Macronutrients are nutrients that we need in large amounts to maintain health and support vital functions. They fall into three main categories: carbohydrates, proteins, and fats or lipids.[14]
They are present in almost all the foods we eat, although often in very different quantities. This is why it is important to eat a good variety of foods to ensure adequate intake of each. And a balanced diet is precisely one that ensures the intake of an appropriate proportion of carbohydrates, proteins, and lipids to meet the body’s energy and nutritional requirements.[11]
An excess or deficiency of any of these macronutrients can contribute to the development of metabolic disorders. For example, excessive consumption of refined carbohydrates can increase the risk of obesity and type 2 diabetes, especially when associated with reduced physical activity, while a protein deficiency can lead to loss of muscle mass and a weakening of the immune system. Similarly, excessive consumption of saturated fat is associated with a higher risk of developing cardiovascular disease.[2]
Contents
Macronutrients: carbohydrates
Carbohydrates are organic compounds made up of carbon, hydrogen, and oxygen, though some also contain sulfur and nitrogen. Most have the general formula (CH2O)n.
Based on their structural complexity, these macronutrients can be classified into three categories.[10]
- Monosaccharides, such as glucose, fructose, and galactose. They are the simplest carbohydrates and are the building blocks used to make more complex carbohydrates.
- Oligosaccharides, which are short chains of monosaccharides, between 2 and 20 units long. Disaccharides are the most common; examples are sucrose, which is common table sugar, lactose, which is milk sugar, maltose and trehalose.
- Polysaccharides, which are polymers formed by more than 20 monosaccharide units. Examples are starch, glycogen, chitin, and cellulose. Oligosaccharides and polysaccharides are formed by monosaccharides linked through glycosidic bonds.[7]
What do carbohydrates do?
Carbohydrates perform multiple functions.
They are a rapidly available source of energy, even under anaerobic conditions, through glycolysis. Their energy content varies slightly between monosaccharides, oligosaccharides, and polysaccharides. Monosaccharides provide 3.74 kcal per gram (15.6 kJ per gram), disaccharides 3.95 kcal per gram (16.5 kJ per gram), while starch 4.18 kcal per gram (17.5 kJ per gram). Therefore, on average, it is possible to approximate to 4 kcal/g (16.7 kJ per gram).[3]
Glucose can also be stored as glycogen in the liver and muscles to be used during periods of physical activity or fasting.[7]
Fibers are polymeric carbohydrates that are not hydrolyzed by human digestive enzymes and therefore not absorbed. Technically, they would not be classified as macronutrients. However, while insoluble fibers pass through the intestine unchanged, soluble fibers are metabolized by the bacteria of the gut microbiota producing short-chain fatty acids that have energy and regulatory functions for colonocytes.[8] Additionally, fibers are able to sequester cholesterol and bile salts, thus exerting a hypocholesterolemic effect.[4][13]
Beyond their energetic function, carbohydrates are involved in cell recognition and communication, thanks to their presence in membrane glycoproteins and glycolipids. They are also part of the structural backbone of DNA and RNA and participate in liver detoxification processes as precursors of glucuronic acid. Finally, they are necessary for normal lipid metabolism and, when adequately present in the diet, allow for protein savings.[14]
For healthy adults, the recommended daily intake is 45-60 percent of the daily caloric intake, which can reach up to 65 percent in the case of very intense physical activity. Monosaccharides and disaccharides, also known as simple sugars, should not exceed 15 percent of the daily caloric intake. To prevent ketosis, the minimum carbohydrate requirement is 2 g per kg of body weight.[12]
Foods high in carbohydrates
The main sources of carbohydrates in the human diet are cereals, such as corn, wheat, spelt, barley, rice, oats, millet, rye, and their derivatives, such as bread and pasta. Potatoes and legumes are also rich sources of these macronutrients. In these foods, carbohydrates are predominantly found in the form of starch.[8]
Fruit, vegetables, and fresh dairy products contain smaller amounts of carbohydrates, generally represented by fructose, glucose, sucrose, and lactose. It should be noted that milk and dairy products are the only significant animal source of carbohydrates, as glycogen content in animal tissues is virtually negligible.[11]
Finally, some foods are composed almost entirely of carbohydrates. Excluding honey, they are all processed foods such as maltodextrin, table sugar, candies, fruit juices, and soft drinks.
