Going vegan from lacto-vegetarian altered liver metabolism in days, mouse study finds

Moving from a lacto-vegetarian diet, which includes milk and dairy, to a strictly vegan one changed how the liver works within a few days in a study on mice, researchers at the University of Geneva (UNIGE) in Switzerland reported this week. The findings, published in the journal Molecular Metabolism and reported on Tuesday, October 13, 2026, show that mice switched to a diet with no animal protein produced glucose less efficiently and cleared ammonia, a toxic by-product of breaking down protein, less well. The researchers said the change was rapid but also reversible once animal protein was put back into the diet. The work was done in animals and has not been tested in people.

In the Indian vegetarian tradition, a meatless diet has usually meant a lacto-vegetarian one: grains, pulses, vegetables and fruit, together with milk, curd, paneer and ghee. A vegan diet goes a step further and drops dairy as well. This study looks at exactly that step, from a dairy-inclusive vegetarian diet to a fully plant-based one, and asks what it does to the liver.

The liver has to manage two linked jobs. Between meals and during fasting, it makes glucose to keep blood sugar steady. When the body breaks down protein, it also has to deal with the nitrogen left over, which first appears as ammonia and is then turned into urea for removal. The Geneva team found that the enzyme glutamate dehydrogenase sits at the centre of both jobs. When they removed it from the liver, the vegan diet caused a severe rise in ammonia and disrupted blood sugar control.

The researchers' explanation turns on the building blocks of protein. Plant proteins contain fewer branched-chain amino acids than animal proteins, and these amino acids help the liver keep blood glucose up during fasting. Remove animal protein entirely, and the liver has to adjust how it handles the amino acids it does receive. In the mice, that adjustment happened within days.

The findings do not show that vegan diets are harmful for people. They come from mice, which differ from humans in metabolism and diet, and the researchers stressed that the effect was reversible. What the work does suggest is that the type of protein in a diet, and not only the amount, shapes how the liver handles sugar and nitrogen, and that the difference between a vegetarian diet with dairy and a vegan one may matter more than is often assumed.

Short-term: The study adds a new question to the debate on plant-based eating, but it does not change dietary advice. People who follow or are considering a vegan diet should continue to plan meals for enough protein from a variety of sources, and anyone with liver disease or diabetes should seek medical advice before making a major change.

Long-term: If similar effects are confirmed in people, researchers may look more closely at protein quality, such as branched-chain amino acid content, when advising those moving from vegetarian to vegan diets, particularly people with liver conditions.

Who is affected: Vegetarians and vegans, people thinking of giving up dairy, dietitians and doctors who advise on plant-based diets, and researchers studying liver metabolism.

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