Fats in the Endurance World


Second only to carbohydrates, fat may be the most misunderstood nutrient in endurance sports. There are those athletes who totally shun it and others, touting its virtues, just as emphatically embrace it. So, is fat good or bad? It‘s certainly not the bad guy that the masses thought two decades ago when the market was invaded with fat-free food. Since then, obesity rates have nearly doubled on our supposed lower-fat diets. But ultrarunners are not the masses (yeah!) and nutrients work a bit differently in the well-trained endurance athlete’s body. Distance runners are calorie-guzzling animals, yet they are lean where it counts – in their muscles. Not only is this important for moving along the trail, but it is vital when it comes to health.

So, is fat good for ultrarunners? We need fats for three primary reasons – to provide essential fatty acids, to provide essential fat-soluble vitamins and to meet energy needs. The latter may be the biggest reason for us compared to the rest of the population but the other two are critical for optimal well-being.

The basic nature of fat plays many roles in our health and in our endurance performance. Its functions are extremely varied as it can serve as a structural component (cell membranes), a hormone component (as cholesterol in testosterone and estrogen), a metabolic regulator (essential fatty acids interact with protein within the cells and affect gene expression) and – very important for the ultrarunner – as our main energy source (triglycerides which break down into free fatty acids) during long events. Without fats, there would be no ultrarunning…our efforts would cap out at about 800 meters…and we would never see all those beautiful single-tracks nor have a clue what to do with our Saturdays, all day.

What we call fat is actually a class of substances known as lipids. These are water-insoluble organic compounds that are further divided into triglycerides, cholesterol and phospholipids. Cholesterol is found only in animal products and is not an essential nutrient for humans because we can manufacture it in our livers. Phospholipids are somewhat like triglycerides and again, not essential in the human body because we can make them from our triglycerides. The triglycerides are the important lipids for us because they are the principal form in which we eat and store our fat. This discussion will center on these substances.

Triglycerides are made up of three fatty acid chains that combine with one glycerol molecule. Most of these are stored in our adipose (fatty) tissue for future energy needs. The fatty acids can be released from glycerol into the blood as free fatty acids (FFA) where they travel to tissues (including muscles) to be used for energy.

  • Dietary fatty acids are classified into the following categories:
  • Saturated Fatty Acids
  • Monounsaturated Fatty Acids (MUFAs)
  • Polyunsaturated Fatty Acids (PUFAs) – including the essential fatty acids (EFAs)
  • Omega-3 Fatty Acid (alpha-linolenic acid)
  • Omega-6 Fatty Acid (linolenic acid)
  • Trans Fatty Acids

Most of the above classifications have to do with the physical structure of the fat molecule and the number and kinds of chemical bonds they have. The more saturated the fat (no double bonds), the more solid it is at room temperature and the more stable it is. Think about the long shelf life of Crisco and Twinkies. The more unsaturated a fat is (more double bonds), the more liquid it is at room temperature, and the more prone to damage from oxidizing. What is important to note is that certain fats are defined as “essential” because:

  • The body cannot make them.
  • They are required for normal cell, tissue, gland and organ function.
  • They must be provided from outside the body, through food or supplements.
  • They can come only from fats; hence fat-free diets cannot supply them.
  • Deficiency results in progressive deterioration of health; however, return of essential fatty acids to the diet reverses these symptoms.

In order to be available for energy during endurance exercise, fats must first be mobilized from our tissues; some from the adipose tissue (our “reserves” of fat) and some from the stores within our muscles (known as intramuscular triglycerides [IMTG]). This process is heightened when exercising and, even though it reaches a maximum rate, that rate is higher in well-trained athletes. First the glycerol molecule splits off from the fatty acids and then the free fatty acids (FFAs) are transported through the blood by carrier proteins. The more slowtwitch muscle fibers one has, the more transporters there are. Also, in the well-trained athlete, more IMTGs are stored right next to the muscle mitochondria where they can efficiently and effectively be used for energy. (NOTE TO READER: Be well trained!) The final step is the actual oxidation, or burning, of the FFAs. This process requires a fair amount of oxygen and is the biggest limiting factor for the ultrarunner. The longer the run, the steeper the terrain, the higher the altitude, the harder it gets. (NOTE TO READER: Include hill repeats, altitude training and long runs…beginning to sound like a training schedule, huh?)

