- Know the importance of lipids and fat intake for human function
- Define the characteristics of fat
- Understand the different characteristics of fats
- Be able to make fat intake recommendations for clients
This post reviews the role of fat in the diet of athletes and active persons and the ways in which fat is metabolized as an energy source during exercise. First, we discuss the function, classification, and dietary sources of fat, including the use of fat-modified foods. This is followed by discussion of the amount of fat typically consumed by all Americans and by active individuals.
The NESTA Sports Nutrition Specialist course is designed for personal fitness trainers, strength coaches and nutrition experts who want to learn cutting-edge techniques for increasing sports performance, reducing recovery time, and enhancing the overall well-being of your clients and athletes.
Next, we review fat metabolism during exercise and describe products and practices used to enhance fat oxidation during exercise. Finally, we provide dietary fat recommendations for active people.
As health professionals, we know there is a lot of misunderstanding about fat as a macronutrient. Like carbohydrates, fats have been scorned for decades as the culprit behind pandemic obesity. But once fat is more clearly understood, it becomes easier to sort through some of the myths and fallacies.
Fat is something that trainers and coaches can easily analyze, assess, and identify within their client’s personal food intake or diet, since there is usually more than enough of it consumed each day. Therefore we may suspect that our clients know very well when they are consuming a high-fat meal but they either haven’t learned to control intake properly, they may not understand the need for consuming certain fats and/or the consequences of imbalance. Obesity and high blood pressure are also impacted by the excessive intake of certain fats. Even though there is no cause/effect relationship proven between high blood pressure and obesity, the two are often seen together.
Because performance and health are both affected by the type of fat consumed, it is important to know more about the quality of this energy-dense macronutrient. In addition to protein, fat is also an essential macronutrient in that the body does not synthesize all types needed for physiological function, and these fats are taken in through food.
Fats or fatty acids, all have a similar structure – a carbon backbone with hydrogen atoms arranged in varied concentrations along the carbon chain. Based on the amount of hydrogen atoms attached, we rank fats as saturated, monounsaturated and polyunsaturated.
Saturated fats – these carbon chains or backbones are full, and cannot take any more hydrogen atoms since they will not fit. This type of fat is solid at room temperature.
Monounsaturated fats are called such because there is one slot along the carbon backbone or chain that can accommodate a hydrogen molecule. This type of fat is liquid at room temperature (olive oil, canola oil).
Polyunsaturated fats have several open slots along the carbon chain and are also liquid at room temperature. This group includes flax seed oil and fish oils (omega group).
Trans fats are more problematic. The process of hydrogenating food creates trans fat. During this process, an unsaturated fat item is “super whipped” with hydrogen atoms; these atoms then bind to the carbon backbone or chain to change the properties of the molecular structure, making the fat solid at room temperature instead of its former state, liquid.
Food labels are changing regarding disclosure of trans fats. Until recently, amounts under a certain threshold allowed the label to state that the food item was “trans fat free,” when there were hydrogenated items listed on the ingredients list. Coach your client to learn and then look for the word hydrogenated on food labels and to avoid trans fats completely. Even in small amounts, this type of fat is correlated with negative effects on LDL cholesterol, elevated triglycerides and insulin levels.
Trans fats are found everywhere! The following is based on current U.S. FDA data:*
51% in baked goods (breads, cakes, cookies, crackers, pies)
22% in margarines
10% in fried potatoes
6% in potato chips, corn chips
5% in shortening
4% in salad dressing
1% in breakfast cereals
The body can only obtain omega-3 and omega-6 polyunsaturated fatty acids through the diet. Because of their role as precursors of other fatty ac- ids that the body cannot synthesize, they have been termed essential fatty acids. About 1 to 2% of the total energy intake should come from linoleic acid. For an average 2,500-kcal per day intake, this is about one tablespoon of plant based oil per day. Foods such as mayonnaise, cooking oils and salad dressings, whole grains, vegetables, and other foods readily provide this amount for us. Fatty fish such as salmon, tuna, and sardines provide the best sources of alpha-linolenic acid or its related omega-3 fatty acids, eicosapentaenoic acid (EPA), and docosahexaeonoic acid (DHA) (2).
