The Truth About Meatless Diets According to Science

The Truth About Meatless Diets According to Science

The other day you went out to dinner with some friends.  Or your extended family.  Or your co-workers.  

You were all eating, drinking, chatting and having a good time, when all of the sudden you glanced around the table and realized — I’m like the only one eating meat!

That got you wondering: have I somehow started to magically attract people who don’t want to eat meat into my life, or are there really more of them around?  

As much as I’d love to tell you your magic powers have finally arrived (and a Hogwarts owl is on its way to your window right now), I’m afraid it’s not you.  More and more Americans are not eating meat.

Meatless Diets are on the Rise

In the late 1990s, only around 2% of Americans reported abstaining from meat.  Today, that number may be as high as 13%.

What’s more, a whopping additional 37% of Americans now report eating a mostly vegetarian diet, meaning they only rarely eat meat.  

You don’t even have to just take people’s word for it, though.

Analysis of what Americans actually buy at the supermarket shows a decisive trend away from meat and towards more plant-based options, starting back in the early 2000s, with no sign of letting up anytime soon.

In fact, all the evidence points to the fact it’s actually likely going to speed up.

Take a look at this study, for example, which shows a bump in the number of vegans from 1% in 2014 to 6% in 2017.  That’s 500%.  In 3 years.  After it took a decade and a half to see the 100-or-so% gain from barely-detectable levels in the 1990s to 1% in 2014.

American vegetarians

Analysis of last year’s numbers have brought businesses to the same conclusion — plant-based diets are seriously on the rise and growing fast.  Big names in the business, like Forbes, even predict that a shift towards purchasing even more plant-based products, such as meat-replacements, non-dairy milk and non-dairy cheeses, and plant-based restaurant foods will likely be the defining food trend of 2018.  

Meatless Motivations

What’s prompted millions of people to suddenly all start passing on the pork?

As you can imagine, there are a lot of reasons.  Really, there are probably as many reasons as there are people who’ve cut back on their meat intake.

Generally, though, most people’s motivations appear to fall into one (or more) of the following four categories:

  • taste preferences
  • environmental considerations
  • animal welfare considerations
  • health considerations

While all of these topics are fascinating, I’m just going to focus just on the health considerations today, since Nutrishativers come here for health and nutrition information!  

If you are interested in learning more about the environmental arguments surrounding not eating meat, I’d recommend checking out this report by the Food and Agriculture Organization of the UN.  If you’d like to see more on the animal welfare arguments, I recommend watching this documentary.  And, if you happen to be curious about why different people might find different foods to taste good, see if you can get your hands on this recent scientific review article. These are all great jumping-off points that will give you a great overview of the issues and tips for further research.

Alright, back to business!  

Meatless Diets and Health

Before we can dig into whether or not those who go meatless for health reasons have science on their side or not, we need to take a closer look at exactly what health reasons they cite!  

What health effects do those promoting a meatless diet claim come with this way of eating?

Well, there are a bunch. According to the Vegetarian Society and Vegan Society homepages, a meatless diet can lower your risk of developing:

  • obesity
  • constipation
  • high blood pressure
  • high cholesterol
  • heart disease
  • cancer
  • type 2 diabetes
  • diverticulitis
  • appendicitis
  • gallstones

Do these claims hold up to the science?

Let’s check it out.


Yes.  A 2017 meta-analysis (a study that combines the data from multiple other studies mathematically, here 94 unique studies) compared those who consumed meat to those who don’t, found those who don’t have lower BMIs.  This is likely the result of eating lots of plant foods, which are, generally, lower in calories than animal-based products.


Yes.  A 2017 review article (a study that combines the data from other studies non-mathematically) of the latest evidence found that those eating meatless diets have more frequent bowel movements with larger, softer stools.  In everyday parlance: they are, indeed, less constipated.  Researchers suggest this is likely the result of increasing fiber intake.

Related: Gut Health: 7 Reasons Why It’s Important

High Blood Pressure  

Yes.  A 2017 review article of the latest evidence concluded those who eat meatless diets have statistically lower blood pressures than those who eat meat.  The researchers suspect a large part of this effect comes from losing weight on meatless diets, though other dietary factors may also play a role.

High Cholesterol  

Yes.  Studies show statistically significant decreases cholesterol levels (around 30 points) in the blood between those who eat meat and those who do not.  This makes sense as animal products, such as meat, are the only sources of dietary cholesterol.

Heart Disease 

Yes. That same meta-analysis from above looked at BMI also found a 25% reduction in the risk of developing heart disease in those that eat meatless diets.  This is likely the result of lowered cholesterol and blood pressure!


