Aviation Safety Ramifications of Flight Crew Personnel Using Ketosis Diets


Fad diets impact the ability to think.

Aviation Safety Ramifications of

Flight Crew Personnel Using Ketosis Diets

By: Loren French

The last 5 years have brought about an explosion in the usage of fad diets to combat overweight bodies and obesity. Some of these diets induce a physiological condition called ketosis to accelerate weight loss. This paper will explore some of the physiology surrounding these diets, their possible impacts to aviation safety, and alternative nutritional strategies for pilots and members of flight crews.

The idea and motivation to research this topic originated during a flight lesson with a pilot whom I was instructing. This pilot had been a previous student for an instrument rating, and he had returned to my flight school for the purpose of obtaining a commercial license. During the course of his entire instrument training as well as the beginning of his commercial lessons I had found him to be very proficient and a generally skillful pilot. About half way into his commercial training his skills took on a dramatic change for the worse. Initially I wrote off the poor performance to a bad day at work or other external pressures. After 4 lessons of poor performance I began to get worried, and questioned the student about possible personal problems and their influence on his flying. The following lesson he told me that he was in the induction phase of an Atkins diet, and that he was in fact having trouble thinking things though quickly, was feeling sleepy and weak in the airplane. The next lesson, miraculously his skills returned to their previous levels. Why? He had decided to give up on Atkins (Hauser, T, 2003, Personal Communication).

Understanding Carbohydrates

In order to understand the Atkins diet and its effect on the body its first important to understand what carbohydrates are, and how they are used in the body. Most people will relate carbohydrates to starchy foods such as bread, potatoes, pasta and sweets. It is true that these foods are rich sources of carbohydrates; however most foods contain a combination of carbohydrates, fats, and proteins. Carbohydrates are classified as either a simple or complex. Simple carbohydrates are sugars, and complex carbohydrates are starches or fibers (Whitney & Rolfes, 2002).

The simple carbohydrates include the monosaccharides glucose, fructose, and galactose as well as the disaccharides. A disaccharide is two monosaccharides bound together. Maltose is formed by the combination of two glucose molecules, sucrose is a glucose and fructose molecule combined, and lactose is the combination of a glucose and galactose molecule. Complex carbohydrates which include starches and fibers are polysaccharides composed of chains of varying length of monosaccharides (Whitney & Rolfes, 2002).

During digestion; sugars, starches, and fibers are broken down into monosaccharides and then absorbed. Glucose has a unique benefit in that it can be absorbed directly into the blood and the body can immediately begin using it. Both fructose and galactose are processed by the liver and converted into glucose. The most important idea to understand about carbohydrates is regardless of whether the carbohydrate is complex or simple, and regardless of whether it is composed of glucose, fructose, or galactose, all carbohydrates eventually become glucose (Whitney & Rolfes, 2002).

The Metabolic Pathways of Glucose

Once glucose is absorbed into the blood, or converted from fructose or galactose by the liver it serves a variety of purposes. The first and most important role of glucose is to fuel the nervous system. This includes the brain, the spinal column, the peripheral nervous system and sensory organs of sight, sound, taste, touch, and smell. Glucose is the primary and preferred fuel source for the brain and nervous system. The secondary fuel source for the brain and nervous system is ketone bodies, which will be discussed later. Neurons, which are the basic building block of the brain and nervous system have no storage capability for glucose, therefore glucose must be present in the blood for the neuron to obtain energy and function(Whitney & Rolfes, 2002).

Secondary to support of the brain and nervous system, glucose can be used to fuel muscle tissue as well as all other tissues. Muscle cells specifically, have an added advantage over neurons. They have both storage for short term supplies of glucose, and they can utilize fat as an energy source very easily where as neurons have neither storage capability nor can they utilize fat (Whitney & Rolfes, 2002).

The third major pathway for glucose is the liver. The liver has the ability take excess glucose and converts it to glycogen. Glycogen is a storage form of glucose that can be quickly broken down to provide energy when needed. Generally, the liver has only enough storage capacity for 4-5 hours of glucose for normal activities, or 1-2 hours for exercise level activity. Although outside the scope of this paper, the mechanics of glycogen storage explain many aspects of eating habits and exercise physiology. These include why we eat when we do, and why the first 10 minutes of exercise are not burning fat, but after 10 minutes fat is burned (Whitney & Rolfes, 2002).

Ketone Bodies

Fueling the nervous system requires a minimum of 50-100 grams of carbohydrates per day. If minimum carbohydrate requirements are not met, the body will modify its energy metabolism to manufacture ketone bodies from fat stores. This physiological response is the body’s safeguard against starvation, and provides an alternate fuel source for the brain, nervous system, and all other tissues of the body using fat stores (Whitney & Rolfes, 2002).

Once intake of carbohydrates is stopped, the initial manufacture of ketone bodies will begin very slowly. Ketone bodies, although they can partially replace glucose as a form of energy for the brain, they cannot replace glucose on short notice. It may take a course of several weeks for body to reach a point where their production exceeds their use. Once production of ketone bodies exceeds their use the condition is known as ketosis. In the time between when carbohydrate intake is halted and the body reaches a state of ketosis, the body may metabolize its own muscle tissue into glucose to keep the nervous system functioning. Even once a state of ketosis is reached, ketone bodies can only supply at most 50% of the necessary energy for the brain, the rest must come from glucose (MedBio World, 2004).