Research shows that regular aerobic exercise impacts the client’s ability to oxidize long-chain fatty acids and there is an increase in fat catabolism during submaximal exercise following aerobic training bouts. This is paired with a decrease in the amount of carbohydrates broken down. However, even for endurance athletes, the improved capacity for fat oxidation cannot sustain the level of aerobic metabolism generated when oxidizing glycogen for energy. As a result, well-nourished endurance athletes rely almost totally on oxidation of stored glycogen in near-maximal, sustained aerobic effort
Fat intake should comprise no more than 35% of total calories. Within that 35%, approximately one-third come from each of the different types of fat (saturated, monounsaturated, and polyunsaturated). If an individual needs to decrease fat intake, this decrease should come primarily from saturated fat foods.
Fish oil supplementation has been shown to be effective with regards to a variety of health markers (e.g., lowering lipid levels, decreasing the risk of cardiovascular disease, enhancing recovery, etc.) without the risks associated with consuming fish potentially high in mercury. Some medications and other contraindications could offset the practical advice or suggestion to use fish oil, so this is an example of the need to know your client and to know about fat supplements. As with all macronutrients, it is best to consume the majority of omega-3 fats from whole foods.
There is a greater use of fat when exercising at lower intensities because of the availability of oxygen. However, due to the lower intensity overall, fewer total calories are burned. Therefore, although the percentage of fat use is higher, the higher percentage is from a lower total calorie usage and the ratio does not change.
To use an example, say you exercise for one hour at a lower intensity. During that 60 minutes, you burn 300 calories. From those 300 calories, let’s say that 60% comes from fat as a fuel source and the remaining 40% is from carbohydrates. In this example, 180 calories have come from fat usage and approximately 120 calories have come from carbohydrate.
If your intensity increased, and you exercised at a higher intensity for a shorter duration, you would have a change in the fuel used. The body’s systems would tap into stored glucose from carbohydrate as the primary fuel used. Consider a 45-minute bout of PA, incorporating higher-intensity exercise, where 400 calories are burned. Then, 240 calories would come from carbohydrate sources and 160 calories would come from fat fuel sources.
We are always burning a combination of carbohydrate, fat, and protein when we exercise, albeit at different rates. It is the many variables, including exercise intensity and duration, state of conditioning, and dietary intake, to name a few, that influence where the body sources its fuel.
The body uses what is needed and available. If a high-fat meal is consumed, for example, there is more fat in the GI tube and therefore, more fat is metabolized. This doesn’t mean that we burn more body fat; sourcing energy from dietary fat is not the same energy pathway used when fuel from stored body fat is sourced – the requirement of need makes it different.
Likewise, if a high-carbohydrate meal is consumed, carbohydrate provides more fuel during a bout of PA. Since the amount of glycogen stored in muscles is limited, the stores of glycogen are depleted somewhat after an overnight fast and if an exercise bout is undertaken in the morning after a night’s rest, then the fuel supply will more likely come from fatty acids.
The key with any successful fitness nutrition plan is to achieve an overall energy deficit. Therefore, the actual fuel source becomes less important than the overall deficit created. A small intake of food before a workout in this scenario would provide additional energy during the time when it is needed most. But instead of focusing on the fuel used during exercise, focus on the type of fuel consumed after exercise. If the main goal is to lose body fat, this awareness is both useful and effective for the client.
