Physical activity and diet


The purpose of this review is to assess the effects of lifestyle intervention programs, specifically related to physical activity and diet, in preventing and controlling type 2 diabetes for individuals at risk and the general population. It has been prepared to provide background information to the Type 2 Diabetes Education Committee at the College of Family Physicians of Canada and others on the current available evidence regarding the efficacy and effectiveness of interventions and strategies used to date. The objective of the review is to provide guidance for translating current evidence into practical clinical strategies for the development of a type 2 diabetes education strategy at the primary health care level.


Worldwide, type 2 diabetes has soared to epidemic proportions and is at the forefront of current public and community health intervention in both Western and developing countries. Type 2 diabetes has been associated with an aging population, a dramatic rise in the prevalence of obesity, and a more sedentary lifestyle.(1;2) It is estimated that 135 million people worldwide had diagnosed diabetes in 1995, and this number is expected to rise to at least 300 million by 2025.(3)

Over 2.25 million Canadians are estimated to have diabetes, and 90% of all cases in Canada are classified as type 2 diabetes.(4) Individuals with type 2 diabetes may have few or no classic symptoms of hyperglycemia and up to one half of all cases of type 2 diabetes may be undiagnosed.(5) Both diagnosed and undiagnosed diabetes are strong risk factors for cardiovascular disease along with the associated risks and complications that result in significant morbidity and mortality.(6) Health care costs for diabetes and its complications in Canada are estimated at about $9 billion a year.(4) Effective primary prevention programs are urgently needed to reduce the clinical and economic health burden of type 2 diabetes.(7)

The development of type 2 diabetes is the result of a complex interaction between genetic and environmental factors and has been researched extensively in the scientific and medical literature.(8)

It is believed that type 2 diabetic patients pass through a phase of impaired glucose tolerance (IGT) before developing diabetes and it is estimated that 25 to 75% of those persons with IGT develop diabetes within 10 years of the determination of IGT.(9;10) Risk factors for developing type 2 diabetes include advancing age, increased body mass index (BMI) and central fat distribution, weight gain in adulthood, ethnicity, family history of diabetes, low birth weight, sedentary lifestyle, higher systolic blood pressure, impaired glucose tolerance, impaired fasting glucose, and a history of gestational diabetes. High glycemic index diet and low cereal fiber intake may also increase the risk.(5)

The changing face of type 2 diabetes is not only evident in the older population, but also among the young. The rise in childhood obesity is associated with a marked increase in type 2 diabetes now seen in adolescents and adults.(11) Also at high risk are specific ethnic groups - blacks, Hispanics, Asian Americans, and First Nations Aboriginals. Risk factors for diabetes that are specific to these populations include genetic, behavioral, and lifestyle factors.(8;12) This wide range in age, culture, and socioeconomic status provides a unique challenge to health care professionals who care for and educate persons with type 2 diabetes.

Primary Care and Type 2 Diabetes

The triad of self-management, balancing appropriate lifestyle choices, and pharmacologic therapy has long been the focus of the intervention and prevention literature surrounding type 2 diabetes. Evidence indicates that there is a range of services and programs that can help individuals change lifestyle behavior patterns contributing to the onset and progression of chronic disease, disability and premature death. However, the integration of these interventions at the primary health care level "continues to be limited and piecemeal".(13)

Ockene et al recognize "that physicians are still perceived by the public as the most reliable and credible sources of health information and advice, and often underestimate the potency and value of even brief counselling efforts" (p. 730).(14) Physicians defined as working within primary care specialties comprise a majority of the physician workforce, and it is estimated that most individuals will visit their primary care physician between one and three times per year.(15) Furthermore, 80-90% of diabetic patients are believed to be cared for by their primary care physician and may need three to eight scheduled office visits per year for usual diabetes care.(16-18) Including and supporting primary care providers in a type 2 diabetes educational strategy offers enormous potential in terms of patient reach and outcome in a variety of settings.