Fats and carbohydrates are only oxidized as a mixture, thus the saying, “fats burn in the flame of carbohydrate”. (NOTE TO READER: Never run completely out of carbohydrates or you won’t be able to burn fat.) The predominant fuel used depends on several factors – intensity of exercise, duration of exercise, level of aerobic fitness, carbohydrate intake before exercise and fats in the diet in general. When exercise is initiated, fat mobilization is increased as much as three times the rate at rest. Concurrently, blood flow is doubled to the adipose tissues in order to deliver FFAs to muscles, and the conversion (known as “re-esterification”) of molecules into fats from ingested or existing nutrients is halved. In other words, we are prepared with fuel to MOVE! At low-intensity exercise we use almost exclusively endogenous, i.e. stored, fats (especially when we are trained). As the intensity of our running goes up, we reach our peak of fat usage at about 63 percent VO2 max, after which carbohydrates become the biggest player. As the duration of our running increases, especially over about six hours according to studies, as much as 90 percent of our energy can come from fat. (NOTE TO READER: However, since even the leanest ultrarunner has about 800 miles worth of fat stored within their skinny-little-self, it is not necessary to eat that pint of ice cream every night.)

The last area of discussion involves supplementation before and during exercise with fat, usually in the form of medium-chain triacylglycerols (MCTs). Remember, the amount of potential energy, or calories, stored in a lean ultrarunner’s body is enough to fuel running at marathon pace for about a week, so it is unnecessary to replace or restock that fat during exercise. In addition, consuming fat while running does not increase the rate of fat usage, nor, in most studies, does it spare glycogen (carbohydrates).

In fact, we do not actually use exogenous (ingested fats) during exercise, only those that are already stored in our bodies. If we try to eat fats while we are running, we may defeat any gain in calories because it takes three times the amount of oxygen to process these fats that it does to process carbohydrates. There is also a very good chance that it will lead to gastric upset since fat is slow to digest and has an inhibitory effect on gastric emptying which will delay fluid and carbohydrates, as well as the fat itself. from reaching working muscles.

However, there are sport nutrition products that contain fat; more specifically, MCTs, because they have slightly different properties. They are water-soluble, are more easily absorbed than most other fats (they do not delay gastric emptying) and they can readily enter the mitochondria in the muscle cell.

Researchers are always looking for an ergogenic aid that may increase performance, if even by a small margin. MCTs can contribute between three and seven per cent of the total energy used in an endurance event (more than that causes the gastrointestinal distress) and yet this may be enough to make a difference in a runner’s overall place in the race. There is one other reason to ingest fats during a long ultra – distracting and excessive hunger. Eventually, every runner needs more than sugar/carbs – if only for psychological reasons – and fats help satiate hunger.

The anti-inflammatory effects of EFAs – omega-3 and omega-6 – help account for the decrease in recovery time following endurance exercise. Mild inflammation occurs in various tissues – muscles, joints, connective tissue – after physical exertion, when the immune system becomes engaged in breaking down dead and damaged cells. The longer the bout of exercise (and the harder the terrain and higher the altitude), the more inflammation can occur. If this post-exercise inflammatory state becomes too pronounced, healthy cells can become damaged. Recovery time increases because tissue damaged during the exertion as well as healthy tissue that became compromised during recovery all need to be repaired and the body can only do this cleanup so fast. Imagine part of the cleaning crew called in sick following a frat party. Consequently, an over-pronounced post-training inflammatory state can occur requiring a longer time for full recovery. A lack of antioxidants contributes to this situation.

Healthy fats are also required to bring the post-event endurance athlete’s body back into energy balance, providing some much-needed calories. While protein and carbohydrates are needed for muscle rebuilding and restored energy, good fats are required for healthy cell membrane and tissue restoration. Omega-3 and omega-6 can also substantially shorten the time for fatigued muscles to recover following more intense activity by facilitating the conversion of lactic acid to water and carbon dioxide.

