Oat and soy milk are the most sustainable options overall, producing 62–78% fewer greenhouse gas emissions per liter than cow’s milk while using less land and causing less nutrient runoff. But “most sustainable” depends on which environmental metric matters most to you, because no single milk wins in every category.
Why No Single Milk Wins Every Category
Sustainability isn’t one number. It’s a bundle of impacts: carbon emissions, water use, land use, pollution from fertilizer runoff, and effects on biodiversity. Almond milk scores well on carbon but poorly on water. Cow’s milk uses the most land and produces the most emissions, yet supports grazing ecosystems in some regions. Soy milk is protein-rich and low-carbon but raises questions about where the soybeans are grown. The “best” choice shifts depending on which problem you care about most and where you live.
Greenhouse Gas Emissions
This is where plant milks pull furthest ahead of dairy. Soy, oat, almond, pea, and coconut milks all produce roughly 62–78% less carbon per liter than cow’s milk. Among plant options, the differences are relatively small compared to the gap between any of them and dairy. If cutting your carbon footprint is the priority, switching from cow’s milk to virtually any plant-based alternative makes a measurable difference.
Water Use: Where Almonds Struggle
Almond milk’s water footprint is its biggest weakness. Almond trees are overwhelmingly grown in California, one of the most water-stressed regions in the world, and they need irrigation year-round whether or not they’re producing nuts. A liter of almond milk produced in California can require substantially more water than a liter of cow’s milk produced in a region with plentiful rainfall. Oat and soy milk generally require far less water than both dairy and almond milk, because oats and soybeans grow in temperate climates where rain does most of the work.
Land Use
Dairy is the most land-intensive option by a wide margin. Italian dairy farms, for example, need roughly 1.5 square meters of land per kilogram of milk when you count both the pasture and the cropland used to grow animal feed. Plant milks skip that conversion step entirely: instead of growing crops to feed a cow that then produces milk, you’re turning the crop directly into a drink. Soy and oat milk both require a fraction of the land that dairy does per liter produced.
Nutrient Runoff and Water Pollution
Fertilizer washing off farmland into rivers and oceans, called eutrophication, is one of the less-discussed environmental costs of milk production. Dairy milk produces roughly three times the freshwater pollution (measured in phosphorus runoff) of oat milk per liter. Soy milk falls in between, with its impact varying based on where the beans are grown. For marine pollution from nitrogen, oat and soy milk are comparable to dairy, though the specifics depend heavily on farming practices. Oat milk consistently performs well on both freshwater and marine eutrophication metrics.
The Almond Pollination Problem
Beyond water, almond orchards create a unique strain on pollinators. Almonds require more commercial honeybee hives than any other crop in the U.S., roughly ten times as many as apples. The consequences have been severe. During winter 2018–2019, about 50 billion bees were lost across commercial operations, more than a third of all U.S. commercial colonies. Beekeepers now routinely lose 30% or more of their hives each year. Almond orchards also receive greater absolute quantities of pesticides than any other California crop, at around 35 million pounds annually, which further pressures both managed honeybees and native bee species.
Soy Milk and Deforestation Concerns
Soy gets a bad reputation because of its association with Amazon deforestation, but the connection to soy milk specifically is thin. The vast majority of the world’s soy crop goes to animal feed, not human food products. Soy milk uses a small fraction of global soy production, and many brands source beans from the U.S., Canada, or Europe rather than from tropical regions. If deforestation concerns you, checking where a brand sources its soybeans is more useful than avoiding soy altogether.
Protein Changes the Math
Sustainability per liter is one way to compare milks, but sustainability per gram of protein tells a different story. Soy milk contains roughly 3.4 grams of protein per 100 ml, comparable to cow’s milk at about 3.3 grams. Oat milk drops to around 0.5 grams, and almond milk sits near 1 gram. A 2024 life cycle assessment found that when you adjust environmental impacts for nutritional content, unfortified plant milks sometimes perform worse than cow’s milk because you’d need to drink so much more to get equivalent nutrition. Fortified plant milks, however, still came out ahead of dairy in these nutrient-adjusted comparisons.
If you’re relying on milk as a protein source, soy is the only plant-based option that matches dairy gram for gram. With oat or almond milk, you’re getting the environmental savings but not the protein, so you’d need to make up that nutrition elsewhere.
Hemp: A Newer Contender
Hemp milk is less common on shelves but has interesting environmental credentials. Hemp cultivation improves soil organic matter and significantly reduces nitrate levels in the ground, which means less nitrogen washing into waterways. It grows quickly, needs relatively little water, and doesn’t require the heavy pesticide applications that almonds do. The main downside is limited availability and higher price, though both are changing as production scales up.
The Bottom Line on Each Milk
- Oat milk: Lowest eutrophication, low emissions, low water use, but very little protein. The strongest all-around environmental performer.
- Soy milk: Nearly as low-impact as oat on most metrics, with protein that matches dairy. Best combination of sustainability and nutrition.
- Almond milk: Low carbon, but heavy water use in drought-prone regions and serious impacts on bee populations.
- Pea milk: Similar emissions profile to oat and soy, with higher protein than most plant milks. Still a niche product with less data available.
- Cow’s milk: Highest emissions, highest land use, and highest freshwater pollution per liter. Nutritionally dense, but the environmental gap between dairy and plant alternatives is large across nearly every measure.
For most people, oat or soy milk represents the biggest sustainability gain with the fewest trade-offs. If you want to match dairy’s nutrition while cutting your environmental impact, soy is the pick. If your priority is the lightest possible footprint across carbon, water, and pollution, oat milk edges ahead.