Results of study on nutrients of fruits and vegetables
The Centre for Food Safety (CFS) today (June 7) released results of its recent study on nutrients of fruits and vegetables commonly found in Hong Kong.
Announcing the results at a press conference, the Centre's Consultant (Community Medicine) (Risk Assessment and Communication), Dr Ho Yuk-yin, said information on nutrient composition of foods was essential for people to choose healthy foods.
The study covered 82 fruits and vegetables, with 49 being sampled from local retail markets. Chemical analyses were conducted to determine the contents of energy and 10 nutrients - carbohydrate, protein, total fat, saturated fat, cholesterol, dietary fibre, sugar, sodium, calcium and vitamin C.
As for the remaining 33 fruits and vegetables, their nutrient contents obtained from overseas database were used and compared.
"Fruits and vegetables are major sources of dietary fibre and vitamin C in our diet, and free of cholesterol. Their energy values and other nutrients such as sodium and fat contents were low in general," Dr Ho said.
"For the fruits tested, their average dietary fibre content in 100 grammes was 2.3 grammes. Avocado, guava, durian, kiwi fruit had high fibre content, ranging from 3 to 6.7 grammes per 100 grammes. However, removing the skin of fruits such as pear and apple would result in the loss of 24 to 46% of their dietary fibre.
"Vitamin C in fruits was high in general, with a mean of 39 milligrammes in 100 grammes. Fruit like guava, black currant and kiwi fruit were comparatively rich in vitamin C.
"The energy content in fruits was low, with an average of 60 calories in 100 grammes. However, durian and avocado were the exceptions. A portion of 122 grammes of durian contained 6 grammes of fat and 179 calories, whereas 15 grammes of fat and 161 calories were found in half of an avocado," he said.
The mean dietary fibre content of 100 grammes of vegetables was 1.9 grammes. Lotus root, garland chrysanthemum, Chinese chives (flower stalks), carrot and broccoli were found to have a higher dietary fibre content, ranging from 2.7 to 4.9 grammes per 100 grammes.
Similar to fruit, vegetables are also a major source of vitamin C in our diet. On average, 100 grammes of vegetables contained 26 milligrammes of vitamin C. Bitter cucumber, broccoli, mustard leaf, Chinese kale and pea shoot had relatively higher vitamin C content.
"Vitamin C would be lost in the process of cooking. The vitamin C content in boiled vegetable is about one third less than that in stir-fried vegetables. However, the public can rest assured that they usually have enough vitamin C through a balanced diet," Dr Ho said.
The energy values in vegetables were low in general, averaging 26 calories per 100 grammes. However, the level of energy content also hinged on the cooking methods. Boiling one catty of vegetables with a teaspoon of oil brought about an increase of 2 grammes of fat content and 18 calories. Stir-frying vegetables with three tablespoons of oil added 45 grammes of fat content and 405 calories.
Salad vegetables such as lettuce and broccoli are commonly consumed with dressings such as Thousand Island dressing and Caesar dressing. The study found that the addition of one tablespoon of these dressings could increase the fat content by about 5 to 8 grammes and 44 to 76 calories respectively.
It also found that nearly all the dietary fibre in fruits such as orange, watermelon, mango and pear was lost in their juices. According to literature, the amount of dietary fibre in juices is also much less than that in whole fruits.
While advising people to eat fresh fruit as far as possible, Dr Ho said fruit like avocado and durian which had high energy contents should be consumed moderately.
"To achieve a balanced diet, people should consume two servings of fruit and three servings of vegetables daily," Dr Ho said.
"It is advisable to choose a wide variety of fruits and vegetables since they offer different nutrients. For those who want to have more dietary fibre, they may consider eating fruit together with their edible peel after washing them thoroughly."
Dr Ho also urged the food trade to offer more vegetable dishes. For boiled vegetables and salads, sauces or dressings should be served separately to allow customers to add their desired amount.
Meanwhile, the CFS has recently enhanced its Nutrient Information Inquiry System, providing nutrient information on 18 parameters of more than 4,300 food items. A 'Food Nutrient Calculator' function has been added to the system for public reference to facilitate them in making healthy food choices. The average nutrient quantity of food intake can be obtained by selecting the food items and entering the consumption amount into the calculator. The public may visit the CFS's website at www.cfs.gov.hk for details.
Ends/Thursday, June 7, 2007