Eating a juicy steak or burger straight off the grill is a true delight for many meat lovers. However, while animals can chow down on raw meat without issue, doing so poses significant health risks for humans. If you’re wondering why this is the case, you’ve come to the right place.

If you’re short on time, here’s a quick answer to your question: Animals have stronger stomach acid and shorter digestive tracts than humans, allowing them to safely consume raw meat that may contain dangerous pathogens.

Humans lack the proper acidic environment and digestive transit time to kill off harmful bacteria before they can make us sick.

In this comprehensive article, we’ll explore the key anatomical and biological differences that make it possible for animals to thrive on raw meat diets while humans fare better with cooked fare. Read on to learn more about:

Stronger Stomach Acid

pH levels in carnivore vs. human stomachs

Carnivores such as lions, tigers, and wolves have a stomach pH of around 1-2, which is extremely acidic. This allows them to kill harmful bacteria that may exist in raw meat and prevent intestinal illness.

In contrast, the human stomach pH ranges from 1.5 to 3.5, which is much less acidic by comparison (NIH).

The strong hydrochloric acid in carnivores’ stomachs essentially sterilizes meat, neutralizing dangerous pathogens like Salmonella, E. coli, and Listeria. Humans lack this highly acidic gastric environment, making us more vulnerable to foodborne pathogens if eating contaminated raw meat.

Ability to kill pathogens

Numerous experiments have demonstrated that pathogenic bacteria are killed much faster in carnivorous animals’ stomachs compared to humans. For example, one study found that E. coli was eradicated 100 times more rapidly in dogs’ stomach contents than in people’s (Riemann et al., 1988).

Likewise, another analysis showed that 99.9% of Salmonella bacteria incubated in dogs’ and cats’ gastric juice was eliminated after only 10 minutes. But in human gastric fluid, a similar reduction took a full 90 minutes (Fukata et al., 1996).

The greater acidity and virucidal activity in carnivores’ stomachs serve to protect them from food poisoning when scarfing down pathogen-laden carcasses. Sadly, we humans lack those reinforced defenses!

Shorter Digestive Tracts

Transit time differences

One of the main reasons why animals can eat raw meat but humans can’t is because animals have much shorter digestive tracts. This means food passes through their systems much faster than in humans, giving bacteria less time to multiply and cause illness. Here’s a comparison of transit times:

Humans 24-72 hours
Cats 12-24 hours
Dogs 10-18 hours

As you can see, transit time for humans is 2-3 times longer than for cats and dogs. This gives bacteria a lot more time to grow and produce toxins that make us sick if we eat raw meat. Animals simply don’t give bacteria enough time to reach problematic levels before the meat passes through.

Less time for bacterial growth

The shorter digestive tracts of animals compared to humans also means there is less space available for bacterial growth. Human intestines are much longer with more surface area, so bacteria have more room to multiply to dangerous levels when raw meat is consumed.

For example, the average length of the small intestine in an adult human is about 20 feet. For dogs it’s only 3-6 feet long. With 5-7 times less space available, dogs have a huge advantage when it comes to eating raw meat safely.

Additionally, hydrochloric acid levels tend to be higher in animal stomachs compared to humans. The increased acidity inhibits bacterial growth and helps break down contaiminants. The combination of shorter intestines and higher stomach acid gives animals an effective defense against foodborne pathogens when eating raw meat.

Differences in Intestinal Flora

Makeup of gut microbes

The intestinal flora of humans and animals differ greatly in terms of composition and diversity. Humans have far less microbial diversity in their guts compared to animals. On average, the human gut contains around 1000 microbial species, while animals like cows and sheep can harbor over 27,000 species in their rumen (stomach compartment).

The dominant microbial groups also vary between humans and animals. In the human gut, the two major phyla are Firmicutes and Bacteroidetes. However, in the rumen of cows and sheep, the main phyla are Bacteroidetes and Proteobacteria.

The rumen microbes are specialized to help the animal digest tough plant materials like grasses and hay. In contrast, the human gut microbes are geared more towards an omnivorous diet.

Another key difference is that many animal guts contain higher proportions of bacteria like Clostridium and Bacteroides. These bacteria produce enzymes that help break down cellulose and other complex carbs in plants.

The human gut has lower levels of these fiber-digesting microbes since our diet is less reliant on grasses and roughage.

Protection from enteropathogens

The complex microbial community in the animal gut provides an important barrier effect against foodborne pathogens like Salmonella, E. coli, and Campylobacter. The dense and diverse microbiota competes with pathogens for nutrients and attachment sites along the intestinal lining.

