it's good to be careful

The downstairs grocery in my building does actually sell diet stuff, e.g., tofu noodles as a substitute for pasta. It also has an increasing variety of diet drinks. That said, the supposedly "zero sugar" cookies you see below were new to me:

Above, you see a vaguely Oreo-like double cookie with creme filling (looks to be more cake than cookie). Above the English word "ZERO," you see the Korean inscription for zero sugar. Really? What does the nutrition label say?

First, it says 48 grams of carbs per 100-gram serving, so we already know it's 48% carbohydrates. That doesn't sound like "zero sugar" to me. There is, however, an entry that says "sugars: 0%." We'll get back to that. Elsewhere, it says "sugar alcohol: 17 g" and "dietary fiber: 3 g." These are components that can be safely subtracted from the carb number, so we go from 48 g of total carbs per 100 g of cookie to 28 g of net carbs. That's an improvement, but when you're stuffing these cookies into your face, are you realistically going to stop at 100 grams? Yeah—me, neither. Besides, from a keto perspective, 28 g of carbs is already more than one's daily carb allowance. So these cookies are a no-go because, from a dietary perspective, carbs and sugar are synonymous.

What about the cookies that actually look like cookies?

As it turns out, this is also filled with the dark side of the Force. Behold:

If anything, these cookies are worse. Total carbs: 60 g per 100 g of cookie. Sugar alcohol: 26 g, which drops the carb count to 34 g. But there's no listing at all for dietary fiber, so these cookies are still worse than the above cookies.

At best, you can torture yourself by eating 100 g of either cookie on, say, a cheat day (but if it's a cheat day, then eat real cookies!). These treats certainly aren't keto, and since what we generically call "carbs" break down into sugars, anyway, the above cookies are by no means sugar-free. What a shame. Want something tasty and zero carb? Eat meat. Go carnivore.

I've learned a lot about reading nutrition labels. A person on keto needs to look for the macros: protein, carbs, and fat. On keto, you're aiming for 75% fat intake (which is admittedly pretty steep), but you should probably focus more on minimizing your carbs. Light keto allows up to 50 g of carbs per day, but classic keto takes you down to 20 g. If something has "zero sugar" but still lists carbs, then you're probably still getting sugar in some form.

Vegans don't like to hear it, but all vegetables contain some amount of carbs—yes, even the leafy stuff. Per unit volume, veggies are more carby than meat. Not all meat is zero-carb, but even the meats that do have carbs contain no more than 2-3 g per 100 g of meat. 

Processed meats need to be handled with care. On "dirty keto," some amount of processed meat is OK (sausages, bacon, etc.), but here, too, look at nutrition labels: some companies sneak in carbs with their processed meats via bread fillers, sugars, etc. You must approach eating with a hermeneutic of suspicion (which is a fancy way of saying suspiciously). The best rule of thumb is to eat things that are as close to their original state as possible; that's one of the foundational principles of the paleo diet.

Why the insane focus on carbs? Because the more we learn about metabolism, the more obvious it is that sugar basically acts like a poison inside the body. All sorts of human maladies, it turns out, have at least some metabolic component to them, and this includes inflammation and cancer. You can starve these conditions out of you simply by cutting sugar out of your diet. I'm not saying anything radical like "keto cures cancer," but according to recent studies, lack of sugar does in fact affect how tumors behave: they become much less robust when there's no readily available sugar to ferment and convert into energy.

In a starvation situation, it works like this: your body will consume all available sugar and carbs first (and through a process called gluconeogenesis, the body can produce its own sugar). Once all the available sugar is gone, the body will start to metabolize fat (the famed ketosis), which is good news for fatties. After the fat is gone, though, the body is capable of metabolizing protein for energy. This isn't necessarily a good thing because, in a starvation scenario, this often means the body will eat its own muscle tissue to keep itself alive. Stay in ketosis, but don't go beyond that.

So watch your macros, focus on carbs, and read those nutrition labels intelligently so as not to be fooled by phrases like "zero sugar" or the equally insidious "no sugar added," which simply means the product already has sugar in it, but no more was added.