Found on Ironman.com and sponsored by Bonk Breaker
Most endurance athletes know their macronutrients. They know that carbohydrates are the main fuel source for exercise, and that it’s important to consume simple carbs before and during exercise and replenish glycogen stores afterwards. They know that protein, made up of amino acids, is the building block for muscles and plays an essential role in recovery.
Fat, however, is one of the most misunderstood nutrients in endurance sports. Some athletes shun it completely, while others embrace it. Often overlooked, dietary fat is an important macronutrient and source of muscle fuel—and one that triathletes need to store for energy. 
In short, dietary fat is a good thing.
Fat as fuel
Whether your muscles are primarily burning stored fat or carbs for fuel depends on the intensity of your physical activity. Fat stores tend to be your fuel source during low- to moderate-intensity exercise, while high-intensity exercise depends on your carbohydrate reserves (blood glucose and muscle/liver glycogen). At high intensities, your carbohydrate stores will last about 90 minutes. At this point, if you do not start fueling with carbohydrate, your blood sugar begins to drop, slowing you down or potentially stopping you. Your body will continue to slow until it can start metabolizing fat for fuel. Ultimately, this puts you on your way to bonking, so you need to keep fueling. (Be proactive with your nutrition and start fueling about 45 minutes into exercise to avoid this downhill spiral.)
Recent Ironman winner (and Bonk Breaker athlete) Healther Wurtele uses bars with dietary fat to give her a slower release of calories. This allows her digestion more time to turn the solid food into useable fuel. “Be on top of your food intake and eat these types of bars prior to feeling hungry to stay on top of your fueling plan,” she says.
Why dietary fat?
Dietary fat is an essential nutrient. Vitamins A, D, E and K are all fat-soluble vitamins that depend on fat for absorption. Vitamin D is especially important for athletes to maintain strong bones, and vitamin E protects cell walls from free radical damage. Fats are also critical for hormonal and metabolic balance. Training can be hard on your body and it’s important to fuel properly to support these systems. In addition to the health benefits, fat simply tastes good. It adds flavor and substance to food, while also helping with overall satiety and fullness.
Are all fats created equal?
No. Limit your intake of hard, saturated fats coming from animal products like meat, butter and dairy. This does not mean that you have to cut these foods from your diet, but aim to eat lean, grass-fed and organic sources in moderation.
Avoid hydrogenated and trans fats found in packaged foods such as pastries, cookies, margarine, some nut butters and crackers. Trans fat raises your LDL (bad) cholesterol and lowers your HDL (good) cholesterol.
Aim to eat plant-based, unsaturated fats such as nuts, seeds, olives and oils. These healthy fats offer protective health qualities. These are the fats you want, especially as an athlete.
Will fat make me fat?
As discussed above, it’s important to consume enough healthy fat in your diet to replenish your muscle lipid stores and for overall health, but watch your portions. Fat is calorie dense, with nine calories per gram of fat. (By contrast, carbohydrate and protein have four calories per gram, or half the calories than fat.)
Remember that a little fat goes a long way. Regardless of what you are eating, consuming more calories than what you burn leads to weight gain and increased body fat. It’s not fat that makes you “fat,” it’s excessive calories.
What does this mean for me as an athlete?
Athletes who include healthy fat in their diets perform better than those who exclude fat. Research has found that athletes who increased their fat intake from 17 percent of calories to 30 percent could run longer and had less inflammation post-workout.
As an IRONMAN athlete, consuming dietary fat before or during moderate-intensity exercise can offer sustained energy. Fuel up about an hour before workouts with oatmeal sprinkled with nuts, yogurt with ground flaxseed, banana with nut butter, or a nutrition bar, such as a Bonk Breaker. In addition, fuel up with healthy fat during the day by adding fish a couple times a week, olives or avocado to salads, nut butters to toast and olive oil while cooking.