Primary prevention of type 2 diabetes can be implemented through either a population or high-risk group strategy, and both have been described as complementary.(1;7;8;19) In Canada, the Diabetes Prevention Strategy provides the starting point to meet this goal.(4;20) Today, regardless of the policy and public health dilemma, family physicians are faced with the challenge of managing the type 2 diabetes population, requiring sound evidence along with adequate resources to guide their practice. The good news is that evidence supporting the effectiveness of preventive lifestyle interventions, such as physical activity and diet, does exist - but translating it into clinical practice remains a formidable task.(21) Furthermore, evidence alone is not sufficient to entice practice change, important barriers occurring at the foundation of care also need to be addressed in order to meet the challenge of diabetes.(2;22)


Study Rationale - Objectives

The objective of this review is to define "best practice" for physical activity and dietary counselling in the prevention and control of type 2 diabetes in Canada - by summarizing relevant evidence-based, literature on the strategies, interventions, tools and resources used by primary health care providers.

Specifically, the literature review aims to provide: evidence that lifestyle interventions in the areas of physical activity and diet are effective in the treatment, control and prevention of type 2 diabetes recommendations for effective tools and interventions that facilitate the implementation of this evidence in the clinical setting information about barriers that preclude and/or impair the adoption of successful interventions a framework from which to work in year 2 of the CFPC educational strategy

Method & Search Strategies

Computerized databases were searched electronically from January 1980 - October 2001. This time frame was determined based on an initial sweep of the literature, recommendation by experts and consideration of relatively recent program implementation in the area of type 2 diabetes within the past twenty years. Multi-databases searched included: MEDLINE (PubMed); all databases within The Cochrane Library, CINHAL(OVID), EMBASE (Lexis Nexis); the websites for the Canadian Diabetes Association, the Canadian Diabetes Strategy, Dietitians of Canada, the Canadian Fitness and Lifestyle Research Institute, the National Institute of Diabetes and Digestive and Kidney Diseases. Bibliographies for selected studies, and previous reviews for relevant articles were also searched. Keywords for the searches included: type 2 diabetes (and all related MeSH terms, such as diabetes mellitus, non-insulin-dependent), physical activity, exercise, exertion, diet, diet therapy, nutrition, feeding behavior, obesity, primary health care, general practice, family physicians, medical office, preventive medicine, intervention, counselling, life style, educational tools, diabetes education, diabetes health promotion and prevention. The search was limited to the English language.

Experts sitting on the College of Family Physicians of Canada Type 2 Diabetes Educational Committee and key experts within the Canadian Diabetes community were contacted for recommendations regarding recent published and unpublished studies. Study authors were also contacted to tackle questions related specifically to primary care provider intervention.(Appendix A) The literature search was facilitated by cross checking and requesting additional searches with librarians at the McMaster University Health Sciences Library, Mr. T. Flemming, and at the Canadian Library of Family Medicine, Ms. L. Dunikowski. (Strategies for searches - Appendix B)

Although this search was an attempt to be inclusive, limitations of English-only criterion may contribute to a reportable bias. Consideration for final inclusion of studies was completed by an independent analysis of two expert reviewers from the College of Family Physicians of Canada Diabetes Educational Committee.


Selection Criteria

Selection of studies considered for review were based on: 1) evidence confirming the efficacy of lifestyle interventions in the prevention, control and treatment of type 2 diabetes and 2) current successful strategies and interventions studied in the primary care domain for prevention, control and treatment of type 2 diabetes that promote lifestyle changes. Final selection was based on inclusion criteria outlined in Appendix C.

Relevance Criteria

studies of efficacy: the interventions promoting physical activity and/or nutrition are based in primary care studies of effectiveness: the intervention could be implemented, facilitated or promoted by primary care physicians in Canada (e.g. are applicable to primary care, feasible to implement, cost-effective) study design: is prospective and includes a control group (one group pre/post designs are not acceptable) outcomes: are reported for participants beyond 1 year We examined the best evidence from primarily health care research on the management and prevention of type 2 diabetes. For all studies, we employed a methodological rating using an adapted version of the Canadian Diabetes Association's criteria for classification of evidence, as outlined in the Clinical Practice Guidelines for the Management of Diabetes.(23) See Table 1.


