Physiology Friday #117: "Anti-obesity" Molecule Explains Why Exercise Suppresses Hunger, and New Recommendations for Protein Intake
This week's newsletter covers new data on how hard exercise may make us less hungry, and provides the latest protein intake recommendations for older adults.
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In today’s newsletter, we will explore why high-intensity exercise might make you less hungry and dive into brand-new recommendations on the optimal protein intake for adults.
Hard exercise may blunt your appetite
It’s generally accepted that exercise makes you hungrier and, to some extent, this is true. When physical activity levels go up, food intake often follows (ask any former college cross country runner…). This makes intuitive sense — as the body uses more energy (calories), it’s going to want to replace those calories, and does so by regulating our hunger signals.
But if you’re like me, you may experience a paradoxical appetite suppression following a particularly hard workout. While a long and slow endurance exercise session might leave you insatiable, a high-intensity interval workout seems to impair appetite for up to a few hours or more. Sometimes after a grueling race or workout, I am unable to stomach little more than a piece of fruit for the rest of the day.
Researchers conducting experiments on mice and horses found that, during a single bout of exercise, a metabolite (molecule) known as N-lactoyl-phenylalanine (Lac-Phe) is released in immense quantities.
When obese mice were injected with the molecule Lac-Phe, they ate less, lost weight, and improved measures of glucose control, suggesting that their overall metabolic health was enhanced. In contrast, mice who lacked the ability to produce Lac-Phe ate more and were significantly heavier than wild-type (“normal”) mice.
Does this “anti-obesity” molecule also exist in humans? Indeed.
Researchers verified the presence of the exercise-induced increase in Lac-Phe in human volunteers undergoing endurance exercise, resistance exercise, and sprint-interval exercise. In fact, Lac-Phe levels were highest after sprint exercise, second highest after resistance exercise, and the least high after endurance exercise.
While this study gives us some clues as to why we might feel less hungry after an intense workout, the applications of these findings expand far beyond the post-workout munchies.
Could Lac-Phe be the next ingredient in a weight-loss or appetite-suppressing drug for the treatment of obesity?
It could be speculated that, in order to mitigate the appetite-enhancing effects of some exercise, high-intensity training should be prescribed to those looking to lose weight. These are all just hypotheses at the moment, but I’m sure future research in humans will seek to build on this very neat study.
Are you eating enough protein?
This week, the British Association for Sport and Exercise Sciences (BASES) released an “Expert statement on optimising protein intake recommendations for skeletal muscle mass in older adults to support healthy aging.”
The focus of the statement was to provide recommendations for protein intake for healthy aging and combatting age-related muscle loss (sarcopenia) in adults >60 years of age. For adults under the age of 60, especially athletes, protein intakes likely need to be higher.
Here’s a nice table from Examine.com on protein intake recommendations for healthy adults (in grams/kilogram of body weight).
These recommendations are also goal-specific, focusing on minimum intakes for sedentary adults, moderately-active adults, highly-active adults and masters athletes, and special considerations — which include disease states, bedrest, immobilization, and preventing frailty.
I’ll end with a conclusion that I feel is warranted. When the topic of protein comes up, you’ll routinely hear the warning that “too much protein will harm your kidneys.” This couldn’t be further from the truth, as summed up nicely by the authors of the expert statement:
“In otherwise healthy individuals, there is no evidence that links a higher protein intake with reduced kidney function. Interestingly, a higher relative protein intake in adults with normal kidney function is associated with a lower incidence of end-stage/chronic kidney disease.”
If you needed an excuse for that extra chicken breast or scoop of peanut butter, consider this your sign.
Thanks for reading. See you next Friday.