12.2 Macro Nutrients
This section of the Nutrition chapter will focus on the macronutrients. As personal trainers, understanding the importance of macronutrients, which include carbohydrates, proteins, and fats, is crucial for guiding our clients toward their health and fitness goals. These essential nutrients are pivotal in determining energy levels, supporting recovery from exercise, influencing body composition, and impacting chronic disease progression.
Each energy system we discussed in Chapter 6 relies heavily on our dietary intake of macronutrients. This section will focus on the chemical composition and functions of carbohydrates, proteins, and fats, examining their roles in maintaining health and fueling physical activity. We will also explore how the body digests and utilizes these nutrients.
12.2.1 Macronutrient 1: Carbohydrates
Carbohydrates, composed of carbon, hydrogen, and oxygen molecules, have a 2:1 hydrogen to oxygen ratio and include sugars, starches, and fibers due to their similar structures. They are classified into three groups based on complexity: monosaccharides, oligosaccharides, and polysaccharides (based on the number of sugar units they contain).
Monosaccharides are the simplest form, containing one sugar group.
Oligosaccharides are short chains of monosaccharide units, such as disaccharides and trisaccharides. Common disaccharides include maltose, sucrose, and lactose (Higdon, 2018).
Maltose = glucose + glucose
Sucrose = glucose + fructose
Lactose = glucose + galactose
Polysaccharides are complex chains of linked monosaccharide units, either straight or branched, including starches, glycogen, and fiber. Plant cells form starches by connecting glucose monosaccharides, resulting in amylose and amylopectin. Amylose has α-1,4 glycosidic bonds, while amylopectin has α-1,6 bonds (Tiwari et al., 2016). Glycogen, similar to starch, is produced by animal cells through glycogenesis. Dietary fiber (cellulose) resembles amylose but has β-1,4 bonds, making it indigestible by humans (Slavin, 2013). Despite this, fiber is essential for digestive health.
Carbohydrate digestion, absorption, metabolism and transport
Carbohydrate digestion involves breaking down complex carbohydrates (oligo- and polysaccharides) into monosaccharides like glucose, fructose, and galactose, eventually released into the bloodstream as glucose. This process occurs throughout the gastrointestinal tract, starting when we consume carbohydrate-rich food. Sensitivity to food cues, particularly sweet or starchy foods, can initiate the cephalic phase of digestion even before the food enters our mouth, causing us to salivate in anticipation.
- The mouth and upper GI tract
When taking a carbohydrate bite, salivary amylases help hydrolyze polysaccharides into smaller carbohydrate chains. The efficiency of salivary amylase depends on the time food spends in the mouth; the less we chew, the faster we swallow, and the less time salivary amylase has to work on the food.
- The small intestine
In the small intestine, pancreatic amylases break down smaller carbohydrate chains into maltose disaccharides. The enzyme maltase then digests each maltose into two glucose units. Starch digestion ultimately yields glucose monosaccharides. Lactose and sucrose disaccharides are hydrolyzed by lactase and sucrase enzymes, producing glucose and galactose monosaccharides (lactose) and glucose and fructose monosaccharides (sucrose). Monosaccharides enter the body through mucosal cells lining the intestine and are transported to the liver via the portal vein.
- The liver
The liver utilizes glucose for energy transfer and glycogen storage, then releases the remaining glucose monosaccharides into circulation. Galactose and fructose are primarily converted to glucose by the liver, although high fructose intakes may lead to triglyceride conversion (Tappy & Lê, 2010). Fructose is a primary energy source and carbohydrate for liver glycogen replenishment (Jentjens & Jeukendrup, 2003). Once the liver processes glucose, cells release it into circulation and take it up.
- The bloodstream
Approximately 20 grams of glucose circulate in the bloodstream every hour, and the body strives to maintain this level (Hall et al., 2016). If blood sugar drops, the body uses new glucose to maintain blood glucose levels and provide immediate energy. Excess glucose is taken up by the liver and muscles for glycogen storage, with the liver storing 80-100 grams and the muscles storing 300-600 grams. Additional glucose can be converted into body fat.
- Transport and Metabolism
Cells acquire glucose from the bloodstream through facilitated diffusion, with transport proteins capturing glucose molecules and transporting them into the cells. In muscle and fat tissue, insulin primarily stimulates glucose uptake, while muscle contractions can also increase uptake without insulin. Different GLUT transporters facilitate glucose uptake, some being insulin-dependent and others not.