One of the most misunderstood concepts in human nutrition is that eating fats does not make us fat. In fact, lack of exercise (which is not the ultrarunner’s problem) can make us fat. Lack of good fats in our diet can be bad for our overall health. Understanding how these good fats contribute to a healthy runner’s diet and recovery is critical. In a nutshell (besides eating the nut), the key is moderation and individualizing your fat intake. Fats are not equal; some are better than others and a few (trans-fats) should be avoided all together.

There are all kinds of recommendations as to what percentage of your calories should come from fat to make up a healthy diet. Thirty percent is a number we often hear, unless you are on a “diet”. Most Americans consume 40 to 50 percent of their daily calories in fats.

When it comes to the distance athlete, it is more important what kind of fat is eaten rather than how many of your calories come from fat sources. If you are training heavily and trying to keep your fat percentage to 30 percent, you may find yourself eating all your waking hours and feeling much too full to run. This is because carbohydrates and proteins carry four calories per gram and fat carries nine calories per gram.

The individualized need for fat is mostly dependent on energy balance. If the assumption is that the ultrarunner does not need to change their body weight or composition, then input needs to equal output. The amount of protein to support the runner’s muscle mass and the amount of carbohydrate to fuel the runner’s training needs to be figured first, then the amount of fat (in calories) needs to be added so that the total calories ingested balance the total calories expended. Fat is a fuel powerhouse at more than twice the energy (nine versus four) calories per gram and for the lean ultrarunner who has trouble getting enough to eat, this source of compact calories can be a big boon to their food intake.

What kind of fat is best? The short answer is unsaturated fats from non-animal sources. We all need fats to absorb the fat-soluble vitamins A, D, E, and K as well as other phytochemicals found in fresh foods, and we need fats for healthy functioning previously mentioned. For the runner who is trying to become leaner, choosing mostly monounsaturated and polyunsaturated fats, especially omega-3 (alphalinolenic acid) and omega-6 (linoleic acid) is key. And we should all avoid trans fats as much as possible. See the accompanying table for different sources of fat.

If you ate only good fats, your fat intake could probably be over 50 percent of your overall calories and you would most likely still never die of a fat-related disease. An interesting example of this was found in observing the Inuit population in the Arctic regions of Canada; their fat sources included raw whale blubber, seal fat and fish, yet they did not die of heart diseases. None of their dietary fats were damaged by processing; instead they were rich in omega-3 and omega-6 fatty acids in the natural state.

Being careful in our choices of fats, and especially our EFAs, can be a crucial factor to our overall good health and our continued ultrarunning performance. Check out some sources of better EFAs below.

Seeds and nuts are rich sources of EFAs. No one seed or nut gives an optimum ratio of omega-3 to omega-6. Flax is the richest source of omega-3, but a poor source of omega-6. Sunflower and sesame seeds contain omega-6 but no omega-3. A variety of seeds and nuts in your diet aid in obtaining both.

High fat, cold-water fish such as sardines, salmon, trout, herring, and mackerel contain omega-3 and omega-6 derivatives.

Oils and products made with health in mind: Products made from organic sources, protected from light, air, and heat, extracted without damaging chemicals, packaged safely and refrigerated if necessary, will retain their health benefits. Care in food preparation (“safe” frying) and storage (dark bottles and refrigeration) is also necessary for EFA-rich oils.


About Author

Sunny Blende, M.S. is a Sports Nutritionist who writes and counsels individuals and teams on fueling for enhanced performance and making healthy food choices. Currently she writes the nutrition column for UltraRunning magazine and runs ultras herself. She has presented at the National RRCA Convention, the National Rowing Convention, Nike San Francisco Marathon Expo, and the Runners World San Francisco Marathon and worked as an assistant with the Los Angeles Marathon Association. An avid master competitor herself, she trains and competes in the San Francisco Bay Area and beyond. Sunny received her Bachelor of Science degree from University of Southern California and her Masters in Human Nutrition degree from University of New Haven. (Photo at left, by Luis Escobar).


    • Thanks for the good article. The Inuit still had heart disease though, they just didn’t often die from it and had much lower rates .