A search of the published literature resulted in retrieval of approximately 130 abstracts of possible related studies and articles. After excluding duplicates and studies that did not relate to the objectives of our review 22 studies or papers were judged to be relevant. Of these, 9 were related to the management (treatment and control) of type 2 diabetes, 7 to the prevention of type 2 diabetes and, 6 to the general lifestyle literature on primary care, physical activity and diet. Overall, there were no reported negative effects of physical activity and diet therapy in the 22 studies reviewed. However, based on full text review and using the criteria described, there were no studies that specifically looked at outcomes related to the intervention of primary care providers as a result of their role in counselling for physical activity and/or diet therapy to either prevent and/or control type 2 diabetes.

While there is direct evidence (Level 1)(9;24-26) in the literature that both physical activity and diet both improve glycemic control and prevent or delay the onset of type 2 diabetes, there is variability in the implementation and evaluation of successful interventions at the primary care level. Many of the intervention studies reviewed produced short-term changes in patient behavior and outcome, but the challenge of implementing "validated" interventions needed to promote long-term maintenance remains. Based on the results of this literature search there is a paucity of studies specifically examining the effect of primary care based or family physician intervention utilizing physical activity and/or dietary behavior as this relates to the prevention and/or management of type 2 diabetes. Similar findings have been reported by Clark investigating the efficacy and effectiveness of physical activity interventions studies for high risk and minority type 2 diabetic populations.(27) Detailed findings of each of the included studies are presented in the Study Grid found in Table 2.


Studies of efficacy utilizing physical activity and diet to control and treat type 2 diabetes

The UKPDS Study, (Level 1)(28;29) produced convincing evidence that improved blood glucose control in people with type 2 diabetes prevents associated complications. The study was designed to determine whether there are differences in outcome between conventional treatment, diet therapy alone and three different regimes of intensive treatment, based on pharmacologic therapy. Diet therapy was used as a baseline control in this study. Wing(30) has examined the outcome characteristics of participants in the diet intervention arm of this study.(31) Of particular interest is that, of all participants in the UKPDS Study who underwent the initial period of diet before randomization, 15% were considered "diet failures" during the first 3 months. Centres identified with "above average availability of dietary advice" achieved the best weight losses and glycemic response during the initial 3 month baseline.(30;31) Wing reports that "some degree of ongoing caloric restriction and continued weight reduction may be needed to maintain fasting plasma glucose levels" for the type 2 diabetes population.(30)

Studies of effectiveness utilizing physical activity and diet to control and treat type 2 diabetes

In this literature review, effectiveness reflects the feasibility of translating successful and efficacious interventions from large reported outcome studies to the primary care setting. It is recognized in the literature that descriptions of the interventions in many of the larger efficacy studies are not well reported, due in part to limitations of publishing criteria.(32) However, as a result of reviewing the best available evidence, there are a wide range of physical activity and dietary interventions available that provide the groundwork for future investigation and substantial improvement in the current lifestyle management for the type 2 diabetes population.

A small randomized controlled study in Finland aimed to assess the effects of a 1-year intensified diet and exercise education regime in middle aged, obese patients with newly-diagnosed type 2 diabetes.(Level 2)(33) Although the study looked at interventions as they related more specifically to the aerobic capacity of participants, the outcomes of weight reduction, normoglycaemia and correction of dyslipidaemias were also assessed. This strategy entailed close follow-up with daily exercise records (without organised and supervised exercise sessions), and was identified by the investigators as the most suitable and cost-effective for clinical practice. Problems, such as motivation and compliance with instructions, and recognizing that instructions for exercise training (which have been made for healthy subjects) are not well-suited or sufficient for diabetic patients were identified. The investigators suggest that individualized instructions are more effective for increasing physical exercise in the type 2 diabetes population, and that a more widespread use of exercise specialists will promote diabetic patients to take part in organized exercise training in the long term.(33)