Macronutrients: proteins
Proteins are macromolecules made up of chains of at least 20 different types of amino acids. Amino acids are linked through peptide bonds in unique, genetically determined sequences to form proteins with specific functions.[10]
Proteins can be of animal or plant origin. Those of animal origin are considered qualitatively superior to those of plant origin as they provide sufficient quantities of all essential amino acids, namely those that we are unable to produce. Plant-based proteins are often deficient of one or more essential amino acids. However, it is possible to obtain an adequate intake of essential amino acids by correctly combining plant proteins of different origins, which complement each other.[6]
It should be noted that, although animal protein sources tend to have a higher biological value, plant proteins are often associated with a higher content of vitamins, minerals, and fiber, in addition to containing less saturated fatty acids. On the other hand, plant proteins may be accompanied by substances that can interfere with their intestinal absorption, such as tannins, phytates, and saponins, redicing their bioavailability.[9]
What do proteins do?
This class of macronutrients performs a wide range of functions in the human body.
They are essential for the growth and repair of tissues, constitute the enzymes that catalyze biochemical reactions, form various hormones and antibodies, and are fundamental for cellular structure, movement, nerve impulse transmission, as well as in the transport of oxygen.[14]
Furthermore, proteins can be used as an energy source, especially when carbohydrate intake is insufficient. They provide approximately 4 kcal per gram (16.7 kJ per gram), similar to the energy yield provided on average by carbohydrates.[3]
Daily protein requirements vary depending on age, gender, to a small extent on physical activity level, and other specific conditions, such as breastfeeding and pregnancy. For healthy adults, excluding pregnant or breastfeeding women, an daily intake of 0.9 g per kg of body weight is recommended up to the age of 60 years, increasing to 1.1 g per kg of body weight after the age of 60.[12]
Foods high in proteins
In human nutrition, proteins come from animal or plant sources.
Below are some of the main sources of animal proteins.[11]
- Meat, such as beef, chicken, turkey, pork, lamb, and processed products like cured and sliced meats.
- Fish, shellfish, and crustaceans, which also contain omega-3 polyunsaturated fatty acids.
- Eggs.
- Dairy products, including milk and derivatives such as yogurt and cheese.
Below are some of the main sources of plant proteins.
- Legumes, such as lentils, beans, chickpeas, peas, and soy, as well as flours derived from them.
- Soy-based products, such as tofu, tempeh, edamame, and miso.
- Whole grains.
- Nuts and seeds.
The limited availability of essential amino acids in plant proteins can be address through specific combinations, such as cereals and legumes, and legumes and seeds/nuts.[6]
Protein powders are also available derived, for example, from whey, soy, or peas, as well as fortified foods enriched with proteins.
Macronutrients: lipids or fats
Lipids, or fats, are a category of organic molecules composed mainly of carbon, hydrogen, and oxygen, with diverse chemical structures that may include cyclic structures.[1]
The most common fats in the diet are triglycerides, made up of a glycerol molecule linked to three fatty acids that can be saturated and/or unsaturated, the relative percentages of which influence the physical and biological properties of the molecule.
Other members of this class of macronutrients are phospholipids, glycolipids, sterols, such as cholesterol, fat-soluble vitamins, and carotenoids, all of which are present in the human diet in much smaller amounts than triglycerides.[5]
What do lipids do?
Within this class of macronutrients, triglycerides, or more specifically, the fatty acids that compose them, are one of the main sources of energy for the body, and provide about 9 kcal per gram (37.7 kJ per gram), more than double the energy of carbohydrates and proteins.[3]
In addition to their energy function, lipids are essential for the formation of cell membranes, the production of steroid hormones, thermal insulation, nerve impulse transmission, and the protection of vital organs. Furthermore, they facilitate the absorption of fat-soluble vitamins and are involved in cellular signaling pathways.[1]
For healthy adults, including pregnant and breastfeeding women, the recommended daily intake is 20-30% of the daily caloric intake, distributed as follows:
- saturated fatty acids should account for less than 10% of the daily caloric intake;
- unsaturated fatty acids should include 5-10% polyunsaturated fatty acids, with 4-8% from omega-6 fatty acids and 0.5-2% from omega-3 fatty acids.[12]
Trans fatty acids should be avoided as their presence, alongside excessive saturated fatty acids intake, is linked to an increased risk of developing various diseases, such as cardiovascular diseases.[2]
The daily intake of cholesterol, which cannot be used for energy, should remain below 300 mg/day.[12]
Foods high in lipids
Like proteins, dietary fats can come from both animal and plant sources.
