Part of the problem in this discussion is the word "detoxification." It gets thrown around without much understanding in the "natural health" world. Go to any health food store and you'll find 1001 things that claim detoxification. The body has a detoxification mechanism that is poorlyunderstood in entirety, although we know a lot about it. That is called the Cytochrome P450 pathway. It is a group of chemical reactions split into two groups: Phase I and Phase II. The liver does about 70% or so of this, and most of the rest is done in the GI tract.
When we talk about "detoxification" at least in my office, what I mean is doing specific things that enhance Phase I, but much more importantly, Phase II, detoxification. Pretty much anything, fasting, Nutri-Slim, whatever, will induce Phase I. Phase II is the tricky part, though, because it requires specific compounds that have to be replenished continually. Diets need to be high in foods like red peppers, garlic, broccoli, Brussels Sprouts, etc to get these compounds effectively. Every time something goes through Phase I, it becomes water soluble and either can be passed in urine or feces, or reabsorbed. Or it becomes highly toxic and needs to go through Phase II. If you've never heard of this, it's actually the drug companies that have done the bulk of the research for things like "1st pass" toxicity and that sort of thing.
So, anyway, after Phase II, the toxic reactive intermediate becomes neutralized by the addition of a sulfur group, methyl group, or a variety of other compounds that could be added to it. Then it gets passed or reabsorbed.
The problem is multifaceted:
1) People don't eat the right foods, so they don't have the capability to perform detoxification properly.
2) People are overloaded by crap in their diet, air and water. Not to mention pharmaceuticals, OTC's, and whatever else people do to themselves.
So, the burdens on the system are higher than they were a few decades ago, even. Evolution doesn't keep up with rapid changes in the environmental outlook like this.
So, yes, the liver is capable of doing things, but look around you and I think you'll see plenty of evidence that we're not so healthy, so something must be amiss. We rank in the high 20's in world health, so we're a pretty sick country by and large.
I have put people on food-based "detox" programs and the changes they experience in 3 weeks are fantastic.