Scientists at the University of Geneva switched mice to a vegan diet and discovered something unexpected: Within days, their livers became less efficient at producing glucose, and the animals became less physically active.
The findings, announced October 13 and published in Molecular Metabolism, raise questions about how quickly the body responds when animal proteins disappear from the diet. However, the experiment involved mice, not people, and does not establish that vegan diets harm human health.
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What Happened After Just Two Days?
Researchers compared mice eating a diet containing animal and plant proteins with mice consuming exclusively plant proteins.
“In just a couple of days, the mice fed an exclusively vegan diet showed less efficient glucose production,” said Pierre Maechler, PhD, a professor at the University of Geneva.
“Furthermore, their livers were less effective at eliminating ammonia, a toxic substance released during the breakdown of amino acids. A significant reduction in physical activity also points to outcome on the entire body.”
The findings suggest that changing protein sources can affect several metabolic processes simultaneously, even before longer-term adaptations become apparent.
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Scientists Identified a Key Liver Enzyme
The researchers focused on glutamate dehydrogenase (GDH), an enzyme that helps connect protein metabolism with glucose production.
In additional experiments, mice lacking GDH in their livers experienced particularly severe ammonia accumulation and problems regulating blood glucose when fed exclusively plant proteins.
But the changes weren’t necessarily permanent.
“Overall, a change in diet composition alters liver metabolism very quickly, but this effect is rapidly reversible,” Maechler explained.
“The body adapts within one to two days to even subtle changes in dietary composition and returns to normal upon the reintroduction of animal proteins.”
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What This Means for People Eating Plant-Based Diets
The peer-reviewed research highlights the importance of protein composition, not simply whether a diet contains meat.
Plant proteins vary in their amino acid profiles, including branched-chain amino acids involved in metabolism.
For people avoiding animal products, the researchers recommend incorporating varied protein sources, including tofu, lentils, and nuts.
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