Understanding Carbohydrates and Insulin: The Key Physiology Behind Low-Carb Diets


by Max Wettstein, Copyright 2012 *This is not medical advice

    There are so many low-carb diets these days, from ‘Atkins’ to ‘Protein Power’ to ‘South Beach’ to ‘The Zone’.  Most of us have tried one or more of these or have adopted our own low-carb version.  With the mainstream medical community finally coming on board with verification studies of the positive health benefits, it looks like the low-carb craze has become more than just a passing trend.  Along with controlling blood-sugar and insulin levels, all of these aforementioned diets control portions and calories as well, and recommend exercise, equally contributing to their huge success.  Given the sedentary nature of our occupation, we as pilots can certainly benefit from watching our carbohydrate intake, not to mention our caloric intake.  Carbohydrates do not necessarily deserve the bum rap they are being handed, and if eaten in moderation of the complex-type, they can be beneficial.  In fact, carbohydrate in it’s digested form of glucose, (blood-sugar), is the primary fuel for our brains, and allows us to mentally function at our optimum.  Reducing carbs to an extreme level can be very unhealthy, causing our body to enter into a state of ketosis when there is no glucose left for brain fuel.  We’ll examine ketosis more, but this ‘emergency’ condition occurs during a state of energy crisis, in order to prevent the brain from shutting down and going into coma.  Ketosis is like our back-up generator, kicking online when our regular power plant shuts down.  Ketosis has many negative effects, including headaches, memory lapses, nausea, dehydration, lethargy, kidney stress/stones, and bad breath.  So while there is a healthy place for a low-carb diet, a No-carb should be avoided and is not recommended by any doctor, nutritionist, trainer, who has any sense.

    It is worth noting before we continue, that the US Food and Drug Administration (FDA) does not yet recognize, define, or regulate the term “Low-carb”.  In fact it is illegal for food companies to market products using this phrase.  Instead you might see descriptions such as, ‘carb-sense’, ‘carb-select’, ‘reduced-carb’, etc.  Furthermore, when you see such products on store shelves, the actual content of carbohydrates contained in them is unregulated as well.  You need to be able to read the product label and decide for yourself if it really is ‘low-carb’.  As a future reference, the Center for Science in the Public Interest (CSPI), proposes that a low-carb food should have no more than six grams of carbohydrates per serving, (24 calories).  Along these same lines, the term “Net-carbs” is not defined by the FDA either, but is calculated by subtracting the fiber-carbs, and the sugar-alcohols, which have negligible insulin impact, from the total carbs contained in the product.

    If you are an athlete or physically train at moderate to intense levels, then you already know that carbohydrates are essential for energy to train as well as post-training muscle recovery.  Carbohydrates are without a doubt the body’s preferred energy source for moderate to intense levels of physical activity and the recovery period following.  What’s more to consider, eliminate carbohydrates from your diet and you have just eliminated a myriad of food and nutrition choices, including grains, cereals, pastas, breads, legumes, fruits and vegetables.  Clearly, we have to make room for carbs and invite them back in to our diets where appropriate.

    Generally speaking we primarily talk about two forms of carbohydrate: Complex and Simple.  Complex carbs digest and assimilate slower, have a lower glycemic-index and are also known as starches.  Simple-carbs are sugars and digest and absorb almost immediately.  Sugar comes in many forms including sucrose, fructose, lactose, corn-syrup, molasses, honey, and others.  Sugar is what the athlete, the low-carb dieter, the diabetic, and you alike, need to be concerned with the most, because sugar in all of its forms has a very high glycemic-index, meaning it triggers a large insulin response when digested.  Sugar can be beneficial for kick-starting recovery following an intense workout.  The large insulin-secretion that sugar induces helps speed nutrients to damaged and depleted muscles.  Sugar rapidly replaces spent glycogen stores.  Other than post-workout meals, it is better to avoid sugar altogether.  Sugar consumption by itself causes rapid rises in your blood-sugar levels, followed by rapid insulin spikes, followed by rapid drops in blood-sugar.  This cycle can cause significant energy and mood swings, and even hypoglemic symptoms.

    Insulin, if you’ll remember, is a hormone secreted by the pancreas that shuttles glucose from the bloodstream to all cells in the body with glucose-receptors.  Your muscles, liver, and fat cells alike have the potential to uptake glucose from your bloodstream.  In fact, in a normal, healthy person the liver and muscle cells will uptake glucose in first priority and store it in the form of glycogen for energy.  (Glycogen is simply stored glucose.)  Only once the liver and muscle glycogen stores have been replenished, will any remaining excess glucose, not required for immediate fuel, be stored in the fat cells.  An average liver can store up to about 400 calories worth of glycogen, (100 grams), and our muscles up to 1500 calories worth.  So our liver and muscles are huge energy reservoirs, full of glycogen.  Glycogen is released in the form of glucose back into the bloodstream when needed for energy, as well as converted into ATP for muscle-cellular energy required every single contraction.  And this is good news because it clearly means that when we eat carbohydrates the first order of business is immediate energy for our brains, second is to replenish glycogen stores in the liver and muscles, and only after these two processes are accomplished will any remaining, unneeded glucose be converted to fat stores.  Again, insulin is the shuttle for getting all of this glucose to the right cells at the right time.  Although insulin does not directly promote fat storage, it does prevent fat burning for fuel when it is circulating in the blood stream.