As mentioned in Chapter 6 on energy systems, glycolysis converts glucose into pyruvate, directly forming ATP and providing substrate for the Krebs cycle and electron transport chain. This process allows all macronutrients to be converted to compounds that enter the Krebs cycle, ultimately driving ATP resynthesis for cellular work.
Glucose is vital for the brain and central nervous system. While the body can produce glucose through gluconeogenesis and ketones, a minimum of 130g daily carbohydrate intake is recommended to meet basic energy needs. However, individual factors such as body size, activity levels, and specific goals may alter this recommendation, and the minimum daily intake can be lower (some suggest even 0 if provided that adequate amounts of protein and fat are consumed) (Institute of Medicine, 2005).
Carbohydrate digestion and absorption rates can influence body composition and health.
The glycemic index
The glycemic index (GI) measures how quickly and significantly a specific food raises blood sugar levels (Jenkins et al., 1981). The GI is determined relative to a reference food, typically 50 grams of carbohydrates from table sugar, assigned a GI value of 100. Then, each food’s GI score is calculated relative to this value.
High glycemic foods can rapidly elevate blood sugar levels, leading to significant spikes in blood sugar and insulin concentrations (Ludwig, 2002). Conversely, lower glycemic index foods, like legumes, nuts, and vegetables, do not cause such dramatic increases, making them preferred for better health and performance.
However, the glycemic index (GI) has limitations, as it becomes less meaningful when consumed as part of mixed meals (Augustin et al., 2015). To address these shortcomings, researchers use glycemic load, considering both GI and serving size (Foster-Powell et al., 2002). Neither GI nor glycemic load are ideal predictors of insulin response to a meal. The insulin index (II) measures the amount of insulin the body produces in response to a specific food. The II is not always proportional to the GI and can vary based on individual factors and food composition.
The GI values can be broken down into three ranges. Food with a low GI is a food that won’t raise your blood sugar as much as a food with a medium or high GI:
Low GI: 55 or less
Medium GI: 56 to 69
High GI: 70 to 100
The following charts highlight low, medium, and high GI foods based on data from Verywellhealth (2023):
Which carbs to eat?
According to Berardi (2013), slow-digesting carbohydrates are crucial for daily consumption as they help control blood sugar, insulin concentrations, energy levels, and body composition. It is recommended to consume a diet rich in unprocessed carbohydrates, which are typically low on the glycemic index (GI) and insulin index (II) scales, as they offer numerous benefits, such as increased micronutrient intake, greater fiber intake, enhanced satiety, a higher thermic effect of feeding, and better blood sugar control (Brand-Miller et al., 2009; Slavin, 2005).
However, during or after exercise, when insulin sensitivity is high, liver and muscle glucose uptake are rapid, and carbohydrate resynthesis is prioritized, rapidly digesting carbohydrates may be beneficial (Ivy, 1998). Processed, rapidly digested, high GI and II carbohydrates may be considered for post-intense exercise sessions to replenish carbohydrate stores in the body.
Dietary fiber
Fiber is a compound found exclusively in plants such as grains, oats, fruits, and vegetables; it is absent in animal foods like meats.
The type of fiber we consume is called dietary fiber, which is composed mainly of indigestible complex carbohydrates (polysaccharides) that make up plant cell walls. These carbohydrates include cellulose, hemicellulose, pectin, gums, mucilages, and algal polysaccharides. While fibers do not provide energy, they play a vital role in the diet as the primary contributor to the dietary fiber (roughage) content.
Dietary fiber has several protective qualities, including promoting efficient intestinal function and the regulation of even absorption of sugars into the bloodstream. It can be classified into two forms: soluble and insoluble. Soluble fiber dissolves in water and forms a gel-like substance that can help lower cholesterol levels, whereas insoluble fiber promotes bowel regularity and prevents constipation (Slavin, 2013).
It is important to note that dietary fiber, present in many unprocessed, slow-digesting carbohydrate foods, comes in soluble and insoluble forms, both of which are indigestible and play essential roles in gut health, satiety, blood fat, and cholesterol regulation and reduced risk of colon cancer (Anderson et al., 2009). The optimal daily fiber intake is around 35 grams for women and 48 grams for men (Institute of Medicine, 2005).
