The science of healthy eating

There is an overwhelming amount of advice about eating on the Internet. Popular advice is often contradictory, some of it influenced by business interests, hoping to promote a certain product or a new fashionable diet. The principles described below are based on human body metabolism: as nutrients (proteins, carbs, fats, vitamins, macro and microminerals, water) provided by foodstuff are needed for optimal healthy metabolism. Much of this science has been known for 40-50 years. Understanding the five basic principles described below helps us make sensible decisions about what to eat.

Healthy Eating


Principle #1

Eat something from each of the 8 food groups every week. You can choose the specific food items from each group that you like the most. Don’t eat one specific food all the time, eat a range of foods from each group.

The food groups are as follows:

  1. Grains: wholegrain bread and baked pastries, oats, porridge, rice, etc.
  2. Pulses / legumes: beans, lentils, peas.
  3. Fruit and vegetables: apples, pears, plums, cherries, kiwis, citrus fruits, nuts, potatoes, beetroot, pumpkins, carrots, tomatoes, salad, cabbage, onion, etc.
  4. Fish: salmon, trout, sea bass, herring, etc.
  5. Poultry: turkey, chicken fillet, etc.
  6. Dairy products: cottage cheese and other products made out of it, yogurt, cheese, milk, butter.
  7. Other non-dairy sources of protein: eggs, red meat, pate, etc.
  8. Natural juices and berries: strawberries, raspberries, blueberries, cherries, orange juice etc.

The human body requires a varied, balanced diet to function well. Different kinds of foods provide us with different nutrients: components in foods that an organism uses to survive and grow. By eating the right quantity and proportion of food items that cover each of the 8 groups listed above (and at the right speed!), we can best meet the basic biochemical needs of our bodies. Be careful that you don’t miss any of the 8 food groups over a long period of time (several months).

Principle #2

In order to provide the body with all required nutrients, it is advisable to eat the right kind of foods at the right time of day – keeping in mind also the right quantity, proportion and speed of eating.


The biggest mistake is to not eat breakfast. When you wake up, your body needs carbohydrates, proteins and a limited quantity of fat.

  • Carbohydrates are vitally needed, regardless of whether you do physical work during the day. The body requires glucose (blood sugar), and the best source is complex carbohydrates, e.g. wholegrain bread, porridge, pasta, cereal, pancakes etc. If you don’t eat the required amount of carbs in the morning, this puts great pressure on your liver, which has to start producing blood sugar. Wholegrain foods are also great for digestion. Human digestion works in a wonderful way: carbs eaten in the morning are digested during the day and are not transformed into fat. This does not mean that one should eat a large quantity of carbs in the morning. If you are short of time, you can occasionally eat a piece of cake or dark chocolate (20-25 grams) during breakfast.
  • Proteins are also needed in the morning. It is recommended to eat eggs, poultry, fish, or various dairy products for breakfast: bioyogurt, cottage cheese, yogurt, cheese, etc. They contain high bioquality proteins.
  • Fat is needed, but in a limited quantity. Butter is not worse than spreadables or margarine. Fish is also a great option: for example a small portion of salmon, trout or herring. This would provide a dose of omega-3 fatty acids as well as proteins.
  • Fruit and vegetables may be eaten. They are not essential for breakfast, but they are essential for lunch and dinner.


This is the best time to enjoy food (if you have had a proper breakfast in the morning). It is important to take time for lunch and have a range of foods that you like. Lunch needs to provide the body with sufficient macro- and micronutrients.

  • Fruit and vegetables should be an important part of lunch: for example, carrot, beetroot, nuts, banana, apple, citrus fruits, salad, tomato, paprika, melon, pumpkin, cabbage, etc. Natural juices as well! Some of the foods mentioned above should be eaten raw. Eating a range of fruit and vegetables provides the body with different water-soluble vitamins, especially B group vitamins and micronutrients.
  • Protein rich fish or meat products are also highly recommended (their bioquality is very high), for example red meat fillet (which provides iron), chicken or fish. Eggs are also very good, as they are the best source of high quality proteins.
  • Fat is also necessary for the body, but again it is important not to exaggerate. Eating too much fatty food or not enough fat has a negative effect. The foods mentioned above are a good source of fat. You may also add butter or extra virgin oil to your lunch.
  • Water – without any added sugar – is the best drink to go with lunch.


