMed (Medline) articles published 2005-2013; 1,175 abstracts and 115 papers were reviewed and ultimately 37 studies were included in the review.
The review identified certain types of interventions that are more successful than others in improving obesity-related outcomes, and identified areas where more research is needed to draw conclusions about obesity-related outcomes:
Diet & Food Policy Changes
Changes with strong impacts were ones that improved the nutritional quality of foods:
- Trans-fat bans
- Sugary food and beverage availability limits
- Higher-fat food availability limits
Changes that had smaller or no impacts in the research to date included:
- Nutritional information requirements
- Supermarkets built in underserved areas
Physical Activity Focused Changes
Changes with stronger impacts included:
- Active transportation infrastructure improvements
- Changes studied after longer-term follow-up periods
More research is needed to look at physical activity effects (not just use of amenities) for built environment changes including:
- Park improvements
- Trails
- Active transportation infrastructure
The researchers noted that a common shortcoming in many studies is that they only measured process outcomes such as food purchases or use of bike/transit infrastructure, rather than measuring the desired health outcomes, such as weight loss.
"Research suggests that people will use new amenities like bike shares, and limit purchases of unhealthy foods in specific contexts like schools," said Mayne. "But it is less clear whether these changes translate into overall improvements in diet and physical activity."
Likewise, only a few studies directly assessed impacts on BMI or weight; thus, the authors concluded that evidence is lacking on whether environmental and policy modifications are successful in maintaining healthy weight or reducing excess weight.
A key value of a natural experiment is that it can narrowly focus on the direct impact of a change in policy or infrastructure on an affected population—making natural experiments an important way to check on what kinds of public policies and investments make real-world impacts on health, and to what degree. The authors concluded that more natural experiments are needed to strengthen the evidence base about obesity-related policies and interventions. They also recommend more natural experiments to explore whether the timing of a change or repeated exposure to the changed condition enhances or reduces impacts on obesity-related outcomes.
The authors generally found stronger results in studies that had longer follow-up periods after a policy change or other intervention.
Explore further: It's tough to shift that weight, studies show
More information: Obesity Reviews, http://ift.tt/1q9dxEm 1/obr.12269/abstract
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© Medical Xpress 2011-2014, Science X network
Credit: Jim Henderson, CC-BY-SA 3.0
Banning sodas from school vending machines, building walking paths and playgrounds, adding supermarkets to food deserts and requiring nutritional labels on restaurant menus: Such changes to the environments where people live and work are among the growing number of solutions that have been proposed and attempted in efforts to stem the rising obesity epidemic with viable, population-based solutions. But which of these changes actually make an impact?
To answer that question, many public health researchers take advantage of "natural experiments"—looking at people's calorie consumption or physical activity levels, either comparing before and after a policy or environmental change, or comparing against a similar group of people not affected by that change. But not all natural experiments are created equal.
"Rigorous science is needed to evaluate these natural or quasi-experiments," said Amy Auchincloss, PhD, an associate professor at the Drexel University School of Public Health who was a member of a research team that authored a new study published online ahead of print in Obesity Reviews: "Impact of policy and built environment changes on obesity-related outcomes: a systematic review of naturally occurring experiments." The review was led by Stephanie Mayne, a doctoral student supervised by Auchincloss, and also co-authored by Yvonne Michael, ScD, an associate professor and associate dean for academic and faculty affairs in the Drexel University School of Public Health.
The Drexel team reviewed the state of the science on this topic, evaluating the results and methods of all previous such studies published in the medical literature, in particular:
- Which policies and built environment changes have been evaluated via natural- or quasi-experiments and what are the results from these studies?
- Are there issues of concern with the studies' design, including methods of assessment?
- What are the limitations of these studies and areas where additional science is needed?
This is the first review that has examined the use of natural- or quasi-experiments to evaluate the efficacy of policy and built environment changes on obesity-related outcomes (body mass index, diet or physical activity). The review included PubMed (Medline) articles published 2005-2013; 1,175 abstracts and 115 papers were reviewed and ultimately 37 studies were included in the review.
