Updated: Mar 20
In the preceding article, you were introduced to macronutrients, namely carbohydrates, fat, and protein. These three macronutrients are the main constituents of our diet. It is important to note, however, that food also contains micronutrients, which we will discuss in the upcoming unit. Furthermore, food is more than simply a "macronutrient delivery system." Macronutrients play a crucial role in several bodily processes, such as digestion, nutrient absorption, hormone production, immune system health, cellular structure and function, body composition, metabolic function, and more. This article will examine some of these processes and highlight the vital role that each macronutrient plays in them. Macronutrients are essential components of our diet, and in this article, we will delve into every one of them.
Carbohydrates are typically classified based on their general chemical structure, which can be divided into three groups of saccharides: monosaccharides, oligosaccharides, and polysaccharides. Monosaccharides are the simplest form of carbohydrates and consist of only one sugar group or chain link. Oligosaccharides, on the other hand, are short chains of monosaccharide units linked together. Disaccharides are the most common form of oligosaccharides, including maltose, sucrose, and lactose. Polysaccharides, as the name suggests, contain many saccharides and are complex chains of linked monosaccharide units that can be either straight or branched. When we refer to starches, glycogen, or fiber, we are referring to polysaccharides. Carbohydrate structure not only affects how they behave when cooked but also how we digest and absorb them. Plant cells create starches by joining glucose monosaccharides together, with amylose and amylopectin being the two main forms. Amylose is a linear polysaccharide, while amylopectin is a highly branched polysaccharide. Animals produce glycogen, which is similar to starch, from glucose monosaccharides in the process of glycogenesis. Cellulose is another polysaccharide similar to amylose, which provides plants with rigid cell walls and is commonly known as fiber.
Unlike starch, fiber's chemical bonds resist human digestive enzymes, and it cannot be broken down or absorbed, although it can be utilized by bacteria in our GI tract. Interestingly, animals that feed on high-cellulose plants have bacteria in their stomachs that can digest it and extract energy from it.
Carbohydrate digestion, absorption, transport, and metabolism is a complex process that starts in the mouth and continues through the gastrointestinal tract. Salivary amylase begins the breakdown of polysaccharides into smaller carbohydrate chains in the mouth, but most of the work happens in the small intestine, where pancreatic amylases turn these smaller carbohydrate chains into disaccharides. These disaccharides are then broken down into monosaccharides by specific enzymes, such as maltase, lactase, and sucrase. All monosaccharides then pass through the intestinal cells into blood vessels that take them to the liver before they enter general circulation. The liver takes what it needs for energy transfer and glycogen storage, and then ships the rest out as glucose monosaccharides, which work their way through the blood until they are taken up into our cells.
The glycemic index is a measure of how quickly and significantly a given food can raise our blood sugar. The less processed and higher fiber a food is, the more complex it's carbohydrate molecules usually are. Because of this, those foods will usually take longer to digest and have a lower glycemic index. High glycemic foods include sugar, candy, breakfast cereal, and bagels, while lower glycemic foods include legumes, whole grains, and vegetables. While the glycemic index is an interesting measure of the physiological response to carbohydrates in the diet, it doesn't tell the whole story. Factors like meal composition, individual variability, and how foods are prepared and consumed can all affect blood glucose levels.
Glycemic load (GL) is a commonly used measure by researchers to assess the impact of food on blood sugar levels. It takes into account both the glycemic index (GI) and serving size of food, providing a more accurate representation of how quickly and significantly blood sugar may increase after a meal. However, like GI, GL also has limitations as it fails to consider other essential nutrients like fiber, micronutrients, phytonutrients, and zoonutrients present in the food.
The insulin index (II) is another crucial measure that determines how the body responds to food, and it is closely linked to health. Although GI and GL are helpful in predicting glucose load, they are not reliable indicators of insulin response to a meal. II measures the amount of insulin produced in response to a particular food and doesn't always match the GI. It's surprising that high-protein and high-fat foods can stimulate greater insulin responses than expected, while some high-GI foods produce lower insulin responses.
People with underlying insulin resistance produce more insulin than healthy individuals when consuming moderate and high GI foods. Thus, II is a better predictor of insulin response and a more accurate measure of how food affects health. Carbohydrates are not created equal, as they all go through different processes in the body to eventually become glucose, which can have varying effects. For example, cellulose is a carbohydrate that isn't used for energy and is mostly excreted, while highly branched chains of amylopectin release glucose gradually. Simple, refined, and processed carbohydrates are quickly digested and leave us feeling unsatisfied, while complex carbohydrates found in whole foods such as vegetables, fruits, legumes, and whole grains keep us feeling full longer and release energy gradually, along with providing other micronutrients, phytonutrients, fiber, and water.
