NUTRITION science has identified almost 50 essential nutrients. Nutrients are chemical substances such as vitamins, amino acids, minerals and essential fatty acids, that the human body needs but cannot synthesise itself, and so must be included in the diet.
Scientists have also discovered more than 1,200 phytochemicals, present in fruits, vegetables, beans and grains and animal products. Although not essential, many of these do appear to have a positive impact on health and wellness.
Of course, all these healthful nutrients and phytochemicals cannot be found together in one food or even one group of foods, and relying on a restricted range of foods carries its own risk, as some nutrients and phytochemcials can be harmful if consumed too excessively.
That's why most dietary guidelines include advice “to eat a varied diet” and why there is increasing interest amongst researchers and health professionals in dietary diversity.
What makes a varied diet?
A varied diet will include a broad selection of foods across the whole range, or most of the traditional food groups, such as vegetables, fruits, cereals, meat, fish and dairy products. A varied diet will also include a good mix of foods within each of these groups – eating two bananas and three carrots each and every day may meet the five portions of fruit and vegetables per day target, but will not provide the body with even half the potentially healthful phytochemicals that scientists have identified in fruit and vegetables.
Research suggests that an intake of 30 or more different foods per week or more than 12 foods in one day usually characterises a diet adequate in essential nutrients. Japan's dietary guideline actually includes advice to aim for 30 foodstuffs a day.
To assess daily food variety, start by grouping similar food together. For examples of food grouping see table 1. Thus, rice congee at breakfast, bread made from a mix of wheat and rye flours at lunchtime, and buckwheat noodles (sobu) for evening meal represent four food types during the day. However, grapefruit juice for breakfast, sweet orange as mid-morning snack and spicy Thai pomelo salad would be counted as one food type for the day.
Variety, balance, moderation are complementary
Selecting a variety of foods daily fits well with another fundamental piece of nutritional advice, which is “aim for balance and moderation”. A balanced diet is a diet that includes enough, but not too much, of each type of nutrient and food group.
For example protein foods such as red meats, fish, and poultry are rich in iron but poor sources of calcium; milk and milk products are also high quality protein foods, rich in calcium but poor sources of iron. So, including both these food groups in a regular diet is one approach to achieving a balance of both calcium and iron.
Moderation also fits well with a balanced and varied diet. For example, a moderate fat intake is fundamental to a healthy diet because some fat (about 15% of total energy content of the diet) is essential for health, but too much is likely to lead to overweight and heart disease.
On this basis, occasional higher fat foods, will contribute to variety without compromising health quality of regular diet, especially if types of fats and oils consumed are varied.
1. Wahlqvist ML et al. Food variety is associated with less macrovascular disease in those with type II diabetes and their healthy controls J Am Coll Nutr. 1989 Dec;8(6):515-23.
2. Kant et al. Dietary diversity and subsequent mortality in the First National Health and Nutrition Examination Survey Epidemiologic Follow-up Study. Am J Clin Nutr 1993; 57:434-440.
3. Savige et al Food variety as nutritional therapy Current Therapeutics 1997; March: 57-67
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