This helps prevent the pathogens from proliferating and causing disease.

In contrast, the relatively lower microbial diversity in humans provides less colonization resistance against enteropathogens. When pathogenic bacteria are ingested, they can more easily find vacant niches to occupy in the human intestines and multiply to infectious doses.

That is why people become ill from eating undercooked meat contaminated with pathogens, while animals generally tolerate ingesting these microbes without problems.

Some key factors that give animal guts better pathogen protection include:

  • More acidic pH in rumen/foregut – inhibits pathogens
  • Faster gut transit time – flushes out pathogens quicker
  • Thicker mucosal layer – better barrier function
  • More competitive exclusion from high microbial counts – outcompete pathogens

Behavioral Adaptations in Carnivores

Careful Food Selection

Carnivores have evolved behavioral adaptations that allow them to safely consume raw meat. One key adaptation is being extremely selective about the meat they eat. Carnivores use their keen sense of smell to carefully evaluate meat quality and freshness.

They generally avoid eating carrion or meat that has begun decomposing, as these foods have a high risk of harboring pathogens.

For example, wolves and hyenas typically only scavenge very recently killed prey, within a day or two of death. In contrast, vultures have extremely acidic digestive systems that allow them to safely eat meat at later stages of decay.

Research shows over 80% of the meat coyotes and African wild dogs consume is prey they killed themselves, allowing them control over meat freshness.

Avoidance of Spoiled Meat

In addition to selectivity about fresh kills, carnivores have been observed avoiding meat that smells spoiled. One study on domestic cats showed that felines use odor cues to detect meat freshness and steer clear of meat colonized by pathogens and fungi.

Wolves have been documented repeatedly rejecting carcasses of prey killed by bears or other wolves, behavior hypothesized to limit risk of tainted meat.

Moreover, carnivores tend to gorge when they make fresh kills, which allows them to consume as much bacteria-free meat as possible before it spoils. Research on African lions indicates that over 75% of the edible parts of large carcasses are consumed within the first day after the kill.

This focus on very fresh meat significantly reduces carnivores’ risk of food poisoning.

Cooking Makes Meat Safer for Humans

Kills Dangerous Microbial Agents

Raw meat can contain various types of dangerous microbes like Salmonella, Escherichia coli, Campylobacter, Listeria monocytogenes, and others that can cause foodborne illnesses in humans (1). Cooking meat at temperatures above 160°F for ground meats and 145°F for whole cuts of meat can effectively kill these microbial pathogens, making the meat much safer to eat (2).

For example, ground beef is frequently contaminated with E. coli. The Centers for Disease Control and Prevention estimates around 265,000 E. coli infections each year in the United States from eating improperly cooked ground beef (3).

Cooking the ground beef to an internal temperature of at least 160°F can destroy the bacteria and prevent illness.

Improves Digestibility and Nutrient Absorption

Cooking also makes the proteins in meat more digestible for humans. Raw meat contains complex proteins that are more difficult for our bodies to break down (4). Applying heat causes structural changes in meat proteins (protein denaturation) that make the proteins easier for our digestive enzymes to access and digest.

In addition, some nutrients like vitamin B12 are bound up in proteins and only become readily available to humans once the proteins are adequately broken down during digestion. Cooking helps release more nutrients from the meat, increasing the total nutrient uptake in our digestive system (5).

Nutrient Bioavailability in Raw Meat Bioavailability in Cooked Meat
Vitamin B12 About 55-60% 91-99%
Folate About 40% 65-85%

As shown above, cooking can significantly increase absorption of certain vitamins and nutrients available from meat (6). The cooking process essentially “pre-digests” the meat, jumpstarting digestibility and allowing our bodies to access more beneficial vitamins and minerals.


  • (1) USDA Food Safety and Inspection Service
  • (2) USDA Meat and Poultry Hotline
  • (3) CDC Estimates of Foodborne Illness
  • (4) Mills, et al. Meat Science. 2017.
  • (5) Santé-Lhoutellier, et al. Meat Science. 2008.
  • (6) Biesalski, Hans Konrad. Meat Science. 2005.
  • Conclusion

    In the end, the discrepancies between carnivores’ and humans’ digestive systems explain why animals can safely eat raw meats while we cannot. Our weaker stomach acid, longer intestines, gut flora and lack of behavioral adaptations leave us vulnerable to foodborne illnesses from uncooked meats.

    So next time you fire up the barbecue or order a burger, make sure to cook that meat thoroughly before taking a bite. While your dog may happily scarf down steaks tartare, we humans need to take extra precautions with our meals. Bon appétit!

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