In a series of 3 papers, Glasgow et al (Level 2)(34-36) aimed to evaluate a medical office-based intervention that focussed on behavioral issues relevant to dietary self-management. The investigators also assessed the cost-effectiveness of implementing the intervention. Results suggest that the brief intervention produced greater dietary improvements than usual care for a number of measures of dietary behavior at 3-month follow-up. Overall, the study revealed that the brief intervention had significantly higher long-term impacts on dietary behaviours such as serum cholesterol level (but not glycosylated hemoglobin), and patient satisfaction than the usual care in patients with diabetes at one year follow-up. The cost of the intervention ($137 US per patient) was reported to be modest relative to many other commonly used practices.(36)

A study in the UK (32) is currently aiming to assess whether a psychological intervention, specifically addressing physical activity and diet, to improve lifestyle self-management in obese patients with type 2 diabetes has an impact on patient behavior. This small, randomized, initial feasibility study intends to evaluate whether a relatively brief intervention can be implemented into routine physician care, and can assist people with type 2 diabetes to make recommended lifestyle changes. The intervention includes assessment and a personalised program to set realistic and manageable goals for lifestyle change. Barriers are negotiated using brief motivational interviewing.

Telephone contact is used to provide maintenance support and relapse prevention. A variety of instruments are also used to improve physical activity and dietary outcomes (although these have not been developed specifically for the diabetic population).(32) Program effectiveness data are not yet available; only baseline results have been reported to date. Although interventions are being administered by a research psychologist the investigators identify the need to replicate their research results using diabetes team members in order to test the effectiveness of the interventions at the primary care level. The investigators do not report on the training and support requirements needed for primary care providers to deliver the intervention.

There is evidence that primary health care providers, other than family physicians, have a significant role in promoting lifestyle change and maintenance for the type 2 diabetes population. It has been recommended that all individuals diagnosed with type 2 diabetes should ideally receive individual, tailored advice from a dietitian.(Level 2)(23;37) Nurses are also identified as having a significant impact in improving the management and quality of life for individuals with diabetes.(Level 2)(38) (Level 3)(39) The long-term outcomes for patients and practice behaviors of primary care providers warrants ongoing investigation in order to better identify the role of health care providers and lifestyle management for the type 2 diabetes population.(40)


Studies of efficacy utilizing physical activity and diet

Epidemiological studies have shown that obesity and a sedentary lifestyle are independently related to the chances of developing type 2 diabetes.(Level 3)(41;42) There are numerous studies indicating the benefits of weight loss and exercise in the treatment and prevention of type 2 diabetes, both to decrease insulin resistance and improve glycemic control. In tandem with the UKPDS study, several well-designed trials suggest that increased physical activity and weight loss may help prevent and delay the development of type 2 diabetes for those at risk for developing the disease.

A study investigating whether reducing dietary fat would have an impact on body weight, glucose tolerance, and conversion to type 2 diabetes in people with glucose intolerance has shown promising results in the long-term (5 years).(Level 1)(43) Patients randomized to a 1 year structured program, aimed solely at reducing the total amount of fat in their usual diet, did lose weight (most notably at the year 1 mark). However, this trend disappeared by year 5, similar to the control group. The investigators further reported that 50% of the "more compliant" intervention group maintained lower fasting and 2 hour glucose at the 5 year mark compared to the control group. This study emphasized the need for interventions to be multi-factorial and longer in duration in order to promote successful outcomes.

