When we lump unlike things together, it confuses us and opens holes in our theories. I'm not normally one to read about diets, dieting advice, or anything of that sort, but in today's article about the Shangri-La Diet, I saw an important distinction that no one's talked about. Something Eliezer said in the comments struck me as odd:

a skipped meal you wouldn't notice would have me dizzy when I stand up

And a few posts later,

I can starve or think, not both at the same time.

Reading these, I thought, that's not what being hungry like feels like for me. But while being hungry doesn't feel like that, those descriptions were nonetheless familiar. And then it hit me.

He wasn't describing the symptoms of hunger. He was describing the symptoms of hypoglycemia, more commonly known as low blood sugar. Blood sugar is one of the main systems responsible for regulating appetite, so for most people, having low blood sugar and being hungry are one and the same. The main focus of the Atkins diet, for example, is reducing swings in blood sugar, thereby reducing appetite. The Shangri-La diet seems like it would have a similar effect.

Being diabetic (the kind caused by immunology, not the kind caused by diet), I monitor and control my blood sugar, so I have ample opportunities to observe how it affects my eating habits and how I feel. Like most insulin-dependent diabetics, I have been trained with a fairly detailed model of blood sugar, how it's affected by food and insulin, and procedures to follow if it's too high or low. The standard procedure for low blood sugar, taught to all diabetics, is to test blood sugar, eat exactly 15g (60 calories) of sugar, wait 15 minutes, then test again. In practice, I have sometimes responded to hypoglycemia, not with 15g of sugar as the procedure specifies, but with 15g of sugar, immediately followed by a thousand plus calories of binge eating - basically, as much food as I could shove down in the time between when I first started eating, and when my blood sugar returned to normal (about ten minutes). This behavior is common among people on diets stricter than they can handle. For me, someone not on a diet, with a mostly full stomach, it's downright odd. Or is it?

Being hungry is not the same as having low blood sugar. Hypoglycaemia feels like extreme hunger (plus a few other symptoms), but while extreme hunger takes a lot of food to get rid of, it only takes 60 calories and 15 minutes to completely eliminate hypoglycaemia. If you're hungry, you ought to suppress it. If you're hypoglycaemic, on the other hand, you need to deal with it swiftly, and in a controlled manner. What happens if you don't? As a diabetic, this, too, is in my training. The pancreas will release glucagon, a hormone that causes the liver to release stored sugar into the bloodstream. Getting rid of stored energy is good for a dieter, right? Well, in this case, no it isn't; the sugar stored in the liver would have been released the next time you exercised. Rather than burning fat, you're burning short-term energy reserves, so that when you do make it to the gym, you'll hit a wall more quickly. And of course, while your blood sugar is low and you aren't eating, you can't focus and you quickly burn through willpower.

Today's best diets prevent low blood sugar entirely, rendering the hunger vs. hypoglycaemia distinction moot. However, if you can't tell the difference between hunger and hypoglycaemia, then you can't tell whether it's your diet failing or your willpower. Blood sugar test kits are affordable and don't require a prescription, and once you know what low blood sugar feels like, you won't need the kit anymore. There is much more to dieting than just controlling blood sugar, of course, but we do know that blood sugar is important. So why has no one proposed the Prick Your Finger diet? Why do none of the popular diets involve measuring blood sugar at all, ever?

Mild hypoglycaemia feels like a caffeine overdose without the energy: irritability, palpitations, and tingling in the extremities. It is a distinctly alien feeling, and includes an urgent desire for food. Only sugar can eliminate it; fat, protein and complex carbohydrates will not help at all, and should be avoided. Severe hypoglycaemia produces other symptoms, but can only be produced using medication.