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Fueled to Perform

In the much-hyped Breaking2 event last spring, Nike®-sponsored elite marathoners tried to run the fastest-ever marathon, breaking the 2-hour threshold. Achieving such a feat—a 4:34-per-mile pace for 26.2 miles—would require extraordinary speed and stamina and exquisite attention to fueling and nutrition. Ultimately, Kenyan Eliud Kipchoge finished the Nike event in 2:00:25, a sliver short of his goal but still in record time—at a 4:36 pace!

Fortunately for the rest of us, the nutritional principles that fuel world-record attempts have ample relevance to everyday exercisers. Elite endurance athletes, weightlifters, team competitors, fitness enthusiasts and newly fit clients preparing for their first 10K can all optimize their diets to achieve personal bests and make their experience more comfortable and enjoyable.

Fitness professionals are well-positioned to help clients translate the latest scientific understanding of effective fueling strategies into improved athletic performance. A great place to begin is with the 2016 joint position paper on nutrition and athletic performance from the Academy of Nutrition and Dietetics, Dietitians of Canada and the American College of Sports Medicine (Thomas, Erdman & Burke 2016). The paper provides key recommendations for exercise professionals and registered dietitians and can be accessed for free at eatrightpro.org or acsm.org.

How should we apply the guidance in this position statement to the needs of our clients while staying within our scope of practice? It will be useful to keep 10 things in mind:

1. Understand Performance Goal

Helping a client master an exercise nutrition plan starts with understanding what the client hopes to achieve. Does he want to earn a personal best at a marathon? Excel during a weekend-long soccer tournament? Improve at a sport or lift a certain amount of weight? Does she want to lose a set number of pounds, gain a specific amount of muscle mass or make it through a training session with the least amount of gastrointestinal discomfort?

Assist your client in articulating a performance goal and translating it into a SMART (specific, measurable, attainable, relevant, time-bound) goal. Then, identify the nutritional factor or focus that’s essential to helping the client achieve that goal. For example:

  • “My goal is to run a marathon in 4 hours at least once before I turn 40.” Focus: speed and endurance.
  • “My goal is to bench-press 235 pounds before the end of the year.” Focus: muscle strength.
  • “My goal is to complete an Olympic-length triathlon without having severe stomach pain.” Focus: GI comfort.
  • “My goal is to increase muscle mass by 5 pounds within the next 3 months.” Focus: muscle gain.

2. Create a Fitness & Nutrition Training Cycle

Athletes often divide an annual fitness training plan (also known as a macrocycle) into discrete cycles (known as mesocycles). Goals change at each stage of the program to give the body the training stimulus most likely to provide peak performance at a specific time.

Nutrition, like fitness, can be periodized for optimal performance. In a periodized nutrition program, energy and nutrient intakes vary based on phase of training and performance goals. For example, a marathon runner may divide training into 4- to 8-week cycles: base (endurance), preparation (strength and endurance) and peak (speed). Team and sports-based athletes often divide training cycles into offseason (conditioning), preseason (skills training), in-season (maintenance of strength and power) and postseason (light-active training and recovery). A periodized strength training program alternates phases of training based on volume and intensity to achieve specific training goals.

Nutritional strategies shift with each phase of fitness training. Table 1 outlines several types of periodized nutrition plans that can help clients hit specific performance goals (Jeukendrup 2017).

3. Differentiate Between Training Nutrition and Performance Nutrition

Ideal fueling for training differs substantially from optimal fueling for competition. For example, a suggested pre-, during- and postnutrition plan for a 13.1-mile outing depends on the goal of the run. Is it a 13.1-mile training run for an upcoming marathon, or is it a race-day, run-as-hard-as-you-can half-marathon?

When you choose a nutrition strategy to support fitness goals, the aim for training is to use diet to help the body develop metabolic efficiency and flexibility (see Table 1). The aim for peak performance is to ensure the body has enough nutrients to meet the fuel demands of exercise and support cognitive function.

4. Gather Baseline Information

When you’re helping a client to optimize nutrition practices, you need a clear understanding of his fitness and nutrition levels. Gather this information by asking the client to keep a 3-day log of all nutritional intake and all fitness and training sessions. There are multiple free online programs and apps that can help you do this.

After the client has completed the log, review it with him to get a sense of the type of nutrients—foods and liquids—he consumes and the timing of his intake before, during and after exercise. Have the client describe his major challenges during training or competition (having low energy, getting stomach cramps, etc.).

And don’t forget to gather objective measures, including age, height, weight and—using an accepted method like calipers, bioelectrical impedance or densitometry (e.g., Bod Pod®)—body composition (lean mass and body fat mass). Be especially sensitive and cautious when assessing and discussing body composition. Body-fat content will vary across the training cycle, body-composition measures are inherently limited, and undue attention to certain body compositions can trigger unhealthful and restrictive dietary changes.

If the client’s goal is weight loss, it should occur at the base phase of training, to avoid loss of performance, and methods used should maximize body-fat loss and preserve lean tissue; examples include small decreases in caloric intake and increases in protein intake.