Results from three prospective intervention studies provide sound evidence that changes in lifestyle are effective in preventing the progression from impaired glucose tolerance (IGT) to type 2 diabetes. The Swedish Malmö study, although not randomized, demonstrated the importance of carrying out a diet-exercise program for a prolonged duration (5 years), participants were less likely to progress to diabetes than those in the control group. (Level 3)(44) The Chinese Da Qing Study, randomized by clinic, reported a 42% reduction in the progression of IGT to diabetes over 6 years, based on an intensive regime of exercise and diet therapy.(Level 1)(9) The Diabetes Prevention Study (DPS) in Finland further corroborates the effectiveness of lifestyle changes (for both men and women), using a rigorous program of diet and exercise therapy; the overall incidence of diabetes was reduced by 58% during the 3.2 years of follow up in this study.(Level 1)(24)

The Diabetes Prevention Program (DPP) in the United States has clearly examined strategies to evaluate the safety and efficacy of interventions that may delay or prevent the development of type 2 diabetes.(Level 1)(45) The DPP study reports, at a 3-year follow up, that participants at high risk for type 2 diabetes can lower their chances of developing the disease by 58% with a program of diet and exercise.(26) The intensive lifestyle intervention described in this study is based on the premise that long-term changes in diet and exercise, along with sustained motivation, promote maintenance of behavior change. The program, delivered by case managers, has created intervention materials, ongoing training and support for intervention staff. Intensive lifestyle interventions for participants included training in diet, exercise, and behavior modification skills; frequent (no less than monthly) support for behavior change, diet, and exercise interventions deemed to be flexible, sensitive to cultural differences, and acceptable to the communities in which they are implemented; combinations of individual and group interventions; structured protocols with the flexibility to tailor strategies individually to help a specific participant achieve and maintain the study goals; and emphasis on self-esteem, empowerment, and social support.(25)

The large number of enrolled participants, diverse ethnic populations, intensity, duration, along with coordinated delivery of intervention(s) by a variety of multi-disciplinary team members, and cost-effectiveness are important considerations when contemplating the generalizability and implementation of such programs at the primary care level.

Other "studies of promise" include two ongoing protocols identified in the Cochrane Library. A systematic review of "Lifestyle Interventions in the Prevention of Type 2 Diabetes"(46) aims to provide a critical appraisal of published intervention studies related to physical activity and nutrition for the type 2 diabetes population. Another identified review aims to evaluate studies related to the intervention of physical activity in patients with type 2 diabetes and healthy, free-living adults, respectively.(47) The timeliness of these reviews will further evaluate the evidence presented to date; however, whether these will provide insight related to interventions delivered at the primary care level remains to be seen.


Lifestyle assessment is recognized as an important element in developing effective intervention strategies in primary care and invokes the experiences of both the patient and health professional.(48) It may be hypothesized that effective interventions aimed at promoting weight loss and increasing physical activity will lower the incidence of type 2 diabetes in those individuals at risk and probably in the general population.(46) Further, it is well recognized that the adoption of a healthy lifestyle, such as exercising regularly, eating well and avoiding obesity may provide a protective effect against elements of other chronic diseases.(49-52)The metabolic syndrome usually associated with glucose intolerance and type 2 diabetes mellitus, which includes hypertension and hyperlipidaemia, may subsequently increase morbidity and mortality from cardiovascular disease.(46;53) As well, the fact that lifestyle interventions promote an improved quality of life for this population shifts the paradigm to promoting health and well being from purely preventing disease.(21;24;53)

As a result of the lack of strong evidence based in the diabetes and primary care literature, as established by the criteria for this review, we found it necessary to examine the existing evidence surrounding lifestyle interventions, in general - specifically related to physical activity, diet and weight loss counselling. Existing tools and programs, validated in primary care (especially within Canada), were then reviewed for recurrent themes in the literature. We also referenced recommendations from the Canadian and American Diabetes Practice Guidelines in order to extrapolate physical activity and diet interventions that might best apply to the type 2 diabetes population.(23;54)

Physical Activity, Type 2 Diabetes and Primary Care

A stepwise increase in physical activity that is integrated into the person's lifestyle should be part of the therapeutic plan for everyone with type 2 diabetes who is able to increase activity. It should be prescribed with specific modifications for people with known occlusive vascular disease (or at high risk of subclinical disease), significant sensory polyneuropathy or advanced microvascular complications. [Grade D, consensus](23) In those at increased risk, a program of weight control through diet and regular exercise is recommended and may prevent type 2 diabetes. [Grade B, Level 1](23)