Although many people think of dietary fat as something to be avoided, fat is important for athletic performance and good health. Fat and carbohydrate are the primary fuels used by the body during exercise. The two fuels are oxidized simultaneously, with the proportion of energy coming from each substrate dependent on the meal prior to exercise; energy fed during exercise; the duration, intensity, and type of exercise; and fitness level. Fat becomes the primary fuel source during endurance exercise events since the body’s supply of carbohydrate in the form of glycogen and blood glucose is limited. Although diets high in carbohydrate are necessary to help replenish muscle glycogen levels after exercise, fat should not be eliminated from the diet.
Research has helped us identify the best mix of dietary carbohydrate, fat, and protein for optimal exercise performance and good health. This mix may change depending on individuals’ personal food preferences and fitness levels, the sports they participate in, and their general health status—yet all macronutrients are important in the diet.
For active people of all levels, it appears prudent to consume a diet primarily from unprocessed carbohydrates, but also to include adequate amounts of protein and healthy fat. The 2005 Institute of Medicine (IOM) Dietary Reference Intakes for the United States and Canada encourage everyone to eat diets providing between 20 and 35% of energy from fat. Because of the role carbohydrate plays in replenishing glycogen, athletes should consume less fat and more carbohydrate than sedentary individuals. Endurance athletes in training are often encouraged to eat moderate- to low-fat diets (20-25% of energy from fat), while athletes trying to lose weight (body fat) may be also be encouraged to obtain 20 to 25% of kilocalories from fat. But less is not always better. Low-fat foods are not always more nutritious. Ultra-low-fat diets (<15% of energy from fat) may not provide additional health or performance benefits over a moderate-fat diet and are usually very difficult to follow.
Fat plays an important role in the diet of the physically active individual. It is a primary source of energy at rest and during exercise. It is twice as energy-dense as carbohydrate or protein, providing 9 kcal/g while carbohydrate and protein provide only 4 kcal/g. This means that 1 tbsp of butter or oil contains ~100 kcal, while it takes four cups of chopped broccoli or one-plus slices of whole wheat bread to provide 100 kcal from foods consisting primarily of carbohydrate. Fat also provides the essential fatty acids and fat-soluble vitamins (vitamins A, D, E, and K) our bodies need (see “Essential Fatty Acids”). The essential fatty acids (linoleic and a-linolenic acid) are the precursors for many regulatory compounds within the body, while fat-soluble vitamins are required for many essential metabolic processes. Fats are a part of the structural component of cell membranes and part of brain and spinal cord tissue. They help keep the skin and other tissues soft and pliable. The body uses fat to store extra energy, which can be used to provide fuel to the working muscles. Fat stored as adipose tissue pads the body and protects the organs. Adipose tissue is also an efficient way to store extra energy in a small space. If all extra energy were stored as carbohydrate (stored glycogen), our bodies would be twice as large as they are. Finally, we can’t ignore the role that fat plays in food preparation—fat tastes good! It makes our foods more palatable by adding texture and flavor. In summary, dietary fat is important for good health and for providing energy to the working muscles. Fat should not be eliminated from the diet; instead, healthy fats should be used in moderation.
Fats or lipids are substances that are generally insoluble in water, but soluble in organic solvents (acetone or ether), and are very rich in methyl or methylene groups. Because they do not mix well with water, the way they are digested, absorbed, and transported in our bodies (as compared with protein and carbohydrate) is altered.
Dietary fats can be classified (don’t confuse this with “categories of fat”) in a number of ways – by their structure or chain length (number of carbons in each fatty acid), by their level of saturation (number of hydrogen atoms attached to each carbon atom), by their shape, or by the commercial processing that the fat has undergone. Chain length is important because it helps determine the method of digestion and absorption, the properties of the lipid, and its function within the body.
