Macronutrients are nutrients available to your body through your diet -- essentially nutrients that are in the foods you consume. Food is comprised of three types of macronutrients -- carbohydrate, protein, and fat. Each one provides important benefits and understanding the role of these macronutrients and how to best manage their consumption in the proper types and ratios is critical to your good health.
From a clinical perspective, the type and amount of carbohydrate one consumes will determine the metabolic response from insulin, the hormone that regulates blood sugar. All carbohydrates are sugars and they are a source of energy for the body. A favourable hormonal response is elicited from low-density carbohydrates (low glycaemia index) meaning that the insulin response is moderate and not in excess. A non-favourable response is elicited from high-density carbohydrates (high glycaemia index) meaning that high levels of insulin are produced primarily to handle the incoming carbohydrate load. Too many carbohydrates, especially of the wrong type, lead to hyperinsulinemia.
In summary, optimal health requires consumption of moderate amounts of low glycaemia carbohydrates. Examples of low glycaemia carbohydrates are green leafy vegetables. Examples of high glycaemia carbohydrates are potatoes, pasta, bananas, and bagels. Unlike protein and fat, from a metabolic caloric perspective there is no such thing as essential carbohydrates meaning your body can survive without them. Recent research, however, has revealed the existence of certain dietary carbohydrates which are necessary for optimal cellular function. These are being referred to as "biological" sugars which go beyond the scope of merely metabolic or caloric needs of the body. These biological sugars are carbohydrates incorporated into the surface structure of the cells of our bodies and help perform biological functions, many of which are extremely important for optimal health.
There are many sources of protein, most of which come from animals although some sources are plant derived. Protein provides essential amino acids that your body uses to make muscle tissue. Without these amino acids, you would eventually waste away and die. Some protein, in the absence of carbohydrate, can be used to produce glucose, which your body needs for energy. Protein elicits a hormonal response from glucagon -- the counter-balance hormone to insulin. A delicate balance between systemic levels of insulin and glucagon, in the proper ratios, is crucial to your good health. The best sources of protein are fish, chicken, and lean cuts of beef. Generally speaking, moderate protein consumption balanced with moderate low-density carbohydrates (spinach, broccoli, etc.) provides the essential amino acids, vitamins and minerals required for good health.
Dietary fat is the last macronutrient and one of the most misunderstood. There are several types of dietary fat -- saturated, trans-fatty acids, monounsaturated, and polyunsaturated. One type of fat, "healthy" fats known as essential fatty acids, is one of the most essential nutrients for optimal health.
Unfortunately, one type of EFA known as Omega-3 fatty acid is most often missing from our diet. It has been estimated that as a society, we are 90% deficient in this nutrient. Why? The mantra espoused for the past 20 years has been high carbohydrate, low or no fat, and no salt! EFA's of the Omega-3 type is crucial for optimal health. EFA's in general are essential and without them, we would die. This is why they are called essential fatty acids. Omega-3 is a type of essential fat, which is usually available from cold water fish, olive oil, avocados, nuts, seeds, and other sources. Again, these are "healthy" fats. EFA's comes from monounsaturated and polyunsaturated fat. Of these, EPA and DHA, two types of Omega-3 fats, are the most essential and the most missing in typical Western diets.
Another type, Omega-6, is readily available through our diet in things like vegetable oil. There exists a huge imbalance in the ratio of Omega-6 to Omega-3 EFA's. Presently it is 20:1. Ideally, this ratio should be no more than 4:1. Therefore, to optimize healthy cells and promote wellness in general, one should consume a daily supplementation of Omega-3 fatty acids, either through diet or supplementation.
The cell membranes of our body are made from dietary fat. In the making of these membranes, the biological process prefers EPA (omega-3) to other types of dietary fat. Healthy cell membranes allow for the fluidity of cell membranes that is necessary for cells to function properly and effectively. Nutrient, water, and mineral transport into and out of individual cells is much easier when cell membranes are flexible and fluid. Trans-fatty acids and saturated fat, both of which come from a poor diet consisting of fast foods versus freshly prepared meals, offer the body the poorest quality of fat from which to construct cell membranes. Replacing bad fats in our diet with healthy fats is fundamental and paramount to optimal health.