Three Things Nutritionists Need to Know About the Body, Brain, and Eating Disorders

 

Three Things Nutritionists Need to Know About the Body, Brain, and Eating Disorders

By Carolyn Hodges-Chaffee, MS, RDN, CEDRD-S

The Low Carb Craze

There are countless types of diets that influence people in all walks of life.  But despite their proliferation, popular diets are not based on scientific research, but on individuals who have experienced some degree of “success.”  People would think that following a simple diet for a few months would be harmless, and would hopefully result in some weight change, but the problem is that some diets can be very harmful for certain people.  Diets should not be taken lightly – they should come with warnings just as drugs do.  Just as medications can affect individuals differently, so too can diets.  For example, some individuals can go on a low-carbohydrate diet without experiencing any cognitive changes, but those who are susceptible to lower serotonin levels can quickly become obsessed and develop disordered eating or eating disorders.  The newest low-carbohydrate diet that has gotten America’s attention is the “Keto” diet, which allows for less than 20 grams of “net carbs” daily (calculated by subtracting the grams of fiber from the total number of carbohydrates).

The Carbohydrate-Protein Link to Serotonin Levels

When individuals who are sensitive to lower serotonin levels follow a low-carbohydrate diet, their bodies don’t have enough carbohydrates and protein (building blocks for serotonin) to make the neurotransmitter.  If they continue to limit their carbohydrates, their serotonin levels will decrease and this causes a change in brain chemistry that can increase feelings of guilt, which in turn may lead to eating even less – and the cycle repeats.  For those who have bodies (and brains) that are sensitive to changes in serotonin, this cycle can be the beginning phase of an eating disorder.

If the amino acid tryptophan (found in many protein foods) is the building block for serotonin, why is it so important to have carbohydrates?  When individuals follow a high protein, low carbohydrate diet there are many amino acids that are consumed.  The tryptophan must cross the blood brain barrier (BBB) to increase serotonin levels in the brain.  Protein is made up of several amino acids and these are competing to cross the BBB; tryptophan is not a great competitor so very little is able to cross the BBB unless carbohydrate is present.  This results in a gradual decrease of serotonin.  Carbohydrate causes the body to release more insulin which promotes amino acid absorption and leaves tryptophan in the blood.  If protein is consumed with carbohydrates then the carbohydrate will drive the majority of amino acids into the muscle, thus the tryptophan is able to cross the BBB much easier. (Food & Mood, Somer, 1999)

The Brain-Gut Connection

The brain has about 10-20% of the serotonin in the body, the other 80-90% is found in the gut.  This sets up the perfect storm for the development of an eating disorder.  As serotonin levels decrease in the body, the gut function slows down and individuals feel full much sooner and become very uncomfortable with nausea and/or bloating if they try to eat more.  As the gastrointestinal function decreases, constipation often occurs.  Imagine the individual who was simply trying to diet, as serotonin levels decrease they begin to feel more guilty about eating and at the same time because of the low levels of serotonin in the gut they also feel full sooner, as well as feeling bloated and constipated.  It hurts to eat, so they eat less and this leads to further decrease of serotonin in the body.  Clients often describe a noticeable change in their thought process.  Initially, they could control their eating behaviors and it was a choice about what and when to eat.  After restricting their intake, eventually they become a slave to their thoughts and have to follow the food rules or spend the day obsessing about everything they put in their mouth.

What begins as a well-intentioned attempt to lose weight and follow the new trending low carbohydrate diet is not a harmless endeavor.  Low carbohydrate diets should come with a warning that anyone who has a history or family history of an eating disorder, obsessive compulsive traits, depression, and/or anxiety may be at high risk to develop an eating disorder by limiting their carbohydrate intake.  Researchers are now exploring the differences in brain chemistry that may put some individuals at higher risk to develop an eating disorder.  What we do know is that glucose (a byproduct of carbohydrate metabolism) is the sole fuel for the human brain (except in prolonged starvation). The brain lacks fuel stores and requires a continuous supply of glucose.  (Https://www.ncbi.nlm.nih.gov, “Each Organ Has a Unique Metabolic Profile-Biochemistry-=NCBI bookshelf-NIH).   How can the brain be fed if there isn’t an adequate amount of carbohydrate?