5. Assess Energy Needs

Base your estimate of the client’s approximate energy needs on the current phase of the training cycle. One way to do this is through the National Institute of Health’s Body Weight Planner (www.supertracker.usda.gov/bwp). Other formulas often used to determine calorie needs include the Harris Benedict and Cunningham equations. Box 1 describes the Harris Benedict Equation. The Cunningham equation is more accurate for athletes but is impractical for widespread use.

6. Align Energy Needs With Caloric Intake

Energy availability—dietary intake minus exercise energy expenditure, normalized to fat-free mass (see Figure 2)—is even more important than energy balance. This measure refers to the energy available for normal, healthy body function.

An energy availability of 45 kilocalories per kilogram of fat-free mass per day is associated with energy balance and optimal health. A chronically reduced dietary intake, particularly consumption of less than 30 kcal/kg of fat-free mass/day, creates relative energy deficiency in sport (RED-S) and can cause low bone-mineral density and menstrual dysfunction along with cardiovascular, gastrointestinal, endocrine, hematological, growth and development abnormalities.

Insufficient energy availability leads to decreased endurance and strength, increased injury risk, diminished training response, impaired judgment, and decreased coordination and concentration; it can also trigger irritability and depression. Figure 2 shows how to determine a client’s energy availability.

If you’re concerned that a client’s energy availability may be inadequate, suggest a referral to a primary-care or sports-medicine physician for further evaluation.

7. Target Macronutrient Needs

Macronutrient needs depend on a client’s performance goals, activity levels (including frequency, intensity, time and type) and multiple other factors. Remember that training goals aim to increase metabolic efficiency and flexibility, while competition goals aim to optimize substrate availability, to support cognitive function, and to manipulate intake of fat, carbohydrate and protein.


In sports nutrition, carbohydrate is a key target because it’s the body’s preferred energy source. It can fuel a wide range of exercise intensities using both aerobic and anaerobic energy systems. The body keeps a relatively low supply of carbs in muscle and the liver, but that can be easily manipulated through diet.

High carbohydrate availability during exercise helps to fuel exercise and maintain concentration while reducing fatigue and perception of effort. Recent research suggests that manipulating carbohydrate intake can enhance the body’s metabolic adaptation to exercise. When athletes “train low”—that is, they start a bout of exercise with low levels of muscle glycogen (maybe because they begin a second training session after glycogen stores are depleted)—several cellular changes kick in to improve metabolic efficiency and performance in future sessions (see Table 1). However, maintaining sufficient carbohydrate intake is important, as this keeps dietary protein and amino acids available for muscle building rather than energy.

In general, athletes need the following amounts of carbohydrate to fuel their sport:

  • low-intensity activities: 3–5 grams/kg of body weight per day
  • moderate-intensity exercise (1 hour per day): 5–7 g/kg BW/day
  • endurance program (1–3 hours per day): 6–10 g/kg BW/day
  • extreme commitment (4–5 hours per day): 8–12 g/kg BW/day

These amounts vary depending on exercise volume and intensity and on the relative importance of high carbohydrate availability for the type of exercise session.


Well-timed protein intake helps repair and remodel muscle tissue, support tendon and bone strength, and increase muscle mass. Athletes need 1.2–2 g/kg BW/day. This intake should be spread throughout the day and include high-quality proteins within 1 hour of strenuous training.


Fats in the form of plasma-free fatty acids, intramuscular triglycerides and adipose tissue are abundant energy sources in the body—and endurance training makes them even more readily available. Scientists have become more interested in the potential to combine high-fat diets with exercise training to increase fat oxidation and spare glycogen stores. However, studies suggest that these diets reduce metabolic flexibility by decreasing the availability of carbohydrate and the capacity to use it as an energy source. Athletes are advised to consume no less than 20% of calories from fat (to avoid deficiencies in fat-soluble vitamins and essential fatty acids) and no more than 10% of calories from saturated fat.


The AND/DC/ACSM joint statement advises moderation of alcohol consumption. Drinking alcohol before exercise suppresses lipid oxidation, increases unplanned food consumption and carries a high calorie load (7 kcal/g). Alcohol impairs exercise metabolism, thermoregulation and concentration during exercise and may interfere with recovery because of the negative impact on glycogen storage, rehydration rates and muscle protein synthesis.

8. Time It

Proper exercise nutrition aims to delay or prevent performance loss from mental fatigue, dehydration, electrolyte imbalances, glycogen depletion, hypoglycemia, gastrointestinal discomfort and acid-base imbalance.

Athletes training to increase metabolic efficiency and flexibility for an event typically benefit most from a periodized program. When the quality of the training or adaptive response is basically unimportant, it’s possible to simply consume what’s needed to meet energy goals or satisfy personal taste. However, when the goal is optimal athletic performance, the latest scientific evidence suggests the following (also summarized in Table 2):


Carbs can be loaded 36–48 hours before an endurance event (90-plus minutes) by consuming 10–12 g/kg BW per 24 hours.

