The Effects of Carbohydrates on Brain Function

Fueling the brain with carbohydrates plays a major role in the recovery from eating disorders. With the hype about the detrimental effects of eating carbohydrates it is not uncommon for people to become overly concerned with avoiding this macronutrient.  The belief that carbohydrates have the ability to cause obesity or illness to the body has been hammered into our minds for the past ten or more years. For many people, this mindset creates a battle between avoidance versus desire and cravings.  The severe shame and guilt of consuming these so called” harmful” foods results in such high levels of anxiety and depression, that  people resort to maladaptive coping strategies in an attempt to stay away from them.   Strategies such as extreme restriction or binging and purging in order to avoid intake of these foods create a perfect environment for an eating disorder to emerge. 


The brain requires approximately 130 grams of carbohydrates daily to optimally function. That’s about 40 % of the calories consumed in an adult’s daily diet.  One can say that carbohydrates are the brain’s fuel.  Despite the fact that the human brain accounts for only 2 percent of the body’s weight, the brain consumes 20% of carbohydrates energy.  The neurons of the adult brain require the highest energy demands of glucose (breakdown of carbohydrates) from our blood supply.  


The brain also requires a 24 hour source of fuel. Even when sleeping, the brain continues to require nourishment.  When these needs aren’t met, the body converts proteins to fuel the brain while depriving the rest of the body of energy.   Unfortunately, protein is not the most efficient source of brain fuel and the body cannot utilize the breakdown of fats for fuel at all.


Carbohydrates perform many functions in the brain. One of these functions is to act as a precursor to the creation of neurotransmitters, which are the body’s communicators throughout the body.  Two neurotransmitters that require dietary carbohydrates are serotonin and dopamine.


Carbohydrates significantly affect tryptophan absorption which in turn controls mood and behavior. Eating a meal high in carbohydrates triggers release of a hormone called insulin in the body. Insulin helps let blood sugar into cells where it can be used for energy, but insulin also has other effects in the body. As insulin levels rise, more tryptophan enters the brain. Tryptophan is an amino acid, or a building block of protein, that affects levels of neurotransmitters in the brain. As more tryptophan enters the brain, more of the neurotransmitter serotonin is produced. However, it is interesting to note that meals higher in protein do not increase tryptophan and serotonin levels.  Carbohydrate based meals increase tryptophan and serotonin levels the best.


Another neurotransmitter known as dopamine also requires carbohydrates to be synthesized.  Dopamine is required for the body to be rewarded with pleasure.  Many people with disordered eating issues who are dopamine deficient may look to increase dopamine levels in the brain with alcohol, caffeine or nicotine.  Excessive shopping or gambling can also increase dopamine levels.  Adding back a sufficient amount of carbohydrates to the diet may decrease the need for these less desirable behaviors.


Carbohydrates also aid in regulating proper blood flow throughout the body and assist the brain with processing information.  Without the proper amounts of glucose entering into the brain, studies have found that people exhibited decreased memory and reaction time, as well as, the inability to stay on task. 

On the flip side, binge eating large amounts of carbohydrates, whether refined or complex, have also been linked to learning disorders, depression, and poor memory. 

Excess refined sugar in the brain and blood appear to decrease a brain chemical known as Brain Derived Neurotrophic Factor(BDNF).  Without proper amounts of BDNF, our brains can’t form memories and learning diminishes.  Low BDNF levels also lower the body’s ability to protect itself from insulin resistance which leads to Type 2 Diabetes.  It also has been linked to depression and dementia, although more studies are needed. 

Binge eating excessive amounts of sugar also reduces the brain’s ability to tell you when you are truly full at a meal because it diminishes the activity in the brains anorexigenic oxytocin system which is responsible for feeling satiated.  The result is compulsive overeating.

Although a specific amount was not mentioned in the study, in my professional opinion, I would probably define “excessive” as greater than 300 grams of carbohydrates daily or greater than 75 grams at one meal.  It is also my opinion, that it may take a significantly lower amount of carbohydrates to alter chemical function of the brain if most of the carbohydrates consumed are from highly refined sources.

Carbohydrates are found in most foods that we consume daily.  All grains, fruits, vegetables and many dairy products contain different amounts and forms of carbohydrates. 

The following sample meal meets the 130 grams per day of carbohydrates required for proper brain function. It is important to also note that the brain functions better when these carbohydrates are evenly spaced throughout the day.

130 Gram Meal Plan for Optimal Brain Function

Breakfast:

  • ½ cup of cooked oatmeal (27 grams of carbs)
  • ¼ cup of slivered almonds
  • 4 oz Greek yogurt

 

Lunch:

  • 1 small side salad
  • 1 tbsp of oil and vinegar
  • 2 slices of whole grain bread (30 grams of carbs)
  • 4 oz of sliced turkey
  • ¼ cup alfalfa sprouts
  • ¼ mashed avocado
  • 1 tsp of mustard

 

Snack:

  • 1 medium apple (20 grams of carbs)
  • 1 tbsp of peanut butter

 

Dinner:

  • 1 cup of butternut squash soup (15 grams carbs)
  • 6 oz of seasoned chicken
  • 1 cup of non starchy vegetables (5 grams of carbs)
  • 1 cup of cooked quinoa (30 grams of carbs)

 

Although society has demonized carbohydrates over the past several years, it is important to remember that everything is moderation is the key to maintaining health. The avoidance, purging or over consumption of this nutrient can change the way the brain functions in many vital areas. 

 

Bibliography:

  • Encyclopedia of Mental Disorders
  • Journal of Appetite Study by Taylor and Colleagues Feb 2009
  • Trends in Neuroscience Oct. 2013
  • European Food Information August 2013
  • Psychology Today April 2013