Fiber, which comes in two forms - soluble and insoluble - can't be digested by our bodies but has many important functions. Soluble fiber is found in foods like oats, beans, nuts, and fruits and vegetables such as oranges, bananas, and carrots. It helps decrease serum cholesterol levels and excrete fat-soluble substances such as sex hormone metabolites. Insoluble fiber is found in vegetables, fruits, whole-grain seed hulls, seeds, and nuts, and adds bulk to stools, ensuring regular bowel movements.
Fiber has many benefits, including helping us feel full longer, lowering our blood lipids and cholesterol, reducing the risk of colon cancer, keeping things moving through our GI tract, and improving overall gut health. The recommended daily intake for fiber is 25 g, but the optimal amount is closer to 35 g for women and 48 g for men, although some clients with inflammatory bowel disease or colitis may feel better with less during flare-ups.
Resistant starch, which resists digestion, is a third kind of dietary fiber that occurs naturally in foods like green bananas and beans, and can also be found in cooked and cooled starches like potatoes, oats, pasta, and sushi rice. Our intestinal bacteria turn resistant starch into short-chain fatty acids, just like dietary fiber. --------------------------------------------------------------------------------------------------------------------------- Fat, also known as lipids, is an essential macronutrient that plays a crucial role in human physiology. Fats are organic molecules composed of carbon and hydrogen elements, arranged in long chains called hydrocarbons. The structure of these hydrocarbon chains and their interaction with each other determines the type of fat. The basic unit of fat is the fatty acid, which consists of simple hydrocarbon chains with special chemical groups at each end.
The presence or absence of hydrogen atoms bonding to the hydrocarbon chain determines whether a fat is saturated or unsaturated. Saturated fats, such as butter, coconut oil, or cocoa butter, have all their available bonding spots filled with hydrogen atoms and are usually solid or semi-solid at room temperature. On the other hand, unsaturated fats, like vegetable oils, are liquid at room temperature and have some available bonding spots in the hydrocarbon chain. The less saturated a fat is, the more fluid it becomes. Polyunsaturated fats, such as omega-3 and omega-6, have more than one carbon that is unsaturated.
Fatty acids can be joined together to form triglycerides, which are the major storage form of fat found in the body. To digest fat, the body breaks down triglycerides into fatty acids and glycerol, which are repackaged before entering the bloodstream. Bile emulsifies triglycerides in the food we eat, dividing them into small droplets that offer more surface area for digestive enzymes to work on. Pancreatic lipase, the major enzyme of triglyceride digestion, hydrolyzes triglycerides and removes the fatty acids from their glycerol backbone in the small intestine.
Once the fatty acids are broken down, they can diffuse across the intestinal cell layer and be repackaged into large lipoprotein particles called chylomicrons. Chylomicrons are released into the lymphatic system and eventually enter the bloodstream through the thoracic duct. Because it takes a long time to break down and transport, fat enters the blood several hours after we’ve eaten it.
Packaged triglycerides circulating in the blood (carried by chylomicrons) are again broken down into free fatty acids and glycerol with the help of an enzyme called lipoprotein lipase. This occurs so they can pass through yet another cell membrane and into the tissues of our body. Once through the membrane, they are either oxidized and used to transfer energy in skeletal muscle or other tissues or converted back into triglycerides for storage in adipose tissue or skeletal muscle. Lipoproteins play a crucial role in transporting fats such as triglycerides and cholesterol in the bloodstream since fat cannot dissolve in water. Phospholipids found in lipoproteins have a hydrophilic head that is compatible with water and a hydrophobic tail that binds well to other fats. Apolipoproteins present in lipoprotein coats act as receptors that help control what the lipoprotein does by binding to other substances.
There are several kinds of lipoproteins, including chylomicrons, very low-density lipoproteins (VLDL), low-density lipoproteins (LDL), and high-density lipoproteins (HDL). Chylomicrons are the largest and transport triglycerides from the intestines to the liver, skeletal muscles, and adipose tissue. VLDL carries newly packaged triglycerides from the liver to adipose tissue. LDL carries cholesterol to all cells in the body, with two types: large buoyant LDL particles (lb LDL) that indicate good health and small dense LDL particles (sd LDL) that indicate poor health. HDL, on the other hand, transports fat and cholesterol from the body's cells back to the liver, which is crucial in the reverse cholesterol transport process.
Dietary fat plays six significant roles in the body, including providing energy, forming and balancing hormones, cell membranes, brains, and nervous systems, transporting fat-soluble vitamins, and providing two essential fatty acids that the body cannot produce, namely linoleic acid and linolenic acid. Most dietary fat comes in the form of triglycerides, which consist of three fatty acids attached to a glycerol backbone. The glycerol backbone is indifferent to the fatty acids that attach to it, and therefore, most dietary fat sources comprise a combination of saturated, polyunsaturated, and monounsaturated fatty acids.
