Monday, June 9, 2008 by Dr. Manny
At the heart of the debate about most low carbohydrate diets are fundamental questions about what is a "normal" diet and how the human body is supposed to operate. These questions can be summarized as follows. Nutritive carbohydrates (starches and sugars) in the diet tend to break down very easily into glucose in the bloodstream (blood sugar) when consumed. Glucose in the blood is used by the cells in the body for energy for their basic function. Excessive amounts of glucose in the blood are toxic to the human body (the reason diabetes causes such serious health problems). In general, unless a meal is very low in starches and sugars the level of glucose will tend to rise to potentially dangerous levels. When this occurs, the pancreas automatically produces insulin to cause the liver to convert glucose into glycogen (glycogenesis) and triglycerides (which can become body fat), thus reducing the blood sugars to safe levels. Diets with a high starch/sugar content, therefore, cause sharp spikes in insulin production. As such the blood sugar levels are highly variable with every meal.
By contrast, if the diet is very low in starches and sugars (low-carbohydrate diets) the blood sugar level can fall so low that there is insufficient glucose to fuel the cells in the body. This state causes the pancreas to produce glucagon. Glucagon causes the conversion of stored glycogen to glucose and, once the glycogen stores are exhausted, causes the liver to synthesize ketones (ketosis) and glucose (gluconeogenesis) from fats and proteins, respectively. Most cells in the body can use ketones for energy instead of glucose, and since ketones are easier to produce, only a small amount of glucose is created (in other words, ketosis is the more significant process in this case). Because diets low in starches and sugars do not tend to directly affect blood sugar levels significantly, meals tend to have little direct effect on insulin levels (and so such diets tend to discourage insulin production in general).
The diets of most people in modern, so-called western nations, especially the United States contain significant amounts of starches (and, frequently, significant amounts of sugars). As such, the metabolisms of most westerners tend to operate outside of ketosis and tend to involve significant insulin production. This has been regarded by medical science in the last century as being "normal." Ketosis has generally been regarded as a dangerous (potentially life-threatening) state which unnecessarily stresses the liver and causes destruction of muscle tissues. The view that has been developed is that getting energy more from protein than carbohydrates causes liver damage and that getting energy more from fats than carbohydrates causes heart disease and other health problems. This view is still the view of the majority in the medical and nutritional science communities.
Most advocates of low-carbohydrate diets (specifically those that recommend diets similar to the Atkins Diet) argue that this metabolic state (using primarily blood glucose for energy) is not normal at all and that the human body is, in fact, supposed to function primarily in ketosis. They argue that high insulin levels can, in fact, cause many health problems, most significantly, fat storage and weight gain. They argue that the purported dangers of ketosis are unsubstantiated (some of the arguments against ketosis result from confusion between ketosis and ketoacidosis which is a related but very different process). They also argue that fat in the diet only contributes to heart disease in the presence of high insulin levels and that if the diet is instead adjusted to induce ketosis, fat and cholesterol in the diet are not a major concern (although most do not advocate unrestricted fat intake and do advocate avoiding trans fat). Further, whereas insulin in the bloodstream causes storage of food energy, when the body is in ketosis, excess ketones (which contain excess energy) are excreted in the urine and the breath.
This debate is on-going and no consensus currently exists.
