 What if there was a supplement that could increase muscle energy and muscle stem cells and it's cheap and easy to get? Would you say it's too good to be true? Well, that's what we're going to find out. Welcome to Lifespan News, I'm Emmett Short. Today we're talking about muscle energy and fat. Here's three facts. One, NAD is an important coenzyme that performs multiple functions including mitochondrial energy production. Two, NAD levels decrease with age, which has been shown to underlie other age-related diseases. Three, supplementing NAD by taking precursors has shown various health benefits in animal models and humans. Many people see this and go, okay, I'm convinced I'll take a precursor. I'll take one. Which one should I take? Now, I'm not saying you should take any of them, but in some studies NR has shown improved physical performance, blood pressure, and several other things. This new clinical trial coming from Finland and published in Science Advances has an interesting twin-based design. The researchers recruited 24 pairs of monozygotic twins, which is what you call identical twins, if you want to weird them out. 20 of the monozygotic twins had substantially different body mass indexes, which is a rare occurrence in identical twins. Usually, they try to stay the same way, you know, to double the wardrobe and have all the hijinks pretending to be one another. That group received escalating doses of NR for a period of five months to see the effects on genetically identical humans with different BMI levels. In the second mini-group of same-sized twins, one of the twins was used as the control group. The average age was about 40, and men and women were almost equally represented, and the daily NR dose was gradually increased from 250mg to 1,000mg over the first month of the study. The study found that NR increased the levels of NAD in the blood by 2.3 times for both twin groups. NR also improved the production of mitochondria in the muscle tissue, and it seemed to activate muscle stem cells, which could help with muscle growth and repair it. But there were some downsides to NR supplementation, so yeah, it might be too good to be true. They found that over the course of the study, body mass and fat percentage increased significantly. Even though the participants didn't seem to be eating more or exercising less, this increase in fat coincided with a decrease in insulin sensitivity, which means that the body may have a harder time regulating blood sugar levels. This is not good news for overall metabolic health, but the study didn't find any changes in cardiovascular health markers like blood pressure or pulse rate. So, according to the researchers, their study provides the first evidence that long-term NR supplementation increases muscle and white adipose tissue in a degeneration in humans regardless of BMI, and shows the value of long-term NAD supplementation studies. I find it interesting that the treatment can boost muscle stem cells without increasing muscle mass, and then fat mass increase and reduced insulin sensitivity are happening also. It's very strange. Understanding the science of exercise is notoriously frustrating. Information often seems contradictory, and new studies seem to overturn years of traditional thinking. Human biology is complicated, and we've looked into this before, including in this LSN episode that explores whether supplementing with rapamycin eliminates the anti-cancer benefits of exercise. Like I said, it's complicated. So what do you think? Does this study change how you feel about NAD and its precursors? Let us know in the comments. There are a bunch of studies coming out on this topic, and we're covering them. So to learn more, check out the Lifespan News NAD playlist here, and make sure to subscribe and click the bell so you can stay up to date on aging research. I'm Emma Short. We'll see you next time on Lifespan News.