Meat is Heat: The Effects of Diet on Global Warming

One of the most prestigious medical journals in the world editorialized that climate change represents “the biggest global health threat of the 21st century.” Currently, chronic diseases are by far the leading cause of death. Might there be a way to combat both at the same time? For example, riding our bikes instead of driving is a win-win-win for the people, planet, and pocketbook. Are there similar win-win situations when it comes to diet?

As I discuss in my video, Diet and Climate Change: Cooking Up a Storm, the foods that create the most greenhouse gases appear to be the same foods that are contributing to many of our chronic diseases. Researchers found that meat (including fish), eggs, and dairy had the greatest negative environmental impact, whereas grains, beans, fruits, and vegetables had the least impact. And not only did the foods with the heaviest environmental impact tend to have lower nutritional quality, but they also had a higher price per pound. So, avoiding them gives us that triple win scenario.

The European Commission, the governing body of the European Union, commissioned a study on what individuals can do to help the climate. For example, if Europeans started driving electric cars, it could prevent as much as 174 million of carbon from getting released. We could also turn down the thermostat a bit and put on a sweater. But the most powerful action people could take is shift to a meat-free diet.

What we eat may have more of an impact on global warming than what we drive.

Just cutting out animal protein intake one day of the week could have a powerful effect. Meatless Mondays alone could beat out a whole week of working from home and not commuting.

A strictly plant-based diet may be better still: It’s responsible for only about half the greenhouse gas emissions. Studies have suggested that “moderate diet changes are not enough to reduce impacts from food consumption drastically.” Without significant reduction in meat and dairy, changes to healthier diets may only result in rather minor reductions of environmental impacts. This is because studies have shown that the average fossil energy input for animal protein production systems is 25 calories of fossil energy input for every 1 calorie produced—more than 11 times greater than that for grain protein production, for example, which is around 2 to 1.

Researchers in Italy compared seven different diets to see which one was environmentally friendliest. They compared a conventional omnivorous diet adhering to dietary guidelines; an organic omnivorous diet; a conventional vegetarian diet; an organic vegetarian diet; a conventional vegan diet; an organic vegan diet; and a diet the average person actually eats. For each dietary pattern, the researchers looked at carcinogens, air pollution, climate change, effects on the ozone layer, the ecosystem, acid rain, and land, mineral, and fossil fuel use. You can see in the video how many resources it took to feed people on their current diets, all the negative effects the diet is having on the ecosystem, and the adverse effects on human health. If people were eating a healthier diet by conforming to the dietary recommendations, the environmental impact would be significantly less. An organic omnivorous diet would be better still, similar to a vegetarian diet of conventional foods. Those are topped by an organic vegetarian diet, followed by a conventional vegan diet. The best, however, was an organic vegan diet.

The Commission report described that the barriers to animal product reduction are largely lack of knowledge, ingrained habits, and culinary cultures. Proposed policy measures include meat or animal protein taxes, educational campaigns, and putting the greenhouse gas emissions information right on food labels.

Climate change mitigation is expensive. A global transition to even just a low-meat diet, as recommended for health reasons, could reduce these mitigation costs. A study determined that a healthier, low-meat diet would cut the cost of mitigating climate change from about 1% of GDP by more than half, a no-meat diet could cut two-thirds of the cost, and a diet free of animal products could cut 80% of the cost.

Many people aren’t aware of the “cow in the room.” It seems that very few people are aware that the livestock sector is one of the largest contributors to greenhouse gas emissions. But that’s changing.

The UK’s National Health Service is taking a leading role in reducing carbon emissions. Patients, visitors, and staff can look forward to healthy, low-carbon menus with much less meat, dairy, and eggs. “Evidence shows that as far as the climate is concerned, meat is heat.”

The Swedish government recently amended their dietary recommendations to encourage citizens to eat less meat. “If we seek only to achieve the conservative objective of avoiding further long-term increases in [greenhouse gas] emissions from livestock, we are still led to rather radical recommendations” such as cutting current consumption levels in half in affluent countries—“an unlikely outcome if there were no direct rewards to citizens for doing so. Fortunately, there are such rewards: important health benefits…” By helping the planet, we can help ourselves.

There are tons of articles on diet and sustainability. It’s such an important topic that I may review the new science once every year or two. When the U.S. Department of Agriculture entered these waters, the meat industry appeared to freak out, and the Dietary Guidelines debate continues.


What about just cutting down on meat in terms of health impacts? See my video, Do Flexitarians Live Longer?.

What are the health and food safety consequences of buying organic? See my video series that includes:

For information on GMOs, check out: 

I’m thrilled to announce that the How Not to Die Cookbook is out today(!), and there’s a great burger recipe in there that I’m sharing as another sneak peek into the book. Get the recipe here. The book is available at all major outlets now. 

In health,

Michael Greger, M.D.

