Some individuals who give up meat for an extended period report unpleasant reactions when they reintroduce it into their diet. But does the human body truly forget how to process meat?
Reducing meat consumption is one of the simplest ways to lessen environmental impact. If every person in the UK adopted a diet with less than 50 grams of meat daily—roughly the size of a single sausage—it would cut carbon emissions on par with removing eight million cars from the roads, researchers estimate, according to BBC News.
UK government data shows a significant drop in meat consumption over the decades, with beef, pork, and lamb intake declining by 62% between 1980 and 2022. While some attribute this shift to environmental awareness, financial constraints also likely play a role.
But does abstaining from meat for a long time alter the body’s ability to digest it? Many vegetarians and vegans have taken to social media to express concerns about digestive discomfort, bloating, or stomach pain upon consuming meat after years of avoidance. However, scientific research on this topic remains scarce.
According to Sander Kersten, a professor of nutrition at Cornell University, the lack of studies doesn’t necessarily mean the phenomenon doesn’t exist—it just hasn’t been thoroughly investigated. “It’s not always a satisfying answer, but sometimes that’s the reality,” he explained, as per BBC News.
Though extremely rare, some individuals do develop an allergy to meat. Alpha-gal syndrome, a condition where the immune system misidentifies animal proteins as harmful, can cause severe allergic reactions, including anaphylaxis. However, this condition is unrelated to a low-meat diet and can instead be triggered by something as unexpected as a tick bite.
For many people who have given up meat, consuming it unknowingly can be emotionally distressing. Kersten, who is a vegetarian himself, notes that such an experience could feel like a personal violation, leading to emotional turmoil, though whether this translates into physical symptoms is uncertain.
From a biological perspective, it is unlikely that the body loses its ability to digest meat over time. Unlike fiber-rich foods, which require assistance from gut bacteria to break down, meat is relatively easy to digest. The enzymes responsible for processing plant proteins also break down meat proteins, as both contain amino acids linked by similar chemical bonds. Since the body continuously produces these enzymes, it doesn’t simply stop digesting meat after a period of avoidance.
A more comparable scenario would be lactose intolerance. Some individuals lose their ability to digest lactose—the sugar in milk—because their bodies stop producing lactase, the enzyme required to break it down. However, this process does not apply to meat proteins, as the enzymes responsible for digestion remain active regardless of dietary changes, according to reports by BBC News.
That said, the human gut microbiome does adapt based on diet. While omnivores, vegetarians, and vegans have slightly different gut bacteria compositions, research suggests the differences are not drastic as long as omnivores consume a variety of plant-based foods. Moreover, microbiome shifts can occur rapidly.
In one study, participants who switched to an all-meat diet exhibited microbiome changes within just one day—though their gut flora returned to normal once they resumed their usual diet. Notably, no significant digestive distress was reported in the study.
Interestingly, sudden increases in fiber intake after a long break may cause more digestive discomfort than reintroducing meat. Gradual dietary shifts are generally easier on digestion. “Depending on the type of fiber, the body can react strongly to sudden changes,” Kersten noted, as per reports by BBC News.
Ultimately, the idea that the body forgets how to digest meat is largely unfounded. If someone experiences stomach issues after reintroducing meat, it is unlikely due to a loss of digestive enzymes—though the phenomenon remains under-researched.
“The body is incredibly adaptable,” Kersten concludes. “It can handle more than we often give it credit for.”