Within day energy balance

· Within day energy balance ·

Hi Saturday Morning Fan,

This week, we are returning to nutrition research and looking not just at how much you eat in a day, but when you eat it. Specifically, we are focusing on within-day energy balance and why long gaps without fuel can quietly undermine health and performance.

Within-day energy deficiency

Endurance athletes are already familiar with the concept of relative energy deficiency and its links to hormonal and metabolic disruption. Most discussions focus on daily energy balance. Did you eat enough across the whole day?

This study asked a different question. Does it matter how energy availability fluctuates within the day, hour by hour?

Study design

The researchers studied 31 male cyclists, triathletes, and runners. They measured resting metabolic rate, tracked energy intake and expenditure hourly across a full 24hr period, and assessed body composition along with key hormones related to energy availability.

The goal was to compare athletes with normal versus suppressed resting metabolic rate and examine how their within-day energy balance differed.

Results

Athletes with suppressed resting metabolic rate spent almost double the amount of time in large hourly energy deficits. They also experienced much larger single-hour energy shortfalls, rather than smaller, more manageable gaps.

Importantly, these larger deficits were associated with higher cortisol and a lower testosterone ratio. In simple terms, this reflects a more catabolic, stress-driven hormonal environment.

What does this mean for you?

The key lesson is simple: avoid large energy gaps during the day.

For most endurance athletes, this means fueling more frequently rather than relying on just a few large meals.

A practical structure might be three main meals and two to three snacks per day. Some of those snacks can be recovery drinks, smoothies, or shakes, especially around training.

Fueling during training sessions also provides another opportunity to support energy availability and training quality.

This approach helps stabilize energy availability, reduce hormonal stress, and support long-term health and performance.

Torstveit, M.K., Fahrenholtz, I., Stenqvist, T.B., Sylta, Ø. and Melin, A., 2018. Within-day energy deficiency and metabolic perturbation in male endurance athletes. International journal of sport nutrition and exercise metabolism, 28(4), pp.419-427.

Have any thoughts, comments, or questions that you'd like to share? Please email us anytime!

Daniel

Endurance Athlete, Coach, and Saturday Customer Support.