Riddle me this, Batman...

If diet soda has no calories, why don't people lose weight when they drink diet soda?  By now, most of us have heard of the Glycemic Index, how much blood sugar response occurs when a food is digested, but until yesterday I had never heard of the Cephalic Insulin Response (CPIR).  I had actually been describing this pathway for years, without any proof that it existed!

So, what is this CPIR and how does it work?  This week's article goes in depth on the topic: Anticipitory physiological regulation in feeding biology, but I'll give you the summary here.  When we eat something sweet, even before it hits the digestive tract, our bodies are already prepped to respond to that sweet stimulus.  When sugar hits the tounge, a message is sent to the hypothalamus, the hypothalamus then sends out a cascade of hormones, one of these being insulin, to prepare the body to recieve sugar.  Insulin, in turn, increases activity of adipose lipoprotein lipase which absorbs sugar from the blood.  So, just by tasting something sweet (and not necessarily swallowing it) we see an insulin response and a decrease in blood sugar.  This "pre-digestive" insulin response is smaller than the one that occurs when we are digesting an actual sugar, but it is there nonetheless.  I think you can see where I'm going with this...

When an artificial sweetner is used instead of a natural sugar sweetner, the CPIR still happens.  So we still see an insulin release, and we still see the corresponding decrease in blood sugar.  When blood sugar goes down, another signal is sent from the hypothalamus- one that calls for sugar intake to increase circulating blood sugar.  In response, we start eating, and we tend to eat foods that are higher in carbohydrates in order to raise blood sugar. 

Usually when I get to this point in the explanation, people tell me "ok, well now that I know that, I just won't eat high sugar things. It will be easy."  Unfortunately, it is not easy to go against thousands of years of evolution.  No amount of willpower can deny these responses- they are there and you will respond to these hormonal signals without even realizing it.  Hence, no one loses weight drinking diet soda. 

That being said, sure it's not as easy as this explanation would make it seem.  The CPIR also has a large role in managing eating behaviors as well. Obese individuals have a blunted CPIR when consuming sweet foods, but normal insulin responses to sweet foods.  Additionally, everyone has a different CPIR and CPIR can vary based on the time of day, food consumed prior to sweet consumption, and past experience/food preference.  There's is always more research to do :)     

 

 

Stress

Let's face it, we live in a stressfull society.  If I ask ten people what is stressing them out right now, I will get ten different answers.  Most people focus on the things that are providing emotional or psychological stress (i.e. their significant other, the stock market, what to make for dinner, the balance of their bank account, etc.), yet very few identify physical stress (exercise) or immune stress (that cold you're fighting off) as sources of stress.  Stress, as we're talking about this week, is any number of situations that causes activation of the fight or flight response.  We all know that in stressful situations, our logical thinking patterns are less clear, attention span may be decreased, and memories are not formed as readily.  This is caused by the blockage of dopamine release and dopamine binding by epinephrine in the system.  That explains short term stress, but what about long term stress?  Very few stresses that we experience in today's society are short term, "flight or fight" responses.  To start loonking at this question, let's start at the very beginning...

Prenatal stress produces learning deficits associated with an inhibition of neurogenesis in the hippocampus, yikes.  Ok, this looks pretty bad.  The above study found that rat pups whose mothers had experienced stress during pregnancy experienced a greater decline in cells proliferation in the hippocampus than rat pups with mothers that did not experience stress during pregnancy.  Lifelong, these changes in hippocampal cell proliferation resulted in a 45% difference between prenatally stressed and non-stressed rats.  The "stress rats" also showed delayed learning on a spatial memory task and had an altered response to the spatial memory task, which normally causes increased cell growth in the hippocampus.  The theory advanced by the researchers here is that the early exposure to stress causes an increase in Hypothalamic-Pituitary-Adrenocortical Axis (HPA) activity, resulting in early exposure to corticosteroids.  Corticosteroids are known to alter the structure and function of the cells in the hippocampus, hence the changes that were demonstrated in this experiment. 

That all seems like really bad news, but here's the good news: a second study (abstract) found that postnatal care desined to decrease infant stress reduced ALL of the effects from the first study.  In addition, other studies have found that rat mothers naturally give their pups extra TLC after a stressful pregnancy.  This additional care post partum may be nature's way of correcting, or "making up for", the harm caused by corticosteriod secretion during the pregnancy process.  Smart rats, now we just need to teach people to do the same, right? :)