Despite its numerous health benefits, the average American consumes only 12 grams of fiber daily (Slavin, 2013), while the average intake of dietary fiber in European adults ranges from 15 to 30 grams daily (Kranz et al., 2018). One easy way to increase fiber intake is by adding three choices from Table below, each providing 10 grams of fiber.
Fiber is an essential component of a healthy diet, critical for our digestive system’s health and reducing cholesterol levels. The total amount of dietary carbohydrates needed varies based on activity levels and body size and should be inversely proportional to dietary fat intake.
Resistant starch
Additionally, resistant starch, which is not fully broken down and absorbed but instead turned into short-chain fatty acids by intestinal bacteria, may offer unique health benefits. An ideal daily intake of resistant starch is around 20 grams, easily obtained from whole plant foods like unprocessed grains, fruits, vegetables, and legumes.
12.2.2 Macronutrient 2: Proteins
Proteins are an organic compound that consist of carbon, hydrogen, oxygen, and nitrogen atoms arranged in specific ways. Unlike carbohydrates and fats, proteins contain nitrogen in their amino groups. The building blocks of proteins are amino acids, which are characterized by four main characteristics:
* an amino group (NH) on one end;
* a carboxyl group (COOH) on the other end;
* a central carbon (called the alpha, a carbon); and
* a side chain (R group), which differentiates one amino acid from another.
When amino acids link together, they form peptide bonds, forming peptides or polypeptide chains that make up the primary structure of proteins.
Amino acids are classified as essential, conditionally-essential, and nonessential. Essential amino acids cannot be synthesized in the body in sufficient amounts to meet the body’s demands and, therefore, must be obtained from food. Conditionally-essential amino acids cannot be produced adequately during periods of illness, injury, or extreme emotional stress. Nonessential amino acids can be synthesized by the human body in sufficient amounts and are not required in the diet.
Proteins are not just linear chains of amino acids; they fold and twist into complex three-dimensional structures, forming secondary, tertiary, and quaternary structures. Secondary structures are formed as amino acids bond with their neighbors and other amino acids further down the chain, creating either α-helix or β-pleated sheet structures. These secondary structures provide strength and rigidity to the protein. Many enzymes, transport proteins, and immunoproteins in the body possess tertiary structures, which are formed when the protein folds in secondary structure formation to create globular shapes. When one or more proteins in a tertiary structure join, it results in quaternary structures. Each protein is treated as a separate sub-unit, but the entire protein, including this new shape, is necessary for optimal function within the body (Murray et al., 2018).
Most dietary proteins are complex structures originating from plant and animal tissues, and their digestion leads to the formation of small peptides and amino acids. Protein quality is evaluated based on the content of essential amino acids and their bioavailability rather than the structural formations (Gropper et al., 2018). The primary structure, or the unique sequence of amino acids, is most important for protein quality evaluation. With adequate amino acids and energy intake in the diet, the body can form all the proteins necessary for optimal physiological functioning, complete with their appropriate secondary, tertiary, and quaternary structures (Rennie et al., 2004).
Protein digestion, absorption, metabolism, and transport
- The stomach
Protein digestion involves the breakdown of proteins into small peptides and individual amino acids. This process begins in the stomach’s acidic environment, where gastric hydrochloric acid denatures the ingested proteins’ secondary, tertiary, and quaternary structures. However, the peptide bonds between amino acids are unaffected by hydrochloric acids, so hydrochloric acid also begins the activation of pepsinogen to pepsin at the same time. Pepsin begins to break down peptide bonds, primarily removing amino acids from the carboxyl end of the peptide chain. The remaining polypeptides and single amino acids are passed along to the small intestine.
- The small intestine
In the small intestine, proenzymes or zymogens secreted by the pancreas now enter the picture. These chemicals include trypsinogen, chymotrypsinogen, procarboxypeptidases, proelastase, and collagenase.
Normally inactive, these proenzymes must be activated (by other enzymes and chemicals also released into the small intestine) to form the enzymes necessary for further peptide digestion. As digestion proceeds, small di- and tri-peptides and free amino acids are produced. While still in the small intestine, these amino acids and peptides are transported across the intestinal brush border for absorption (Murray et al., 2018). Multiple energy-dependent transport systems with overlapping specificity exist to aid in absorption. In other words, different amino acids and peptides are absorbed in different ways requiring ATP.
