Dietary Approaches and Health Outcomes (DA-HO) Scoping Review (2020)
Dietary Approaches and Health Outcomes: A Scoping Review
The objective of this scoping review is to identify and characterize systematic reviews examining diet or energy restriction interventions among adults in the general population who are healthy or who may have chronic disease. Understanding the landscape of these interventions in the literature will help to inform the scope and the development of future systematic reviews in this area.
What is the availability of literature examining diet or energy restriction interventions in adults in the general population?
Target Population: Adults (18 years and older) in the general population with or without chronic disease(s) or co-morbid condition(s).
Interventions: Studies examining a prescribed diet or fasting (energy restriction) regimen as the primary intervention, either alone or as part of a lifestyle intervention (i.e., education, exercise, behavior therapy).
Outcomes: Pre-post weight status or BMI. May also include pre-post-secondary health outcomes (cardiovascular, metabolic, and functional outcomes) such as body composition, lipids, blood glucose, blood pressure, insulin resistance, improvement in symptoms, clinical events (i.e., myocardial infarction, stroke), occurence of type 2 diabetes, cardiovascular disease and all-cause mortality, etc.
Location: Outpatient, ambulatory or community-based care
Search Dates: January 1, 2010 - February 20, 2020
Study Designs: Systematic reviews or meta-analysis of randomized controlled trials, controlled clinical studies or cohort studies.
Databases: Medline, Embase, CINAHL, PsycINFO, Web of Science, Cochrane Database for Systematic Reviews
Results: The Evidence Analysis Center conducted a scoping review of systematic reviews (SRs) to identify and characterize studies examining diet or fasting [intermittent energy restriction] interventions among adults who are healthy or who may have chronic disease. In the final analysis, the scoping review found the following:
- A total of 92 SRs published between 2010 and February 2020 met the inclusion criteria. Of these, 83% were published within the past five years of this review.
- Although not required, 31.5% of the SRs assessed quality of evidence according to outcome, which was assessed in highest numbers between 2018 and 2019.
- Approximately one-quarter of the SRs were interested in only studies of overweight and/or obese subjects, generally defined by BMI. All other SRs either did not specify weight status or included any weight categories.
- Almost half of the included SRs either did not specify or were open to any populations with comorbid conditions. A small number specified generally healthy populations, either with or without comorbidities. Of those focused on populations with specific diseases or conditions, almost one-third of SRs were interested in patients with glucose metabolism disorders such as diabetes, impaired fasting glucose/prediabetes, impaired glucose tolerance, or insulin resistance.
- The types of outcomes reported were generally consistent and similar across SRs. Besides weight status, which was a required criteria, the majority focused on intermediate outcomes, such as other body composition measures and cardiometabolic outcomes (e.g., glycemic control, blood lipids, blood pressure, and inflammatory markers). A few SRs reported incident events, development of disease or mortality.
- The primary purpose of most SRs fall into two major categories: cardiometabolic risk or disease and weight loss or weight maintenance.
- The wide range of diets covered were organized into 12 diet categories: 1) high or restricted CHO (n=30), 2) regional dietary patterns (n=19 total) such as Mediterranean, Nordic, and Tibetan, 3) restricted or modified fat (n=17), 4) vegetarian dietary patterns (n=16 total) including vegetarian or vegan, portfolio, Ornish and macrobiotic, 5) glycemic index or load (n=13), 6) high protein (n=12), 7) IER (n=11), 8) meal replacements (n=11), 9) paleolithic (n=8), 10) Dietary Approaches to Stop Hypertension (n=6), 11) CHO restricted/high protein named diets (n=5 total) including Atkins, South Beach, and Zone, and finally, 12) other named or commercial diets (n=4 total) including Weight Watchers (WW), Jenny Craig, Biggest Loser Club, and five others.
- Eighteen of the 92 SRs evaluated more than one diet or dietary pattern across the 12 diet categories.
This scoping review of SRs provides researchers and RDNs with a comprehensive mapping of the evidence available on various dietary approaches and health outcomes in adults in the general population. Moreover, the project team was able to delineate diet overlap and describe the heterogeneity among diets, and identify areas warranting further research. As a consequence, the EAC prioritized the need to collate evidence related to macronutrient modification, specifically restricted CHO diets.
The comprehensive findings of this scoping review serve as a foundation on which the EAC will build future reviews on various dietary approaches to aid RDNs in communicating evidence-based nutrition science to their patients, clients, and the general public.
The full results of the scoping review titled Dietary Approaches and Health Outcomes: An Evidence Analysis Center Scoping Review will be published in the Journal of the Academy of Nutrition and Dietetics. The citation will be provided once the manuscript is published.
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