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Weight regulation part 3: What about carbohydrates?

Since the 1970s we have been told by a majority of nutrition and medical professionals that fat, especially saturated fat, is the culprit in all of our ills from obesity and cardiovascular disease to diabetes and cancer.  We have been urged to cut our fat intake down to abnormally low levels.  Since protein intake remains relatively stable, cutting down on fat means increasing our intake of carbohydrates. We have complied admirably and more and more of us have gained weight and become insulin resistant and eventually diabetic.  The remedy for this, we are told, is to cut calories and exercise more.  But this is a recipe for hunger, not tolerable in the long term, as well as a slower metabolism that tries to conserve energy. We have also been told that virtually no one has a hormone problem.  We just eat too many high calorie, high fat foods.

It is true that to gain weight we must take in more energy than we expend.  However, the way that our bodies partition the energy from the food we eat into either use or storage is tightly regulated by our internal chemical signals (hormones) and by genetics. What if, instead of a defect in calorie balance, excess weight is a defect in the regulation of fat metabolism; a disorder of fat accumulation, not necessarily of overeating?  The release of fat to be used as energy may be impeded or the deposition or synthesis of fat promoted, resulting in weight gain.  If an abnormal number of the calories we eat go into storage in our fat tissue, the rest of our body’s cells and tissues will perceive an energy deficit. Hunger and satiety are manifestations of metabolic needs and physiological conditions at the cellular level, and so they’re driven by the needs of our bodies, not our brains. Cells must receive sufficient energy to function; we eat to maintain the flow of energy to our cells and tissues.

The substance that regulates the flow of energy in our bodies is insulin, which is an anabolic or storage hormone.  Made in the beta cells of the pancreas, insulin is secreted into the bloodstream in response to glucose levels in the blood.  Carbohydrates in the form of starches (bread, rice, potatoes, corn, anything made of wheat flour, etc) all are digested into glucose, which passes from the digestive tract directly into the blood.  Sugar and high fructose corn syrup do the same, except they also contribute fructose. After eating carbohydrates the glucose level in the blood rises, stimulating the pancreas to release insulin.  Insulin is necessary for the transportation of glucose from the blood across the cell wall into the cell.  The more refined the carbohydrates and the more easily digestible they are the more and faster insulin is released.  It is this insulin that plays a primary role in the fattening process.  For it is the chronic elevation of insulin brought on by a high carbohydrate (especially refined carbohydrate) diet that is the prime suspect in the cause of weight gain.

A very simplified explanation of how this works might look like this.  Excessive carbohydrate intake, especially of processed carbohydrates, leads to chronically elevated insulin levels.  Cells become resistant to the insulin signals to let in the glucose, so the pancreas increases its insulin output in order to remedy the situation, resulting in higher than normal insulin levels.  This condition eventually develops into insulin resistance. Interestingly, muscle and other tissue cells become insulin resistant but the fat cells (adipocytes) remain inordinately sensitive to it, meaning that the excess glucose in the blood is transported into adipocytes where it is converted into fat (triglycerides) for storage.  In fact, glucose is not only converted to fatty acids, it is also necessary in order for fatty acids to be assembled into triglycerides. High glucose and insulin in the blood also cause the triglycerides to remain inside the fat cells where they cannot be broken down for energy.  So we have plenty of stored fuel within our fat cells but it is not accessible to be used for energy as long as we have high levels of glucose and insulin in our bloodstreams.  Our body perceives this situation as starvation at the cellular level, hunger ensues, and we eat more.  Fatty acids can only be released into the bloodstream to be used for fuel when insulin and glucose levels are low.  And they are seldom low if we eat a high carbohydrate diet.  Our insulin levels are elevated for longer periods than nature or evolution intended, and we fail to balance fat oxidation with fat deposition.  So the problem of inordinate weight gain may well be hormonal for most of us! Incidentally, it is normal to burn fatty acids for most of our energy needs.  They are the logs on our metabolic fire.  Glucose acts more like the kindling, burning quickly and fueling a desire for more.

So far we have talked about glucose, but what about fructose?  While fructose does not raise insulin levels, it is transported directly from the small intestine to the liver.  In the liver it enters the metabolic pathway that builds fatty acids and triglycerides.  Thus fructose is considered the most lipogenic (fat-building) carbohydrate.  Sugars such as sucrose (table sugar, 50% glucose, 50% fructose), high fructose corn syrup (usually 55% fructose, 45% glucose) and agave syrup (75-90% fructose) stimulate fat synthesis more than glucose alone.

It has been said that it is impossible to gain weight on a diet devoid of carbohydrates.  The efficacy of low carbohydrate diets for weight loss has been shown both anecdotally and experimentally (more about these in future posts).  The answer for most of us, however, comes back to the ongoing theme of this blog—eat real food.  Vegetables are predominantly carbohydrates but are not concentrated or refined and come packaged with many other nutrients and fiber.  Fruits contain fructose but in moderate quantities.  If made into juice, however, the sugar content is concentrated many times over. Moderate quantities of whole starchy foods are fine unless you need or want to lose weight or suffer from insulin resistance or diabetes.  Generous quantities of meats, eggs, natural fats, unsweetened dairy products, vegetables and fruits do not cause weight gain unless combined with refined carbohydrates!

And why, you might ask, do the medical and nutritional experts advise us to eat more carbohydrates?  If I were a conspiracy theorist I might think that the generous contributions and research grants they receive from the big food companies that are so good at turning out a myriad of cheap processed high carbohydrate foods has something to do with it.  Also, if we eat a diet high in refined carbohydrates we will eventually become sick and need pharmaceutical intervention.  There is lots of money to be made by keeping us sick and treating us for it!

Reference

Taubes, Gary.  2007.  Good Calories Bad Calories. Challenging the Conventional Wisdom on Diet, Weight Control, and Disease. Alfred A. Knopf, New York.  601 pp.

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