「肉類不耐症」：我們的身體會忘記如何消化肉類嗎？

Many individuals who decide to stop eating meat have reported feeling unwell when they return to it. This leads to an interesting question: can our bodies actually forget how to digest meat? Reducing meat consumption is one of the easiest ways to lessen our impact on the environment. For instance, if everyone in the UK adopted a low-meat diet, consuming less than 50 grams of meat daily, it would be equivalent to removing eight million cars from the roads. According to data from the UK government, meat consumption is on the decline, and an increasing number of people are exploring the idea of eating less meat. However, if someone abstains from meat for an extended period, does this affect their body's ability to digest it? This is a common concern among vegetarians and vegans, who often share their experiences and raise questions about the effects of reintroducing meat into their diets. Unfortunately, there is limited research on whether consuming meat after a long break can lead to digestive issues. Sander Kersten, a professor of nutrition at Cornell University in the United States, states, 'A lack of evidence does not mean it does not exist; it simply means it has not been studied. ' While this may not be the most satisfying answer, it is a reality we must face. The enzymes responsible for digesting meat are the same ones that break down other types of proteins. It is important to note that while it is rare, some individuals can develop an allergy to meat, known as Alpha-gal syndrome. In this condition, the immune system mistakenly identifies animal proteins as harmful invaders. This allergy can develop even after years of consuming meat, but it is not directly related to switching to a low-meat diet. For many people who avoid meat, discovering that they have unknowingly consumed it can be emotionally distressing. Kersten, who identifies as a vegetarian, explains, 'That can make some people very sad. I am not sure if it would lead to physical symptoms, but it could certainly trigger a lot of anger. ' When we consider the biology of digestion, it is not as likely as one might think that the body could lose the ability to digest meat over time. Generally, meat is quite easy to digest, especially when compared to the fiber found in fruits, vegetables, and legumes. To break down fiber, our bodies rely on our microbiome, which contains microbes that produce the necessary enzymes for digestion. Furthermore, the enzymes that digest plant proteins are the same as those that digest meat proteins. These enzymes recognize and break specific chemical bonds in proteins, regardless of whether they originate from plants or animals. Proteins are made up of smaller units called amino acids, and enzymes can typically break them down regardless of their source. This process differs from the digestion of lactose, the sugar found in milk. To digest lactose, our bodies require a specific enzyme called lactase. Individuals who do not produce enough lactase, known as lactose intolerant, may experience digestive discomfort after consuming dairy products. However, with meat proteins, it does not make sense to assume that the body would somehow stop producing the enzymes necessary for comfortably digesting a hamburger. These enzymes are always present, breaking down any protein that enters our system, whether it comes from peas, soybeans, or steaks. The human gut microbiome does change based on dietary habits. Sometimes, this means that the specific types of bacteria present in the gut change, or the microbes may produce different enzymes. Research has shown that while there are differences between the microbiomes of omnivores and those of vegetarians and vegans, as long as omnivores consume a variety of plant-based foods, their microbiomes can be quite similar. However, it is important to note that microbiomes can shift rapidly in response to dietary changes. For example, one study found that individuals who switched to a fully animal-based diet experienced a significant change in their baseline microbiome. Interestingly, their microbiome returned to normal once they resumed their previous diet. Participants in this study were encouraged to report any discomfort they experienced, but no significant findings were published. If anything, it is the sudden introduction of large amounts of fiber after a long absence that could lead to digestive issues. It is advisable to gradually ease into such dietary changes. Kersten advises, 'Depending on the type of fiber, you can have some pretty strong reactions to it. ' In summary, if you are concerned about your body losing the ability to digest meat, it should not deter you from continuing to reduce your meat consumption. If you have experienced an upset stomach after eating meat following a long break, it is unlikely that a loss of enzymes is the cause. Kersten reassures us, 'The body is quite adaptable. It can do more than you think.