Eating meat, particularly red and processed varieties, is linked to higher rates of heart disease, certain cancers, and type 2 diabetes. It also takes a heavy toll on the environment, requiring vastly more water and land than plant-based protein sources while generating greenhouse gas emissions on par with the entire global transportation sector. Here’s what the evidence actually shows.
Heart Disease and a Chemical Called TMAO
When you eat red meat, bacteria in your gut break down certain nutrients abundant in it and produce a compound called trimethylamine N-oxide, or TMAO. This chemical promotes cholesterol deposits in artery walls and makes blood platelets stickier, raising the risk of clot-related events like heart attack and stroke.
The effect is measurable and significant. In a controlled feeding study funded by the NIH, participants who ate roughly eight ounces of steak daily (about two quarter-pound burger patties) for one month had triple the blood levels of TMAO compared to when they ate the same amount of protein from either poultry or plant sources. When they switched off the red meat diet, their TMAO levels dropped back down. Plant-based proteins don’t supply the same precursor compounds that gut bacteria convert into TMAO, which is one reason plant-heavy diets consistently show lower cardiovascular risk.
Cancer Risk: What the Classifications Mean
The International Agency for Research on Cancer classifies processed meat (bacon, sausages, hot dogs, deli meats) as a Group 1 carcinogen, the same category as tobacco smoke and asbestos. That doesn’t mean processed meat is equally dangerous as smoking. It means the evidence that it causes cancer is equally strong. Red meat sits one tier below, classified as Group 2A: probably carcinogenic to humans.
Processed meat is most strongly tied to colorectal cancer, with evidence also pointing to stomach cancer. Red meat is associated with increased risk of colon and rectal cancer, and research suggests links to prostate and pancreatic cancer as well. One mechanism involves heme iron, which is abundant in red meat. High heme iron intake promotes the growth of specific bacteria in the gut, including Fusobacterium and Clostridium species, that are connected to colorectal carcinogenesis.
Type 2 Diabetes Risk
A large meta-analysis published in The Lancet, pooling data from 1.97 million adults across 31 cohorts in 20 countries, found that all three major types of meat raised the risk of developing type 2 diabetes. Processed meat carried the highest risk: each 50-gram daily serving (roughly two slices of deli meat) was associated with a 15% increase. Unprocessed red meat showed a 10% increase per 100 grams daily, and even poultry carried an 8% increase at the same serving size. These aren’t enormous jumps from a single serving on a single day, but they compound over years of habitual intake.
What Meat Does to Your Gut
Beyond TMAO, a diet high in red meat shifts the gut microbiome in ways that favor inflammation. Red meat consumption increases the production of uremic toxins, including indoxyl sulfate and p-cresyl sulfate, compounds that stress the kidneys and promote systemic inflammation. The heme iron in red meat also encourages the growth of bacteria like Streptococcus bovis and Helicobacter pylori, both of which are implicated in colorectal cancer development.
Plant-based diets, by contrast, tend to feed bacteria that produce short-chain fatty acids, which protect the gut lining and reduce inflammation. The shift can happen relatively quickly. Changing your protein sources for even a few weeks produces measurable changes in gut bacterial populations.
The Environmental Cost of Meat
Livestock production accounts for roughly 14.5% of all human-caused greenhouse gas emissions, approximately the same share as every car, truck, ship, and airplane on Earth combined. About 80% of those livestock emissions come from cattle and other ruminants. The total includes direct emissions (mostly methane from digestion and manure) plus indirect contributions from deforestation to create grazing land, energy used in production, and growing animal feed.
Water use tells a similar story. Producing one kilogram of beef requires approximately 15,400 liters of water, with some estimates ranging as high as 43,000 liters depending on the production system. Compare that to soybeans at about 2,145 liters per kilogram, or beans at roughly 2,668 liters. Even lentils, which are relatively water-intensive for a plant crop, need only about 5,874 liters per kilogram, less than half the water footprint of beef at the low end. Chicken and pork fall between beef and plants, at roughly 2,300 and 3,500 liters per kilogram respectively, but neither comes close to the efficiency of plant proteins.
Longevity Differences in Large Studies
The Adventist Health Study 2, which followed over 73,000 people, found that vegetarians had a 12% lower risk of dying from any cause compared to non-vegetarians. The strongest results came from pescatarians (people who eat fish but no other meat), who showed a 19% lower risk of all-cause mortality. Even semi-vegetarians, who ate meat occasionally, trended toward lower mortality, though their results didn’t reach statistical significance.
These are observational findings, so they can’t prove meat itself is the sole cause of the difference. Vegetarians in these studies may also exercise more, smoke less, or have other healthy habits. But the pattern holds across multiple large cohorts and persists even after researchers adjust for factors like smoking, exercise, and overall calorie intake.
Nutrients You Need to Plan For
Cutting out meat isn’t without trade-offs, and pretending otherwise doesn’t help anyone make a good decision. Meat provides several nutrients that are harder to get from plants, not because plants lack them entirely, but because your body absorbs them less efficiently from plant sources.
Vitamin B12 is the most critical gap. It’s produced exclusively by microorganisms and accumulates in animal tissues. Unfortified plant foods contain essentially none of it, so anyone eliminating meat needs a reliable source through fortified foods or supplements. B12 deficiency can cause nerve damage and anemia, and it’s consistently more common among vegetarians and especially vegans.
Iron is the second major consideration. Red meat contains heme iron, which your body absorbs at rates of 15 to 35%. The non-heme iron in plants is absorbed at just 2 to 20%, and compounds called phytates in beans, grains, and lentils reduce absorption further. This is why iron deficiency is more prevalent among people who don’t eat meat, particularly women and children. Eating vitamin C-rich foods alongside iron-rich plants helps improve absorption.
Zinc follows a similar pattern. Meat provides zinc with absorption rates of 25 to 40%, while plant-based zinc is less bioavailable due to those same phytate compounds. Lower zinc and selenium intakes on meat-free diets can affect immune function and thyroid health over time. Creatine, carnitine, taurine, and long-chain omega-3 fatty acids are also found primarily in animal products, though your body can synthesize small amounts of each on its own.
None of these gaps are insurmountable. They just require awareness. A well-planned plant-based diet with appropriate supplementation (especially B12) and attention to iron and zinc sources can meet all nutritional needs. The key word is “planned,” because simply removing meat without replacing its nutrients leaves real gaps.