It would seem from the billions of dollars spent annually on vitamin supplements that Australians recognise the importance of nutrients. The essential nutrients include eight amino acids, two types of fats, minerals and the vitamins (organic molecules that the body cannot synthesise). These are known as essential nutrients because the absence of any one of these will cause deficiency symptoms and eventually death. Plant foods provide all of the essential nutrients. But plants also contain other “phytonutrients” (phytochemicals). These include dietary fibre, anti-oxidants, cancer fighting chemicals and other biologically active substances perhaps numbering 100,000 in total. These non-essential nutrients are “essential” for good health and longevity. Meats, eggs and dairy foods lack these phytonutrients, or at best contain only trace amounts.

Nutrient density is an important consideration in making healthy food choices. A good question to ask yourself when choosing foods is “does it contain dietary fibre and nutrients”? If the answer is no then perhaps that item should not be a significant part of your diet. Other factors such as energy density and fat content are also relevant. We consider that there is more evidence to support a high carbohydrate diet based on starchy foods such as grains, legumes and potatoes than a diet based on oily plants such as nuts, seeds and avocados.

What is nutrient density?  Put simply it’s how concentrated the vitamins, minerals and phytonutrients are in your diet. Nutrient density can be expressed as nutrient units per gram of food, but then high energy density foods, such as nuts and oils, would appear high in nutrients but you could not eat as much off them as say broccoli or spinach because you would get too many calories. So we express nutrient density in nutrient units per calorie of that food. (This too can sometimes be misleading because some vegetables have so few calories that you simply could not fit enough calories worth on your plate to obtain the nutrients in, say 500 calories). It gets increasingly complicated as we delve deeper. A particular plant food might be high in some nutrients and lower in others which is why we recommend eating a wide variety of plant foods rather trying to find one “super food” that has everything.

The nutrient density of your total diet is not just influenced by your high nutrient choices but also by your low nutrient choices. High calorie, low nutrient foods reduce your total nutrient intake. This is because they use up your total day’s calorie needs, and you therefore eat less of the other more nutrient dense foods. For example, spreading margarine on a piece of bread adds about an extra third to the calorie count of that slice: it now contains 4/3 of the original calories. But the ¼ of the calories that comes from the margarine contributes almost no nutrients, so the buttered bread still only contains the nutrients of the plain bread. Therefore the nutrient density has been reduced to ¾ of what you would get from eating all of those calories from bread. You have effectively lost ¼ of the iron, protein, thiamine, dietary fibre and other nutrients. The same happens when we use oil in cooking, or eat a lot of sugar, such as from soft drinks. “But”, you protest, “I am going to eat just as much bread, whether or not it has margarine on it”. Let us explain this fallacy in more detail.

You have a daily calorie budget to divide up among different foods. How you spend it is your choice. How many calories you have to spend each day is pre-determined by your metabolism. You have limited control over this. You can exercise more and your budget will be a little bigger but you still have to eat within your calorie budget. Why do you have to? If you habitually exceed your daily calorie budget then your body will be forced to store the over budget calories as fat, and you will gain weight. Most people understand this, but do not fully appreciate the implications of the calorie budget in respect to nutrients.

Many health conscious Australians believe that they eat a high fibre diet, and our nutritional authorities tell us that we can get plenty of dietary fibre by eating some whole grains and vegetables along with meat, dairy, and good oils. You may think, sure I eat chicken, eggs, dairy foods, good oils and processed grains in moderation but I also eat high fibre breakfast cereal, and some vegetables and fruit: I eat a high fibre diet. The following pie charts illustrate how fibre intake decreases as you use up your daily calorie budget on foods that contribute no dietary fibre. Note that they are for concept only and do not imply exact proportions.

Fraction of food calories that contributes dietary fibre (blue):