Fueling & Nutrition: optimizing performance and health by replacing what you spend.
by Tim Fleming, MSc & Endurance partner, Connor Spencer, MSc, SENr
It’s clear that a “good” nutrition regimen is key for optimal health and performance. Just to name a few, nutrition contributes to an athlete’s energy requirements, vitamin and mineral requirements, hydration needs, affects body composition, and influences immune function. So, pending the athlete’s training regimen in terms of intensity and duration of sessions, and their metabolic function, “good” nutrition can be portrayed in different ways.
Additionally, fueling requirements are influenced by these variables, where fueling is nutrition stripped down to one’s hierarchy of needs during exercise: water, sodium, and carbohydrate pre, during, and post exercise. Proper fueling can positively impact a nutrition regimen and conversely, under-fueling can negatively impact a nutrition regimen - so there’s a relationship between these two strategies.
For example, the fueling strategy and the quality (micro & macronutrient content), quantity (calories), and timing (pre & post-exercise) of the nutrition variable are very different for an athlete who trains primarily for shorter distances and has a metabolic preference for carbohydrates as the energy source for sprint training than an athlete who trains for ultra endurance with a metabolic preference for fat as a substrate. For each of these athletes the quantity requirement would be vastly different, but more importantly, how to define the quality necessary to fulfill the exercise outflow would also look very different.
By this, it’s important to pair nutrition and fueling to the exercise demands of the individual’s metabolic profile. Think of it as replacing what’s been spent. Most training regimens have different types of workouts on any given day, so it would make sense that there’s no single nutrition & fueling paradigm that works all of the time. Rather, nutrition & fueling should be built on a day-by-day, session-by-session model.
To make this assessment of an athlete’s macronutrient and fueling requirements we conduct metabolic/exercise testing to measure these aspects of the athlete’s metabolic profile.
Looking at the nutrition report below in figure 1 obtained from an exercise test for a well-trained cyclist, if the athlete does a 1-hour steady-state ride at 186w they have very little “fueling” need for carbohydrate intake to maintain that output for that duration. This athlete has a carbohydrate storage capacity (as glycogen) of 474g (calculated according to their active muscle mass), so in this instance, and assuming this athlete has a full tank, the fueling requirement is almost nil because they only burn 50g of carbohydrate in this session. Also, this means that their nutrition quality variable, when off the bike, could be defined as “lower carbohydrate and higher nutrient” consisting primarily of vegetables, beans and legumes and fewer grain-based carbohydrates.
Figure 1. Nutrition report showing the caloric demand and substrate utilization (per hour per unit of work in watts) for a well-trained cyclist. Note the change in substrate (fat and carbohydrate (CHO)) as intensity increases towards the anaerobic threshold (319w).
Continuing with this example, let’s take this ride and make it 4-hrs at 186w instead of 1. Now the output is significant when looking at the total carbohydrate burn (200g). With that much of a dent in the glycogen stores, if this athlete does not fuel accordingly, he/she may be subject to not only fatigue, but also cravings for carbohydrate when the timing of the intake doesn’t optimize glycogen replenishment and can lead to elevated insulin levels during the day, which is not a healthy or appropriate state.
Now let’s look at the difference if there’s more intensity, if they do 40 minutes of interval work at the anaerobic threshold (319w) mixed into a 2-hour ride that otherwise includes time at FATmax (215w). This would add up to 279g – 185g from the interval work plus 94g from the time spent at 215w – which is more than half of this athlete’s glycogen stores, so here we have the combination of duration and intensity changing not only the fueling requirement to optimize this workout, but also the quality of nutrition for the entire day.
By this, quality would include a higher carbohydrate requirement in the nutrition regimen where more whole grains and/or simpler carbohydrates provide higher “quality” in the context of the outflows.
In some instances, training with low glycogen stores is warranted; however, if you take this latter example and continue with a low carbohydrate nutrition regimen this athlete will be chronically underfunded over several days which can lead to poor health and/or a lack of proper physiological adaptations. Even more so when taking into consideration a multi-sport athlete who completes more than one training session per 24hr period.
In summary, when implementing training, nutrition, and fueling plans the first step is assessing the athlete’s metabolism during exercise and their need for specific macro nutrients on any given day of training or competition. Assessing this need can lead to more appropriate training recommendations and nutrition support, and therefore, improve both performance and overall health.