Interestingly, amino acids compete for transport by common carriers in the small intestine. As a result, branched-chain amino acids (BCAAs) are absorbed faster than smaller amino acids. As di- and tri-peptides use different carriers than individual amino acids, these peptides are absorbed more quickly than free-form amino acids. This is important to note since large dietary intakes of free amino acids (usually in supplement form) may lead to “congestion” at the transport level, delaying entry into the bloodstream (Gropper et al., 2018). Once absorbed, these amino acids and peptides can experience one of a few fates. First, some of these amino acids can be used in the intestinal cells for energy or to synthesize new proteins such as hormones, new digestive enzymes, etc. For example, the amino acid glutamine is used as a primary source of energy in intestinal cells.
Further, glutamine appears to stimulate gastrointestinal cell growth. Therefore, some ingested glutamine is used at the intestinal cell level. If glutamine is deficient in the diet, glutamine will be exported from the plasma amino acid pool and muscle cells to provide raw materials for intestinal glutamine needs. Beyond their use in intestinal cells, ingested amino acids and peptides can also be delivered to the liver (via hepatic portal circulation) for processing and distribution to other body cells.
- The liver
The liver is the primary site for amino acid uptake after a meal. For every 100 g of amino acids taken in, about 20 g will be released into the systemic circulation, 20 g will be used for protein synthesis in the liver, and the remaining 60 g will be catabolized in the liver. The amino group is removed for the production of energy, glucose, ketone bodies, cholesterol, or fatty acids (this being determined by the specific amino acid that was broken down, nutritional status in the body, and physical state of the body).
Of the 20 g of protein synthesized, 14 g of this protein will remain in the liver, and 6g will be released into systemic circulation for use by other tissues throughout the body. Once absorbed, amino acids and peptides can be used for energy, synthesize new proteins, or be delivered to the liver for processing and distribution to other body cells. The liver is the primary site for amino acid uptake after a meal. About 20% of the amino acids taken in are released into the systemic circulation, 20% are used for protein synthesis in the liver, and the remaining 60% are catabolized in the liver for the production of energy, glucose, ketone bodies, cholesterol, or fatty acids (Gropper et al., 2018). Additionally, the breakdown of amino acids in the liver produces necessary nitrogen-containing chemicals, such as urea, which is excreted in urine to prevent toxic buildup in the body (Murray et al., 2018). The synthesis and catabolism of amino acids in the liver play a vital role in maintaining nitrogen balance and ensuring the proper functioning of various bodily processes.
In the liver, the amino group is first removed from catabolized amino acids, and the remaining carbon skeleton is used to produce energy, glucose, ketone bodies, cholesterol, or fatty acids. The usage depends on the specific amino acid, nutritional status, and other physical demands on the body. Transamination can occur if other amino acids need to be formed. After deamination and transamination, ammonia is produced, which is used for urea synthesis and excretion.
Approximately 14 g of the 20 g of amino acids that enter the bloodstream from the liver are branched-chain amino acids (BCAAs). These BCAAs contribute to the plasma amino acid pool, which exchanges with amino acids and proteins in cells. The pool, totaling around 100 grams in the plasma, is replenished from dietary amino acid absorption and the breakdown of body tissues (Gropper et al., 2018).
After a meal, blood amino acid levels, especially BCAAs, increase. The rate of increase depends on the digestion speed of the protein consumed. Slower-digesting proteins (meat, casein) release amino acids gradually, while faster-digesting proteins (eggs, whey) release them quickly. These rates can be compared to the glycemic index, with slower-digesting proteins resembling low GI carbohydrates and faster-digesting proteins resembling high GI carbohydrates (Murray et al., 2018).
Amino acids extracted from plasma by tissues are used for various functions, including muscle protein synthesis, neurotransmitter synthesis, and tissue enzyme synthesis. The eventual production of new proteins is regulated by genetic signaling and is dependent on amino acids and energy availability in the body (Phillips, 2014). Additionally, amino acids can be used for intra-organ nitrogen and carbon transfer. For example, during amino acid metabolism, ammonia released is bound to glutamate to form glutamine, which then shuttles ammonia to other tissues for incorporation into body tissues or excretion. During exercise, alanine is released from muscle and transported to the liver. The carbon skeleton is converted to glucose, and the nitrogen group is removed for incorporation into other amino acids or excretion (Brosnan & Brosnan, 2006).
