5 common rumours about healthy eating debunked

The Internet is awash with healthy eating advice, but you can't believe everything you read.

A recent survey on the top five false healthy-eating rumours online was featured at the 3rd Chinese Nutrition Communication Conference, which was organised by leading Chinese health publication Life Times, Amway China, and the Chinese Health Education Center, an affiliation under the National Health and Family Planning Commission. The organisers co-operated with several influential websites and mobile news apps to find the most frequent posts with bad nutrition information seen by netizens. From May 7 to 12, the online survey received 39,229 responses, and sorted out the top five most widespread false rumours on healthy eating.

Here are the five rumours, refuted by Ma Guansheng, a top Chinese nutritionist with the School of Public Health at Peking University.

1. Eating eggs increases the risk of heart disease, because egg yolk contains large quantities of cholesterol, which will hurt the heart.

Ma: Cholesterol in the human body has two origins. The body usually produces 1,000 milligrams a day and another 300 to 500 milligrams are often from food. An egg contains only about 200 milligrams of cholesterol, and it is difficult to change the blood-cholesterol level by eating eggs.

Besides, there are various vitamins and trace elements in egg yolk. Not eating eggs reduces the chance to get such nutrients. Studies have shown it is safe for most people to eat an egg a day, although for people with cardiovascular problems, it may vary.

2. Eat sugar-free food and you won't gain weight.

So-called sugar-free food only means the food doesn't contain sucrose. A lot of drinks have sugar, and studies have indicated drinks containing sugar will increase chronic disease risk. Biscuits, bread and desserts also contain sugar to some extent. Some institutes suggest that for the majority of people, sugar in food should be less than 10 per cent, with 5 per cent being ideal.

Also: In lots of sugar-free food, the percentage of fat is often high, and fat provides twice the calories as sugar does in same amount of weight.

3. Lemonade helps prevent cancer.

It is true that lemons have diversified nutrients, including vitamins and minerals, but if we think about the quantity of Vitamin C, the same amount of green pepper has three times of Vitamin C content of lemon.

The World Cancer Research Fund and the United States National Cancer Institute have proved with evidence that eating fruits and vegetables can reduce the risk of cancer, but what they mean is fruits and vegetables as a whole, not just one kind of fruit, and you certainly cannot prevent cancer through drinking fruit-flavored water.

Lemonade can increase intake of Vitamin C, but diet influences the incidence of cancer through a combination of factors.

4. Drinking fruit and vegetable juice is helpful in losing weight.

The rumour says having six glasses of fruit and vegetable juice a day for a month without eating anything else will help you lose at least 2.5 kilograms of weight.

It is true that only drinking fruit and vegetable juice will reduce weight in a short time, but the weight loss is mainly from loss of water, and users will regain the weight quickly once they stop the fast.

The method is also very risky, because fruit and vegetable juices have few other nutrients except vitamins and minerals, and the body will be under nourished if the fast goes on.

To lose weight, diet, exercise and a healthy lifestyle are all indispensable.

5. Leftover vegetables are not edible, because they have a lot of poisonous nitrites.

Professor Fan Zhihong of the China Agricultural University once did an experiment on this question. She put cooked vegetables in a refrigerator, and 24 hours later, quantity of nitrites in the vegetables almost doubled, from 300 milligrams per kilograms to 700 milligrams. However, despite the increase, she pointed out that a person needs to eat almost 30 kilograms of vegetables in order to get poisoned by the nitrites in the food.

Vegetables have nitrites, but differ in amount. Cucumbers, beans and tomatoes usually have a low level of nitrites. We suggest people not cook too many vegetables in order to avoid leftovers, and to put the some of the cooked vegetables in the refrigerator as soon as they are cooked.