All the other variables and laws of physics still apply.
All the fad diets that cut out a certain type of food all really just work because of calorie restriction. Look at the "cookie diet" for an example.
For me, I'm 6'2, I went from 210 to 175 over 10 months (while adding significant muscle mass, suggesting fat loss of 40+ lbs). I did this by changing my diet: I eat nothing for breakfast. One cup of coffee with cream. For lunch, I eat only fruit. Seasonal. Always an apple, sometimes two, berries and grapes, that sort of thing. Sure they're good for you in a non-processed-foods sense but they also are very high in sugar.
I eat a very large dinner.
I always, always eat dessert. Always.
I work out 3 mornings a week, those days I eat half my "lunch" right after my work-out.
Obviously I'm sharing an anecdote but I mention it just because it echo's the research I mentioned and as a testimonial that it works for me. I eat an absurd amount of sugars and carbs but my total calories are restricted and I'm in fantastic shape.
I eat some junk on the weekends myself, that's how I get perspective on drastic changes in my energy levels.
Or, instead you can switch into fat-burning mode and have a constant blood sugar and not feel hungry nor have to skip meals. Lots of good stuff too, eggs, spinach, olive oil, flax, etc. Doc says my bloodtest numbers some of the best he's seen.
Fad diets are suspect, but this isn't one of them. When was the last time in the wild you saw a chimpanzee or early human eating a loaf of bread, pasta, or cookies? Never, because they are man-made creations. The fad diet is the empty-carb diet pushed by the modern world, the results of which are obvious.
Humans have evolved over millions of years eating veggies, fruit, nuts, meat, etc.
I'm forming an idea, that there is nothing wrong with these two approaches. Rather there is a choice. Perhaps some of us prefer trading off in favor of tasty sweets, while some of us prefer stable blood sugar. You can live much longer than our poor ancestors with either approach. So, let's not bash the A- students on the other side because they're not perfect.
This is 100% bullshit.
(Yes! It's multivariate integral calculus, back from your youth to haunt you!)
Anyway, the second problem is that blood sugar in healthy individuals is very well regulated anyway. The blood sugar pathologies you see in obese individuals are usually pathologies of obesity, not the other way around.
The third problem is that carbohydrates, even simple ones, don't have a monopoly on short-term blood sugar effects. Insulin is usually identified as the primary regulator of blood sugar, but insulin is affected very strongly by protein as well as by carbohydrates. This is because insulin actually has a whole bunch of functions, only one of which is blood sugar regulation.
Biology is really complicated. It's the worst spaghetti code ever. It works, but there's no modularity, no information hiding, no clean APIs, everything is a global variable and there's not even the most basic concurrency controls. It's very hard to reason about.
But because it is so robust, it is easy to do thing A, get result B and attribute the results to factually incorrect theory Z9-gamma-pink-battleship.
Not to mention elegant in the way the human body runs perfectly on early-human food.
I'm not obese, and when eating sugar/starch I end up sleepy at times and starving a few hours later. Everyone knows it... moms have been telling us for decades if not centuries, not to give sugar to children.
Proteins/fats must be converted, meaning their glycemic index will be much lower. As such, a day or two after I substituted green-veggies & nuts for grains the difference was palpable.
I have not been stuffed or starving for over a month, lost my spare tire, and am loving it. Fits perfectly with everything I learned in chem, bio, and nutrition at uni. long before this became a movement. I don't think of this as FSM, rather differential equations such as these: http://17calculus.com/calc08-app-ccfluids.php
There are benefits to keeping blood sugar levels stable whether people want to believe it or not.
Effects of an oral and intravenous fat load on adipose tissue and forearm lipid metabolism. http://www.ncbi.nlm.nih.gov/pubmed/9950782
"Six subjects were fasted overnight and were then given 40 g of triacylglycerol either orally or as an intravenous infusion over 4 h. Intracellular lipolysis (hormone-sensitive lipase action; HSL) was suppressed after both oral and intravenous fat loads (P < 0.001). Insulin, a major regulator of HSL activity, showed little change after either oral or intravenous fat load, suggesting that suppression of HSL action occurred independently of insulin."