Atkin’s Induction Period

The Atkins diet is principally based on usage of body’s physiological response to starvation, ketosis. During the 2 week induction period of the Atkins diet, a person is instructed to consume no more than 20 grams of carbohydrates per day, however zero carbohydrates is recommended. The concept is that this extinction of carbohydrate intake will kick-start the body into a state of ketosis, where by burning of body fat becomes faster and more efficient. This extinction of carbohydrates is accomplished by limiting one’s intake to foods containing purely fats and proteins (Atkins Nutritionals, 2004).

Debates over the long term health effects and the efficiency of this diet will continue for some time, but the short term effects of this initiation period can be easily examined. Probably the greatest ramification of the Atkins diet is the effect on the brain and nervous system during the period of induction.

We’ve established that the brain needs glucose to operate efficiently or ketone bodies as a secondary energy source. Second, we’ve established that storage of glucose in the form of glycogen contained in the liver is limited to several hours. Third, we’ve also established that a state of sufficient manufacture of ketone bodies can take several weeks to reach. This means that during the period of induction from when the intake of carbohydrates is restricted, until at least the time where a state of ketosis is reached the body’s nervous system is being starved of fuel.

To function properly, the brain and body needs to maintain blood glucose homeostasis. If blood glucose levels fall below normal the result can be weakness, dizziness, and fatigue. In some rare cases, extreme fluctuations of blood glucose level can be fatal. There is also evidence to indicate that brain cells susceptibility to seizures in increased by lack of glucose and lack of oxygen. The flight environment provides ample opportunities for varying degrees of hypoxia, even in pressurized aircraft. In extreme cases the lack of oxygen in the flight environment compounded with a lack of glucose due to an Atkins diet could induce seizures in a flight crew member (Reinhart, 1996) & (Indiatimes Fitness & Health 2002).

There are many other more subtle side effects that are commonly associated with low blood glucose. These side effects include the inability to focus, headaches, dizziness, confusion, weakness, nervousness, and significant deterioration in attention abilities. Researches at The University of Edinburgh concluded that auditory and visual information was processed more slowly when the brain was temporarily deprived of glucose. All of these mental impairments have no place in the flight environment, and their presence signifies a significant threat to the safety of a flight (Reinhart, 1996) & (The Franklin Institute Online 2004).

In addition to the ramifications on the nervous system, there are a host of other common side-effects that present safety considerations to aviation operations. Atkins Nutritionals, the organization that promotes the Atkins diet states that common side-effects of the Atkins diet include headaches, irritability, nausea, dizziness, fatigue, constipation, dehydration and diarrhea. Each of these side effects results in the pilot or flight crew member being impaired to some degree. Irritability will have profoundly negative consequences on crew resource management and communication between other flight crew members and air traffic control. Dehydration will only be exacerbated by the dry air of the flight environment (Atkins Nutritionals, 2004) & (Reinhart, 1996).

A Better Nutritional Approach for Pilots

Analyzing the effects of the Atkins diet on a physiological basis shows us that although the diet may be good for weight loss, the mentally impairing effects on the brain creates safety concerns for aviation. It is reasonable to conclude that any diet that starves the brain of glucose is not acceptable for flight crew use.

A better nutritional approach for pilots wishing to loose weight is to do so using a conventional diet moderate or high in carbohydrates and low in fat. A successful weight loss plan will include a balance diet of moderate to high intake of carbohydrates, low total fat, low simple sugar intake, very low saturated fats, and high fiber with stress placed on quality nutrients. A quality nutritional plan should limit caloric intake to provide weight loss of 2-5 pounds per month (Whitney & Rolfes, 2002).

Following the USDA food pyramid diet will result in a dietary plan with these properties, while still supplying the brain and nervous system with ample amounts of glucose. There are several other diet approaches which can also provide the necessary carbohydrate intakes. These include The South Beach Diet, the American Heart Association Diet, the Ornish Plan, Pritikin Diet, and the Scarsdale Diet (Agaston, 2003).


High protein, low carbohydrate diets present a safety risk to aviation operations because of the possible mental impairments that may result from low blood glucose. Corporate flight departments, airlines, and flight schools would be wise to prohibit such nutritional approaches. Because of the popularity of these diets, recurrent training for flight crews should include education about the risks of such diets as well as alternative nutritional approaches.


Whitney, E. N.& Rolfes, S. R., (2002). Ninth Edition Understanding Nutrition. Belmont, CA: Wadsworth/Thompson Learning.

Agatston, A. M.D. (2003). The South Beach Diet. New York, NY: Random House.

Atkins Nutritionals. (2004, April 5). Frequently Asked Questions. Retrieved April 5, 2004

The Franklin Institute Online. (2004, January 13). The Human Brain. Retrieved April 5, 2004 from http://www.fi.edu/brain/carbs.htm

Indiatimes Fitness & Health. (2002, November 16). Epilepsy Is Not Genetic, Mostly: Dr. Nirmal Surya: Neurologist. Retrieved April 5, 2004

MedBioWorld, (2004, April 5). Blood Sugar is Stable. Retrieved April 5, 2004 from http://www.medbio.info/Horn/PDF%20files/homeostasis1.pdf

Hauser, T. (2003, March 30). Personal Communication.

Reinhart, R. O. (1996). Basic Flight Physiology. New York, NY: The McGraw Hill Companies