Dinner is not meant to replace missed breakfast or lunch. It is best to eat it between 5-7pm if possible. The quantity of food needs to be moderate. A large quantity of carbs for dinner is easily converted to body fat.

  • Fruit and vegetables are an excellent choice for dinner. These can be eaten during breakfast and lunch too, for example, as part of salad, but they should form a more significant part of dinner.
  • Proteins are important for dinner as well, for example fish, poultry, cheese, cottage cheese, bio yogurt, yogurt.
  • It is important to limit the quantity of carbohydrates you eat for dinner. The later you have your dinner, the more important it is to avoid carbs-rich foods: pastry, pancakes, sweet cakes, pasta, potatoes, etc.

If you are unable to follow the guidelines mentioned above every single day, you should not worry about it too much. As long as you follow these rules on most days, your body will function well and can easily handle days when you don’t make the healthiest choices.

Principle #3

Try to eat the right quantity and proportion of food across the entire week – and at the right time, and at the right speed – to ensure your body receives all necessary nutrients.

Different food items can be divided in two groups: some should be eaten every day and others, a certain number of times per week.


  • Wholegrains: bread, cereals, porridge
  • Dairy products and milk: cottage cheese, cheese
  • Fruit and vegetables, natural juices
  • High quality cold-pressed oil (extra virgin oil)
  • Fresh water

A certain number of times per week

  • Poultry (chicken, turkey): at least 3 times a week
  • Fish: at least 4 times a week
  • Eggs: at least 4 times a week
  • Red meat (pork, lamb, beef): no more than 2 times a week
  • Pulses / legumes: 2 or more times a week

If you happen to eat these foods less frequently than what is suggested above, you will still be able to obtain useful nutrients — just not at the sustained level that is necessary for the body.

Principle #4

Follow the three basic truths of healthy eating, described below.

Make sure you obtain the right balance of nutrients from the foods you eat: the right quantity and proportion of carbs, fats and proteins.

  1. The food you eat needs to be varied and contain plenty of fruits and vegetables, in addition to meat and poultry. The best proportion is on average 75-85% plant-based products, and 15-25% of animal-based products. NB! Plant-based products need to be totally dominating among the foods that you eat.
  2. The quantity of food should be moderate, and equivalent to the daily expenditure of energy (physical work, exercise). There is no need to panic when sometimes the quantity of food is not ideal: it is fine to eat a bit too much one day and not enough the other day.

Principle #5

When you are being sold a “revolutionary” healthy product or diet and claims that it is based on a scientific “breakthrough” or new “natural ingredients”, it is usually an attempt to make money.

Phrases like revolutionary breakthrough and miracle diet are just part of an aggressive marketing strategy. The basic science of healthy eating applies to all humans, and has been known for decades. When someone claims to have made a new breakthrough, it is usually just a marketing trick.

Ten additional recommendations

  1. Leave at least three hours between the main meals (breakfast, lunch and dinner). Ensure that the quantity of food you eat is moderate.
  2. Eat a variety of food, and feel free to substitute food items for other ones within the same food group. However, when you give up a certain food group for a longer period of time, it will have serious negative health consequences in the long term.
  3. In terms of regular eating, boiled food is always healthier than fried or grilled.
  4. Try to avoid adding too much salt or eating foods that contain a lot of salt.
  5. Drinking too much strong tea or coffee has a negative effect on obtaining micronutrients.
  6. Food items that have gone off (with traces of fungus), e.g. nuts, pastry, jams, need to be discarded immediately and should not be eaten under any circumstances.
  7. Food that is past the ‘best before’ date should not be eaten, as micro-organisms may produce hazardous substances.
  8. Foods that have been toasted, grilled or fried too long and have become dark brown or black (e.g. over toasted bread, potatoes, pasta, grilled vegetables or meat) are not healthy.
  9. Try to avoid foods that contain artificial colours and artificial preservatives.
  10. Drink fresh water.

Source: NHS & Mihkel Zilmer, Professor of Medical Biochemistry and Doctor of Medical Science, Faculty of Medicine, University of Tartu