Below are some of the main sources of animal fats.[1]
- Fresh red meats, such as beef and pork, particularly fattier cuts.
- White meats, such as chicken and turkey, which are lower in fat than the red meats except for the skin.
- Fatty fish, such as salmon and mackerel, which are also excellent sources of omega-3 polyunsaturated fatty acids.
- Dairy products, particularly long-aged cheeses.
- Eggs, particularly the yolk.
- Butter and lard.
In the Western diet, many fats come from plant sources and are often found in processed foods like ready-made meals and baked goods. Below are some examples of foods rich in plant-based lipids.[5]
- Vegetable oils, primarily olive oil, the cornerstone of the mediterranean diet, that is rich in monounsaturated fats, polyphenols and tocopherols. Other oils include sunflower, corn, and soybean oils, which are high in omega-6 polyunsaturated fatty acids, as well as coconut and palm oils, which are high in saturated fatty acids. All vegetable oils are composed entirely of lipids.
- Nuts and seeds, such as walnuts, almonds, hazelnuts, flax seeds, chia seeds, and sunflower seeds, high in unsaturated fats and omega-3 fats, although their omega-3 are less biologically valuable than those from fish.
- Peanut butter and other nut butters, such as almond butter and cashew butter.
- Avocado, the only fresh fruit to have a high fat content, mainly monounsaturated fats.
- Margarine
References
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- ^ a b Bechthold A., Boeing H., Schwedhelm C., Hoffmann G., Knüppel S., Iqbal K., De Henauw S., Michels N., Devleesschauwer B., Schlesinger S., Schwingshackl L. Food groups and risk of coronary heart disease, stroke and heart failure: A systematic review and dose-response meta-analysis of prospective studies. Crit Rev Food Sci Nutr 2019;59(7):1071-1090. doi:10.1080/10408398.2017.1392288
- ^ a b c Bender D.A. Benders’ Dictionary of Nutrition and Food Technology. 8th Edition. Woodhead Publishing. Oxford, 2006
- ^ Brown L., Rosner B., Willett W.W., Sacks F.M. Cholesterol-lowering effects of dietary fiber: a meta-analysis. Am J Clin Nutr 1999;69(1):30-42. doi:10.1093/ajcn/69.1.30
- ^ a b Chow C.K. Fatty acids in foods and their health implication. 3th Edition. 2008. doi:10.1201/9781420006902
- ^ a b EUFIC. Plant-based protein: all you need to know to get enough of it. Last updated: 05 January 2022
- ^ a b Garrett R.H., Grisham C.M. Biochemistry. 4th Edition. Brooks/Cole, Cengage Learning, 2010
- ^ a b Kiely L.J., Hickey R.M. Characterization and analysis of food-sourced carbohydrates. Methods Mol Biol 2022;2370:67-95. doi:1007/978-1-0716-1685-7_4
- ^ Marinangeli C.P.F., House J.D. Potential impact of the digestible indispensable amino acid score as a measure of protein quality on dietary regulations and health. Nutr Rev 2017;75(8):658-667. doi:1093/nutrit/nux025
- ^ a b Nelson D.L., Cox M.M. Lehninger. Principles of biochemistry. 6th Edition. H. Freeman and Company, 2012
- ^ a b c Raymond J.L., Morrow K. Krause and Mahan’s Food & the Nutrition Care Process. 15th Edition. Elsevier. April 27, 2020
- ^ a b c d Società Italiana di Nutrizione Umana-SINU. LARN – Livelli di assunzione di riferimento per la popolazione italiana. 2014
- ^ Soliman G.A. Dietary fiber, atherosclerosis, and cardiovascular disease. Nutrients 2019;11(5):1155. doi:3390/nu11051155
- ^ a b c Stipanuk M.H., Caudill M.A. Biochemical, physiological, and molecular aspects of human nutrition. 3rd Edition. Elsevier. 2012