A 2026 study published in the Proceedings of the National Academy of Sciences examined the environmental impacts of the 2025–30 Dietary Guidelines for Americans, which were released in early 2026. The researchers argue that the guidelines must be revised to prioritize plant-based over animal-based foods to align with scientific evidence on public and planetary health.
The 2025–30 Dietary Guidelines for Americans advise avoiding ultra-processed foods and recommend higher protein intake, chiefly from animal sources. The study assessed land use, nitrogen fertilizer use, freshwater use, and greenhouse gas emissions for diets following these guidelines compared with the current Mean American Diet. Researchers constructed isocaloric diets of 2,500 kcal with protein levels of 0.8, 1.2, and 1.6 g/kg body weight, eliminating all ultra-processed foods. They also compared two high-protein diets—one using plant protein and the other animal protein.
The findings showed that while eliminating ultra-processed foods reduced freshwater use by 7%–19%, increasing protein intake to 1.2–1.6 g/kg—levels consistent with current American consumption and the new guidelines—raised environmental impacts by up to 32%. This increase stemmed from greater land use, nitrogen fertilizer application, and greenhouse gas emissions. Ultra-processed foods currently account for 40%–58% of the environmental impact in the Mean American Diet, and they provide about two-thirds of the energy consumed by U.S. youth and 60% for adults.
Critically, the diet with animal-based protein had a greater environmental impact than the one with plant-based protein. The high plant-based protein diet demonstrated substantially lower environmental burdens. The authors concluded that replacing ultra-processed foods with plant-based whole foods would benefit both public and planetary health, whereas substituting them with animal-based foods would cause net environmental harm and have uncertain public health effects.
"The 2025–30 Dietary Guidelines for Americans must be revised to align them with established science and evidence, which requires prioritizing plant-based foods over animal foods," wrote Shepon A, Makov T, Katz DL, and Eshel G, the study’s authors. They noted that even a nationwide shift to grass-fed beef could support only about half of current U.S. beef consumption.