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Does exercise intensity dictate the hunger that follows?

What I’m about to reveal is much more than a testament to great writing and an infatuation with fiction. It’s also proof that the cliche “the journey is more important than the destination” is much more than a cliche.

That it’s the truth. That it has substance.

Because if I’m thoroughly immersed in a novel, I don’t pick up where I left off when I start anew the next day. Instead, I go back a chapter or two.

While discovering how the major conflict gets resolved at the end is always satisfying, I don’t read primarily for that reason. Why I really read any piece of fiction is to vicariously experience what the characters experience - and that provides far more than transitory entertainment.

It teaches me about myself, and what I learn makes me better. But this type of learning typically comes from a second reading, so I find myself backtracking my way through the best novels.

Bettering yourself by reading is not limited to rereading fiction obviously. You can learn loads, for example, when you read factual articles about health and fitness the first time.

Rarely will they contain the sorts of orderly endings you’ll find in novels, though. To wit: When you read one about the latest obesity research, don’t expect it to end with a cure.

Whether or not one will ever be found is a moot point. What’s not debatable is this.

If there’s a way to eat, a manner in which to exercise, or any new information at all that can help you from becoming overweight or obese - or help you lose weight already added and unwanted - you need to know about it.

That’s why today’s topic sounds more like an actor in a Far East film than a molecule produced by your body: Lac-Phe. And what an interesting and potentially life-altering little molecule it is.

Past studies found increased levels of Lac-Phe in the blood of mice after they ran on a treadmill, and even more when they ran until exhaustion. That led to the one cooperatively performed at a number of universities, including Stanford and Baylor, and published in the June 2022 issue of Nature.

The researchers first confirmed the results of the prior studies and then tried a number of new twists. One of them made it impossible for a group of mice to metabolize Lac-Phe.

They then had those mice exercise to exhaustion on treadmills five times a week for several weeks and allowed them to eat as much as they wanted. But instead of the intense exercise blunting their appetites, the reverse occurred.

The mice unable to process Lac-Phe ate so much that their weight increased by 25% on average.

The researchers also injected Lac-Phe into “diet-induced obese mice” and again allowed them to eat as much as they wanted. During the next 12 hours after the first injection, however, these mice consumed about 50% fewer calories than a control group of normal weight.

A similar pattern emerged over the 10-day study and led to the injected mice losing weight, lowering body fat, and improving their glucose tolerance.

In a New York Times article about the study, Gretchen Reynolds’ “Why Does a Hard Workout Make You Less Hungry?”, Jonathan Z. Long, a professor of pathology at Stanford University School of Medicine and senior author of it, offers a suggestion. If you normally find exercise increases your appetite, increase the intensity of it.

It’s an idea, he explains, that makes intuitive and evolutionary sense. “If you’re sprinting from a rhino or some other threat,” he discloses, “the autonomic nervous system yells at the brain to shut down digestion and any other unneeded processes.”

Now the lazy among us are probably more than willing to wait for a Lac-Phe pill rather than up the intensity during exercise - if they’re even exercising at all. But there’s a pretty good chance such a pill will never be produced.

Long and his colleagues found only injections of Lac-Phe, not oral dosing, produced the aforementioned effects on food intake and body weight, meaning pill forms of Lac-Phe probably get decomposed in the digestive system.

They also found, though, that humans also produce more-than-baseline amounts of Lac-Phe in the hour after any exercise - and that intense exercise increases the amount and lengthens the time of its production.

Long and his colleagues made that discovery by having eight healthy young men do three different types of workouts. One involved lifting weights; the other two, riding a stationary bicycle.

One of the two cycling workouts was done at a leisurely pace for 90 minutes, but the other included several 30-second sprints.

Blood levels of Lac-Phe were highest after the ride that included sprints. The ride that was always leisurely paced produced even less Lac-Phe than weightlifting.