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Thursday, February 25, 2010

Carbs, carbs, carbs


Has there been any more debated food group over the last decade than carbohydrates? Nope! 

Do they make us fat?  Are they killing our kids?  How many carbs do we need in our diet?  If you're sedentary do you need them?  If you exercise, surely you need them?   Can we survive without carbohydrates?  Do you need carbs post-workout?

Why are they the topic of such hostile debate?
 
A carbohydrate is an organic compound that includes simple sugars, disaccharides, and starches.  A carbohydrate’s role is supplying energy.  Most tissues in the body can use glucose for fuel and most will use glucose unless it's not available.  If not derived from food, the body enlists gluconeogenesis to provide glucose from the liver responding appropriately, as needed, to glucagon (a peptide made and secreted from alpha cells in the pancreas).  When glucose is not available, fat and ketones are used for energy.



A carbohydrate is one of three key macronutrients.  Protein, carbohydrates, and fat comprise the majority of one's diet.  A carbohydrate represents 4 kilocalories/gram.  Government dietary guidelines suggest a diet comprised of 50% carbohydrates.  I'd guess the typical American eats at least that amount in the form of fruits, vegetable, breads, pasta, and hoards of processed carbohydrates loaded with processed fat, processed sugars, and horribly unhealthy chemicals.

Are carbs making us fat and killing our kids? Let me be clear first.  Obesity is due to an imbalance of energy.  The law of thermodynamics proves that if you consume more calories than you expend, you'll gain weight.  Conversely, if you consume less calories than you expend, you'll lose weight.  Simple physics folks.  Sometimes we make it much more difficult than it really is, but I digress.
 
Carbohydrates increase blood glucose and spike insulin levels; some more than others. The insulin-spiking exception(s) are fibrous carbohydrates such as broccoli, cabbage, asparagus, lettuce, tomatoes, onions, garlic and the like. Fibrous carbs are a great source of carbohydrate for this reason, plus they offer lots of vitamins, minerals, and key antioxidants vital to health. Concerning this discussion, we are referring to those carbs that spike insulin levels and override the body's system with glucose.

I'd argue that carbohydrates are a key culprit in obesity.  According to some research (Monash University (2008, August 22). Killer Carbs: Scientist Finds Key To Overeating As We Age.), the more carbohydrates that you consume, the more likely you are to eat more than you need.  This is likely due to carbohydrates' effect on free radicals and hormones in the body (ghrelin being one example).  Try it for yourself.  Eat a meal mostly comprised of carbohydrates and see how often you continue to go back to the kitchen for more food, time and time again.  Combine the fact that most processed carbs are loaded with sugar and laced with trans fats and omega 6's (among other things) and you're looking at a recipe for obesity and diabetes.

In the body's normal response to carbohydrate intake (and other macros to a significantly lesser degree), the pancreas is enlisted to release two hormones, insulin and amylin from pancreatic beta cells.  Amylin is responsible for glucose appearance; insulin is responsible for glucose disappeance through uptake by body tissue and muscles.  When the pancreas is pounded hour after hour, day after day, week and week, and year after year, it eventually begins to wear down and become less efficient.  The result? Insulin resistance, obesity, diabetes. 

The body becomes resistant to insulin, leading the body to produce more and more insulin.  This, in-turn, wears out the pancreas and leaves an inefficient system that eventually causes obesity and leads to type-2 diabetes.  [Often times, we don't know what comes first, obesity or diabetes; by the time diabetes is diagnosed, the patient has often had diabetes for 10-15 years.  After diabetes has set in, it becomes a vicious cycle of obesity and an increased lack of glucose control.]  All the while, since the pancreas has been beaten to death, amylin is also not working properly.  This leads directly (due to the endogenous effects of amylin being blunted) to a reduction in satiety, an increase in food intake, an acceleration of gastric emptying, and a resultant rise in glucagon secretion leading to the production of more glucose (recall that glucagon should only be stimulated in the absence of glucose, not in addition to).  As you can see, a diet rich in carbohydrates (especially in the absence of exercise) doesn't have a lot of upside.  To be fair to our sugary, starchy friend -- carbs are incredibly important and useful in fueling elite athletes, i.e. triathloner, marathoner, cyclers, etc.  But, that's the exception not the norm.

So do we need carbohydrates?

Contrary to popular belief, dietary carbohydrates are NOT essential. Nobody covers the science and facts behind nutrition better than Lyle McDonald.  How Many Carbohydrates Do You Need? addresses the highly contested issue of carbohydrates superbly.  Read it.  It's very helpful in understanding the role of carbohydrates.

I believe a diet comprised of 55-60% protein, 15-20% carb, and 20-25% fat is the most 'user' friendly macronutrient combination.  It's much easier to maintain lean muscle and minimize fat gain if kept within your calorie range.  The Primal Blueprint details a similar type of nutrition regimen.  Participation in endurance sports may warrant a higher percentage of carbohydrates in order to efficiently fuel your body.  Is that always the case?  As I was writing this blog post (I usually work on posts the night before or a couple of nights before it posts to the blog), a 'testimony' that addresses this very issue of carbs for endurance showed up on Mark Sisson's MDA.  Check it out.

Until next time...

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