Protein in diet
Amino acids, the building blocks of proteins, are crucial for various bodily functions, including structure, hormones, enzymes, immune chemicals, and transport proteins. Essential amino acids, which the body cannot produce, must be obtained through a protein-rich diet (Gropper et al., 2018). Inadequate daily amino acid intake can lead to a net negative protein balance, making maintaining a consistent amino acid pool challenging without dietary intervention.
The body can produce 12 non-essential amino acids, while the diet must supply eight essential amino acids. To maintain an adequate intake of essential amino acids, consuming protein sources that provide the necessary amino acids for optimal functioning (Murray et al., 2018).
Several protein quality indexes measure a protein’s ability to supply essential amino acids, including Protein Efficiency Ratio (PER), Biological Value (BV), Net Protein Utilization (NPU), and Protein Digestibility Corrected Amino Acid Score (PDCAAS). Most of these methods, except PDCAAS, rely on rodent studies to determine protein quality. However, rats have different amino acid requirements than humans, so we recommend using PDCAAS for regulatory purposes. Still, different individuals and companies use various standards, so each method should be considered cautiously when applying rodent data to humans.
PDCAAS, the current "gold standard" for protein quality, is based on human amino acid requirements. It considers limiting amino acids and calculates protein quality by comparing the amount of the limiting amino acid in the test protein to a high-quality reference protein.
Animal proteins such as meat, poultry, eggs, fish, milk, and cheese rank highest in protein measures, while plant proteins rank lower (Berardi et al., 2017). Although many plant foods contain all essential amino acids, their proportions vary. Plant-based eaters should maintain a varied intake and consider complementary protein choices (Young & Pellett, 1994). Legumes, for example, are rich in lysine, which is often limited in plant-based diets (Messina, 2014).
To prevent protein deficiency, sedentary adults should consume a minimum of 0.8 g of protein per kg of body mass (World Health Organization, 2007). However, during high-intensity training or low energy or carbohydrate intake periods, protein requirements may increase to 1.4-2.0 g/kg (Phillips & Van Loon, 2011). Higher protein intakes may also benefit immune function, metabolism, satiety, weight management, and performance (Westerterp-Plantenga et al., 2012). Additionally, higher protein intake has been shown to promote muscle hypertrophy and strength gains, particularly in resistance-trained individuals (Schoenfeld et al., 2018).
Concerns about the safety of higher protein intakes have been largely debunked, and within reason, they appear to have no negative consequences (Devries & Phillips, 2015). Protein and amino acid supplements can be used when whole-food protein intake is limited, but real food options are often preferred due to their more complete micronutrient profile (Thomas et al., 2016).
Whey Protein and Anabolism
Whey was once a by-product that dairy farmers discarded. However, whey has been the number-one protein of choice for the last decade. Whey is vital for any athlete attempting to enhance their strength. To understand whey’s importance, turn to the Biological Value Scale, developed to measure specific proteins’ quality. It rates just how efficiently the body uses a specific protein source. The higher the biological value, the more amino acids, and nitrogen the body retains from the food a person eats – this translates into the potential for quality muscle growth and strength. Egg whites used to be at the top of the biological chain, with a rated score of 100—whey rates at 106 to 159. More nitrogen is retained in the body with whey and enters the bloodstream much faster than other sources. Thus, the body can receive nutrients as fast as possible after strenuous training for a full recovery and growth potential. Immediately following a workout, your muscles need valuable amino acids to increase anabolism and prevent muscle breakdown.
Although it is beneficial to consume whey protein after a workout because of the temporal restoration of contractile function, the effects are only small to medium.
Whey protein is also high in branched-chain amino acids as well as glutamine. Whey is known as an anabolic protein since it increases protein synthesis with greater efficiency than other sources. There are three types of whey proteins: whey concentrate, whey isolate, and whey hydrolysate. The concentrate is between 50% and 80% proteins. The isolated version separates whey from lactose, ash, fats, and carbohydrates so that you receive 90% to 97% protein. The best types are either ion exchange or cross-flow micro-filtered whey isolate. The isolate is the most expensive, but you get more protein per gram of powder. The hydrolysate is partially digested and broken down into di- and tri-peptides before it hits your stomach. It will then enter the bloodstream quickly.
