It comes down to basic physiology. Your body converts the carbohydrate you eat into glucose, raising blood glucose levels. An increase in blood glucose triggers the release of insulin, which causes glucose levels to go down – but also causes fat build-up in cells.
Your physician should know this. I took the graduate physiology course taught to medical students at the University of Pittsburgh School of Medicine in 1977. I was a graduate student in Biomedical Engineering at Carnegie Mellon University at the time.
Insulin is the fat hormone. High levels of insulin promote fat buildup in the body. This is a long-established fact.
Guyton continues “… insulin promotes the utilization of carbohydrates for energy, while it depresses the utilization of fats. Conversely, lack of insulin causes fat utilization mainly to the exclusion of glucose utilization … Furthermore, the signal that controls this switching mechanism is principally the blood glucose concentration. When the glucose concentration is low, insulin secretion is suppressed and fat is utilized almost exclusively for energy; when glucose concentration is high, insulin secretion is stimulated, and carbohydrate is utilized almost exclusively. Therefore, one of the most important functional roles of insulin in the body is to control which of these two foods from moment to moment will be utilized for energy.”
So through its influence on insulin secretion, blood glucose concentration controls whether our bodies are metabolizing carbohydrates or fat for energy. According to Guyton, “At the normal fasting level of blood glucose of 80 to 90 mg./100 ml., the rate of insulin secretion is minimal … As the concentration of blood glucose rises above 100 mg./100 ml. of blood, the rate of insulin secretion rises rapidly … Thus, the increase in insulin secretion under a glucose stimulus is dramatic both in its rapidity and in the tremendous level of secretion achieved. Furthermore, the turn-off of insulin secretion is almost equally as rapid, occurring within minutes after reduction in blood glucose concentration back to the fasting level. This response of insulin secretion to an elevated blood glucose concentration provides an extremely important feedback mechanism for regulating blood glucose concentration. That is, the rise in blood glucose increases insulin secretion and the insulin in turn causes transport of glucose into the cells thereby reducing the blood glucose concentration back toward the normal value.” Electrical engineers like me call this a “negative feedback loop”.
What do we eat that causes blood glucose levels to rise? Guyton says “The foods on which the body lives … can be classified as carbohydrates, fats, and proteins. … In the ordinary diet … glucose represents about 80 percent of the final products of carbohydrate digestion …” Digestion transforms fat primarily into monoglycerides, free fatty acids, and glycerol, and protein into amino acids – not glucose.
It’s the carbs we eat that cause glucose levels to rise, thus insulin to increase, leading to fat storage. Eating carbs makes us fat. High carb, low fat diets are simply not supported either by scientific theory or by experiments on humans. My own tests on myself show this very dramatically.
It astonishes me that few physicians and dieticians consider metabolism when they recommend diets. Established metabolic science puts the burden of proof on those pushing high carb, low fat diets. Wouldn’t anyone with an elementary understanding of metabolism expect high carb diets to lead to increased body fat? Physicians, in particular, should know better – they took the same physiology course I did. If your physician or dietician tells you to go on a high carb, low fat diet, remind him or her that carbs metabolize into blood glucose, which increases insulin levels, which in turn promotes body fat. Tell him or her to look it up in his or her physiology or nutrition textbook. And if I were you, I would start looking for a new doctor or dietician.
Don’t calories = body fat? Calories are measured by a calorimeter, which measures the amount of energy released by burning a sample. Why would you expect the energy in food as measured by burning a sample to have a direct association with how fat is accumulated through complex metabolic processes in the human body? While the amount of food we eat is no doubt contributory to the amount we weigh, there is substantial evidence that people on low carb diets have greater success losing weight that those on restricted calorie diets.
If you are diabetic – all the more reason to be on a low carb diet. I never stop being amazed by doctors and dietitians who insist that diabetics eat high carb, low fat diets. Diabetes is fundamentally a disease of carbohydrate metabolism. I think of myself as having a disability: as a Type 2 diabetic, I am carbohydrate-challenged. It should be obvious that the first thing to do is to drastically cut back on carbs, yet the dietitians seem much more concerned about the “risks” of not enough carbs in the diet. The Academy of Nutrition and Dietetics, formerly the American Dietetic Association, actually puts starchy food at the top of its list of what diabetics SHOULD eat! Do they think calling themselves an academy will get people to start taking them seriously? I’ve never seen any evidence that humans need to eat any starch at all – indeed, just the opposite: truly low carb diets win convincingly in clinical diabetes studies.
Low carb is great for Type 1 as well as the obvious choice for Type 2 diabetes, as shown by Dr. Richard Bernstein, who has lived with Type 1 diabetes for 66 years. Type 1 diabetes is far easier to control on a low carb diet.
For more information on why we get fat and how the nutrition establishment got on the wrong path, see Gary Taubes’ 2002 New York Times Magazine article “What if It’s All Been a Big Fat Lie?”, his new book “Why We Get Fat and What to Do About It“, and – if you have lots of time – his tome “Good Calories, Bad Calories”.