Written by: Kevin Cann
Leptin is a hormone that was discovered in 1994. It plays a critical role in energy homeostasis, hunger, satiety, and behavior. Leptin is released from our white adipose tissue and communicates with the brain regarding how much fat we have in storage. When this system is working properly along with the other energy homeostatic hormones insulin, glucagon, and adrenaline, our weight remains at a healthy level.
Under normal circumstances we seek out food when leptin levels are low, and should be satiated when leptin levels are high. Leptin also follows a circadian rhythm. Levels should be low in the morning, stimulating us to eat, and they should be high in the evening, with the lowest levels around noon and the highest after midnight (http://www.google.com/url?sa=t&rct=j&q=&esrc=s&frm=1&source=web&cd=9&cad=rja&ved=0CGUQFjAI&url=http%3A%2F%2Fhrcak.srce.hr%2Ffile%2F44314&ei=ApdMUr2_Kozi8gT86oHABA&usg=AFQjCNEN0hed7rHDC_ZLHnG49i3gEyVqbw ). It is unclear the reasons for this rhythm, but blood sugar control may be the issue. Leptin’s rhythm is in direct opposition to cortisol’s daily rhythm. In fact the glucocorticoids associated with our fight or flight response may play a modulatory role in leptin synthesis (http://www.ncbi.nlm.nih.gov/pubmed/11824503 ). This means that if we do not manage our stress we can put ourselves in a dysfunctional leptin rhythm.
Just like with insulin and adrenaline, as leptin levels rise, our leptin receptors become desensitized to the hormone and we can develop leptin resistance. This means when our white adipose tissue sends the signal to our brains telling us to stop eating, our brain does not hear the message and we continue to eat. Dysfunction in the circadian rhythm of leptin can directly cause leptin resistance (http://edrv.endojournals.org/content/31/1/1.full ) as can eating a diet high in processed foods (http://www.ncbi.nlm.nih.gov/pubmed/21418711 ).
Leptin may actually be the major player in the metabolic dysfunction that causes obesity, as it is tied to a number of different hormones responsible for weight gain and disease. Leptin may play a role in the pathophysiology of thyroid dysfunction with the regulation of uncoupling proteins (http://www.eje-online.org/content/149/4/257.full.pdf ). It even has been theorized to play a role in the formation of cancer (http://www.ncbi.nlm.nih.gov/pubmed/16110483 ). One area that I find to be extremely interesting is the role that leptin plays on dopamine.
Dopamine is our hunt and reward neurotransmitter. It is responsible for memory, focus, and energy levels. Dysfunction in the dopamine pathways has been implicated in neurodegeneration, ADD, ADHD, and various mood disorders such as schizophrenia. Dopamine is also a popular target for addictive drugs such as cocaine. Dopamine also plays a critical role in our drive to eat.
The dopamine response to overeating is very similar to that of addictive drug behavior (http://www.nature.com/neuro/journal/v13/n5/full/nn.2519.html ). Processed foods can elicit a greater reward response than fruits and vegetables. For example, can you eat more broccoli or ice cream? This increased influx of dopamine can cause our cells to become desensitized to the neurotransmitter. According to Dr. Kenneth Blum’s Reward Deficiency Syndrome, we will become addicted to anything that balances out our biochemistry. If we are dopamine deficient and eat foods that raise dopamine levels enough to balance us out, we will become addicted. Even with adequate levels of dopamine we can be in a deficient state due to the desensitization of receptors. If we become desensitized to dopamine, we will need to eat more of these foods to elicit the same balancing act.
Leptin communicates directly with dopamine pathways. Leptin may raise dopamine levels enough to make it easier to resist rewarding foods. Remember according to Dr. Blum if we are deficient in a neurotransmitter we will seek out foods and substances that balance us out. Leptin can help us avoid this situation. However, if we are leptin resistant our dopamine levels may become deficient and we will crave sugary foods. Leptin injected into the dopamine center of the brain has even been shown to cause rats to eat less and lose weight (http://www.news-medical.net/news/20090805/Leptin-influences-baseline-dopamine-levels-and-motivation-to-eat.aspx ).
In my practice I use questionnaires to determine neurotransmitter deficiencies, and almost everyone has a deficiency in dopamine. There are many factors that play a role here, but leptin resistance is one that cannot be overlooked. This may also be one way how leptin could be implicated in certain mood disorders and addictive behaviors. Low levels of leptin have been associated with depression (http://www.ncbi.nlm.nih.gov/pubmed/18032111 ). This may explain why treatment with specific amino acids and anti-depressant medications do not have a 100% success rate. Mood may not be able to be improved in the presence of leptin resistance. This makes proper nutrition, exercise, and lifestyle behaviors even more important when treating mood disorders and other diseases. It also shows us how little we truly understand in the dynamics of disease.
Leptin being a relatively new discovery makes it difficult to truly understand. The more I research it the more I feel it may be the major player in metabolic control. Spacing meals out five hours apart, getting adequate sleep, having good vitamin D levels, and managing stress can all have positive effects on leptin. As we learn more about this powerful hormone we can develop better treatment protocols to get it back on track.
Also be sure to check out my previous post on how meal frequency affects leptin levels here: http://robbwolf.com/2013/07/18/meal-frequency/ .