While the health benefits associated with intentional weight loss for some complications of obesity (such as elevated lipids and diabetes) are well documented, high-quality studies to back many other potential health benefits are harder to find.
Just how well (or poorly) the putative health benefits of long-term intentional weight loss are documented for each of the many conditions associated with obesity, is now detailed in a comprehensive review of the literature that we just published in the Annual Reviews of Nutrition.
The 40 page long review, which includes almost 250 relevant publications, supports the following main findings:
- Defining and assessing clinically relevant obesity and weight change are challenging tasks. In a given individual, there is often little relationship between the magnitude of obesity and measures of health.
- Despite its modest effect on long-term weight loss, behavioral modifications thatimprove eating behaviors and increase physical activity constitute a cornerstone for integral and sustainable weight management.
- Intentional weight loss is associated with a clinically relevant reduction in blood pressure, improvement in cardiac function, and reduction in cardiovascular events. The duration and magnitude of weight change required to achieve a significant benefit are still unclear.
- In individuals with impaired glucose metabolism at any stage, intentional weight loss achieved by any means is associated with a proportional reduction in T2DM prevalence, severity, and progression.
- Intentional weight loss is consistently associated with a clinically relevant reduction in triglycerides and increase in HDL cholesterol. The effects of weight loss on LDL cholesterol are less consistent.
- Overall, nonalcoholic fatty liver disease is commonly associated with excess weight and can show marked improvement with behavioral, pharmacological, and/or surgical weight loss. Very rapid weight loss, however, may worsen liver histology in some patients. Simi- larly, gallbladder disease is not only common in patients presenting with obesity but also highly prevalent after intentional weight loss.
- Obesity is widely recognized as a key modifiable risk factor for osteoarthritis, with sig- nificant improvements in pain and function reported with weight loss.
- Obstructive sleep apnea and obesity hypoventilation syndrome tend to improve with moderate weight loss; however, complete resolution is not common and is related to very significant weight loss.
- Asthma and COPD are clearly associated with obesity. Sustained weight loss seems to be associated with a significant improvement in asthma symptoms. Data for COPD are rather limited.
- Pregnant women who under go bariatric surgery seem to be less likely to present obstetric complications such as gestational diabetes, preeclampsia, and macrosomia.
- Data on weight loss and suicide are controversial. Caution may be in order when con- sidering bariatric surgery in patients with a history of suicide ideation or attempt.
- Data suggest that long-term weight loss is associated with an improvement in health- related quality of life. The amount of weight loss required to achieve a significant change, however, remains controversial.
However, there are many other issues where putative benefits of intentional weight loss remain even less clear than with the above.
For many conditions we will likely not know the long-term benefits of obesity treatments till better treatments become available and are tested in affected individuals.
But just how much evidence is there that any of this is actually beneficial to your health (i.e. if you are not a mouse).
This question was addressed by Benjamin Horne and colleagues from Salt Lake City, Utah, in a paper published in the American Journal of Clinical Nutrition.
The researchers review the evidence on various forms of fasting from the published literature, which consists of a grand total of three randomised controlled trials, together involving about 100 participants, with durations ranging between 2 days to 12 weeks.
Although all three trials reported some benefits in terms of body weight, cholesterol and other surrogate markers, the authors failed to find any study that looked at actual clinical endpoints (e.g., diabetes or coronary artery disease].
To be fair the authors did find two observational studies in humans (both involving the first author of this study), where fasting was associated with a lower prevalence of heart disease or diabetes but, as readers should be well aware, these types of studies cannot prove causality.
I guess it would be fair to say that the popular enthusiasm about the health benefits of various forms of fasting, as far as their benefits for humans are considered, appear largely based on hope and hype – at least as far as clinically meaningful outcomes are concerned.
This is not to say that fasting, whether alternative day or otherwise, may not well have some medical benefits – fact is, we just don’t know.
Or rather, as the authors put it,
“whether fasting actually causes improvements in metabolic health, cognitive performance, and cardiovascular outcomes over the long term; how much fasting is actually beneficial; and where the threshold of hormesis resides (i.e., a balance between long-term benefit from fasting compared with harm from insufficient caloric intake) remain open questions….considerable additional clinical research of fasting is required before contemplating changes to dietary guidelines or practice.”
