March 2025

Food satiety, vector stores, heat training, TeenTrainer progress, clock wars

Karl Etzel
March 12, 2025

Rough start to the new year for this newsletter…alas, I am trading communication for productivity on a few key projects. I hope you’re all getting ready for spring and adjusted to the time change last weekend.

Speaking of the time change, in case you’re trying to decide where to come down on the debate of daylight savings time vs. standard time, the science & health community are virtually unanimous in supporting standard time.

Permanent standard time is the optimal choice for health and safety: an American Academy of Sleep Medicine position statement - PubMed

Rishi MA, Cheng JY, Strang AR, et al. Permanent standard time is the optimal choice for health and safety: an American Academy of Sleep Medicine position statement. J Clin Sleep Med. 2024;20(1):121-125.

Cycling is going great, I registered for the Death Ride in early July in Markleeville, CA and I’m back to doing 100 mile rides regularly. I’ve also been heat training, doing 1 hour rides on my Wahoo Kickr trainer with a couple of layers of clothing and no fans on. There’s good science behind the benefits of this, mainly through the mechanism of increasing blood plasma volume although there are a few other ways it helps.

Effects of Heat Adaptation on Physiology, Perception, and Exercise Performance in the Heat: An Updated Meta-Analysis - Journal of Science in Sport and Exercise

Purpose Heat adaptation (HA) is a popular strategy to combat the negative effects of thermal stress. The HA literature has expanded since a 2016 meta-analysis, and we provide an updated meta-analysis, incorporating 39 additional studies and advanced analysis. Methods Following Pubmed searches, full-text original articles using human participants were reviewed using the four-stage PRISMA process. Data were extracted by at least two of the authors. Hedges’ g effect sizes, 95% confidence intervals, and prediction intervals were calculated. Correlations were run where appropriate. Results One hundred and thirty-five total articles (96 previous, 39 new) were reviewed. Medium-term (8–14 days), active, constant work HA regimens remain the most common despite a recent focus on isothermal, passive, and short-term (≤ 7 days) alternatives. HA still improves subsequent exercise performance and capacity in the heat (g = 0.7), reduces resting core temperature (g = − 0.6) and heart rate (g = − 0.5), and increases sweat rate (g = 0.4) but the effect sizes are lower than previously reported. HA has a moderate or larger effect (g > 0.5) on lowering sweat onset temperature, mean heart rate, sweat sodium and chloride concentrations, resting thermal sensation, and thirst sensation, and increasing resting plasma volume. There is considerable heterogeneity within the data for most variables. Conclusion HA regimens can reduce physiological and perceptual strain and improve subsequent exercise performance and capacity in the heat. Longer regimens may be more effect than shorter ones, but the data are lacking. Passive HA is a practical, effective alternative to active HA.

link.springer.com/article/10.1007/s42978-023-00263-8?utm_source=chatgpt.com

I’ve been following the rides with ketones (Ketone-IQ), which has been shown in early studies to increase EPO production. More blood volume, more red blood cells, more VO2. Between the heat training and my general increase in riding volume, it’s been nice to see VO2max data headed in the right direction. I suspect 58 is a bit optimistic but I trust the trendline and it’s been all up for about 6 months.

Lately I’m working more on TeenTrainer and adding some functionality to make it more useful, although much of it is not yet visible to users. Send it a message (just text 878.348.TEEN) and see how it works. The latest thing I’ve figured out is how to quickly turn an image of a calendar into a JSON file, which can be stored in a vector database so that an LLM can answer questions about the calendar. This is extensible to many other types of data, for example a product catalog, a menu, etc.

Comfort food tends to be warm. Maybe this paper explains part of why. I’ve always felt soup was a superfood when it comes time to lean out and drop a few pounds. From the article: “Hot food temperature increased satiety hormones (CCK and GLP-1), independent of food macronutrient composition.”

Food temperature altered macronutrients induced changes in satiety hormones; glucagon - like peptide -1 and cholecystokinin and their correlation with subjective satiety

journals.lww.com/jfcm/fulltext/2024/31030/food_temperature_altered_macronutrients_induced.6.aspx

The thumbnail ski slope photo is from Heavenly, I had a great trip with my son (just 1, my older son is out of the nest and onto his next adventure in life). My only other visit to Heavenly a few years ago was underwhelming, so I was happy to have really good conditions this time around. It will be my only ski trip this winter, as much as I love skiing I realized last year that it is very time consuming to head to the mountains regularly all winter. Besides, I’m having a great time on my bike here in the Bay area.