The review identified certain types of interventions that are more successful than others in improving obesity-related outcomes, and identified areas where more research is needed to draw conclusions about obesity-related outcomes:
Diet & Food Policy Changes
Changes with strong impacts were ones that improved the nutritional quality of foods:
- Trans-fat bans
- Sugary food and beverage availability limits
- Higher-fat food availability limits
Changes that had smaller or no impacts in the research to date included:
- Nutritional information requirements
- Supermarkets built in underserved areas
Physical Activity Focused Changes
Changes with stronger impacts included:
- Active transportation infrastructure improvements
- Changes studied after longer-term follow-up periods
More research is needed to look at physical activity effects (not just use of amenities) for built environment changes including:
- Park improvements
- Trails
- Active transportation infrastructure
The researchers noted that a common shortcoming in many studies is that they only measured process outcomes such as food purchases or use of bike/transit infrastructure, rather than measuring the desired health outcomes, such as weight loss.
"Research suggests that people will use new amenities like bike shares, and limit purchases of unhealthy foods in specific contexts like schools," said Mayne. "But it is less clear whether these changes translate into overall improvements in diet and physical activity."
Likewise, only a few studies directly assessed impacts on BMI or weight; thus, the authors concluded that evidence is lacking on whether environmental and policy modifications are successful in maintaining healthy weight or reducing excess weight.
A key value of a natural experiment is that it can narrowly focus on the direct impact of a change in policy or infrastructure on an affected population—making natural experiments an important way to check on what kinds of public policies and investments make real-world impacts on health, and to what degree. The authors concluded that more natural experiments are needed to strengthen the evidence base about obesity-related policies and interventions. They also recommend more natural experiments to explore whether the timing of a change or repeated exposure to the changed condition enhances or reduces impacts on obesity-related outcomes.
The authors generally found stronger results in studies that had longer follow-up periods after a policy change or other intervention.
Explore further: It's tough to shift that weight, studies show
More information: Obesity Reviews, http://ift.tt/1q9dxEm 1/obr.12269/abstract
Medical Xpress on facebook
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It's tough to shift that weight, studies show
Feb 24, 2015
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 kee ...
Childhood obesity prevention programs impact LDL-C, HDL-C
Dec 03, 2014
(HealthDay)—Childhood obesity prevention programs are beneficial for low-density lipoprotein cholesterol (LDL-C) and high-density lipoprotein cholesterol (HDL-C), according to a systematic review and meta-analysis ...
Renewed call in Lancet for governments to get smart to curb obesity
Feb 20, 2015
A University of Otago economist has written in the latest issue of the prestigious medical journal The Lancet that Government policy-makers serious about curbing the obesity epidemic should take into account the evidence from b ...
Too many food choices exacerbate the battle against obesity, researchers find
Feb 23, 2015
Some scientists say that when mothers eat poorly during pregnancy, they pass along traits to their children that make them more likely to have poor diets and have related health problems.
Study of weight-loss strategies for people with disabling conditions finds more approaches needed
Mar 10, 2015
A review of nutrition and weight-loss interventions for people with impaired mobility found strategies are sorely lacking for people with neurological disabilities, according to a team of researchers from Case Western Reserve ...
Recommended for you
New study suggests connection between body temperature and obesity
Mar 19, 2015
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Study: Fast-food curb did not cut obesity rate in South LA
Mar 19, 2015
A much-hailed law that restricted the opening of new stand-alone fast-food restaurants in one of the poorest sections of Los Angeles did not curb obesity or improve diets, a new study found.
Sense of smell may reveal weight bias
Mar 18, 2015
Could our reaction to an image of an overweight or obese person affect how we perceive odor? A trio of researchers, including two from UCLA, says yes.
High sugar consumption linked to obesity, research finds
Mar 17, 2015
People who eat more sugar are much more likely to be obese than those who eat less, according to a landmark finding by University of Reading scientists.
What we talk about when we talk about obesity
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In philosophy classes, one of the first lessons in logic that students learn is what fallacies are and how to avoid them. One of my favorites is the false dichotomy, mainly because of its crystal-clear examples: you'r ...
Babies' body mass index may predict childhood obesity
Mar 11, 2015
Body mass index (BMI) during infancy may help to predict if a child will be obese by age four. In a study focused on the infant BMI-childhood obesity relationship in a cohort with a majority of African-American children, ...
User comments
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