It is important to consider the big picture when it comes to fat intake. Humans evolved to eat a varied and seasonal diet that included a mix of fat types that naturally occur in different types of foods. A relatively equal balance of fat types is ideal, which can be achieved by consuming a wide selection of diverse, whole, less-processed foods such as nuts and seeds, avocados, dairy, eggs, fatty fish, poultry, wild game, beef, pork, and lamb, olives, and extra-virgin olive oil. When possible, choosing wild-caught or pasture-raised animal products and fish can provide a better fatty acid profile. Minimizing or avoiding refined and processed foods containing industrially produced and artificially hydrogenated fats is also recommended. In some cases, supplementing with specific fat types, particularly omega-3s, may be necessary. Personalizing a nutrition plan to each individual's unique body, preferences, and needs is crucial.
Saturated fats are hydrocarbon chains that are “saturated”, or filled with hydrogens, which make them chemically stable, resistant to oxidation, and don't easily degrade. Unlike artificially created “hydrogenated” fats, which are chemically unstable, saturated fats are found in foods like beef, pork, lamb, eggs, full-fat dairy, coconut, and cacao. They are solid at room temperature because they are packed with hydrogens, leaving little room to be liquid. Saturated fats sometimes get a bad rap for causing heart disease, but human physiology is more complex than that. Our liver makes most of the cholesterol in our body, and we need it for many important jobs in our body, including the production of steroid hormones. Recent meta-analyses have found that dietary saturated fat is not significantly associated with an increased risk of cardiovascular diseases. The biggest culprit in many chronic diseases is excess body fat, which leads to systemic inflammation and metabolic disruption.
To be healthy, a lot of saturated fat combined with a lot of sugar, and processed, or refined carbohydrates is not recommended, and saturated fats should be balanced with other fat types, including monounsaturated and polyunsaturated fats.
Omega-3 and omega-6 unsaturated fatty acids are also essential to our diet. Omega-3 fatty acids, including alpha-linolenic acid (ALA), docosahexaenoic acid (DHA), and eicosapentaenoic acid (EPA), are important for brain function, normal growth, and development. They also have anti-inflammatory effects and can reduce the risk of chronic diseases, such as heart disease, stroke, and cancer. Good sources of omega-3s include fatty fish, such as salmon, mackerel, sardines, flaxseed, chia seeds, and walnuts. On the other hand, omega-6 fatty acids, such as linoleic acid (LA) and arachidonic acid (AA), are also important for our health, but excessive consumption of omega-6s can lead to inflammation and increase the risk of chronic diseases. Sources of omega-6s include vegetable oils, such as corn, sunflower, and soybean oil, as well as nuts and seeds. Maintaining a balance between omega-3 and omega-6 fatty acids is important for optimal health. --------------------------------------------------------------------------------------------------------------------------- Proteins are one of the three macronutrients essential to human nutrition, and like carbohydrates and fats, they are composed of carbon and hydrogen molecules. However, unlike carbohydrates and fats, proteins contain nitrogen as part of their amino groups. The smallest unit of protein is the amino acid, which has four main characteristics: an amino group, a carboxyl group, a central carbon, and a side chain. When amino acids are joined together, they form peptides or peptide chains, which make up the primary protein structure.
Most proteins are not just long chains of amino acids; they form secondary, tertiary, and quaternary structures. Secondary structures are formed as amino acids bind to their neighbor and to other amino acids further down the chain, giving proteins strength and stiffness. Many enzymes, transport proteins, and immunoproteins in the body have tertiary structures, which are formed when the protein, in secondary structure formation, loops together to form globular shapes. Quaternary structures are formed when one or more proteins in a tertiary structure join together. Molecules’ chemical structures are important, but so are their physical structures and shapes, which can affect how they behave and fit together with other molecules.
Protein digestion starts in the acidic environment of the stomach where gastric hydrochloric acid denatures the secondary, tertiary, and quaternary structures of ingested proteins. The enzyme pepsin then breaks down peptide bonds. The resulting polypeptides and single amino acids are passed to the small intestine, where proenzymes secreted by the pancreas, such as trypsinogen, chymotrypsinogen, procarboxypeptidases, proelastase, and collagenase, activate and break down proteins further.
Different amino acids and peptides are absorbed in different ways through the cells of the intestinal brush border. All need ATP for active transport, using carriers. Amino acids compete for transport by common carriers in the small intestine. As di- and tripeptides use different carriers than individual amino acids, short peptides are absorbed more quickly than free-form amino acids. Once absorbed, amino acids and peptides can be used for energy or to synthesize new proteins, such as hormones and new digestive enzymes. Ingested amino acids and peptides can also be delivered to the liver (via hepatic portal circulation) for processing and distribution to other cells of the body.
The liver plays a significant role in protein absorption, with most amino acids going there. Of the 100 grams of amino acids ingested, about 20 grams will be used for protein synthesis in the liver, while about 60 grams will be catabolized in the liver, and about 20 grams will go into systemic circulation.
