In conclusion, the modern world has brought much many convenient advantages but also some problems for people. However, the really most important is not the way modern machines affect us but the way we live will tell us if keep fit in modern world is easy or difficult.

Not sure what you're trying to say here. A better way to word this might be: 'Most importantly, however, the way we utilise modern technology in our lives will tell us whether keeping fit in the modern world is easy or difficult.

Good job! Hope this helps :)

Is it easier or more difficult for people to have a healthy lifestyle in the modern world?

Instead of 'machines', 'technology' would probably be a better alternative. The second half of the last sentence sounds a little awkward, how about 'However, our reliance on this technology has led to problems/issues with our health'?

Many people think that it is not as easy as it was in the past to keep fit and have a healthy lifestyle. They have the right to say that. As that, as computers, smartphones and iPads have become so popular that almost everyone has one of them and spends for hours playing with them. This is the main reason why many children don't go outside often and become myopic. The food in the modern world is also not as fresh and clean as it used to be. The appearance/use of pesticides and herbicide has made the quality of products like vegetables worse. Furthermore, the culture of fast food is one of the reasons why there are many people get obesity today. Perhaps there is a better way to phrase this: '... one of the reasons for our high obesity rates'.

However, the modern world has brought many benefits too. We now hasve hospitals in almost all pastparts of the world with the well-qualified (sophisticated)  machines and (well-educated) doctors. There are the methods of for curing some diseases like cholera and dengue as these diseases used to be very harmful and hadhave killed many people in the past. That is why people live longer now. The appear of obesity can also be cured by following the diet and exercises from doctor's advice. How about 'The current high levels of obesity can also be improved/lowered by following diet and exercise advice given by doctors'?

Is it easier or more difficult for people to have a healthy lifestyle in modern world?

Many people think that it is now it is not as easy as in the past to keep fit and have a healthy lifestyle. They have the right to say that so. As computers, smartphones and Ipads became so popular that almost everyone has one of them and spend for hours playing with them. This is the main reason why many children don't go out side often and become myopic(nearsighted ). The food in the modern world is also not as fresh and clean as it used to be. The appearance of pesticides and herbicide has made the quality of such products like vegetables  much worse. Furthermore, the culture of fast food is one of the reasons why there are many people get obesity suffering from obesity today.

However, the modern world has brought many benefits too. Now we now has hospitals in almost all past parts of the world with the well-qualified machine  and doctors highly qualified doctors and advanced equipment.There are the methods of curing some diseases like cholera, dengue as these diseases used to be very harmful and had killed many people in the past. That is why people live longer now. The appearance  of obesity can also be cured by following the diet and exercises from doctor's advice.

In conclusion, modern world has brought much convenient convenience but  and also some problems for people. However, the really mostly important is not the way modern machines affect us, but only the way we live will could  tell us if keeping fit in the modern world is easy or difficult.