Tang et al. (2009) conducted a seminal study comparing the effects of three different protein sources (hydrolyzed whey isolate, micellar casein, and soy isolate) on acute changes in muscle protein synthesis at rest and after a single bout of resistance exercise. The authors found that all three protein sources significantly increased muscle protein synthesis rates at rest and following resistance exercise.
Extending these findings, multiple studies have reported the ability of different forms of protein to significantly increase fat-free mass during resistance training. Cermak et al. (2012) performed a meta-analysis of 22 published studies involving 680 participants, examining the impact of protein supplementation on changes in strength and fat-free mass. They concluded that protein supplementation positively affected fat-free mass and lower-body strength in both younger and older participants.
Similarly, Morton et al. (2018) published a meta-analysis, including a meta-regression approach, with data from 49 studies and 1863 participants. They found that protein’s ability to positively impact fat-free mass accretion increases up to approximately 1.62 g of protein per kilogram of body weight per day, with higher amounts beyond that not appearing to promote more significant gains in fat-free mass.
Although more research is needed in this area, the evidence indicates that the protein needs of individuals engaged in intense training are elevated—athletes who achieve higher protein intakes. In contrast, training may promote greater changes in fat-free mass.
A balanced essential amino acid (EAA) blend combined with whey protein is more anabolic than a whey protein-based recovery product alone, with the anabolic response being dose-dependent .
Adding leucine to whey protein does not result in a more significant anabolic response in muscle compared to whey protein alone in healthy young volunteers.
12.2.3 Macronutrient 3: Fats
Fats are organic molecules consisting of carbon and hydrogen elements connected in extended chains known as hydrocarbons. The organization of these hydrocarbon chains and their interactions define the type of fat.
Fatty acids, the simplest units of fat comparable to monosaccharides in carbohydrates, are composed of basic hydrocarbon chains with distinct chemical groups at each end—a methyl group (CH) on one end and a carboxylic acid group (COOH) on the other.
There are two primary types of fatty acids based on their level of saturation (the number of hydrogens linked to each carbon along the hydrocarbon chain): saturated fatty acids and unsaturated fatty acids. Unsaturated fatty acids can be further classified into monounsaturated fatty acids (with only one unsaturated carbon) and polyunsaturated fatty acids (with multiple unsaturated carbons). The widely-discussed omega-3 and omega-6 fats are both polyunsaturated fatty acids, and their names and functions are determined by the specific locations of unsaturated carbons along the fatty acid chain.
Fatty acids can combine (similar to how monosaccharides join to form oligo- and polysaccharides) to create triglycerides. As the name suggests, a triglyceride is formed when three (“tri”) fatty acids attach to a glycerol molecule. Triglycerides are the primary form of fat found in the diet and the major storage form of fat in the body.
Fat digestion, absorption, metabolism and transport
The digestion of fat in the body involves breaking down triglycerides into fatty acids and glycerol, which are then repackaged before entering the bloodstream (Gropper et al., 2009). This primarily occurs in the small intestine, where bile emulsifies dietary triglycerides into smaller droplets, making them more accessible to digestive enzymes. Pancreatic lipase is the primary enzyme responsible for triglyceride digestion, breaking them down into fatty acids and glycerol.
Once broken down, fatty acids can cross the intestinal mucosa and be repackaged into lipoprotein particles called chylomicrons. These particles are released into the lymphatic system and eventually enter general circulation. Due to this extensive breakdown and transport process, absorbed fat enters the blood several hours after consumption.
Chylomicrons are broken down into free fatty acids and glycerol by lipoprotein lipase in the blood. These components can then pass through cell membranes and enter various tissues in the body, which can be oxidized for energy transfer or converted back into triglycerides for storage.
When fatty acids are needed for energy transfer, they undergo beta-oxidation to form acetyl-CoA, which enters the mitochondrion for the Krebs cycle. This process ultimately leads to the resynthesis of ATP, which can be used for cellular work.
Fat in the diet
Dietary fat plays six significant roles in the body (Gropper et al., 2009; Simopoulos, 2002):
* It provides an energy source (being the most energy-dense macronutrient);
* It helps manufacture and balance hormones;
* It forms cell membranes;
* It constitutes our brains and nervous systems;
* It helps transport fat-soluble vitamins A, D, E, and K; and
* It supplies two essential fatty acids the body cannot produce linoleic acid (an omega-6 fatty acid) and linolenic acid (an omega-3 fatty acid).
