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:

Does Rye Bread Protect Against Cancer?

Previously, I’ve explored the beneficial effects of flaxseeds on prostate cancer (Flaxseeds vs. Prostate Cancer), as well as breast cancer prevention and survival (Flaxseeds & Breast Cancer Prevention and Breast Cancer Survival & Lignan Intake). The cancer-fighting effect of flaxseeds is thought to be because of the lignans, which are cancer-fighting plant compounds found in red wine, whole grains, greens (cruciferous vegetables), and especially sesame seeds and flaxseeds, the most concentrated source on Earth. But this is based on per unit weight. People eat a lot more grains than seeds. Of the grains people eat, the highest concentration of lignans is found in rye. So, can rye intake decrease the risk of cancer? Theoretically yes, but unlike flaxseeds, it’s never been directly put to the test… until now.

In my video Does Rye Bread Protect Against Cancer?, I discuss the evidence that does exist. If you measure the levels of lignans in the bloodstream of women living in a region where they eat lots of rye, the odds of breast cancer in women with the highest levels do seem to be just half that of women with the lowest levels. But lignans are also found in tea and berries, so we couldn’t be sure where the protection is coming from. To get around this, researchers decided to measure alkylresorcinol metabolites, a class of phytonutrients relatively unique to whole grains.

Researchers collected urine from women with breast cancer and women without, and the women with breast cancer had significantly lower levels compared to those without. This suggests that women at risk for breast cancer consume significantly lower amounts of whole grains like rye. But if we follow older women in their 50s through 60s, the intake of whole grain products was not associated with risk of breast cancer. A similar result was found in older men for prostate cancer. Is it just too late at that point?

We know from data on dairy that diet in our early life may be important in the development of prostate cancer, particularly around puberty when the prostate grows and matures. If you look at what men were drinking in adolescence, daily milk consumption appeared to triple their risk of advanced prostate cancer later in life. (Learn more about milk and prostate cancer in my video Prostate Cancer and Organic Milk vs. Almond Milk.) So, researchers looked at daily rye bread consumption during adolescence.

Those who consumed rye bread daily as kids did appear to only have half the odds of advanced prostate cancer. This is consistent with immigrant studies suggesting that the first two decades of life may be most important for setting the pattern for cancer development in later life. These findings are certainly important for how we should feed our kids, but if we’re already middle-aged, is it too late to change course? To answer this question, researchers in Sweden put it to the test.

Researchers took men with prostate cancer and split them into two groups. One group got lots of rye bread, while the other got lots of high-fiber, but low-lignan, wheat bread. There’s been some indirect evidence that rye may be active against prostate cancer—like lower cancer rates in regions with high rye consumption—but it had never been directly investigated… until this study. Biopsies were taken from the subjects’ tumors before and after three weeks of bread eating, and the number of cancer cells that were dying off were counted. Though there was no change in the cancer cell clearance of the control bread group, there was a 180% increase in the number of cancer cells being killed off in the rye group. A follow-up study lasting 6 weeks found a 14% decrease in PSA levels, a cancer marker suggesting a shrinkage of the tumor.

The researchers note they used very high rye bread intakes, and it remains to be tested if more normal intake levels would have effects that are of clinical importance. As a sadly typical American, my lack of intimate familiarity of the metric system did not flag the “485 grams” of rye bread a day as far out of the ordinary, but that translates to 15 slices! Rather than eating a loaf a day, the same amount of lignans can be found in a single teaspoon of ground flaxseeds.


I’ve created several videos on flaxseeds for both breast cancer prevention and treatment, including Flaxseeds & Breast Cancer Prevention, Breast Cancer Survival and Lignan Intake, Flaxseeds & Breast Cancer Survival Epidemiological Evidence, and Flaxseeds & Breast Cancer Survival: Clinical Evidence.

What’s more, flaxseeds may help with cyclical breast pain (Flaxseeds for Breast Pain), prostate cancer (Flaxseed vs. Prostate Cancer), diabetes (Flaxseeds vs. Diabetes), and hypertension (Flaxseeds for Hypertension).

And if you’re wondering Which Are Better: Chia Seeds or Flaxseeds?, get the answer in the video!

The wonders of whole grains are also discussed in Whole Grains May Work as Well as Drugs, Can Oatmeal Reverse Heart Disease?, and Can Oatmeal Help Fatty Liver 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: