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Applying the science of nutrient timing

Timing nutrient ingestion is a concept that has become increasingly popular in the world of sport performance. The primary goal between training sessions is to recover; as a result, nutrition becomes a key component that allows the body to adapt to the imposed training demand.

The timing, type, and volume of carbohydrate, protein, and fat consumed throughout the day are critical to restoring overall muscle function and body homeostasis. After several decades of scientific research, we now know that centering an athlete's food and fluid consumption before, during, and after exercise can significantly enhance the recovery and adaptation process.

A training adaptation that most athletes seek to optimize is the ratio of muscle and fat mass in the body. This is due to the positive relationship that body composition has with producing peak results. To develop a nutrient timing system that can assist in optimizing body composition, athletes and coaches need to consider three components: the level of energy needed to sustain training, the function of an athlete's food and its role in performance, and the goals of the training cycle.

Ensuring that athletes have optimal fuel has been highlighted as a key factor in training and competition success; however, athletes are also frequently concerned about body weight and composition. Studies assessing the patterns of food intake by athletes have shown that the type of food consumed and timing of meals are vital to managing weight and maintaining a high level of muscle mass and an ideal level of body fat.

Body weight and composition are a result of the balance between food intake and energy expenditure. More important for an athlete is the concept of energy flux. This is the rate at which energy (food) is consumed in relation to the rate at which it is expended, whether through daily living or through exercise. Athletes desire a high energy flux, which has been shown to help improve body composition through increasing muscle mass and decreasing body fat. To achieve this, an athlete needs to develop a nutrient timing system that steadily provides balanced energy to the body. The body thereby maintains and improves levels of muscle while simultaneously decreasing fat stores in response to exercise and nutrition.

Understanding the function that food plays in the recovery and training adaptation process is another important aspect of developing a timing system for nutrient ingestion. Food should serve a function in the body, whether it is to rapidly recover the muscles from training or to keep glucose (carbohydrate) levels in the blood stable between meals. Meals or snacks can have a fast, moderate, or slow rate of digestion and absorption depending on the ratio and type of carbohydrate, protein, and fat that the food contains.

When a slower response is desired, an athlete should consume foods that have a higher level of fiber (in relation to sugar content and total carbohydrate), healthy fat, and protein. Conversely, as fat and fiber decrease, a food is able to be absorbed into the body at a much more rapid rate than if those nutrients were present; this is especially true when the sugar content of food is high. Identifying the foods that quickly enter the blood and those that have a slower and steadier release of energy is vital to optimizing a nutrient timing system.

The development of a nutrient timing system that accounts for energy flux and the functionality of an athlete's food requires an understanding of periodization. Periodization refers to the structuring of an athlete's training program; it involves the intentional planning of training volume and intensity for optimized performance.

For some athletes, periodization will encompass a 3-month period; for others, it will be a year-long process. This long period is known as a mesocycle. Based on an athlete's primary performance goal, a mesocycle will have macro- and microcycles that reflect the progressive process of training that an athlete will take to achieve that goal.

A macrocycle is typically 3 to 4 weeks long and defines a block of training. A microcycle usually lasts 3 to 10 days and reflects with greater definition the manipulation of intensity and volume of training for the macrocycle. As the training volume and intensity change throughout the days and weeks of these cycles, so should the volume and ratio of carbohydrate, protein, and fat in the athlete's nutrition plan.

An athlete's nutrition plan should support the primary performance goal that is set for the mesocycle. On a day-to-day basis, the athlete will focus nutrition on the goals of the current microcycle by manipulating the volume and types of food consumed to match the training demand.

To begin using a nutrient timing system, an athlete should answer the following questions:

  • What is the primary goal of training?
  • Based on the current macrocycle, what is the key function that nutrition should serve (for example, reduce body weight, improve fat use during training)?
  • Based on the current microcycle, on what days of the training cycle does the athlete perform the most work?
  • At what times of day is the majority of energy expended?
  • How much energy is expended throughout the day? How does this vary day to day?
  • Is the athlete eating something at least every 3 hours?


Krista Austin, PhD, CSCS, is a performance nutritionist and exercise physiologist.
Contact her at and visit her website at