Preparation for events under 90 minutes can include 7–12 g carbohydrate/kg BW/24 hours. The best carbs for this purpose have low levels of fiber, fat and protein and optimize gut comfort.

In the 1–4 hours before exercise, athletes should consume 1–4 g
carbohydrate/kg BW.

During Exercise

No fueling strategy is advised for exercise under 45 minutes.

For efforts of 45–75 minutes, small amounts of carbohydrate, including mouth rinse (rinsing the mouth with a sports drink), may be helpful. Frequent contact of carbohydrate with the mouth and oral cavity can stimulate the brain and central nervous system to boost feelings of well-being and increase work outputs.

For activity lasting 1–2.5 hours, athletes should consume 30 g carbohydrate/hour. They should find a fueling plan that meets their needs and is comfortable for their gut.

For ultra-endurance exercise lasting 2.5–3 hours, they should aim to consume up to 90 g carbohydrate/hour. Higher intake levels are associated with better performance. Products that include glucose and fructose mixtures allow a greater rate of oxidation.

Consuming some protein during extended resistance training sessions may help to increase muscle protein synthesis.

After Exercise

When the recovery period between two demanding sessions is less than 8 hours, the best refueling strategy is to consume 1–1.2 g carbohydrate/kg BW/hour for 4 hours and then resume usual daily fuel needs. Alternatively, athletes can expect a similar rate of glycogen repletion if they consume 0.8 g/kg carbohydrate and 0.4 g/kg protein per hour in the first 4 hours.

To optimize muscle protein synthesis, they should consume 15–25 g of high-quality protein within 2 hours of an exercise bout. Given that exercise enhances the rate of muscle protein synthesis for up to 24 hours after exercise, new guidelines suggest consuming 0.3 g/kg BW every 3–5 hours after key exercise sessions to build muscle mass. Studies suggest that dairy proteins are the most effective, given their high leucine content, though lean meat, soy and eggs may also be beneficial.

9. Determine Fluid Needs

A fluid deficit of more than 2% of body weight can impair cognitive function and aerobic exercise performance, so it’s imperative that clients replace fluids lost to sweat during exercise. Athletes need about 5–10 milliliters/kg BW (2–4 ml/pound) in the 2–4 hours before exercise. During exercise, fluid needs vary depending on the intensity, duration, weather, altitude and other factors.

The goal is to consume enough fluids to avoid >2% loss of body weight. Athletes can estimate their needs by weighing themselves immediately before and after exercise, taking fluid consumption and urinary losses into account. Generally, most athletes need 0.4–0.8 liters per hour. Cold beverages can reduce body heat and improve performance in hot temperatures.

Sodium should be consumed when exercise lasts longer than 2 hours or produces high sweat rates. Athletes—especially recreational athletes in extended exercise bouts—should be sure not to overconsume liquids, which can lead to a somewhat rare but very dangerous condition called hyponatremia.M

After exercise, athletes should rehydrate at a rate of 1.25–1.5 L of fluid per kg of weight loss during exercise. Including salty foods or fluids will improve fluid retention.

10. Consider Key Micronutrients

Exercise stresses metabolic pathways and may boost demand for certain micronutrients. This can become problematic in athletes who severely restrict caloric intake, eliminate one or more food groups from their diets or consume a poorly planned diet. Nutrients most likely to be inadequate include calcium, vitamin D, iron and some antioxidants. See Table 3 for daily micronutrient needs and food sources.

Is There a Role for Supplements?

Advise athletes to tread carefully with supplements and make sure they scrutinize these factors:

  • the nutritional or performance benefits a particular supplement claims to offer
  • the quality of the evidence that the product will address an athlete’s goals
  • their own previous experience and benefit (or not) from the supplement
  • the health and legal consequences of using the supplement

Few supplements have good evidence of a notable performance benefit. For example, vitamin and mineral supplements do not improve performance unless they’re reversing a pre-existing deficiency. Many sports drinks, bars and gels offer a practical choice for meeting sports nutrition goals, but such options cost more than whole foods. For some supplements (such as creatine, caffeine, sodium bicarbonate, beta-alanine and nitrate), there may be evidence of benefit in certain situations, but athletes should weigh potential risks and individual considerations before using them.

In any case, it is outside the scope of practice of a health and fitness professional to advise clients to take any particular supplement.

Test It

The best fueling program is highly personalized, taking into account the athlete’s sport, training phase, individual goals, tastes and food preferences, degree of gut sensitivity, adherence, and performance response. Ultimately, the best way to know if a program will work for an athlete is to test it.

Take a Team Approach

It is within scope of practice for health and fitness pros to discuss nutrition with clients and share information from position papers like the one put out by the ACSM/DC/AND (the information source for this article). But sometimes it’s prudent to refer clients to other professionals, such as a registered dietitian certified in sports dietetics (CSSD), for help with developing individualized sports nutrition programs.

Ultimately, a strategy that pairs fueling and fitness can enable clients to far exceed their performance goals

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