While there is evidence that weight loss can be beneficial for the treatment of polycystic ovary syndrome (PCOS), there are few studies that have actually done this in a controlled fashion – even fewer in adolescents.
To test the feasibility of a dietary intervention aimed at weight loss in adolescents, Wong and colleagues from Boston Children’s Hospital, conducted a study, the results of which are published in Pediatric Obesity.
The study was conducted in 19 overweight and obese adolescents with PCOS and not using hormonal contraceptives, who were randomised either to a a low-glycaemic load or a low-fat diet.
In the 16 participants who completed the study, reduction in body fat on either diet was minimal (between 1.2 and 2.2%) with no changes in bioavailable testosterone (as the primary outcome of the study).
Not only did recruiting adolescents for this study pose a challenge (in part due to widespread use of hormonal contraception) but also the impact on weight and biochemical hyperandrogenism were marginal at best.
Clearly, as the authors note,
“Innovative strategies are needed to recruit adolescents for studies aimed at assessing independent effects of diet on features of PCOS.”
Exactly what those innovative strategies may look like, remains an open question.
Before you respond “of course” – you may wish to take a look at the systematic review by Laura Cobb and colleagues from Johns Hopkins University, published in OBESITY.
The authors looked at 71 Canadian and US studies that examined the relationship between obesity and retail food environments and concluded that,
“Despite the large number of studies, we found limited evidence for associations between local food environments and obesity. “
To be fair, the researchers also concluded that much of the research in this area lacks high-quality studies, that would lead to a more robust understanding of this issue.
In fact, the authors had to slice and dice the data to tease out “positive” findings that included a possible relationship between fast food outlets and obesity in low-income children or an inverse trend for obesity with the availability of supermarkets (a supposed surrogate measure for availability of fresh produce).
Of course, not finding a robust relationship between the food environment and obesity should not be all that surprising, given the many factors that can potentially play a role in obesity rates.
(Readers may recall that there used to be similar enthusiasm between the role of the built environment (e.g. walkability) for rising obesity rates, till the research on this issue turned out to be rather inconclusive. )
None of this should be interpreted to mean that the food or built environments have nothing to do with obesity – however, we must remember that these type of studies virtually never prove causality and that the factors that determine food and built environments are in fact almost as complicated as the factors that determine individual body weights, so finding a robust relationship between the two would be rather surprising.
Allow me to predict that with the increasing trend of fast food outlets offering healthier (or rather less-unhealthy) choices and supermarkets offering ample amounts of “fast food” and a vast array of unhealthy packaged foods, any relationship between retail food environments and obesity (even if it does exist), will be even harder to prove that ever before (outliers are no better than anecdotal evidence and should generally be ignored).
Changing food environments to provide better access to affordable healthier foods should be a “no-brainer” for policy makers, irrespective of whether or not the current environment has anything to do with obesity or not (the same could be said for walkability of neighbourhoods and the prevention of urban sprawl).
Today’s guest post comes from Catherine B. Chan and Rhonda C. Bell, Professors in Human Nutrition at the University of Alberta. It describes their Pure Prairie Eating Plan (PPEP) and how they went about developing this rather unique venture into eating local.
Healthy eating is a key factor in preventing and treating chronic diseases such as heart disease, stroke, cancer and diabetes. According to the World Health Organization, good nutrition is one of 4 key factors that could help postpone or avoid 90% of type 2 diabetes and 80% of coronary heart disease.
The Mediterranean Diet has gained popularity as a healthy diet, but evidence gathered through research on Canadian prairiegrown products (canola, flax, barley, pulses, dairy and meats) demonstrates that many local foods have similar nutritional qualities and would be more acceptable and accessible to people who live in Alberta, Saskatchewan and Manitoba.
Our recent project was conceived to develop, test and demonstrate the potential health benefits of a dietary pattern based on foods that are commonly grown and consumed in a “made in Canada” menu plan.
How the Pure Prairie Eating Plan (PPEP) was developed
The original purpose of the menu plan was to help people with type 2 diabetes adhere to the nutrition recommendations of the Canadian Diabetes Association (CDA) by focusing on healthy food choices with a local flavour. The menu plan concept integrates knowledge gained through research related to consumer behavior, behavior change, and nutritional quality of dairy, meats,
canola, pulses and grains.