    Incidentally, it should be noted the carbohydrates are not the only macro-nutrient that triggers insulin secretion.  Protein does as well.  Yes, our beloved protein.  However, protein does not have nearly the large effect on insulin-release that carbs do, and so for most low-carb diets, protein is considered to have a negligible effect on insulin levels.  Fat is the only macro-nutrient that has absolutely no effect on insulin.

    Insulin, unlike some hardcore, low-carb fanatics would have you believe, is very essential to our health.  For athletes, insulin is responsible for muscle growth and recovery, and glycogen replenishment.  In fact, without insulin, our bodies have no access to glucose, and therefore no energy.  Ketosis can help provide an emergency source of temporary brain-fuel by breaking down fatty acids and amino acids into ketones for energy, in order to save our brain from slipping into coma, but ultimately we need our primary energy source of glucose and its transport hormone, insulin, to survive.  Type-1 diabetics are individuals who do not produce insulin at all, and when they consume carbohydrates their bloodstream gets overloaded with glucose, (A dangerous condition known as hyperglycemia), because it has no means of transport to the cells of the body.  This type of diabetic has to inject his or herself with insulin for their entire life and closely monitor their blood-sugar levels throughout the day, especially after meals.  Type-2 diabetes, also known as ‘adult-onset’, is much more common, and although it can be hereditary, in most cases can be prevented, or cured through diet and exercise.  A type-2 diabetic produces insulin, but for various reasons, usually due to obesity, sedentary lifestyle, and chronic, excess sugar consumption, has acquired intolerance to glucose, meaning their liver and muscles cells uptake glucose very poorly, if at all.  This state of poor glucose uptake is also termed as ‘insulin-resistance’.  But the problem is not with the pancreas or insulin production as is the case with type-1 diabetes, but rather with the body’s cells not absorbing the glucose properly.  The end result is low-energy, excessive conversion of glucose to fat stores, and glucose build-up in the bloodstream.  Eventually the pancreas tries to compensate for the excess blood-sugar by over producing insulin, and overtime, may stop insulin production altogether.  The body has no choice but to pass glucose out through the kidneys to help alleviate the resulting state of hyperglycemia which causes many adverse health effects.  A downward spiral of poor carbohydrate metabolism and increased obesity is set in motion, with chronic hyperglycemia reeking havoc on overall health.

    Okay, so why all that talk about diabetes?  Because the whole premise behind every low-carb diet stems from medical research of Type-2 diabetes and the goal to control blood-sugar and insulin levels through diet and exercise is the same.  If you’re a normal, healthy person who eats reasonably and is moderately active, you probably metabolize carbohydrates just fine, as Mother Nature intended.  However, if you are a sedentary individual who does not exercise and are overweight, you may be already heading down the road of glucose intolerance, overproduction of insulin, and eventually type-2 diabetes.  A low-carb diet will definitely benefit you, not to mention a consistent exercise program.  Considering that 65% of our country is now considered ‘overweight’, it is no wonder that so many are following some version of a low-carb diet.

    Exercise needs to be quickly addressed, because the physiological benefits go way beyond the immediate calorie expenditure and metabolism boost.  Exercise literally restores/enhances your body’s glucose uptake ability.  Athletes, for example, metabolize carbohydrates efficiently, and their livers and muscles soak up blood-sugar like huge sponges.  There is no glucose left over to be stored as fat, and their insulin serves as an anabolic, nutrient-rich, shuttle to the cells.  This is what happens, physiologically, over time, to all of us, if we stay on a realistic but consistent exercise program.  We will metabolize, uptake, and utilize the carbohydrates we eat to provide abundant, sustaining energy, rather than convert and store them as fat.  So as long as you’re exercising consistently, you can give in to that sweet tooth, within reason, and not worry about your weight or your health.

    There is a time and a place for low-carb dieting, especially if you’re sitting in the cockpit all day, and are unable to exercise.  But carbohydrates are not the enemy, and if you select them whole-grain and unprocessed, they are usually packed with healthy fiber and nutrients, providing sustained energy.  A ‘no-carb’ diet however, is extremely unhealthy and is never recommended, not even for diabetics.  In addition, follow a consistent exercise program, or at least strive to stay active, and you’ll most likely never have an issue metabolizing carbs efficiently.  Finally, if your low-carb diet centers mainly on animal-derived protein, you should have your LDL cholesterol checked periodically, as many unaware dieters have reached dangerously high levels of this heart disease-causing cholesterol.

Sources: MT Sinai School of Medicine Total Nutrition Guide; Sports Nutrition for Endurance Athletes by Monique Ryan; Encyclopedia of Modern Body Building by Arnold Schwarzenegger; The Fat Burning Diet by Jay Robb; The Zone by Barry Spears; My personal dieting experience!                

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