A Simplified Description of Low-Carb Diets
The basics of "food fates;"
1. Carbohydrates (starch, glycogen, sugars) are digested (in the digestive system) to simple sugars. These are transported through the bloodstream. Individual cells take them up, essentially convert them to glucose, and do things with them.
2. The thing that cells prefer to do with glucose is "burn" it to extract energy. Some other cellular molecules can be produced from glucose, so not all of it is burned--but the vast majority is.
3. Cells cannot use glucose to produce all 20 of the amino acids. Therefore, a diet without protein leads to malnutrition and potentially death.
4. Proteins are digested to amino acids. The amino acids are transported to individual cells, which take them up and do things with them.
5. Amino acids are the building blocks of protein. Usually, amino acids are used to build protein. In muscle cells, much of the protein is the actin and myosin that make the muscles work. In other cells, the protein is the enzymes and structural proteins that are required for cells to function.
6. Some cells can "burn" amino acids for energy. Therefore, a diet without carbohydrates is tolerable. Indeed, carnivores like wolves live on such a diet quite happily.
7. Fat is another molecule that we can "burn" for energy.
Basic food vs activity: common sense
1. When we eat more "energy molecules" than we need, our "fat cells" store the excess by converting it to fat molecules. When we eat less than we need, our fat cells mobilize the fat, and we burn it for energy. Weight gain, weight loss, and weight maintenance is determined by our relative rates of food intake (consuming calories) and activity (burning calories).
2. Different people have different "setpoints" for their metabolic balance. On the same food intake, some people will gain weight while others do not. There is no point in trying to be heavier or lighter than your natural setpoint leads to. But don't pretend you have a high-weight-gain setpoint when you simply eat a lot.
Physiological interactions among cell types
1. Brain cells can only metabolize glucose for energy.
2. Muscle and liver cells can metabolize glucose or fat for energy.
3. Liver cells can convert glucose to fat, for storage in fat cells. They do this when there is plenty of glucose around.
4. Liver cells can also build glucose from amino acids. This takes energy, an is therefore inefficient (since they can't use photosynthesis). They do this when there is too little dietary carbohydrate to keep the blood sugar level adequate. Then, the liver must use amino acids to produce glucose (so the brain cells can survive--see #1).
5. When liver cells convert amino acids to glucose, they start by converting the amino acids into an "intermediate" chemical compound. This intermediate is the starting material for building glucose. This intermediate is also the starting material for the metabolism of fat. Therefore, liver cells cannot metabolize fat if they must produce glucose. Biochemists phrase this as "fats burn in the flame of carbohydrate." Without carbohydrate in the diet, fat is metabolized inefficiently.
Implications for various diets
1. On a diet that lacks carbohydrates, we "burn" amino acids for energy. We also use amino acids to produce glucose to keep our brain cells alive. We cannot metabolize fat very well, so the fat is excreted as "ketone bodies." This is why you can use "keto-sticks" to test for ketones in your urine. Because we cannot metabolize fat very well, Atkins says that it's okay to eat as much as you want.
2. On the other hand, a diet that lacks carbohydrates is really bad if it does not have enough dietary protein to supply both energy needs and blood glucose. Under these conditions, the body switches to "starving" physiology, and breaks down muscles to provide the necessary amino acids to build glucose. This makes sense: if muscles atrophy, they can (in principle) re-grow once food is again plentiful. However, if the brain dies, then it no longer has a need for food.
3. On a diet that has carbohydrates and adequate amounts of protein, we "burn" the glucose that we obtain from dietary carbohydrate. We use the amino acids from the protein to maintain our cellular protein. As long as we don't eat so much carbohydrate that our bodies store the excess by converting it to fat, we maintain our weight.
4. On a diet that contains carbohydrates, proteins, and fat, we are more likely to gain weight because we have two sources of energy molecules--the carbohydrate and the fat--so we are more likely to have plenty of excess material to store as fat. A normal American diet is rich in all three of these, and usually is not accompanied by sufficient activity to offset the amount of food that is eaten. This accounts for the increase in frequency of overweight and obese Americans.
5. Therefore, a diet that provides adequate amounts of proteins, only modest amounts of fat, and modest amounts of carbohydrate, should be somewhere in-between these extremes. Limiting the energy-foods prevents converting the excess to fat (since there is no excess). Consuming some carbohydrate provides an adequate source of blood glucose without "pirating" the amino acids (or one's own muscles).
What diet is best?
The Atkins diet over-emphasizes the fact that fat metabolism is inefficient in the absence of dietary carbohydrate. It recommends eating fat with reckless abandon. The long-term effects on heart disease are unknown. (For a typical American diet, saturated fat correlates with heart disease.) To achieve zero-carbohydrate intake, the Atkins diet recommends eliminating fruits and vegetables as well as foods that are rich in starch, such as potatoes, bread, rice, and pasta. Unfortunately, eliminating fruits also eliminates the main source of antioxidants and vitamin C, which protect against certain forms of cancer. Therefore, the Atkins diet goes overboard, and results in at least two consequences that are ill-advised: not eating fruits and vegetables, and eating large amounts of saturated fat. Both seem destined to lead to health problems.
A less-extreme low-carb diet has, however, been around for a long time. This is the type of diet recommended by physicians for patients with type 2 diabetes. This diet lowers the intake of carbohydrates, particularly in the form of sugar (i.e. soft drinks) and highly-starchy foods (such as potatoes or white bread). The diet does not eliminate carbohydrates altogether, and encourages the consumption of fruits and vegetables. In fruits and most vegetables (except root vegetables like potatoes and yams), the starch concentration is not that great. Therefore, they provide a good source of vitamins and antioxidants without also providing too much carbohydrate. This diet also does not recommend eating large amounts of fat.
From the negative aspects of the official, Atkins diet, and from the fact that the "diabetes diet" works quite well, we can reach a reasonable conclusion: moderating the intake of carbohydrates, rather than eliminating them altogether, is reasonable. Recent studies show that a simple way to do this is to stop drinking soft drinks.
There is an alternative, of course. Since weight gain occurs when the calories taken in exceed the calories expended in activity, one could simply eat less food (the ELF diet), or one could be more active. For errands within a few miles of home, walk rather than drive. Take up a sport, like Tae Kwon Do or soccer. Stop using the elevator. To quote the Royal Canadian Air Force Manual, when you need to use the restroom, don't use the one on your floor of the building. Use one two floors up or down, and take the stairs--two at a time at a run.