How long am I going to live? Nobody really knows the answer to that question, but scientists are very interested in trying to understand the various factors (因素) involved. Firstly, it depends a lot on what you eat. The country with the longest average lifespan is Japan. On average, women live to 82.5 years and men live to 76.2 years. Scientists think that diet in Japan is a main reason that Japanese people live a long time; they usually eat lots of fish and seafood and not much junk food. As well as diet (饮食), lifestyle habits also seem to make a difference to lifespan. On average, married people live longer than single people and pet owners live longer than non-pet owners. Being mentally active and doing physical exercise are also very important lifestyle habits.

Studies of very old people, however, don’t always support the scientific theories. Many old people don’t eat healthily and don’t do much exercise. Jeanne Calment, the world’s oldest person ever, certainly goes against scientific ideas. She was born in France in 1875 and died aged 122. Did she use to have good lifestyle habits? Well, according to scientists, she had some very good habits: she did plenty of physical exercise and used to ride a bicycle until she was 100. She was good at thinking positively and she didn’t use to worry about things. Scientists are surprised, however, by one of her other habits: she didn’t used to eat very healthily. She used to eat more than two pounds of chocolate a week.

So there is another factor involved in how long we live. Scientists now think that some people were born with genes (基因) that protect them from aging and diseases better than other people. For example, Jeanne Calment probably had a gene that stopped her from getting cancer (癌症) that other people may get aged forty or fifty. Some scientists believe that we can change our genes by eating a low-calorie diet. Experiments with mice show that when they eat one third fewer calories every day, they live forty percent longer. In human terms, that’s the same as living to 170 years old. There’s no proof that it works in human, however, and perhaps it’s best to enjoy the days you’ve got rather than be hungry all your life! 

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