Fructose, Hunger, and Inactivity – Leptin and Insulin

I watched a video last night posted by the Ancestral Health Symposium about fructose, fat storage, and energy expenditure. Even if you’re not struggling with obesity, I think there is a lot to glean from Dr. Lustig’s research on fructose. He is an MD who did “six years at Rockerfeller – 3 in the laboratory of biochemical endocrinology and 3 in the laboratory of neurobiology and behavior.”

“The Trouble With Fructose: A Darwinian Perspective” by Robert Lustig, MD

Some of my notes follow. This really isn’t an article. It’s a collection of points I jotted down while listening.

“One reason the low carb diet works so well for most people is because it lowers your insulin.”

“Insulin makes you feel like crap.” Keeping your insulin levels low will actually result in higher energy, less carb cravings, and better leptin sensitivity. “When your insulin goes down, you don’t crave carbs.”

Leptin helps to regulate your appetite and energy expenditure. When you’re leptin resistant, you won’t get a sugar high, your body will try to conserve energy and find more food.

Lustig says that “if we could fix leptin resistance, there wouldn’t be obesity.” And that the very act of losing weight makes you more leptin sensitive and so you have more energy and less food cravings.

“Insulin blocks leptin,” so that your body thinks it’s in a state of starvation even when it technically isn’t.

Lowering insulin actually makes the body leptin sensitive.

(So, it isn’t really fair to ask kids or anyone to go exercise because they are lacking in energy due to their weight issues or bad diet choices. So, you’ve got to start with their diet or, as Lustig might suggest, hormone replacement therapy.)

He goes on to say that “our body is like two compartments. Our heart, our brain, our lean body mass, and our fat. And so there is a competition going on for the same molecule of glucose. What determines which way the glucose goes? Your insulin. The less insulin, the more goes to you. The more insulin, the more goes to fat.”

Fructose is a bad sugar that contributes to the obesity epidemic – to insulin and leptin resistance.

“If you take in 120 calories of glucose, the majority of the glucose gets metabolized by the rest of the body… Only 24 calories hit the liver… The overwhelming majority of glucose gets converted to glycogen. Glycogen is non-toxic. Glycogen is liver starch. Your body wants to make glycogen.”

“Glucose is not very good at contributing to obesity because not much of it gets stored as fat.” (He goes over the biochemical process behind this in the video) “You would have to eat a whole lot of glucose to get fat.”

“Consume a 120 calories in sucrose. Glass of orange juice. The glucose will do the same 20 80 split… but the entire bolus of fructose will have to be metabolized by the liver… If you overwhelm your liver to deal with carbohydrate, what happens?”

(For a description of the various types of sugars check here.)

“Fructose induces insulin resistance which then induces leptin resistance.”

(Seems to me, then, that the best carbohydrate to eat is starch, which is a polymer of glucose molecules.  So let’s not encourage our kids to eat as much fruit as they want but rather to eat starchy foods for their carbs. Weston Price actually noted that the many traditional kids refused fruit even though it grew all around them and preferred, instead, starch.)

The Darwin bit is mentioned at the end, which I won’t spoil for you. Essentially, it boils down to seasonal insulin resistance.

Enjoy the video. It’s long and complex but with all the talk of carbohydrates in the Paleo community right now I thought it might be helpful. Plus, I really am going to post an article soon about low carb, what I think about it these days, why you might not want to do it, and how you can succeed without it.

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