The degree of fatty acid saturation also can determine its functions within the body, the effect on health, and even its use within food products. The shape of a fatty acid can alter its characteristics and thus its function within the body: A fatty acid that has a trans configuration or shape will function differently from the same fatty acid with a cis configuration. For example, a trans fatty acid may have a negative effect on blood lipids, while the same fatty acid in the cis form does not. Finally, processing can change the saturation, chain length, and shape of fats. One of the most common fat-processing methods is hydrogenation of oils, wherein the double bonds of fatty acids are broken and extra hydrogen is added, making the fat more saturated. This makes the fat more solid at room temperature and converts some cis fatty acids to trans fatty acids. Corn oil margarine is an example of a partially hydrogenated fat—the double bonds found in the monounsaturated and polyunsaturated fatty acids in the corn oil are broken, and additional hydrogen is added. The more solid the form of margarine, the more hydrogenated the product. Thus, stick margarine has more highly saturated fat than tub or liquid margarine.
Dietary fat is found primarily in the form of triacylglycerols (frequently called triglycerides), where three fatty acids are attached to a glycerol backbone. The fatty acids can vary in chain length (the number of carbons) and in the degree of saturation.
Food also contains other forms of lipids such as cholesterol, phospholipids, and sterols. In general, animal fats provide approximately 40 to 60% of their energy as saturated fats and 30 to 50% as monounsaturated and polyunsaturated FAs; fats from plants provide only 10 to 20% of their energy from saturated FAs with the rest from monounsaturated and polyunsaturated FAs.
Some foods are classified as fats due to the primary composition of the food being considered. One example, butter, is considered a saturated fat because it is 65% saturated but even butter contains some mono- and polyunsaturated FAs. Now think about olive oil – which is considered monounsaturated because 74% of its fat is monounsaturated, yet it still contains some saturated and polyunsaturated F’s. So even though a food may have different types of fat, the primary type – or that in the greatest amount – determines the type of fat.
Foods high in fat, such as oils, butter, cream, margarine, and dressings (mayonnaise and salad dressings) are generally termed visible fats because almost 100% of the energy (kcal) in the food comes from fat. Many of these foods are used as additives or condiments to prepared foods. When we add butter to mashed potatoes, the client can clearly see the fat they are adding to their food, it is visible.
Invisible fats are bit sneakier, since they are incorporated into prepared foods such as cookies, chips, or even hidden in casseroles. They are not easily visible as fats. Some would say these are hidden fats. Most of the fat consumed by our clients comes from invisible fat. Foods often high in invisible fats are meat products, dairy products, baked goods, and most convenience and fast foods.
During exercise, the primary energy sources are carbohydrate (glucose) and fat (FAs). The relative amounts used of each depend on factors such as exercise intensity and duration, level of physical fitness, composition of the meal prior to exercise, and the energy-containing products consumed during exercise. As you might have already guessed, fat reserves stored in the body are almost unlimited. The total amount of energy stored as boy fat will vary, based on an individual’s size and percentage of body fat. Although there is some debate, about 3 to 4% of body fat is biologically essential for normal functions and is used at cell membranes and tissues. Women, having higher amounts of body fat than men, usually have higher totals of stored energy in the form of fat even though body weight is less.
In addition to adipose tissue fat (subcutaneous fat and deep visceral fat), the body also stores fat within the muscle as intramuscular triacylglycerol. The amount of fat stored here is difficult to estimate and varies with fitness level, daily training time, and dietary fat intake; but it appears that even lean people have plenty of stored energy in the form of adipose tissue. Therefore, dietary recommendations to active people usually focus on making sure that the diet contains an amount of fat adequate to replace muscle triacylglycerol stores and to provide sufficient energy. Essential FA intake has to be part of any eating plan you recommend to a client.
Although active individuals and athletes typically self-report carbohydrate intakes to be the within the recommended percent range of energy intake, fat intake is more variable depending on the athlete’s gender and activity type. Most of your clients will not be deficient in fat intake, but clients who train for longer durations or at greater frequencies may change increase their intake to 35% of total consumption. However, clients or athletes in endurance sports, such as marathon runners and cyclists, will typically lower their fat intake and instead switch to a higher carbohydrate intake; this is different than sprinters and field event athletes, who would be more concerned with available energy in the more acute sense.