Protein synthesized in the liver is used for various functions in the body, with 14 grams remaining in the liver and six grams being exported to the plasma in the form of plasma proteins such as albumin, globulins, and lipoproteins. Protein is an essential macronutrient that plays many critical roles in our bodies. It's responsible for building and repairing tissues, supporting the immune system, producing hormones and enzymes, and much more. Unlike fat and carbohydrates, our bodies cannot store protein for later use, so we need to consume it regularly to maintain our health. We are constantly breaking down old proteins and building new ones, and we need to replace the lost amino acids through our diet.
While protein is found in almost all foods to some extent, not all protein sources are created equal. Our bodies need a mix of essential amino acids that we can only obtain through food, and different types of protein have different amino acid profiles. Eating a varied and seasonal diet that includes a wide range of whole, less-processed foods can help ensure that we get all the essential amino acids we need. However, for some people, it may be useful to supplement with protein powders, particularly for those who have trouble consuming enough whole-food protein or need fast-digesting proteins for quick replenishment, such as athletes.
Amino acids are the building blocks of protein, and they are categorized into three groups: non-essential amino acids, essential amino acids, and conditionally essential amino acids. We can synthesize non-essential amino acids in our bodies, but we need to obtain essential amino acids from our diet. Conditionally essential amino acids are needed in greater amounts during physical stress or illness, and we may not synthesize them effectively, so we need to consume them through our diet.
All foods contain some amount of protein, and some foods are considered high in protein, such as lean meats, poultry, fish, eggs, dairy, beans, and legumes. However, not all protein sources have the same quality. Several protein quality indices exist that measure how well a protein source provides the essential amino acids we need. While these measures may not be critical for most people, they can be helpful for those who are malnourished or have special dietary needs.
It's important to remember that all protein adds up, and we can get protein from many sources. A meal that includes multiple protein sources, such as beef chili with beans and guacamole, can provide the accumulated protein from all the ingredients. Protein is essential for human survival, So the quality of protein in one’s diet is crucial for optimal health and fitness. The Protein Digestibility Corrected Amino Acid Score (PDCAAS) is currently the “gold standard” of determining protein quality because, unlike PER, BV, and NPU, it is based on human amino acid requirements. PDCAAS accounts for the number of limiting amino acids in a protein and compares the amount of this amino acid in the test protein to the amount in a high-quality reference protein. This value is multiplied by how truly digestible the protein is. The PDCAAS takes several factors into account, making it a reliable measure of protein quality.
The average person eating a standard diet is probably not protein deficient. However, this does not mean they are getting optimal levels of protein. For sedentary, generally healthy adults, about 0.8 g of protein per kg of body mass is enough to cover basic daily requirements. But our protein needs can go up if we train hard frequently or have a heavy physical job. Protein is also necessary for the repair and rebuilding of tissues, hormones, and the immune system. Recommendations for athletic protein intakes vary, and one probably does not need more than 2.2 g of protein per kg of body mass per day.
While most people benefit from slightly higher levels of protein, some may require a lower-protein diet due to health conditions such as kidney disease, certain metabolic diseases, liver disease, problems with gastric emptying, or homocystinuria. There are various supplement options available to meet your nutritional requirements. These include protein powders such as whey, casein, milk protein blend, and egg white, and plant-based proteins like pea, hemp, rice, and sacha inchi proteins. These supplements can help you maintain a healthy protein balance in your diet.
Aside from protein powders, there are other supplement possibilities that can benefit certain people. For instance, branched-chain (BCAA) supplements, especially leucine, are ideal for those limiting their energy intake, training fasted, and/or requiring additional peri-workout and post-workout recovery support.
Additionally, glutamine supplementation may enhance immunity and gastrointestinal health, while arginine supplementation may speed up wound healing. Furthermore, lysine supplementation can alleviate cold sore severity, frequency, and healing time.
However, it's worth noting that individual amino acids are only effective if there's a specific need for them. Therefore, it's crucial to consult a healthcare professional before beginning any supplementation regimen to ensure it's appropriate for individual needs. In conclusion, Macronutrients play a vital role in providing our bodies with the energy and essential building blocks needed to maintain good health. By understanding the importance of protein, carbohydrates, and fats in our diets, we can make informed decisions about the foods we eat and how they affect our overall well-being. In the next article which will be our final article in the series, we will delve into the world of Micronutrients, exploring the vital role that vitamins, minerals, and other essential nutrients play in keeping our bodies functioning at their best. Read from here: The Importance of Micronutrients: Vitamins, Minerals, and Electrolytes for Optimal Health. By incorporating both Macronutrients and Micronutrients into our diets, we can ensure that we are providing our bodies with the full spectrum of nutrients needed for optimal health.