The most recent US dietary guidelines have taken a sudden U-turn, suggesting that there should be doubling of animal protein intake in the country. In a recent analysis, scientists warn that the new diet—which also recommends reducing the intake of ultraprocessed foods—would more than offset any benefits of that move with the suggested spike in animal proteins, triggering rising greenhouse gas emissions, land, and fertilizer use.
The guidelines result from the work of a scientific panel called the Dietary Guidelines Advisory Committee (DGAC), which meets every five years to review and update dietary recommendations for the United States. Those are usually adopted into the official guidelines: these were the focus of the current PNAS research.
In it, the scientists looked at the environmental outcomes of current and previous dietary recommendations. They simulated diets in which ultraprocessed foods (UPFs) were completely eradicated, alongside varying levels of suggested protein intake—in one scenario matching animal protein intake to previous years’ guidelines, which suggested Americans should consume about 0.8 grams per kilogram weight of protein. In another, they simulated a diet that reflected the upper bound of what the new guidelines recommend, which is a doubling of that previously suggested protein intake to 1.6 grams per kilogram weight.
In each case they explored the greenhouse gas impact, land-use, and fertilizer consumption effects of the particular diet, and compared the findings with the mean American diet.
This revealed that even though the new diet does cut environmental impacts by reducing intake of UPFs—which have a high animal protein content overall—this was more than offset by the rising animal protein intake. In fact, the analysis shows that increasing protein intake would cancel out the environmental benefits of UFPs by an excess of 32%.
The paper highlights one plus of the new suggested diet, which is a reduction in water use by between 7 and 19%, compared to the mean American diet. However it notes that the suggested diet would otherwise “confer net environmental harm” across almost all environmental metrics. And besides, a diet low in UPFs but higher in plant-based proteins would tick all boxes, the study finds, lowering water use even further, bringing down greenhouse gas emissions, fertilizer, and land use.
“There is considerable potential benefit for both public and planetary health if prevailing diets remove UPFs, and replace them with plant dominated whole foods,” the researchers write.
Meanwhile, nonprofits, scientists, and health professionals not involved in the research have collectively noted that the new guidelines reject the majority of recommendations made by the DGAC science panel, and that the process this time around involved significant conflicts of interest with the US meat and dairy industries.
As a closing note in the PNAS paper, the researchers call for an urgent realignment of the guidelines with established science and evidence, which time and time again has shown the harmful effects of excess meat and dairy consumption on human and planetary health.
Shepon et. al. “The 2025–2030 Dietary Guidelines for Americans are associated with higher land, water and nitrogen use, and greenhouse gas emissions.” PNAS. 2026.
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