Yes.  Though the effect was small, this meta-analysis found an 8% decrease in total cancer risk in those consuming a meatless diet.  

Type 2 Diabetes  

Yes.  A different 2017 meta-analysis found a 23% reduction in the risk of developing diabetes among those eating meatless diets.  This may be due, at least in part, to the reduction in BMI.


Yes.  At least among men, those eating no meat have statistically lower rates (about 58%) of diverticulitis, a painful condition that causes little balloon-like pockets to form in the colon.  This is likely the result of increased fiber intake and reduced risk of constipation.


Maybe.  The evidence for protection against appendicitis is much less overwhelming. Here is one study, for example, showing a statistically significant difference in rates of appendicitis between those that eat meat and those that don’t.  The authors, however, didn’t control for confounding factors, like gender (more men got appendicitis in the study, for example), so it’s hard to say for sure how large of a role diet itself played.


Maybe.  Similar to appendicitis, the evidence is less strong for this condition than some of the others, but some studies do suggest those following meatless diets might have half the risk of developing gallstones.  This is thought to be due to a decrease in cholesterol, a major risk factor for the formation of a gallstone.

Related Article: Digestive Enzymes After Gallbladder Removal — Helpful or Hokum?

Well, that’s 8 for 10 for sure.  10 for 10, possibly.

It looks like a meat-free diet may really help protect you from some serious diseases.

Downsides of a Meatless Diet

Just because a vegetarian or vegan diet can protect against some diseases, doesn’t necessarily mean it couldn’t increase the risk of other conditions.  Since a meat-free diet, by definition, requires removing foods from the diet, people often worry that this way of eating can result in low intakes of nutrients you need to prevent illnesses. Specifically, there has been concern that meat-free diets may be deficient in nutrients specifically concentrated in meat.  

Which nutrients are these?

  • calcium
  • vitamin D
  • vitamin B12
  • iron
  • omega-3 fatty acids
  • protein

What does the scientific evidence say about these concerns?

Let’s take them one at a time, and start with the biggy.


There has long been a concern that meat-free diets don’t contain enough protein and can put you at risk for a protein deficiency.

This concern stems from the fact that meat is a concentrated source of protein, meaning you don’t have to eat a lot of it to get a lot of protein.  Most plant foods, contain comparatively little protein, meaning you have to eat larger volumes of food to get the same amount of protein.  The concern is, if you don’t increase the sheer amounts of food you eat on a meat-free diet,  you could end up falling short and not giving your body all the protein it needs.

Not getting enough protein would put you at risk for muscle wasting, loss of healthy organ tissue, and general loss of well-being.

Are those concerns justified?

It doesn’t look like it.  Though those eating a meatless diet do appear to get less protein in their diet each day (65 g vs. 87 g for men and 47 g vs. 66 g for women), they still get above the recommended minimum for protein intake (53 g for men and 46 g for women).  

There is a very little risk of developing a protein deficiency on a meatless diet.

Read Next: How To Train As a Vegan Athlete: 4 Tips From an Exercise Expert

Omega-3 Fatty Acids

Omega-3 fatty acids are health-promoting fats that are found concentrated in algae and fish.  Since most people in the west don’t consume algae and strict vegetarians and vegans don’t consume fish, it was suspected they were at high risk for a deficiency.  

An omega-3 fatty acid deficiency could put you at risk for unhealthy changes to your nervous system, cardiovascular system, and immune system.

What did researchers find when they tested the blood of people who consumed strictly fish-free diets?

Their blood levels were, indeed, too low.  But no lower than people who consumed normal western diets.

Taking a vegetarian 250 mg omega-3 supplement made from algae oil once per day was found to be a simple, effective way to raise blood levels of these important fatty acids up to healthy levels.

Increasing your intake of omega-3-rich vegan foods can also be helpful.


Meat contains lots of iron, specifically a type of iron called heme-iron, that is easier for your body to absorb.

This fact leads many people to suspect those on vegetarian or vegan diets might be at high risk for iron deficiencies.

Iron deficiencies can put you at risk for anemia, a condition where your body cannot carry enough oxygen in your blood.

This concern has seemed to pan out.  Compared to the average population, vegans, particularly women following a vegan diet, do appear to have a higher rate of iron deficiency (40% vs. 11%) despite statistically consuming more total (plant) iron in their diet than omnivores.

Interestingly, the increased rate of general deficiency among vegan women does not appear to translate to an increase in overt deficiency symptoms.  Among the general population, that rate is thought to be between 2% and 5%.  Among vegan women, the rate was found to be 4%, suggesting the scope of the problem may be less than it initially appears.

