In addition to cutting emissions from food production, say the authors, rewilding the freed-up land would remove around 8.1 billion tonnes of carbon dioxide from the atmosphere every year for the next 100 years.
Of course, the idea that billions of people worldwide would voluntarily give up their steaks, sausages, and cheeseburgers simply to curb climate change may seem far-fetched.
But perhaps they would think twice if they knew how much it would benefit their own health.
Recent research suggests that people who eat little or no meat tend to have a lower risk of cancer, in particular colorectal cancer and prostate cancer in men.
Diets that combine a reduction in meat and dairy consumption with increased intake of fruits, vegetables, whole grains, and healthy fats, bring further health benefits.
People who eat a typical Mediterranean diet, for example, have a lower overall mortality rate and a lower risk not only of cancer but also cardiovascular and metabolic diseases.
A series of clinical trials now suggests that eating a “green” Mediterranean diet, or green Med diet, may provide additional benefits on top of those provided by the regular Mediterranean diet.
The diet, which adds extra plant foods rich in polyphenols and aims to avoid meat completely, is also better for the planet.
“Eliminating meat intake — beef, pork, lamb — is by far the most important single way to reduce the carbon footprint from diet,” said Dr. Meir Stampfer, Ph.D., professor of epidemiology and nutrition at the Harvard T.H. Chan School of Public Health in Boston, and one of the authors of the green Med studies.
“The contribution of meat to greenhouse gas emissions is enormous compared with other foods,” he told Medical News Today.
Biodiversity and human health
Dr. Stampfer pointed out that the total area needed for meat production includes a lot of land for growing crops to feed livestock.
So by reducing the amount of land around the world that is devoted to producing meat, the green Med diet could play a major role in the preservation of biodiversity.
In its 2020 report “Biodiversity for Nutrition and Health”, the World Health Organization (WHO) describes a virtuous circle that links varied, plant-based diets, human health, biodiversity, and sustainability.
“The significance of pressures generated by human activity on both climate change and biodiversity loss, and their impacts on nutrition and health outcomes, cannot be overstated,” the authors conclude.
What is the classic Mediterranean diet?
A traditional Mediterranean diet contains the following elements:
The diet provides an abundance of polyphenols, monounsaturated and polyunsaturated fatty acids, and plant fiber.
Importantly, the classic Med diet also avoids refined grains, highly processed foods, and products with added sugars.
Scientists believe that, in combination, these features help lower levels of bad cholesterol, reduce oxidative stress and inflammation, and improve insulin sensitivity.
Green Mediterranean or ‘green Med’ diet
Scientists in Israel, Germany, and the United States reasoned that replacing all the remaining meat in the diet with plant-based proteins could supercharge these health effects.
Over the past few years, they have conducted three clinical trials of their green Med diet on a cohort of 294 people with abdominal obesity. Participants’ average age at the start of the trials was 51 years.
Over the course of their studies, they were all given free gym membership and advice about physical activity.
The researchers randomly assigned them to three diets:
People in Thailand and other Southeast Asian countries eat Mankai as a “vegetable meatball.” Previous research by the same scientists showed that Mankai provides all the essential amino acids plus vitamin B12, making it an ideal meat substitute.
In the first study, the researchers examined possible extra heart health benefits of eating a green Med diet.
They report that after 6 months, both Med diets led to greater weight loss and metabolic benefits than standard dietary advice.
However, the green Med diet led to a greater reduction in waist circumference and several other measures of cardiovascular risk.
For example, participants who ate this diet had improved insulin sensitivity, lower blood pressure, lower levels of bad cholesterol, and less inflammation compared with those on a standard Med diet.
Fat storage in the liver
For their next study, the researchers compared the amount of fat in the liver of subjects after 18 months on the three different diets.
They discovered that people who ate the green Med diet lost more fat in their liver than those on the regular med diet.
This may reduce their risk of nonalcoholic fatty liver disease, which affects around 25% of people worldwide and can lead to potentially fatal cirrhosis and liver failure.
Finally, the researchers used magnetic resonance imaging (MRI) to examine the effect of the three diets on loss of brain volume over 18 months.
