 Hippocrates said all diseases begin in the gut. Previously I have talked about fecal transplants, transferring the stool of healthy people into the colons of patients suffering from inflammatory bowel disease, multiple sclerosis, even psychiatric problems like depression, bipolar disorder, and alcoholism, to repopulate their gut with good bacteria in hopes of improving their conditions. What about fecal transplants for aging? Might the fountain of youth be a fountain of poop? If you give mice with accelerated aging a fecal transplant from healthy mice, they perk up and live longer. But what about human poop? We don't yet have human-to-human aging data, but we do have mice transplanted with fecal matter from a centenarian. Mice-fed poop from a 101-year-old versus poop from a 70-year-old, lipofuscin is an age pigment that's widely used as a biomarker for aging. And lipofuscin accumulates significantly less in the brain tissue of centenarian poop-fed mice, raising the possibility that we will one day be using centenarian fecal matter for anti-aging purposes and to promote healthy aging. Why bathe in the blood of virgins when you can dine on the dung of the venerable? To be continued once human-to-human data are published. Poop you may want to avoid is from overweight stool donors, given this case reported about weight gain after a fecal transplant. 32-year-old woman had always been of normal weight until she received a fecal transplant from a healthy but overweight donor, her daughter. After the transplant, she became obese, gaining more than 40 pounds. She said she felt like there was a switch inside her body. Her gastroenterologists reported no matter how much she ate or exercised, she couldn't take the weight off. She's very frustrated. The same thing happens in mice, giving mice fecal pellets from an obese mouse resulted in nearly a doubling in fat mass compared to lean mouse pellets, despite eating significantly fewer calories. This proves gut flora can play a pivotal role in obesity in mice. What about in people? Researchers decided to study pairs of human twins discordant for obesity, meaning one twin was fat, the other skinny. What would happen if you switched their microbiomes? The siblings may have been squeamish, so the researchers reverted to mice again. Mice-fed stool from the obese twin rapidly swelled in size, but not those fed from the lean twin, despite comparable calorie intakes. Co-housing the mice together prevented the weight gain. However, the lean type bacteria jumped over to rescue the mouse-fed stool from the obese twin. But, and here's the critical point, only the context of a healthier diet. The microbial cure only worked when the mice were fed low-saturated fat, high-fiber diets, which makes sense since the lean type bacteria appeared to be fiber feeders. Together, the researchers concluded these results illustrate how a diet high in saturated fats and low in fruits and vegetables can select against human gut bacteria associated with leanness. The results of the twin study suggest that the role of our gut flora in obesity is just to help take fuller advantage of a more healthful diet. So, if the twins had actually swapped their stool, the obese twin might have only lost weight if they combined the microbial makeover with healthier eating to aid the colonization of the better bugs. With the new bacteria on board, though, the healthier diet could have resulted in more weight loss, even eating the same number of calories. But you don't really know until you put it to the test. There have been previous published attempts, randomized double-blind placebo-controlled trials showing no weight loss benefit to getting lean donor fecal transplants, but they kept people on the same crappy diets that led to obesity in the first place. Who cares if you keep putting slimming fiber-feeding bacteria into your gut if you don't give them any fiber to eat? They'll just starve and die right off. So, maybe you have to do both, pairing gut-bacteria modulation with a dietary intervention. But if you do a plant-based diet along with a transplant and they lose a bunch of weight, how do you know if the transplant had anything to do with it? Which brings us to this study. What they did is put people on a healthy plant-based diet supplemented with green tea and green smoothies until they lost about 20 pounds over 6 months and grabbed a fecal sample. Then they were randomized. To spend the rest of the year constantly seeding their gut with the healthy microbiome they had achieved at maximal weight loss or to placebo capsules. The question was, once they go back to their regular diets, were those getting the constant infusion of their own skinny poop, help them keep the weight off? Yes. They found that participants who lost weight on a healthy diet and were then fed capsules containing fecal matter collected during the diet period for months after the maximal weight loss were gained less weight than participants given placebo capsules. So, the plant-based diet appeared to produce the optimal fecal microbiome for preventing weight regain. But rather than eating your own plant-based poo, why not just stick with the plant-based diet?