Vitamin B12

Vitamin B12 is an important enzyme involved in helping your cells make DNA and regulating your metabolism.  

Though B12 is made by microorganisms, not animals, it concentrates in meat as animals eat the microorganisms.  This makes meat one of the primary sources of vitamin B12 for humans.

Do those eating a meat-free diet have lower levels of vitamin B12?


Studies show those consuming a vegetarian or especially a vegan diet (since there is also B12 in other animal products such as milk and eggs that vegetarians consume) often have extremely low intakes of vitamin B12, putting them at serious risk for developing a deficiency.

A vitamin B12 deficiency can put you at risk for anemia (via a different mechanism than iron), neurological problems, or suffering a heart attack or stroke.  

Those eating a meat-free diet are advised to eat foods fortified with B12 and take a B12 supplement (at least 10 micrograms per day).

Calcium & Vitamin D

Meat and fish are also important sources of calcium and vitamin D making a decreased intake of these key nutrients in those eating a meat-free diet.

Overt calcium deficiencies lead primarily to just loss of healthy bone.  Overt vitamin D deficiencies, on the other hand, not only cause healthy bones to break down but also impair immune function, increase the risk for high blood pressure, promote heart disease and increase the likelihood of developing cancer.

For those consuming a vegetarian diet, the risk of over deficiency is considered pretty low because dairy and eggs are also highly concentrated sources of calcium and vitamin D.

Vegans, however, who consume no meat, dairy or eggs, may be at high risk.  Indeed, studies show that vegans often consume less vitamin D and calcium than omnivores.

Meatless Diets and Bone Health

How serious is this for vegans’ bones?  Studies show mixed results.  Some indicate a greater risk of fracture, while others don’t.  Researchers think that the decrease in calcium and vitamin D intake in those eating entirely plant-based diets is largely counteracted by an increase in vitamin K intake, as vitamin K also helps protect bones.  

This suggests that vegans should load up on leafy greens, which are rich in vitamin K. Conveniently, leafy greens are also one of the best, most concentrated sources of plant calcium, as well, making them a win-win for vegan bone health.

What about the other effects of a vitamin D deficiency?  Are vegans at greater risk?  They may be.  In a study conducted in Vietnam, 27% of vegans had vitamin D levels in their blood consistent with a deficiency (< 20 ng/mL) compared to 7% of non-vegans.  Since the bone-protective effects of vitamin K do not extend to other effects of an overt vitamin D deficiency, vegans should be concerned about developing other deficiency symptoms.

How can vegans prevent or correct a vitamin D deficiency?  There are two options.

     1. Getting more sunlight

Human skin makes vitamin D when it is bathed it in natural sunlight.  Getting a few minutes (15-30) of mid-day sun directly on the skin (no long sleeves, long pants or sunscreen) is usually enough to prevent a vitamin D deficiency.  As long as the sunshine doesn’t have to shine through too much atmosphere (i.e. the person is near the equator, or it’s summer.)

Those living far from the equator have to turn to option 2 in the winter.

     2. Taking a supplement

Taking 2,000 international units (IUs) of vitamin D (preferably D3) each day can prevent a vitamin D deficiency.

Learn More: The Truth About the Vitamin D Supplement Buzz: Does the Hype Hold Up to the Science?

Meatless Diets: Yay or Nay?

That was a pretty long list of nutrients that those eating a meatless diet have to pay attention to!

Do those deficiency risks, and the extra effort in planning your diet required to avoid them, make meatless diets a no-go?

In my opinion: no.  While a meatless diet can take a little effort to do healthily, so can an omnivorous diet.  After all, there are incredibly important nutrients that you can easily get in spades with a meatless diet that are often low in standard western diets, such as folate, vitamin C, vitamin E and fiber.

Combine this with the reduction in risk for serious chronic diseases, such as heart disease and cancer seen with a meat-free diet, and the weight of evidence comes out in favor of a vegetarian or vegan diet.

I give meatless diets, if you want to give one a try, a: yay.

Take Home Message

Motivated by taste preferences and ethical, environmental and health concerns, an ever-growing number of people are switching to a meat-free diet.  

Though there are specific nutrients that require more attention on a meatless diet, the extra effort involved in finding supplements and/or specifically planning meals around these nutrients may be outweighed by the significant reductions in disease risk that come with these types of diets.

The health claims made by those promoting meatless diets are not trumped-up or made-up and, should you decide you want to follow this dietary trend, you may reap significant health benefits.

Have you been considering switching to a meat-free diet?  Did this article help you decide if you really want to give it a go?  Any questions I missed?  Let me know in the comments below!

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