Brain atrophy in a region called the hippocampus vital for memory formation is an early marker of cognitive decline in aging and neurodegenerative diseases such as Alzheimer’s disease.
The researchers report that in subjects 50 years or older, both med diets were associated with significantly reduced shrinkage of the hippocampus.
But the green Med diet appeared to provide the greatest protection against brain atrophy.
Polyphenols can cross the blood-brain barrier, where they help to reduce inflammation and promote the growth of new nerve cells in the hippocampus.
So it makes sense that the green Med diet — which the researchers say doubles the polyphenol content of the classic Med diet — was associated with a greater reduction in brain atrophy.
It is important to note that 88% of participants were middle-aged males who all had obesity. The results may therefore not apply to females, younger age groups, or people without obesity.
In addition, the number of people in the studies was relatively small.
What makes the diet so effective?
The researchers believe that a combination of reduced red and processed meat consumption and increased polyphenol intake is responsible for the health benefits of the green Med diet.
For example, levels of Mankai-derived polyphenols in participants’ urine were significantly associated with reduced shrinkage of the hippocampus.
But eating less red and processed meat was also independently and significantly associated with reduced shrinkage of this region.
Mankai is relatively expensive and not widely available in stores.
MNT asked senior author Iris Shai, professor of nutrition and epidemiology at Ben-Gurion University of the Negev in Beer-Sheva, Israel, whether other high protein plants may be equally beneficial as meat substitutes.
“Mankai was just a test case,” she replied. She said other plant sources of protein would work just as well.
“You don’t need to get the polyphenols within the same food source as protein,” pointed out Prof. Stampfer.
“For example, numerous studies show the benefits of berries, which have little protein but lots of phenols,” he said.
However, he said further studies would be needed to evaluate the benefits of different food sources because polyphenols are a large, varied group of compounds.
“As for protein, you can easily get all the protein you need without eating any meat, or without eating any animal products,” he added.
Alternatives to Mankai
Nutritionists told MNT that several alternatives to Mankai are widely available.
“For the protein and mineral content as well as a boost of omega-3 fatty acids, ground flax, hemp, and chia are good alternatives to include in the diet,” said Katie Cavuto, MS, RD, a nutritionist and executive chef of Saladworks.
“Quinoa is also a complete protein that is rich in polyphenols,” she added.
Unusually for a plant, Mankai also provides vitamin B12, which is often lacking in vegan diets. But Cavuto said edible algae, such as spirulina, and seaweeds, such as nori, are also good sources of this vitamin.
Dr Donald Hensrud, MD, associate professor of nutrition and preventive medicine at the Mayo Clinic College of Medicine in Rochester, MN, recommended vegan cereal or plant-based milks fortified with vitamin B12.
“It is sometimes easiest to take a supplement of vitamin B12,” he told MNT.
“Vitamin B12 is nontoxic, so taking too much is not an issue,” he added.
There are also alternatives to walnuts as sources of polyphenols, as detailed in the Mayo Clinic Diet plan.
“If somebody isn’t a fan of walnuts, there are plenty of other options to include polyphenols,” said Prof. Hensrud.
Each type of nut has a different nutrient profile, he pointed out. For example, almonds are relatively high in calcium, and Brazil nuts are high in magnesium.
“Therefore, if you like mixed nuts, they would provide the widest variety of nutrients,” he said.
Plant foods to avoid?
Plant-based foods have a much smaller impact on the environment, in particular in terms of carbon emissions.
However, not all plant sources are equal. For example, huge quantities of water go into growing almonds and cashews, often in areas where water is in short supply.
It is also worth taking into account that almond farmers often use a lot of fertilizers and pesticides.
To minimize environmental harm, therefore, Brazil nuts, hazelnuts, and peanuts may be better choices.
Avocados, which are popular among vegans and vegetarians, may be among the worst offenders in terms of sustainability.
Most avocados on supermarket shelves originate in Central and South America, so they have a large carbon footprint for customers in Europe, for example.
They are usually grown as a monoculture, which means little or no biodiversity, and require a lot of water.
It takes 320 liters of water to grow a single avocado.