Ok, this is all fine and good for the various types athletes who transform vast amounts of energy daily. Perhaps, because of the muscle groups involved in swimming, swimmers would be better served to garner the majority of their calories from sugar and not fat. Let's assume he is correct (even though I doubt he is - I am entirely sure those sugar-hungry muscles could at least partially switch over to ketone usage if forced to in a sugar-depleted state; I acknowledge performance might not be as good however).

What about 99.5% of the rest of the population? I don't see what relevance this has for the rest of us. The majority of human beings aren't even facing glycogen depletion. What impact do those "bagels and bananas" have on the rest of us? Where does all that quick fuel go? I'll tell you where, the sugar is stored as fat we can't even burn, leaving us with more adipose and low energy levels (reactive hypoglycemia).

Because we ate so much sugar before from the bagel and banana, this necessitated an abnormally high secondary insulin response. The author fully acknowledges this. Seeing as our glycogen is already full, and seeing as we won't be doing much exercise, the insulin turns sugar into fat. No problem you're thinking, you'll just seamlessly make the transition into fat burning and use up the energy that way! Wrong.

When insulin is high, the catabolic (body fat burning) hormone glucagon is low. You can't burn body fat in a hyperinsulinemic environment, it is physiologically impossible. Insulin is an anabolic hormone, insulin rises in the fed state. It acts on consumed energy to mobilize it for energy, use it for tissue building, store it as fat. The logic behind an elevated insulin level means there is (or your body thinks there is) more than enough energy being consumed. This is what your body thinks, so it will never raise the catabolic, tissue wasting hormone (glucagon) when it knows insulin is high. The problem is, modern high carbohydrate food (either selectively bred or processed) is not a natural part of the human diet. The insulin/glucagon axis did not evolve to handle it. Such foods overwhelm the body with so much energy in a relatively short period of time that it "fools" the body into thinking it is in a feast-state even when it might not be.

For example, say you drink a small snack of 120 calorie fruit juice. The fruit juice, despite its low calorie level, is absorbed almost immediately and entirely into the blood. Your body sees that 120 calorie cup of fruit juice, and it thinks you are positively GORGING yourself. You’re body has evolved to see that kind of rise in blood sugar and think "WOW look at how high our blood sugar is... this is really weird… we must be eating a TON of berries, nuts, and meat! What a feast! Better shut off glucagon to stop body fat burning ASAP!! Better raise insulin to store all this precious fuel for later!!"

Your body has no idea that you merely “spiked your sugar” with a processed fruit juice snack. It’s never seen the types of sweet fruits humans have selectively bred, nevermind their more refined higher glycemic state known as “fruit juice”. Your body also did not evolve to handle the added refined grain sugars consumed with the fruit juice. Your body was not designed to know what “high glycemic” or “high carb” is and how to handle it effectively. That your snack contained only a grand total of 120 calories, but as far as your body is concerned you must be gorging yourself on hundreds if not thousands of calories of meat, nuts, berries, low sugar fruit, and veggies. Your body was designed to assume that all foods are like the foods it evolved on, and therefore it has no efficient regulation mechanisms to handle rapid rises in sugar. Your body responds to this the only way it knows how. It responds as it would if it were in a feast state – it raises insulin, and shuts off body fat burning.

The author expects us to believe the body seamlessly regulates sugar levels; that the abnormal spikes in sugar are always so neatly handled by our hormones to keep energy balance evened out in the end. This is far from the truth. Even for relatively young, healthy human beings, high carbohydrate consumption is associated with energy highs (sugar rush) and lows (sugar crash). The high happens when sugar spiked (like when a kid eats some candy). The low happens when the sugar is all gone but the insulin/glucagon axis is still disturbed and out of balance (insulin levels are high, but sugar is now too low and because of the high insulin your body can’t switch over to fat burning… thus putting you in an energy-depleted state). The older you are, the more likely it is that you have or will develop significant intolerance to handle this unnatural diet. Genetic potential also plays a role – some human “families” have a better ability to handle it than others (hunter-gatherer type peoples have less tolerance for it, Europeans and Asians have slightly better tolerance). If high carbohydrate consumption were normal, this wouldn’t be. A higher fat, low sugar diet does not produce these energy level peaks and valleys. Everyone would be able to tolerate it, except in isolated instances of abnormality (genetic or environmentally induced). That’s not the case. Virtually every single human being has some problem with sugar. If nothing else, almost everyone feels more energetic and less dependent on consumption when they eat more fat & protein and less sugar.