PS: If you haven’t yet, you can subscribe to my free videos here and watch my live, year-in-review presentations:

What Animal Protein Does in Your Colon

There’s a take-off of the industry slogan, “Beef: It’s What’s For Dinner” – “Beef: It’s What’s Rotting in Your Colon.” I saw this on a shirt once with some friends and I was such the party pooper—no pun intended—explaining to everyone that meat is fully digested in the small intestine, and never makes it down into the colon. It’s no fun hanging out with biology geeks.

But I was wrong!

It’s been estimated that with a typical Western diet, up to 12 grams of protein can escape digestion, and when it reaches the colon, it can be turned into toxic substances like ammonia. This degradation of undigested protein in the colon is called putrefaction; so, a little meat can actually end up putrefying in our colon. The problem is that some of the by-products of this putrefaction process can be toxic.

It’s generally accepted that carbohydrate fermentation—the fiber and resistant starches that reach our colon—results in beneficial effects because of the generation of short-chain fatty acids like butyrate, whereas protein fermentation is considered detrimental. Protein fermentation mainly occurs in the lower end of colon and results in the production of potentially toxic metabolites. That may be why colorectal cancer and ulcerative colitis tend to happen lower down—because that’s where the protein is putrefying.

Probably the simplest strategy to reduce the potential harm of protein fermentation is to reduce dietary protein intake. But the accumulation of these toxic by-products of protein metabolism may be attenuated by the fermentation of undigested plant matter. In my video, Bowel Wars: Hydrogen Sulfide vs. Butyrate, you can see that a study out of Australia showed that if you give people foods containing resistant starch, you can block the accumulation of potentially harmful by-products of protein metabolism. Resistant starch is resistant to small intestine digestion; and so, it makes it down to our colon where it can feed our good bacteria. Resistant starch is found in cooked beans, split peas, chickpeas, lentils, raw oatmeal, and cooled cooked pasta (like macaroni salad). Apparently, the more starch that ends up in the colon, the less ammonia that is produced.

Of course, there’s protein in plants too. The difference is that animal proteins tend to have more sulfur-containing amino acids like methionine, which can be turned into hydrogen sulfide in our colon. Hydrogen sulfide is the rotten egg gas that may play a role in the development of the inflammatory bowel disease, ulcerative colitis (see Preventing Ulcerative Colitis with Diet).

The toxic effects of hydrogen sulfide appear to be a result of blocking the ability of the cells lining our colon from utilizing butyrate, which is what our good bacteria make from the fiber and resistant starch we eat. It’s like this constant battle in our colon between the bad metabolites of protein, hydrogen sulfide, and the good metabolites of carbohydrates, butyrate. Using human colon samples, researchers were able to show that the adverse effects of sulfide could be reversed by butyrate. So, we can either cut down on meat, eat more plants, or both.

There are two ways hydrogen sulfide can be produced, though. It’s mainly present in our large intestine as a result of the breakdown of sulfur-containing proteins, but the rotten egg gas can also be generated from inorganic sulfur preservatives like sulfites and sulfur dioxide.

Sulfur dioxide is used as a preservative in dried fruit, and sulfites are added to wines. We can avoid sulfur additives by reading labels or by just choosing organic, since they’re forbidden from organic fruits and beverages by law.

More than 35 years ago, studies started implicating sulfur dioxide preservatives in the exacerbation of asthma. This so-called “sulfite-sensitivity” seems to affect only about 1 in 2,000 people; so, I recommended those with asthma avoid it, but otherwise I considered the preservative harmless. I am now not so sure, and advise people to avoid it when possible.

Cabbage family vegetables naturally have some sulfur compounds, but thankfully, after following more than a hundred thousand women for over 25 years, researchers concluded cruciferous vegetables were not associated with elevated colitis risk.

Because of animal protein and processed food intake, the standard American diet may contain five or six times more sulfur than a diet centered around unprocessed plant foods. This may help explain the rarity of inflammatory bowel disease among those eating traditional whole food, plant-based diets.

How could companies just add things like sulfur dioxide to foods without adequate safety testing? See Who Determines if Food Additives are Safe? For other additives that may be a problem, see Titanium Dioxide & Inflammatory Bowel Disease and Is Carrageenan Safe?

More on this epic fermentation battle in our gut in Stool pH and Colon Cancer.

Does the sulfur-containing amino acid methionine sound familiar? You may remember it from such hits as Starving Cancer with Methionine Restriction and Methionine Restriction as a Life Extension Strategy.

These short-chain fatty acids released by our good bacteria when we eat fiber and resistant starches are what may be behind the second meal effect: Beans and the Second Meal Effect.

I mentioned ulcerative colitis. What about the other inflammatory bowel disease, Crohn’s?  See Preventing Crohn’s Disease With Diet and Dietary Treatment of Crohn’s Disease.

 In health,

Michael Greger, M.D.

PS: If you haven’t yet, you can subscribe to my free videos here and watch my live, year-in-review presentations: