Y: PEPTIDE YY
Guess who’s back back back…back again….HORMONES! I did indeed give you a fair warning in “E” Endocrine System letter that hormones control absolutely everything. Hunger is no exception. Today’s letter “Y” is for “YY, PEPTIDE YY”. It is a hormone that pays rent to our gut in order to hang out there and respond to changes in our nutritional status.
From a high level, peptide YY (PYY) inhibits food intake, while its nemesis hormone, ghrelin, encourages food intake….hence why ghrelin is also known as the “hunger hormone” (source).
HUNGER & FULLNESS: AN ACTION PACKED THRILLER
Two key areas of the brain are involved in toggling our appetite: the brain stem and the hypothalamus (source) 🧠 The brain stem receives messages from the digestive tract via the handy dandy vagus nerve, while the hypothalamus receives messages from the blood. The brain stem and the hypothalamus are given assignments via command from both nutrition & hormones (You can think of this like a new Ikea desk: you are the brain stem, your feeling of "hunger" is the new Ikea desk you just bought, and your hormones are the instruction manual)
These two brain buddies (brain stem & hypothalamus) collect information about the body's nutrient status and respond accordingly in one of two ways:
- HUNGER → eat + store energy
- SATIETY/FULL → stop eating + spend energy
FUN FACT: Obesity & PYY
According to several studies, obese subjects show fasting plasma concentrations (i.e.: blood measurements taken while their tummies are empty) of PYY are reduced, "leading to the hypothesis that PYY deficiency may contribute to the pathogenesis of obesity" (source).
Due to it's appetite suppressing powers, Peptide YY (PYY) has been under the microscope in recent years as a potential therapeutic infusion option for severe obesity and obesity-related morbidities (source).
WHEN DOES PYY MAKE AN APPEARANCE?
PYY is muted during fasting - foodless periods - and at its highest peak roughly ~30 minutes after a meal. Ghrelin is the opposite: it peaks while we are fasting, but is typically muted ~30 minutes after a meal (source). This is because PYY is said to decrease appetite, so it’s highest right around when our bellies are full.
PYY levels in the blood rise within 30 minutes after a meal because that is typically how long it takes your grub to surf through your mouth, dowwwwwn the esophagus, through the stomach, and into the small intestine! (recall: small intestine is where the majority of absorption occurs) 🙃
FUN FACT: Highest PYY levels are...
PYY levels are lowest in the morning and are elevated after breakfast (aka meal!!), rise further after lunch (aka meal!!) and reach their daily peak a few hours after dinner (aka meal!!!) (source).
The Secret Sauce: "Intuitive Eating"
Intuitive Eating is essentially the innate 'hunger-satiety' system that we are born with. It's something we all have access to, is free of membership fees, payment plans, or special requirements to meet. This system is hard-wired into each and every one of us; no download, data entry, or macronutrient required (source).
In a nutshell, with this system you eat only after you’ve experienced belly hunger, and stop when you’ve had just enough. It sounds easy...but, as we know, we've been primed to ignore these primitive signals from our belly and instead listen to social media "fit tea" ads, celebrities, etc...so this internal regulating system is much easier said than done.
Your energy expenditure ebbs and flows depending on what you have going on during the day. When you depend on your hunger and satiation signals to take the lead, your food intake will naturally adjust as necessary to coincide with your energy output, or how many calories your body is using. PYY and ghrelin will work in perfect harmony via their ''hunger-satiety system" to ensure your tum and brain are thriving...it's legitimately the system humans were born to survive with! To learn more about it, I love this Girls Gone Strong article that breaks it down with advice and tactical take away.
Peptide YY & Post-workout Hunger
Exercise has been shown to decrease appetite for a handful of reasons. The relationship between fitness and eating is famously prickly. Studies have shown that people who start working out without also managing their caloric intake typically drop few if any pounds over time, and may gain weight. Plenty of factors play into that outcome, including someone’s current fitness, body mass, diet, gender, genetics, metabolic rate and even the timing of exercise (source). A few reasons sited here are:
- Hormones: Some evidence suggests that following exercise, hormones are released that reduce hunger and food intake.: grehlin—which stimulates your appetite—and peptide YY—which suppresses your appetite. A 2008 study published in the AJP Regulatory Integrative and Comparative Physiology found that running for an hour on the treadmill caused ghrelin levels to drop and peptide YY levels to spike, leading to not feeling very hungry
- Mood / self esteem boost: “Another potential explanation is that exercise boosts mood or self-esteem, which then improves motivation to eat well or within one’s diet" (source).
- Lac-Phe: A new molecule combination of lactate and the amino acid phenylalanine; it's released in response to the high levels of lactate released during exercise. The more intense the exercise, the more lac-phe was produced and, at least in mice, the more appetite seemed to fall. (source). For example, a leisure 60-minute cycling workout (aerobic - requiring oxygen) yielded LESS lac-phe than 30-second sprints (anaerobic - no oxygen required) on a treadmill.
- This particular idea of greater intensity = greater appetitie suppression makes physiological and intuitive sense! Per Dr. Jonathan Z. Long, a professor of pathology at Stanford University School of Medicine, “If you’re sprinting from a rhino or some other threat, the autonomic nervous system yells at the brain to shut down digestion and any other unneeded processes.”