It might also be helpful to consider that when a macronutrient is cut or reduced from an eating plan, the intake for energy has to come from the remaining macronutrients. If a trainer was to reduce carbohydrates for a client (most likely in error), the client’s energy needs would then have to be fueled from fat and protein (not ideal) since there is no carbohydrate substrate for the glucose pathway. In this case, the distribution of energy as carbohydrate, fat, and protein will change. If the total energy intake is too high or low to maintain body weight and programmed physical activity, your client’s goals my not be fully realized. Examining clients’ food intake requires assessing total energy intake and distributing energy as needed from each of the macronutrients.
Since saliva contains the enzyme lingual lipase, the breakdown of fats actually begins in the mouth during chewing. This enzyme also splits triglycerides in fatty acids and glycerol.
Many trainers and coaches believe that fat has to be cut in excessive amounts from active clients’ eating plans. But fat is a major energy source during exercise, and the ability to tap into stored fat during exercise can improve a client’s performance. Fat can be sourced from intramuscular fat, stored adipose tissue (fat), lipoproteins present in the bloodstream, or fat consumed during exercise. Factors that determine fat usage during exercise include the client’s fitness level, the type of exercise, the intensity and the duration of exercise.
There are usually plenty of available fat reserves in the muscles and the ability to transport FAs from adipose tissue is also influenced by the amount of available stores of carbohydrate as well as the amount of carbohydrate fed during exercise.
Adipose tissue is dense in terms of energy and, as such, contains the largest reservoir of stored energy within the body. But to use this fat as a fuel source, the body must mobilize F’s and actively transport them to the working muscle during exercise.
Breaking down fat from adipose or muscle tissue to Free Fatty Acid (FFA’s) and glycerol happens through a process call lipolysis. This process begins with the sympathetic nervous system directing the stimulation of hormone-sensitive lipase (HSL) to occur. Once PA has started, the concentrations of epinephrine in the blood also rise as part of this metabolic pathway.
Lipoprotein transport blood lipids contribute to the use of fat used during PA. Two lipoproteins of note – because they are highest in triacylglycerols – are chylomicrons and very low-density lipoproteins (VLDLs).
Chylomicron levels in the blood would be high in a client who exercises after consuming a meal. Chylomicrons are mobilized because they play an important role in transporting dietary fat to the body’s tissues. From there, fats are either used for energy production or stored as body fat. As mentioned, another lipoprotein you may know of, VLDLs, also carry triacylglycerols and are therefore part of the mobilization effort.
FAs in lipoproteins have to be freed up and released from the triacylglycerols before they are able to enter the muscle cell. Another enzyme lipoprotein lipase (LPL) is responsible for cleaving the FAs from the triacylglycerol molecules in blood lipoproteins. The FFAs are then available for transport into the muscle cells for energy production or for storage, or into adipose tissue for storage. Since most of your clients will not train so strenuously after a large meal, the amount of energy resulting from blood lipoproteins is not great or significant.
Fat is obviously an important component in the eating plan of any active client. During times of heavy training, recommendations or guidelines include intake of approximately 20-35% of all energy consumed. Protein and CHO needs will also need to be included and will all depend on your client’s body size and goals.
Fat should not be eliminated from your client’s eating plan entirely. Clients who limit fat intake to levels below 15% of their total energy intake should be coached to ensure that they consume sufficient levels of essential fatty acids.
For clients who are striving for a calorie deficit (to lose weight), an eating plan can (and should) indicate lower-fat intake totals of approximately 20-25% of energy from fatty acid sources.
Clients who are concerned about body weight should be encouraged to discuss any questions they have related to selecting low-fat or reduced-fat foods with you as their trainer. Learning the difference between products labeled as reduced-fat, low fat, and fat free is important. Recommend low-fat variants of whole-fat foods – since these will provide the same micronutrients, protein, and carbohydrate composition as the full-fat versions of food but are lower in fat and energy.
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