As previously mentioned, most dietary fat comes from triglycerides, consisting of three fatty acids connected to one glycerol backbone. Different fatty acids can join to create various permutations of triglycerides. Thus, most dietary fat sources combine saturated, polyunsaturated, and monounsaturated fatty acids For instance, while eggs and red meat are often perceived as saturated fat-rich foods, eggs contain more monounsaturated fatty acids than saturated ones. 39% of the fat in eggs is saturated, 43% is monounsaturated, and 18% is polyunsaturated. Beef contains 55% saturated fat, 40% monounsaturated fat, and 4% polyunsaturated fat.
A food’s predominant type of fatty acid affects its chemical properties, such as texture. Foods with a higher proportion of saturated fatty acids tend to be solid at room temperature, while those with more unsaturated fatty acids are typically softer or liquid. The balance of fatty acids consumed influences overall health.
Maki (2021) discusses the potential link between high saturated fatty acid (SFA) intake and atherosclerotic cardiovascular disease (ASCVD) risk. The evidence suggests that replacing SFA with unsaturated fatty acids may reduce ASCVD risk. The author recommends limiting SFA intake to <10% of total daily energy for the general healthy population and even lower for patients with hypercholesterolemia. Higher SFA intakes might affect inflammation, cardiac rhythm, hemostasis, apolipoprotein CIII production, and high-density lipoprotein function.
Excessive intakes of these saturated fats, when not balanced with unsaturated fats, have also been linked to Alzheimer’s disease, poor blood viscosity, breast cancer, kidney disease, diabetes, multiple sclerosis, stroke, and prostate cancer. These acids can be found in beef, coconut, palm kernel, butter, cheese, milk, and palm oil.
However, not all saturated fats have these associations with chronic diseases. For example, stearic acid (another saturated fat found in cocoa butter and beef) may lower LDL levels. Therefore, saturated fat should not be universally considered unhealthy.
Problems with saturated fat intake may only arise when combined with other poor dietary choices, such as high sugar and processed/refined carbohydrate intake or imbalanced unsaturated fat intake. Therefore, recommendations to avoid saturated fats are misguided, as they can be healthy when refined carbohydrate intake is low and unsaturated fat intake is balanced.
Omega 3, Omega 6
Saturated and unsaturated fats have different chemical bond structures, with unsaturated fats, including omega-3 and omega-6, being considered “healthy fats” due to their benefits for blood triglycerides, cholesterol, inflammation, and metabolism. However, it is crucial to maintain a balanced omega-6 to omega-3 ratio, which has become highly disproportionate in modern diets. A healthy balance involves using fewer omega-6-rich vegetable oils and more omega-3-rich foods.
Omega-6 and omega-3 fats have essential bodily functions, but problems occur when the mechanisms are imbalanced. Omega-3 fats, like ALA, DHA, and EPA, play critical roles in cellular health, cardiovascular function, nervous system function, and immune health. They also contribute to forming certain eicosanoids, which have opposing actions to omega-6 fats, demonstrating the importance of maintaining a balance between the two.
Trans-fats
Trans fats, often discussed in the media, have different chemical configurations than naturally occurring unsaturated fats. Most trans fats in our diet result from industrial fat processing, where unsaturated fats are hydrogenated, causing them to harden at room temperature. This process improves taste, shelf life, and “mouth feel” but negatively impacts health.
Trans fats pack tightly into our cell membranes and can distort the cell membranes, thus leading to increased risks of coronary heart disease, cancer, and other chronic diseases. Trans-fat (T-fat) consumption has been linked to various health risks, with coronary heart disease being the primary concern. Additionally, T-fats negatively impact brain function and the nervous system. When T-fats are integrated into brain cell membranes, they disrupt neuronal communication, reducing mental performance. Studies have also found a connection between T-fat intake and increased depression risk. Furthermore, emerging evidence suggests that T-fats may play a role in Alzheimer’s disease development and age-related cognitive decline (Ginter, 2016).
In conclusion, it is vital to maintain a balanced intake of saturated, monounsaturated, and polyunsaturated fats, including a balance between omega-3 and omega-6 fats, for optimal health. In addition, dietary fat and carbohydrate intake should be inversely proportional, meaning when fat intake is high, carbohydrate intake should be lower, and vice versa.