Diet and health are two closely linked subjects. Different kinds of food contain different kinds of nutrients. There is not a single kind of food which can provide all the nutrients our body needs. Having a balanced and diversified diet can enable us to get a full complement of nutrients which are vital to our staying healthy. On the contrary, inappropriate diet and nutritional imbalance can lead to many diseases.
Food is the source of energy and nutrients. Eating a broad variety of food can help us absorb different kinds of nutrients so as to support our body movement, maintain normal functions and repair cells and tissues. Nutrients can be categorized as follows:
-          Marco-nutrients provide energy, which include carbohydrate, protein and fat, is required in large amounts in the diet.
-          Mirco-nutrients include vitamins and minerals.
What is a balanced diet?
Categorizing food by their nutritious attributes, there are five major food groups: (i) Grains; (ii) Vegetables and fruits; (iii) Meat, fish, eggs and beans; (iv) Milk; and (v) Salt, oil and sugar. Different age groups require different intakes from these five food groups. The Healthy Eating Food Pyramid for the Elderly provides guidelines for elderly persons to maintain a balanced diet by following the food proportion recommended.  
According to the Healthy Eating Food Pyramid for the Elderly, grain, which is at the bottom of the Pyramid, should be taken as the major dietary source and should make up the largest portion of our diet each day. Then eat an appropriate level of vegetables, fruits, meat, fish, eggs, beans and dairy products. Reduce salt, oil and sugar which is on the top of the Pyramid. In addition, we should drink 6 to 8 glasses of water each day as water can help transfer the values of foods to different parts of the body and also help dispose wastes in the blood. 
Nutrients:    carbohydrates in particular starch, vitamins, plant-based protein and dietary fibre
Functions:  sources of energy, to meet the day-to-day needs of the body
Sources:      congee, noodles, rice, breakfast grains, bread, biscuits
Recommended:  brown rice, oatmeal, vermicelli, wholegrain bread, wheat cake
Avoid:         instant noodles, fried noodles, fried rice, cakes, waffle, pastry
Vegetables and fruits
Nutrients:   rich in vitamins, minerals, antioxidants and dietary fibre
Functions:  to protect cells, prevent constipation and chronic diseases
Sources:     leafy vegetables, fruits, tubers, beans, edible fungi (mushrooms), dried fruits
Recommended:  fresh seasonal vegetables and fruits and naturally dried fruits
Avoid:       preserved vegetables and fruits, sugared dried fruits, canned fruits, fruit juice with sugar added
Meat, fish, eggs, legumes
Nutrients:    rich in protein, vitamins, calcium, iron and dietary fibre
Functions:   to build and repair cells, to support the metabolism of the body
Sources:      meat, poultry, fish, seafoods, eggs, beans, nuts, seeds
Recommended:  lean meat, fish, beans, bean products, nuts
Avoid:          fatty meat, chicken skin, chicken claws, internal organs, canned meat, preserved meat, barbecued meat, deep-dried legume
Nutrients:      Calcium, protein and vitamins
Functions:  keep teeth and bones healthy
Sources:      milk, cheese, yogurt, calcium-added bean milk
Recommended: low-fat or skimmed milk, low-fat cheese, low-fat yogurt, calcium-added bean milk
Avoid:         whole milk, full-cream cheese, condensed milk, chocolate milk, ice cream and other kinds of dairy products with high sugars
Salt, oil, sugar
Source: animal fat, plant-based fat, table salt, soy sauce, seasonings, sugar, candies, soft drinks
Recommended: low-fat, low-salinity, low-sugar foods, method of cooking with little or no oil, natural seasonings
Avoid:  deep-fried foods, preservd foods, candies, soft drinks, desserts, sugar-added drinks
Bon appetit with the “Rainbow Diet”
A lot of elderly persons begin losing their appetite after the sensitivity of their taste buds begin to fail and they are required to follow the “less oil, less salt and less sugar” rule in their diet. However, colours can make a change. By choosing foods of different colours as ingredients, we not only enhance their appetite by the attractive presentation of the dishes, but also provide them with the natural nutrients of the vegetables and fruits the food nutrients of such are not easily replaceable. Different colours of vegetables and fruits have different food values. The growing popularity of the recent “Eat the Rainbow” trend is proof to the awareness of the importance of a balanced diet through eating on a daily basis foods of all seven colours – red, orange, yellow, green, purple, black and white.
Functions:  “Red” foods contain Vitamin C and can help enhance immunity, resist inflammation, and prevent infection in the respiratory system. “Red” vegetables contain lycopene which has antioxidant effect and is good for prostate health.
Sources:       tomato, red pepper, beetroot, strawberry, red beans, etc.
Functions:   “Orange” foods contain carotene which helps prevent night blindness,  loss in vision and dry eyes. It keeps the cardiovascular and immunity systems healthy.
Sources:      carrot, pumpkin, yam (sweet potato?), orange, papaya, etc.
Functions:   “Yellow” foods contain Vitamin C and carotene which strengthen the immunity system, and keep the nose, lungs, throat and skin healthy.
Sources:       yellow pepper, corn, lemon, pineapple, chestnut, etc.
Functions: “Green” foods are rich in folic acid, and help relieve emotional unsteadiness and enhance immunity. “Green” foods also help protect the liver.
Sources:      green leafy vegetables, cucumber, bitter gourd, peas, etc.
Functions:  “Purple” foods are rich in anthocyanin which helps keep the eyes healthy and relieve eye fatigue. They also have antioxidant effect and keep the cardiovascular system healthy.
Sources:     purple potato, eggplant, purple broccoli, purple rice, taro, etc.
Functions:   “Black” foods are rich in iron. They contain antioxidant which delay muscle ageing and help keep the skin healthy.
Sources:      Fungus (including black ear), black beans, black sesame seeds, mushrooms, etc.
Functions:   “White” foods contain allicin, flavonoids and selenium. They help enhance metabolism of the body, remove fatigue, kill germs, and are good antiviral and antioxidant agents.
Sources:      onion, garlic, fungus, cauliflower, barley, etc.
In the process of understanding a balanced and diversified diet, we also understand food nutrients and how different nutrients help build our body.  With this knowledge, we can make sure that the food we cook and eat is both delicious and nutritious.
Related websites:
5-Colour Diet – Red, Orange/ Yellow (Hong Kong Est Cluster Nutrition Information Web)
5-Colour Diet – Green (Hong Kong Est Cluster Nutrition Information Web)
5-Colour Diet – Blue/Purple (Hong Kong Est Cluster Nutrition Information Web)
5-Colour Diet – White (Hong Kong Est Cluster Nutrition Information Web)
Food Nutrients (Centre for Food Safety)