Isocaloric but Very Different

May 11, 2011

“It’s all about calories.” It’s a widely held belief, and as I discussed in my two part series on thermodynamics (1, 2), it’s really hard to measure all those calories and that  “calories in vs. calories out” says nothing about where food is stored or used.

Unfortunately, most people don’t care to think about the issue in depth. So here’s a nice easy one.

Let’s take a look at two isocaloric diets: Diet #1 is 2.5cups of table sugar per day, and Diet #2 is 4.5lbs of chicken breast. Both diets come in at 2000 cals/day.

If you switch to one of these diets from a long-term 4000 cal/day junk food regimen, you’ll likely lose weight on both diets (this is how you get stuff like “The Twinkie Diet”). Likewise for weight gain transferring from a super low-cal diet.

That’s not what we’re talking about. Let’s say that we’re looking at a reasonably healthy person used to eating just about 2000 cals/day of a reasonably “balanced diet” (whatever that means). We’ll call this our “normal person” (NP).

The first issue is that NP will die on the all sugar diet. Oops. Well up until that point, NP will lose muscle and gain fat. All that incoming sugar can be used in three ways – immediate energy, glycogen storage in muscle (for later energy use), or storage as fat (called de novo lipogenesis). DNL is meant to happen in small amounts, and does in the context of a healthy diet. However, a diet like #1 will force DNL to step into overdrive, making sure you store the majority of the unused sugar as fat.

Notice that none of the options for incoming sugar is “build muscle.” That’s because you can’t build muscle on an all sugar diet. In fact, you’ll be guaranteed to break down your own muscle to provide the amino acids your body requires. Obviously, an all-sugar diet is extreme, but this muscle breakdown happens even with an all-sugar snack.

So Diet #1 leaves NP fatter and less muscular. Oh yea, and diabetic in a hurry.

How about Diet#2? I’m not about to recommend an all chicken breast diet (a little low-fat and monotonous for my tastes), but it sure as hell blows Diet#1 out of the water. All that protein will stimulate glucagon release with the insulin, increasing systemic insulin sensitivity. This (along with the low-carb nature of Diet #2) will promote healthy blood-sugar regulation – meaning fewer cravings and no more “2:30 feeling.”

Some of the more astute readers out there may be saying that protein can become glucose in the body. It’s true, and it’s called gluconeogenesis. The truth is that it’s pretty damn hard to eat the 500g of Protein required to hit 2000 calories, and I’m not sure how the body would respond to an intake of that sort. From what I’ve seen, gluconeogenesis produces on the order of 40-100 g of glucose per day. However, this process is not energy efficient, and it uses fat for fuel. That’s right, NP would have to burn fat to get sugar. Even if NP’s body really wanted to store that protein as fat, it would have to convert it to glucose (requiring fat to be burned as fuel), then convert that glucose to fat via DNL.

So Diet #2 provides plenty of substrate for muscle maintenance/building, makes storing fat pretty tough, and leaves NP feeling sated and alert.

Which NP would you rather be? I know I’d rather be #2, which is why my diet looks more like chicken breast than table sugar.


Also, I think it is interesting to note that 2000 cals of sugar weighs 1.1 lbs, 4 times less than 2000 cals of chicken breast. And the chicken breast actually contains micronutrients vital for existence.

Entry filed under: Basics, Calories, Food Choices. Tags: .

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