A recent scientific symposium on the dose-response relationship of physical activity and health outcomes and an evidence-based review (1991 to 1999) of this relationship to physical activity in the context of population health reports that "the importance of relative versus absolute intensity of effort depends on the desired health outcome, and that many issues remain to be resolved".(55;56) Evaluation of studies in terms of the effect of physical activity on glucose homeostasis reveals modest improvement but no evidence for a specific dose-response relationship.(56) Studies exploring associations between physical activity and the incidence of maturity-onset type 2 diabetes have indicated that absolute versus relative intensity for required energy expenditure has not been determined, and that there is a need to distinguish between acute and chronic metabolic effect for this population in a systematic way.(56)

A meta-analysis completed by Boulé et al(57) has indeed addressed this issue further by systematically reviewing and quantifying the effects of exercise on glycosylated hemoglobin (HbA1c) and body mass in patients with type 2 diabetes. The authors conclude that exercise does reduce HbA1c by an amount (approximately 0.66%) that should decrease the risk of diabetic complications. However, the studies reviewed did not find a significant greater weight loss in the exercise groups compared to the control groups. The authors conclude and support the benefits of exercise on its own for the type 2 diabetes population, addressing the fact that exercise is not to be promoted solely as an "avenue for weight loss".(Level 1)(57)

Eakin et al have reviewed primary-care based physical activity intervention studies in the literature from 1980 to 1998.(Level 1+)(58) The authors sought to identify practical and effective strategies for use in family practice settings to enhance patient physical activity levels. This unique review incorporates the RE-AIM framework, used to evaluate the literature in terms of the public health impact of health promotion activities. None of the studies included in this review specifically identified type 2 diabetes within the population being investigated. Overall, the review considers three specific evidence-based recommendations which emphasize promoting short-term changes in patient physical activity: 1) an initial focus on physical activity only, as opposed to multiple risk factors 2) tailored interventions and written materials to enhance success rates and 3) counselling can be successfully implemented by a variety of health care team members, although the person delivering the intervention should be the one most likely to do so consistently, given time, training and interest. The authors found no clear relationship between the type of "interventionist" and effectiveness of the intervention, although the majority of studies in this review included interventions delivered by physicians. Finally, the authors conclude that "enough is known to recommend physical activity" but questions remain regarding the consistency of implementation and long-term maintenance of outcomes.(58)

The Activity Counseling Trial Research Group (ACT)(Level 1)(59), in the United States, has recently evaluated patient physical activity counselling in primary care by comparing two interventions with current recommended care and with each other. Participants in the ACT study were assigned to one of three groups: 1) current recommended care (physician advice and written educational materials; 2) assistance (all the components received by the advice group plus interactive mail and behavioral counselling which utilized patient readiness to change, at physician visits); and 3) counselling (assistance and advice group components plus regular telephone counselling and behavioral classes). Disappointingly, this study found that the two counselling interventions (differing in type and number of contacts) were equally effective in improving fitness over two years compared with advice care for women. However, in men, neither of the two counselling interventions was more effective than advice care. This study addresses the issues of both time and cost. Assistance interventions were estimated at approximately $500(US dollars) and counselling interventions at approximately $1100 per participant over the two years of the ACT study. The investigators also recognize that it is unknown whether the assistance and counselling interventions could be incorporated feasibly into primary care practices using existing resources. Except for the provision of physician advice, interventions were delivered by ACT health educators.(59)

Physician-Based Assessment and Counseling for Exercise (PACE)(Level 1)(60-62) is a brief, behavior-based tool for primary care providers counselling healthy adults. Research has demonstrated that the PACE intervention is effective in helping patients move towards more healthy active living. The PACE program is acceptable to health care providers, office staff, and patients.(61) As well, the program does not require staff to have special medical training, and can be used effectively by a wide range of primary care providers. However, a recent study assessing the effectiveness of this intervention recognizes the need for further ongoing studies in order to examine repeated counselling effects in the long-term.(63)

