The effect of diet on pilot performance

Lindseth, Lindseth, Jensen, Petros, Helland and Fossum (2011) [1] have conducted an ad-hoc clinical research experiment in an attempt to determine whether pilot performance is directly affected by varying dietary protein, carbohydrate and fat levels. The researchers concluded that a high protein diet resulted in significantly poorer (p < .05) overall flight performance when compared to other experimental treatments. This article provides an overview of their research and summarises the results.

Experiment Results

The research experiment was constructed to measure the effect of varied diets (independent variable) on student pilot deviation from specific flight path parameters in a simulated flight environment (dependent variable). High deviations from a theoretically perfect flight path were interpreted as a reduction in cognitive performance. In addition, cognition and memory tests were carried out at the conclusion of each diet period to validate flight performance results. These tests were also used to identify correlations between deviations and cognitive test results.

Flight performance

The means listed in table 1 indicate the mean level of deviation from a perfect flight path by experiment participants. A higher score reflects a higher level of deviation. Confounding variables have been minimised so that variation in means may be attributable to the manipulated diet. The level of significance was determined by a repeated measures ANOVA test which considered whether a statistical difference in the means actually exists. The level of significance for this research was set at 5%.

Table 1. Diet effect on flight parameters
Diet		Airspeed	Altitude		Heading		Overall
	Mean	P	Mean	P	Mean	P	Mean	P
Control	9.6	ns	172.6	< 0.1	35.3	ns	217.5	ns
Protein	10.4	ns	217.1	ns	23.4	< 0.1	250.9	ns
Carb	10.1	ns	169.2	< 0.1	26.9	ns	206.2	< 0.1
Fat	10.8	ns	150.8	< 0.01	28.9	ns	190.5	< 0.1
ns - not significant p < 0.1 highly significant p < 0.01 very highly significant

It can be noted that no significance differences were observed for variations in airspeed between diet types, some differences in altitude variations and a slight heading improvement on the protein diet However, the overall means show the high carbohydrate and high fat diets resulted in significantly (p < 0.1) better performance than both the protein and control diets.

Cognition and memory tests

The results of these tests are ambiguous. The researchers did not identify any significant results from the cognition test and only limited significance from the memory test. However, when correlating these results with mean deviation scores from the tested flight parameters, some significant correlations were noted. For instance, a highly significant (p < .01) correlation was noted for airspeed while a significant (p < .05) correlation was noted for altitude deviations. There was also a highly significant (p < .01) correlation between the cognition and memory tests. The article states that overall flight performance scores correlated significantly with the results of the two tests but no data is given to validate this statement.

The correlations demonstrate that the effect of diet on flight performance is related to a reduction or improvement in cognitive performance and therefore, that the tests were a useful indicator of this effect. However, the researchers concluded that the correlations were indicative only of a statistical correlation and not as a reliable, standalone measure of pilot performance.

Method

Experiment design

The experiment was a repeated measures, counter-balanced, crossover design.

Sample

A convenience sample of 45 third year collegiate student pilots were selected for this study. The mean age of the group was 20.80 years, SD 1.90 with a mean flight experience of 146.60 hours, SD 38.60. The mean Body Mass Index for the sample group was 24.80, SD 3.50. This mean BMI is at the high end of the recommended ideal BMI range of 20.0 - 24.9. While BMI does not define body fat to muscle mass ratio, this mean BMI tends to suggest the sample group had a higher measure of body fat and a regular diet relatively high in fat. This is inline with the typical western pattern diet with an average dietary fat intake of 35% and also is evidenced by the fat content of the experiment control diet (35%).

Variables and manipulation

The independent variable in this experiment was varied macronutrients in the diet of the participants. Four dietary treatments were applied for four days with two weeks between treatments. The variation of protein, carbohydrate and fat in the four diets is defined table 2. On the last day of each diet period the participants were required to complete a simulated flight exercise followed by memory and cognition tests.

Table 2. Macronutrient variations in experiment diets
Diet	Protein (%)	Carb (%)	Fat (%)
Control	15	50	35
High Protein	56	22	22
High Carb	22	56	22
High Fat	22	22	56

Internal Validity

The researchers took various measures to minimise confounding variables including conducting the intervention as a double-blind experiment, randomly assigning the order of the diets, allowing a two week period between diet manipulations, carefully controlling the food intake of each participant and maintaining a consistent environment for each of the flight performance tests. A dietician prepared each of the diets to ensure that nutrient content was correct for each experiment condition. Although the sample is unlikely to be reflective of a more diverse population the experiment did have high internal validity.

Analysis

While it is generally accepted that diet, and consequently nutrition have an effect on performance, clinical trials have typically focussed on the physical performance of athletes. The research of Lindeth et al is unique in its specific focus on cognitive function and pilot performance and the results are surprising.

It is difficult to determine exactly what this study shows, does a high fat or high carbohydrate diet improve hand eye coordination, spatial reasoning and concentration? (Skills beneficial to pilot performance). Or conversely, does a high protein diet cause a reduction in these abilities? Lindseth et al have inferred the negative, that protein was responsible for the greatest number of errors while suggesting that the other diets may have helped pilots to perform consistently well.

With increasing focus on cognitive limitations and fatigue management in pilots, this research is highly relevant. However the long term health impact of a high fat or high carbohydrate diet and how pilots are able to practically integrate such controlled diets into their lifestyle remain to be seen.

Bibliography

1. Lindseth, G; Lindseth, P; Jensen, W; Petros, T; Helland, B; Fossum, D (2009). Dietary Effects on Cognition and Pilots' Flight Performance. The International Journal of Aviation Psychology, 21(3), 269-282.