Participant selection and study design
A sample of 22 Caucasian women was recruited for this study. Given the lack of research in this area involving young healthy women, power analysis was not performed. Participants were included only if they had no health conditions that could be worsened by fasting or that could affect their ability to balance (diabetes, recent/chronic head injuries and/or lower extremity disabilities, low blood pressure, vestibular and/or inner ear problems). Participant recruitment was completed through advertisement in the University bulletin after the study design and protocol were approved by the authors' institutional Research Ethics Board. The participants provided signed informed consent prior to participation.
The present study adopted a within subject counterbalanced crossover design, given the many advantages inherent in this design--all subjects served as their own controls and therefore reduced possible error variance, while reducing the needed sample size. Each participant was tested under fasting and non-fasting conditions, with half of the participants randomly assigned to start under the non-fasted condition and the remaining half completed the fasted trial first. The conditions were reversed during the second trial and the two trials were separated by a two week duration time span to avoid learning effects. All participants completed the same set of tests at each trial, in the same order. Standardized testing procedures and equipment were used throughout the study. The testing took place in the investigator's research laboratory. Snack bars and juice boxes were available for the participants to consume after study testing. No other incentives were provided to the participants.
Fasting and non-fasting protocol
Participants were provided with the fasting/non-fasting protocol prior to each test period. Thus, it was not possible to blind study participants to the testing condition. All laboratory tests took place between 9 and 11 am in order for all participants to avoid time of day variations. For the fasting trial, participants were asked to refrain from consuming food or beverages for a minimum of 12 hours prior to testing. Specifically, all participants were instructed to consume an evening meal before 8 pm prior to the day of testing and to refrain from any food or beverages until the time of testing in the laboratory. Fasting protocol was planned to mimic the scenario of skipping breakfast which is common among young women, or overnight fasting necessary for certain blood tests (e.g., fasting blood glucose). For non-fasting tests, participants were instructed to maintain normal eating habits on both the day prior to and the day of testing. In both test conditions, participants were asked to refrain from strenuous physical activity to minimize the role of carry-over effects such as fatigue, muscle damage, or physiological potentiation. Prior to each testing period, a pre-trial checklist was completed to provide information on each participant's past 24 hours of activity (e.g., timing of last meal, exercise performed, and injuries/health episodes since the previous contact).
The measures included: a background questionnaire, nutritional intake, balance tests, and a pre-trial checklist.
This questionnaire was used to elicit information related to the participants' demographic characteristics (age, education, ethnicity, employment, and financial status) and health status (perceived health, tobacco use, and physical activity level). The questionnaire was completed by the participants once, prior to the first testing period.
A 24-hour food recall was used to collect data on average caloric intake of the participants. The recalls were conducted by the student investigator trained in the protocol, using a standard form and adopting strategies to avoid recall bias by asking the participants to record food intake for 24 hours prior to the food recall interview . Recalls were collected once during the study period and at mid-point between the two trials.
Physical testing included: 1) dynamic balance and 2) static balance. These measures were completed twice, once in the fasted condition and again in a non-fasted condition.
The functional reach (FR) test was used to assess dynamic balance . For this test, the difference in centimetres between the participant's standing arm length and maximal forward reach was recorded. While standing with feet flat on the floor, the standing arm length was measured using a metric measuring tape fixed to the wall. Participants were then asked to reach as far forward as possible, without taking a step, without their heels leaving the ground or without losing balance. Three trials were performed with the farthest reach identified as the final score.
The single limb stance was used to assess static balance . This test can be performed in various time durations (e.g., 10, 25, 45 seconds or maximum time to exhaustion or termination) as well as with and without the use of a force platform. In the present study, the test was conducted on the gym floor and the maximum duration the participant could maintain a single limb stance was recorded in seconds on both the dominant and non-dominant legs, as well as in eyes open and eyes closed conditions , to avoid ceiling effect, given the involvement of healthy young women in this study. The dominant leg was determined by assessing which foot took the first step when participants were asked to initiate gait. Participants stood on the dominant leg, raising their non-dominant leg to a 90 degree angle at the hip and the knee joints while keeping their hands down by their sides. In this study, the test was terminated if the participant voluntarily asked to stop for any reason (e.g., sore leg), if the knee dropped below 90 degrees, if one placed the foot on the floor, or began to use arms to maintain balance. The reasons for the termination of the test were recorded for each of the four static balance testing conditions. The same set of termination criteria were used in both the fasting and non-fasting trials. Trials were conducted using the same protocol for both legs and under both conditions--eyes open and eyes closed. A practice trial was provided to each participant to ensure proper form was used during the actual trial. One test trial was completed for each condition to prevent fatigue and practice effects.
During each test session, participants completed a pre-trial checklist. This checklist gathered information related to fasting duration, level of physical activity prior to testing, and any change in health since recruitment or first testing.
Data from the two trials were numerically coded and entered into a Statistical Package for the Social Science database  for analyses. Descriptive statistics (means and frequencies) were used to describe the demographic and health characteristics as well as balance measures. Subsequently, paired t-test was conducted to examine the changes in balance performance scores for the two trial conditions. Completed dietary recalls were entered into a dietary analysis program, Food Processor SQL , and were used to calculate an average nutrient intake for a 24-hour period. Similarly, foods consumed for breakfast (in the same 24-hour period) were analyzed using Food Processor SQL to calculate the average nutrient intake. Based on the difference of nutrient intake for the whole day versus breakfast, an average "caloric loss" for fasted trials was calculated. The significance level was set at (p ≤ 0.05) for all statistical procedures.