I have a family history of both alzheimer’s and cancer. The conventional wisdom on both of these seems to be that they’re pretty lifestyle independent. There’s not a lot I can do to avoid them, since I don’t smoke and I drink only moderately. Having watched several family members succumb to Alzheimer’s, I would do a lot to avoid the same fate myself.

Alzheimer’s

Good Calories, Bad Calories lays much of the blame for Alzheimer’s on, you guessed it, carbohydrates. It seems the diabetics are twice as likely to get Alzheimer’s as non-diabetics, and diabetics who take extra insulin are four times as likely to get it. GCBC consistently uses this type of thing as evidence that they share the same cause.

Alzheimer’s disease is associated with the presence of compounds called amyloids in the brain. These amyloids are misfolded protiens that are toxic to nerve cells. They also form plaques in the brian which can kill nerve cells.

The human body has an enzyme that can clear out the amyloids. The enzyme is IDE, which is Insulin-Degrading Enzyme. As expected from the name, IDE primarily degrades insulin. If there’s a ton of insulin around, there might not be enough IDE to degrade the amyloids as well. That’s certainly the claim GCBC makes.

Since high carbohydrates can lead to high insulin levels, they may also be responsible for Alzheimer’s.

Cancer

Along with diabetes and obesity, cancer appears to increase greatly as societies westernize. The reason for this is commonly held to be environmental pollutants, but apparently many missionary doctors have noticed cancer increasing as diets change. Indiginous people living in their traditional ways have less cancer than indiginous people in the same location who have switched to western diets. Sugar consumption also apparently correlates extremely closely with breast cancer incidence across countries.

GCBC draws a link between carbohydrates and cancer (you knew that would be true, right?). This time, the intermediate hormone that GCBC implicates is IGF, or insulin-like growth factor. Insulin-like growth factors are present in the body normally and apparently serve important signalling functions. When large amounts of insulin are present, it causes even more IGF to be present. The insulin binds to sites that would have been bound by IGF, leading to higher blood concentrations of IGF.

There’s some research showing that IGF (specifically, IGF-1) stimulates the growth of prostate and breast cancer tumors. Tumors will often have two to three times as many receptor sites for IGF as normal cells. GCBC makes a pretty strong claim that IGF is the main reason that people in western civilizations develop cancers. The theory seems to be that mutations occur all the time, but having high levels of IGF allows cells with cancerous mutations to thrive. The extra IGF tells the cells to proliferate and grow. And if the receptor sites on a tumor get filled up by insulin instead of IGF, that just allows the absorption of more glucose to fuel the cancerous growth.

Honestly this section of the book was the least convincing to me. It seems plausible, but the mechanism suggested by GCBC is a lot less fleshed out than the mechanisms suggested for heart disease.

General Longevity

IGF and insulin have also been linked to longevity. Slower growth leads to longer life in many species. There’s even a fairly strong link in many species between calorie restricted diets and longer life in several animals, including larger primates.

Animal studies on calorie restriction show that the longer lived animals have lower blood sugar levels, lower insulin levels, and very high sensitivity to insulin. The conclusion drawn by GCBC is that carbohydrate restriction is the main cause of longevity benefits, and carbohydrate restriction is necessary to get the calorie restriction used in these studies. One study has shown that feeding glucose to worms shortened their lives, though I haven’t seen any research about that in large animals.

The obvious implication from GCBC is that eating fewer carbs will lengthen your life. While carb restriction is definitely easier than calorie restriction, it still seems like a pretty severe diet change for most people. Given what GCBC has to say on premature dietary suggestions made in the past, I’m not making any huge changes now.