Relationship between Climate Change and Environmental Sustainability: A Systematic Review
The Link Between Dietary Patterns, Health, and Environmental Impact
As evidence of climate change and its far-reaching effects continues to mount, the need to understand the relationship between human activity, environmental sustainability, and public health has become increasingly critical. One area that holds significant potential to address this multifaceted challenge is the examination of dietary patterns and their impact on both health and the environment.
The 2015 Dietary Guidelines Advisory Committee (DGAC) conducted a comprehensive systematic review on this topic, assessing the alignment between food patterns that are nutritionally sound and support health, and those that are more environmentally sustainable. Given the rapid pace of research in this field, an update to this review was warranted to capture the latest evidence and further strengthen the conclusions.
Defining Sustainable Diets
The Food and Agriculture Organization (FAO) has provided two relevant definitions that frame the scope of this discussion:
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Food Security: “Food security exists when all people at all times have physical and economic access to sufficient, safe, and nutritious food to meet their dietary needs and food preferences for an active, healthy life.”
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Sustainable Diets: “Sustainable diets are those diets that have low environmental impact and contribute to food and nutrition security and a healthy life for present and future generations. Sustainable diets are protective and respectful of biodiversity and ecosystems; culturally acceptable; accessible; economically fair; affordable; and nutritionally adequate, safe, and healthy while optimizing natural and human resources.”
These definitions underscore the importance of considering not only the immediate health benefits of dietary patterns, but also their long-term sustainability and impact on the environment. Achieving food security for current and future generations requires a holistic understanding of the relationship between human dietary choices, environmental outcomes, and population health.
Evaluating Dietary Patterns and their Impacts
Dietary patterns are defined as the quantities, proportions, variety, or combinations of different foods and beverages in diets and the frequency with which they are habitually consumed. Well-characterized dietary patterns that promote health include the Dietary Approaches to Stop Hypertension (DASH) diet, the Mediterranean dietary pattern (MDP), vegetarian diets and their variations, and the Healthy US-Style Eating Pattern.
These patterns, when consumed in appropriate caloric concentrations, have been shown to support healthy growth and development while reducing the risk of preventable chronic diseases, including cardiovascular diseases, type 2 diabetes, obesity, and some cancers. Furthermore, these eating patterns have been associated with improved functional health in older adults.
On the other hand, the current average dietary patterns in many developed countries, which tend to be higher in animal-based foods and lower in plant-based foods, have been linked to considerable environmental impacts. The global food production system is responsible for over 70% of freshwater use, up to 30% of human-generated greenhouse gas (GHG) emissions, and 80% of deforestation, highlighting the urgency to address the sustainability of our dietary choices.
Systematic Review Methodology and Findings
The original DGAC systematic review, published in 2015, examined the relationship between population-level dietary patterns, health outcomes, and environmental sustainability. This review identified 15 studies that met the inclusion criteria, which were further supplemented by an additional 8 studies in the updated review, spanning the literature published between January 2014 and July 2015.
The studies included in the review used a variety of methodologies, such as modeling, life cycle assessment (LCA), and land use analysis, to compare the health and environmental impacts of different dietary patterns. The patterns examined ranged from average national dietary patterns to well-characterized patterns like the DASH diet, MDP, and various vegetarian diets.
Across the studies, consistent evidence emerged indicating that dietary patterns higher in plant-based foods (e.g., vegetables, fruits, legumes, seeds, nuts, whole grains) and lower in animal-based foods (especially red meat), as well as lower in total energy, are both healthier and associated with a lesser impact on the environment. This dietary pattern differs significantly from the current average consumption patterns in many developed countries, including the United States.
Key Insights from the Systematic Review
The updated systematic review confirms and strengthens the conclusions of the original 2015 DGAC review, providing a robust body of evidence on the relationship between dietary patterns, health, and environmental sustainability.
1. Healthier Dietary Patterns are More Sustainable
Dietary patterns that align with dietary guidelines, such as the MDP and DASH diet, were consistently shown to be more environmentally sustainable than the average consumption patterns in the respective countries. These patterns, which emphasize plant-based foods and limit animal-based foods, particularly red and processed meats, were associated with reduced GHG emissions, land use, water usage, and energy consumption.
2. Reduced Meat Consumption is Key
The evidence consistently identified meat, particularly ruminant meats like beef and lamb, as the single food group with the greatest impact on the environment, primarily in terms of GHG emissions and land use. Dietary patterns that reduced meat consumption, whether through vegetarian, pescatarian, or flexitarian approaches, were associated with lower environmental impacts.
3. Sustainable Diets Can Be Affordable
While some studies found that sustainable dietary patterns may be more expensive than average consumption patterns, others demonstrated that health-promoting and environmentally sustainable diets can be achieved without significant increases in cost to the consumer. Approaches that optimize food choices, reduce energy intake and density, and increase the proportion of plant-based foods were shown to be both healthier and more sustainable at comparable or even lower costs.
4. Limitations and Future Research Needs
The reviewed studies primarily relied on modeling and LCA techniques to assess the environmental impact of dietary patterns, rather than direct observational data. Additionally, most of the studies were conducted in European countries, limiting the generalizability to other regions. Further research is needed to refine the understanding of the relationship between specific production practices, regional factors, and the environmental performance of different dietary choices.
Implications and Conclusions
The insights from this systematic review highlight the significant potential for dietary patterns to contribute to both improved public health and environmental sustainability. By aligning our dietary choices with patterns that are higher in plant-based foods and lower in animal-based foods, particularly red and processed meats, we can achieve substantial reductions in GHG emissions, land use, water usage, and energy consumption, while also promoting better health outcomes.
These findings have important implications for food and nutrition policies, as well as individual dietary choices. Incorporating sustainability considerations into dietary guidance, and incentivizing the adoption of more sustainable dietary patterns, could help address the pressing challenges of climate change, environmental degradation, and food security for current and future generations.
As the scientific evidence on this topic continues to evolve, it will be crucial for policymakers, healthcare professionals, and the public to stay informed and engaged in the ongoing dialogue. By working together to understand and promote sustainable dietary patterns, we can take a significant step towards a more resilient and healthier future.
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