IB Syllabus focus:
‘Lower-trophic, plant-based diets yield more food per land area and can reduce impacts; overall sustainability also depends on supply chains, food miles and cultural dietary shifts.’
Food choices shape environmental outcomes. Understanding trophic levels, diets, and sustainability helps evaluate how agricultural systems and human consumption patterns affect ecosystems, efficiency, and global food security.
Trophic Levels and Diets
Trophic Levels Explained
Trophic level refers to the position an organism occupies in a food chain, determined by how it obtains energy.
Trophic Level: The hierarchical position in a food chain, such as producers (plants), primary consumers (herbivores), and higher-level consumers (carnivores).
Humans may consume at various trophic levels, but diets rich in animal products place us higher in the chain compared with plant-based diets.
Energy Transfer Between Levels
Energy transfer between trophic levels is inefficient. Typically, only about 10% of energy from one level is passed on to the next.
An energy pyramid illustrating producers at the base and successive consumer levels above, with energy decreasing by roughly an order of magnitude at each step. This directly supports the 10% transfer concept that constrains higher-trophic diets. Source.
This means producing food from plants is more energy-efficient than raising animals, as significant energy is lost through respiration, metabolism, and waste.
Diets and Environmental Impact
Plant-Based vs Animal-Based Diets
Plant-based diets are generally more sustainable because they require less land, water, and energy input per unit of food produced.
A comparative chart of land use per 100 grams of protein across foods, showing notably higher land footprints for ruminant meats versus legumes and other plant proteins. This visual underpins the land-efficiency advantage of lower-trophic, plant-based diets. Extra detail: specific products are shown beyond those named in the notes to provide meaningful context. Source.
Animal-based diets, especially those reliant on ruminant livestock, have high environmental footprints.
Plant-based diets:
Lower trophic level consumption
Greater land-use efficiency
Reduced greenhouse gas emissions
Animal-based diets:
Higher trophic level consumption
Larger resource demand
Greater methane and CO₂ emissions
Greenhouse Gas Emissions: Gases such as CO₂, CH₄, and N₂O that trap heat in the atmosphere, driving climate change.
Water and Land Use
Plant-based diets typically use less water and agricultural land.
Meat production requires vast grazing areas and feed crop cultivation, accelerating deforestation and biodiversity loss.
Food Supply Chains and Sustainability
Food Miles
Food miles represent the distance food travels from production to consumption.
A chart showing transport accounts for ~5% of global food-system greenhouse gas emissions, with a breakdown by transport mode. This figure illustrates that production-stage processes dominate impacts compared with distance travelled. Extra detail: the modal breakdown (e.g., road, sea, air) is included to contextualise why “local vs. global” is often less important than what is eaten. Source.
Food Miles: The distance food items travel from farm to consumer, influencing total carbon footprint.
While local produce may reduce emissions, factors such as storage and production efficiency can sometimes outweigh transport impacts.
Supply Chain Inefficiencies
Even sustainable diets can lose value through poorly managed supply chains. Losses occur at multiple stages:
Harvest losses (damaged crops left in fields)
Storage losses (pests, spoilage)
Processing and distribution losses
Consumer waste
These inefficiencies exacerbate resource use regardless of dietary choice.
Cultural Dietary Shifts
The Role of Culture
Dietary habits are heavily influenced by culture, religion, and socioeconomic status. For example:
Traditional diets may emphasise grains, legumes, or meat.
Economic development often shifts diets toward more animal protein.
Cultural acceptance can accelerate or hinder transitions toward sustainable food systems.
Barriers to Change
Cultural resistance: Strong traditions tied to food.
Economic pressures: Meat often symbolises wealth and status.
Accessibility: Plant-based alternatives may be unavailable or expensive in some regions.
Evaluating Sustainability in Diets
Factors Affecting Sustainability
A diet’s sustainability is not determined solely by trophic level but also by:
Farming practices (organic vs industrial agriculture)
Transport and distribution networks
Food storage and preservation methods
Consumer waste management
Thus, while lower trophic diets are inherently more efficient, sustainability requires holistic assessment.
Key Considerations
Nutritional adequacy must be balanced with environmental efficiency.
Equitable access to sustainable food is crucial for global food security.
Policy interventions (e.g., promoting plant-based diets, reducing subsidies for intensive livestock farming) can reshape food systems.
Links to Broader Environmental Systems
Soil and Water Impacts
Intensive livestock farming accelerates soil degradation, erosion, and water pollution from nutrient runoff.
Plant-focused farming systems generally exert lower pressures, though monocultures may still harm biodiversity.
Carbon Balance
Livestock are major emitters of methane, a potent greenhouse gas.
Shifting diets can reduce emissions and help maintain soils as carbon sinks rather than sources.
Summary of Key Processes
Lower trophic diets = more efficient land use and reduced emissions.
Higher trophic diets = energy loss, higher land and water demand, increased pollution.
Supply chain inefficiencies magnify environmental impacts.
Cultural and economic factors determine the feasibility of adopting sustainable diets.
FAQ
Lower trophic level diets, such as plant-based diets, allow more people to be fed from the same land area. Energy losses at higher trophic levels mean that large amounts of crops grown for animal feed could instead directly support human populations.
Ruminants, such as cattle and sheep, produce methane through enteric fermentation, a potent greenhouse gas. They also require extensive grazing land and large amounts of feed crops. This combination makes them less sustainable compared to non-ruminant livestock or plant-based food sources.
Eating seasonal and locally produced food reduces reliance on long-distance transport and energy-intensive storage. This can lower greenhouse gas emissions.
However, the benefits depend on farming practices; local but resource-intensive production may be less sustainable than efficient imports.
Expanding pasture and feed crop production for animal-based diets often leads to habitat loss and reduced species diversity.
Plant-based diets, especially when diversified beyond monocultures, can help conserve ecosystems by lowering pressure on forests, wetlands, and grasslands.
Governments may implement:
Subsidies for fruit, vegetables, and legumes.
Taxes on high-emission foods, such as beef.
Public awareness campaigns linking diet to climate change.
Support for plant-based innovation and school meal programmes.
These measures can shift demand toward more sustainable consumption patterns.
Practice Questions
Question 1 (2 marks)
Define the term trophic level and explain why diets based on lower trophic levels are generally more energy efficient.
Mark scheme:
1 mark: Correct definition of trophic level (e.g., the position an organism occupies in a food chain, based on how it obtains energy).
1 mark: Explanation that energy transfer between trophic levels is inefficient (~10%), so diets at lower levels (plants) conserve more energy.
Question 2 (5 marks)
Discuss how cultural and supply chain factors influence the sustainability of plant-based diets compared with animal-based diets.
Mark scheme:
1 mark: Identification of cultural influences (e.g., traditions, religion, socioeconomic status shaping dietary choices).
1 mark: Explanation of barriers to dietary change (e.g., cultural resistance, meat as a status symbol, accessibility of plant-based foods).
1 mark: Identification of supply chain inefficiencies (e.g., harvest, storage, processing, consumer waste).
1 mark: Link between these inefficiencies and sustainability outcomes (e.g., even efficient plant-based diets lose sustainability with waste).
1 mark: Balanced comparison showing how both cultural and supply chain factors can enhance or limit the sustainability of either diet.
