Plant-based diets: eating for our health and the planet

The term “plant-based diets” has become popular in recent years. These types of diets, which are traditional for some parts of the world (eg in Asia and the Mediterranean region), are rich in vegetables and fruits, plant oils (mainly olive oil), and fish, but consumption of meat and dairy products is traditionally low. Numerous studies have shown that these types of diets are beneficial for human health.

On the other hand, diets of affluent western societies have changed significantly during the past 60 years towards a diet that is rich in meat, refined carbohydrates, sugar, and saturated fats. This type of diet is not only associated with a higher risk of chronic diseases such as cardiovascular diseases, diabetes and several types of cancer, but it also has a strong impact on our planet’s climate.

Production of animal products such as meat and dairy needs more energy than the production of plant products, hence, by reducing our consumption of animal products, we can save significant amounts of energy. For example, in Switzerland, about 30% of environmental impacts are due to food production, transportation and consumption (PDF).

An international group of nutrition scientists has proposed a diet that meets most nutrition requirements, while simultaneously taking sustainability and planetary health into account. This diet is often called the “EAT-Lancet Reference Diet” or “Planetary Health Diet”. It’s mainly plant-based, meaning that carbohydrates come from whole grains, proteins are mainly from legumes (such as beans, lentils, peas, but also soy food and peanuts), and fats are mostly unsaturated plant oils. Animal products are not forbidden, but their consumption is recommended to be limited.

Our research group at the University of Zurich, in collaboration with colleagues from other universities, was interested as to whether this type of diet, which is thought to reduce the damaging impact of food on our environment, also has beneficial effects on our health, particularly regarding the risk of cancer.

To try to answer our question, we needed a dataset in which the food consumption of the participants was assessed, but in which participants were also followed up for a number of years so that we could know how many of them were diagnosed with cancer. The UK Biobank is a large cohort in the UK that includes more than half a million people. Using data from this large cohort, we have examined how closely people were following the recommendations of the EAT-Lancet Reference Diet in 2005–07, and how many of them had been diagnosed with cancer until 2019.

Sustainability lowers cancer risk, too

When we compared those participants whose diet was closest to the EAT-Lancet Reference Diet with those who ate a less sustainable diet, we saw that an environmentally friendly diet was indeed associated with a lower risk of cancer. Better adherence was linked to a 10% lower cancer risk. However, we did not see a particularly strong protective effect for a specific type of cancer.

The results of our study are consistent with those of other groups trying to answer the same research question using different data sets. This strengthens our conclusions that a planet-healthy, plant-based diet can promote health.

In fact, plants are excellent sources of most of the essential vitamins and minerals in our diet. When a plant-based diet is balanced, products of animal origin are only needed in moderation to provide us with the few essential vitamins that cannot be found in plant sources (eg vitamin B12).

Greater focus should be given to exploring different plant-based foods, as well as on how to prepare plant foods – in particular legumes – so that more people are able to cook and enjoy these types of foods. Consumers, researchers and cooks need to team up to develop climate-friendly recipes. In Switzerland, we have published the first cookbook that only contains climate-friendly recipes. And recently World Cancer Research Fund developed Budget-friendly recipes: Good for you, good for the planet.

• Dr Nena Karavasiloglou, a researcher, was formerly a Postdoc at the University of Zurich. Dr Sabine Rohrmann is at the University of Zurich. Read more about their grant funded by World Cancer Research Fund, including papers published from this grant.