During its development, it was recognized that a diet healthy for people with diabetes is a diet healthy for everyone. This notion was reinforced in a Consensus Conference with people living with type 2 diabetes, who felt strongly that their diet should not be different from others.
This approach provided knowledge that formed the basis of a 4-week menu plan focused on foods that are grown and readily available in the Canadian prairies. The plan consists of 28 days of diabetes-friendly menus including 3 meals and 3 snacks each day, approximately 100 recipes, tips for healthy eating, pantry and grocery lists and other helpful information.
If followed consistently, the menus meet the recommendations of Eating Well with Canada’s Food Guide on a daily basis, and over 1 week averages approximately 2000 kcal/day with macronutrient distribution consistent with health recommendations.
The menus also provide total fibre between 25 and 50 g/day. Many of the recipes have been obtained from our provincial agricultural commodity groups (see http://pureprairie.ca/oursponsors/).
The recipe ingredients feature many homegrown foods from each food group. They are quick and easy to make…and tasty!
Our Research Findings
Funding was secured through the Alberta Diabetes Institute to pilot test the menu plan concept in a 12-week intervention that measured both quantitative (disease biomarkers) and qualitative (acceptability, accessibility and acceptability) responses to the menu plan of 15 people with type 2 diabetes.
The results, published in the Canadian Journal of Diabetes, showed that most participants liked the menu plan and their A1c decreased by an average of 1%.
However, many were not used to cooking from scratch and cited time as a barrier to using the menu plan more. The benefits of the menu plan included more structure in participants’ diets, increased frequency of snacking, increased awareness of food choices, purchasing healthier foods and better portion control.
Participants were aware of better blood sugar control. Participants were pleased with the variety of food choices and liked the taste of the recipes. They also liked the flexibility of the menu plan.
In the second phase, which included 73 participants, we included a 5-week curriculum delivered in a smallgroup setting with a facilitator and included assessment of hemoglobin A1c as a measure of blood sugar control as well as cardiovascular risk factors. Nutrient intake was assessed using a computerbased 24-hour recall system called WebSpan.
In this study, 86% of those enrolled completed all aspects of the programme, including the 3-month followup. On average, there were decreases in A1c (0.7%), body mass index (0.6 kg/m2) and waist circumference (2 cm). (Note that a decrease in A1c of 0.5% is considered to be a clinically relevant improvement in blood sugar control.)
Although the weight loss was relatively small, it correlated with the reduction in A1c more strongly than any other factor examined.
Analysis of nutrient intakes showed decreases in total energy intake (127 kcal/day), total fat (7 g), total sugar (25 g) and sodium (469 mg).
The Pure Prairie Eating Plan (PPEP)
With promising outcomes regarding the nutritional adequacy and acceptability of the menu plan, and with encouragement from Alberta agricultural commodity groups and others, we packaged and rebranded the menu plan as the Pure Prairie Eating Plan (PPEP): Fresh Food, Practical Menus and a Healthy Lifestyle.
PPEP is available for purchase in selected bookstores throughout the prairies and proceeds from its sale will be used to further research into improving the lifestyle behaviours of Canadians with or at risk of chronic diseases.
For a listing of bookstores currently stocking PPEP, or to buy online, click here
Healthcare providers wishing to purchase 6 copies or more can contact email@example.com for a discount.
We would like to acknowledge the financial support of our sponsors.
Dr. Catherine Chan is Professor of Human Nutrition and Physiology at the University of Alberta. Her research (Physical Activity and Nutrition for Diabetes in Alberta, PANDA) focuses on the development, implementation and evaluation of healthy behavior interventions as well as on identification and testing of healthy food ingredients. She is also the Scientific Director for the
Diabetes, Obesity and Nutrition Strategic Clinical Network of Alberta Health Services.
Dr. Rhonda Bell is Professor of Human Nutrition and leader of the ENRICH project (Promoting Appropriate Maternal Body Weight in Pregnancy and Postpartum through Health Eating) at the University of Alberta. The ENRICH project aims to develop and promote practical strategies for women to maintain healthier weights during and following pregnancy.