Nutrients are substances in food that provide the body with energy, structural materials and other factors that support human function during growth, maintenance, and repair. They may also reduce the risk of developing certain diseases. This sounds pretty straight-forward, but the world of nutrients is, actually, a confusing one. After all, there are just so many! And they all do different things, come from different foods and are needed in different amounts.
Macro vs. micro nutrients
There are two broad classifications of nutrients: macronutrients and micronutrients. The macronutrients are the nutrients we need in large amounts – protein, carbohydrates, and fats. The micronutrients are nutrients we need in small amounts, though are no less essential to health. These consist of the vitamins and minerals.
The macronutrients are the components of food that provide energy, measured in calories. They are often called the energy-yielding nutrients, as no others nutrients yield energy. They each have other functions, but providing energy is one role they share and the role that sets them apart from other nutrients.
Carbs are probably the macronutrient we are most likely to think of when we think energy and this is really because sugar is a carbohydrate. Fruit, vegetables, and grains are our main wholefood sources of carbs, but for many of us, carbs creep into our diet when added to processed foods. It is true that providing energy is a major job of carbohydrates, but they actually don’t contribute as much energy to the diet gram for gram as one of the other macronutrients – fat. Each gram of carbohydrate provides 4 calories.
Carbohydrates are actually the macronutrient of which we need the most. The National Health and Medical Research Council’s Nutrient Reference Values stipulate that we need to obtain 45-65% of our daily energy from carbohydrates, preferably in the form of vegetables, wholegrains, legumes and fruit. The reason carbohydrates are so esteemed by the body is that they provide the main source of energy for the body, not to mention the most easily used. All bodily systems, including the nervous system, renal system (kidneys), muscular system (including the heart), need carbohydrates to function.
Carbohydrates also provide fiber which helps maintain digestive function and gastrointestinal health. High-fiber diets are associated with a range of positive health outcomes from reduced risk of certain cancers, reduced body weight and reduced risk of cardiovascular disease.
In their whole or complex form, carbohydrate-rich foods also provide a range of other essential nutrients which are not only critical to body function and health, but also to the optimal utilization of the energy provided by the carbohydrates.
Avoiding empty calories
Carbohydrates are found in most foods but mainly fruit, vegetables, and grains. Sugar is probably the best known of the carbohydrates, and so anything made with sugar is a source of carbs: biscuits, cakes, pastries, soft drinks etc., but these are not ideal foods for providing this important nutrient as they come without any essential micronutrients nutrients, and purely provide energy to the diet. These sorts of foods are commonly referred to as ‘empty calories’ and are one of the major dietary contributors to the obesity epidemic.
Sugar is also added to many commercial products that do not actually taste sweet. These ‘hidden’ sugars are regularly added to soups, sauces, crackers, etc. and contribute a significant amount of energy to our diets without us being aware. This is especially true in relation to ‘low fat’ foods.
Often those products have large amounts of sugar (and flavors etc.) to compensate for the taste and texture lost by taking out fat. The irony for these foods is that excess sugar just turns into fat anyway.
Consuming lots of low fat, but sugar-laden foods will add fat to your body – they are usually highly processed too. The other downside of that is that all that sugar messes with your insulin levels, causing disordered blood sugar levels, food cravings, and the health impacts that come along with that.
For optimal health, meet your carbohydrate requirements from wholegrains, legumes, and vegetables (including leafy green and other colorful vegetables, including capsicum, cabbages, sweet potato, broccoli, spinach, kale, carrots, beetroot, and so on.
Like carbohydrates and sugar, many people associate protein with one main food: meat. Certainly meat, poultry and fish are the main sources of protein to the diet, but protein is in many other foods including dairy, legumes, nuts and seeds and – to a lesser extent – in grains and some vegetables.
Perhaps because of its association with meat, protein is assumed to have only one real function in the body – to build muscle. It does do that of course, but it has numerous other functions. One such function is as an alternative fuel source for times when glucose is low. One gram of protein yields 4 calories of energy – just the same as carbohydrate although this is straight forward a conversion.
Protein is made up of building blocks called amino acids– and there are around 20 of them. Eight of them must be obtained in the diet, and so are called ‘essential’. These amino acids are then used to make and repair muscle and connective tissue, make enzymes and hormones, and make blood clotting factors – clearly critical functions for the human body.
Unfortunately, the intricacies of the amino acids make protein a little different to the other macronutrients. We must obtain those eight essential amino acids in our diet. Meat and other animal sources of protein contribute all of the essential amino acids however plant sources are deficient in certain amino acids. As a result, plants must be combined in order to ensure good levels of all the essential amino acids. Combining plant-based, incomplete proteins to make complete proteins is called complementary proteins.
This is pretty easy and most traditional food cultures were doing it long before amino acids were understood. Examples include Mexican (corn and beans), Japanese (miso/tofu and rice), Indian (lentils and rice or bread), African/Caribbean (rice and beans), and Arabic (sesame and chickpeas or chickpeas and bread).
The current recommendation is that 15-25% of our daily energy come from protein. For optimal health, use a range of protein sources, including a small amount of lean meat, fish at least 2 or 3 times per week, and plant sources including legumes, nuts, seeds, soy and tofu, and grains.
Fat is the macronutrient that contributes the most energy per gram. In fact, each gram of fat yields a huge 9 calories. So you would kind of expect that being a source of energy was a major role of fat in the diet, and yes it is, but it functions more as a reserve of energy – for those times when we need to keep a steady supply of fuel until we can eat again.
And energy is certainly not the only function of dietary fat. Perhaps the most important function of dietary fat is growth and development, but they are also needed to absorb certain nutrients (specifically the fat soluble vitamins: A, D, E & K), and provide protection to body organs through insulation and cushioning, maintaining the structure and integrity of cell membranes and body linings.
Like the other macronutrients, fat is found in most foods – meat, poultry, fish, dairy, oils, grains, nuts and seeds, and legumes. It is also widely found in many commercial products: biscuits, salad dressings, ice cream, fried foods, biscuits and crackers and many other foods. Debate has raged for decades about the merits or dangers of dietary fat. This was partly fueled by its high energy composition, but also because saturated fat (predominantly from animal sources) was believed to directly cause heart disease and obesity.
Fats – not all bad?
There is less certainty these days about the dangers of moderate saturated fat intake and heart disease, and, indeed, the evidence is increasing that the real culprit is trans fats, the type of fat that is found in many commercial baked products and margarines. As such, although the recommendation is that 20-35% of daily calories are derived from fat, for optimal health, it is recommended that the fat is predominantly from unsaturated sources (olive oil, fish, avocados, nuts, and seeds) which have been shown to reduce risk of disease, including cardio and cerebrovascular disease.
It is not simply enough to eat food, you need to be aware of your macronutrient requirements and adjust your food intake accordingly. For example, bodybuilders often require more protein whereas endurance athletes often need more carbohydrates while those looking to lose weight may need to reduce their fat and/or carb intake. By juggling the ratios of the macronutrient groups to suit your personal needs, you are much more likely to get the results you want from both your training and your diet.