The surgeon Umberto Veronesi died on 8 November at his home in Milan. On 28 November he would have turned 91. One of the greatest oncologists of the century, Veronesi was an international reference point in the fight against cancer, as well as scientific director of the European Institute of Oncology (Ieo) in Milan. In 2003 he established the Umberto Veronesi Foundation for the Progress of Sciences, which works to develop a culture of scientific research and promote it. During the six months of the universal exposition in Milan (Expo Milano 2015), we interviewed him about the importance of adopting a balanced diet in which meat – in particular – plays a secondary role. For personal wellbeing and for the good of the planet.

From an ethical standpoint, what difference is there – if any – between eating meat and eating fish?
Fish too are part of the harmonious balance of living beings, and the committed vegetarian avoids eating them. The substantial difference between the consumption of fish and the consumption of meat is to be found in health, because while meat contains harmful elements, fish contains elements that are extremely valuable to the human body.

Some studies suggest that reducing meat consumption is one of the ways to cut CO2 emissions into the atmosphere and halt global warming. Should the United Nations also set a limit on meat consumption?
I think it would be a great thing for the United Nations to set a limit on meat consumption, but not so much for the climate as for the unsustainability of meat consumption. I am glad that young people are taking ownership of the global warming issue, but the catastrophe that awaits us if we do not reduce the number of meat-eaters on planet Earth is a different one: insufficient food and water for future generations, and thus self-destruction. At present the Earth's inhabitants number seven billion, to which we must add four billion farmed animals. Even today, water and food are insufficient for approximately one billion people who, primarily in Africa, are dying of malnutrition and hunger. This is because farmed animals, destined to feed a small portion of the population – namely the West (Europe and North America) – consume a considerable share of agricultural production and available water.

This critical scenario is set to worsen with the economic growth of emerging countries (China, India and South America), which, as they acquire prosperity, are also adopting "Western" lifestyles, including dietary habits. Until now, Westerners have been able to afford a meat-based diet at an extremely high cost to the rest of humanity and the environment.

What would happen if the Chinese, Brazilians and Indians began eating meat like Westerners? In a short time we would have more farmed animals than people on Earth. By 2050 – so very soon – the inhabitants of our planet will number nine billion, and 95 per cent of the demographic increase will occur in emerging countries that hold this symbolic conception of food. Meat consumption would rise from the current 220 million to 460 million tonnes. With tragic consequences such as the collapse of global water and agri-food resources.

The efficiency of meat production is extremely low. To obtain one kilogram of meat requires 15,000 litres of water, whereas to obtain one kilogram of grain requires 1,000. Animals therefore convert into food only 10 per cent of what they receive. A measure from the United Nations for the survival of humanity would be most welcome.

One of the absurdities, one of the paradoxes when we talk about food today is that there are more obese people in the world than malnourished ones. What must be done to stay healthy?
It is scientifically proven that vegetarians live longer and in better health, so there is no doubt that a vegetarian diet is beneficial. A diet rich in red meat and saturated fats of animal origin is a cause of cancer, obesity (which is a disease in itself) and many cardiovascular diseases. It is also proven that plants contain molecules that protect us from illness. Against specific forms of cancer we know of lycopene from tomatoes, indole-3-carbinol from cruciferous vegetables, catechin from tea, polyphenols from citrus fruits and many other substances. Proteins exist in abundance in nature. In legumes, for example.

In your book Verso la scelta vegetariana, il tumore si previene anche a tavola you state that you have always been able to choose your food. Where does the ethical threshold lie for people who have no choice?
Without the possibility of choice there is no ethics. If ethics is a system of criteria for defining what is right or wrong in human actions, it is clear that where a person does not have the possibility of acting in two different ways – one right and one wrong – there can be no ethical threshold.