The Step Test Exercise Prescription (STEP)(Level 1)(64) intervention builds on the tailoring of counselling behavior to match behavior readiness by introducing a specific training heart rate prescription to improve fitness. The intervention of the counselling and prescription are delivered by a family physician in the office setting. Patients are "staged" and given counselling to overcome barriers and to realize the benefits of improving individual physical fitness. When patients have achieved appropriate readiness, they are given an exercise training heart rate target based on the performance of a simple office stepping test.(65) This test and prescription have been validated in improving fitness (V02 max) and have been found to be acceptable and improve knowledge among a large group of primary care physicians.(64)

Consideration as to whether specific populations, such as type 2 diabetes, have been evaluated using the physical activity interventions described was not determined in this review.

Diet, Type 2 Diabetes and Primary Care

All people with diabetes should receive individual advice on nutrition from a registered dietitian. [Grade D, consensus](23) Nutritional recommendations for people with diabetes are the same as Health Canada's recommendations for the general population. The distribution of nutrients may be tailored to the individual patient depending on needs and personal preferences. Meal-planning, using approximately 55% carbohydrate and 30% fat content often serves as a starting point in the development of specific recommendations. [Grade D, consensus] Detailed nutritional management of diabetes is further outlined in Guidelines put out by the Canadian Diabetes Association.(66) In those at increased risk, a program of weight control through diet and regular exercise is recommended and may prevent type 2 diabetes. [Grade B, Level 1](23)

A review of weight loss in the management of type 2 diabetes provides current evidence that indeed weight loss does improve glycemic control, however "the magnitude of the improvement is related to both the magnitude of weight loss and characteristics of the patient as well as the need to improve weight loss, especially in the long-term" (p.272).(30) The literature also suggests that diabetes dietary self-management and weight control programs have been found unsuccessful unless they are very intensive and continued over long periods of time.(30) Programs and strategies suffer from high attrition rates at follow-up and poor maintenance of changes made in the longer term. There is a pressing need for practical, ongoing lifestyle self-management interventions that are tailored into routine usual care and are capable of reaching a broader audience.(32)

The fact that individuals fail to maintain significant weight loss and eventually regain weight within 1-2 years addresses issues of noncompliance and the challenge of altered metabolism in diabetes control. (67) The obesity and weight loss literature identify that most patients want more help with weight management than they are currently receiving from primary care physicians and that physicians can provide initial effective, adequate dietary counselling by delivering brief advice along with distribution of individualized written material. Successful outcomes are optimally achieved when counselling is further augmented with dietitians, although this may not always be feasible.(68-70)

In a meta-analysis completed by Brown et al (Level 1+)(67) it was found that of all the dietary interventions reviewed the successful effect of diet was primarily the result of studies using very low caloric diets (VLCDs). The degree of caloric restriction involved in VLCD's appears to improve initial weight loss and glycemic control. However, even when used with behavioral treatment, weight losses have not been maintained in the long term (30). It has also been acknowledged that the most commonly prescribed American Dietetic Association (ADA) diet has not been well researched from the perspective of weight loss.(67) The ADA diet has demonstrated moderate effects for the variable of weight loss and large effects for the variable of metabolic control to date.(67) No studies were found describing the outcomes of following the principles of Canada's Food Guide to Healthy Eating for the at risk or type 2 diabetes population in this current review.

Evidence regarding successful long-term medical nutrition therapy delivered by primary care physicians for those patients at risk for and diagnosed with type 2 diabetes, along with the population at large, is variable.(71-74) A study in the United States has evaluated a nutrition intervention for primary physicians and the hyperlipidemic population.(14) The results of this randomized controlled trial suggest that brief physician nutrition counselling supported with an office program can produce beneficial changes, which is promising in the short-term. Currently, the focus of many such brief educational interventions for primary care physicians falls once again on training or promoting physicians to be more effective in using patient-centered advice or counselling in a busy clinical office.

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