I didn't read that book. For the hypothesis however, I got a good counter to it.

OK so it's all about evolution, survival and adaptation, right? First is that we are addicted to everything that keeps us alive, so food, water, air, sleep, sex, and so forth. If we weren't addicted to all that, we'd die. We could argue that we have the intellect to figure out that we need food and water, but what about all the other species, how do they manage? Right, so it's an addiction, a physiological mechanism that ensures our survival in spite of absence of intellect. This mechanism works with hormones and enzymes to trigger certain behaviors so we hunt for food, water, a mate, and so forth. The brain is directly controlled by this mechanism. This is why for example that semi-starvation causes neurosis, we're not adapted to go hungry. On the other hand, full starvation doesn't cause neurosis - the same mechanism shuts down hunger - so we can think clearly, ya?

The above is how our physiology works. What about the sugar in fruit, how does that fit in? We could argue that we are also adapted to eat as much sugar as possible for some necessity, but there's a better explanation. The plants that produce fruit full of sugar, they have adapted too. They adapted to produce addictive fruit that will ensure their survival. Those plants that didn't adapt this way, died off or adapted a different way that does not support the need-sugar hypothesis. Fruit is seasonal, there's just not enough to do anything for us in any regards. Bear in mind that the seed is indigestible to us, also an adaptation of the plant to ensure its survival, and even without knowing it's indigestible, we don't eat it cuz it just tastes bad. The fruit fiber is also indigestible to us, no benefit whatsoever to be had there. Basically the only thing digestible is the addictive substance.

So the hypothesis says we're adapted to eat as much sugar as we must through a physiological mechanism that ensures our survival, but the better explanation says that the plants are adapted to produce a substance that takes advantage of our mechanism of survival for their own survival, regardless of our own survival. We could argue that our survival is their survival, of course, cuz if we died from that addictive substance, we wouldn't be there to repeat the experience, no survival for the plant past the first taste, ya? But remember, fruit is seasonal, so dose is unlikely to be of any significance with respect to both our and their survival - we can handle a few fruit once in a while and still survive, and the plants only need that much so they survive.

We could make a parallel with producers of addictive substances. Their survival depends on the addictive property of their product, and that addictive property relies on our physiological mechanism. But it's bad business to kill one's customers, so the dose is carefully measured to ensure survival of those customers for repeat business. Indeed, overdose is typically a result of inconsistent or unreliable or unknown dose, rather than of the substance itself or even of the user. In the case of those plants that produce fruit, it wasn't intentional, it was a product of natural selection. Those plants that produced fruit that was toxic enough to kill, didn't survive. Those plants that produced fruit that wasn't addictive enough, didn't survive either.

We could argue that we use glucose all the time and that's a carb, so that's why we must eat carbs, ya? But the sugar in fruit contains fructose, we don't use that. Instead, we convert it to triglycerides in the liver. Well, if we need to obtain fructose for the purpose of conversion into triglycerides, there's a much more effective way to get it - eat fat - and our liver is fully capable of dealing with fat in all respects, from digestion to absorption to metabolism to storage to conversion into different FFAs or into useful things like cholesterol for example and so forth. Furthermore, eating fat is self-limiting, it's basically impossible to eat too much fat, in spite of being just as addicted to that. The hypothesis is refuted on that point, but it brings up another point - satiety.

We're addicted to food and stuff, so how do we make sure we don't overdo it? Satiety. The same mechanism that ensures we eat something, also ensures that we stop eating it when we've had enough. If something causes us to eat as much as there is rather than as much as we need, this thing bypasses this second part of the mechanism. Food doesn't do that. So, do we actually need to eat as much carbs as we need, or is there something else going on here? Carbs is a drug produced by plants to ensure their survival, regardless of our own, but the mutual adaptation makes it so there's just not enough carbs produced and available to us to kill us. The hypothesis says "today with all that sugar, this mechanism is overwhelmed". Well, no shit, but the hypothesis is wrong in all other respects.

Don't take any of this too seriously, I just made it up as I wrote it.