I Tried the Longevity Diet for 30 Days — Here's What Happened to My Body

Dr. Valter Longo's new book, The Longevity Diet 2.0, came out in April, and it's been all over my social media. The premise is simple: eat a mostly plant-based diet, restrict calories for 12 hours a day, and do a 5-day fast-mimicking diet once a month. The claims are bold — better health, longer life, reduced risk of disease. I'm always skeptical of diet books, but the science behind Longo's work is solid. He's been researching aging at USC for decades. So I decided to try it for 30 days. Here's what happened.

The Rules I Followed

The longevity diet isn't complicated, but it's restrictive. Here are the basics: all meals within a 12-hour eating window (I chose 8 AM to 8 PM). Mostly plants — legumes, whole grains, nuts, and vegetables. Fish up to three times a week. Very little meat (none for me, since I'm already mostly vegetarian). Low protein for most of the day, with a higher protein dinner. And once a month, a 5-day period of eating only 800-1,100 calories per day, with specific macronutrient ratios. I also took a daily multivitamin and omega-3 supplement.

Week 1: The Hardest Part

The first week was rough. I'm used to snacking in the evenings, and the 12-hour eating window meant I had to stop eating at 8 PM. The first three nights, I went to bed hungry. The food itself was fine — I ate a lot of lentil soup, quinoa salads, and roasted vegetables. But I missed cheese. And chocolate. And bread with butter. By day five, I was cranky and craving everything I couldn't have. I almost gave up. But I reminded myself that it was only 30 days.

Week 2: The Fasting-Mimicking Diet

This was the part I was most nervous about. Longo's fasting-mimicking diet (FMD) involves eating specific amounts of nuts, olives, and vegetables for five days. I bought the official ProLon kit, which costs about $250. The food is... not great. The soups are bland, the crackers are dry, and the olives are the only thing that tastes good. But the science says it works — the FMD is designed to trigger cellular repair mechanisms while providing enough nutrients to avoid the dangers of water fasting. By day three, I felt surprisingly energetic. By day five, I felt light and clear-headed. I lost 4 pounds during the fast, mostly water weight.

Week 3: The Energy Shift

After the fast, something changed. My energy levels stabilized. I used to crash in the afternoon, but now I felt alert all day. My digestion improved — no bloating, no discomfort. I also noticed my skin looked clearer. I'm not sure if that's from the diet or just from eating less processed food, but I'll take it. The cravings were mostly gone. I no longer missed cheese or chocolate. I actually looked forward to my lentil soup and kale salad.

Week 4: The Final Push

The last week was easy. I had settled into a rhythm. Breakfast was oatmeal with berries and nuts. Lunch was a big salad with chickpeas and tahini dressing. Dinner was fish with roasted vegetables. I felt good. I also had a blood test done at the end of the week. My fasting glucose dropped from 95 to 82. My LDL cholesterol went from 130 to 108. My inflammation marker (CRP) dropped from 2.1 to 0.9. Those are significant improvements for just 30 days.

The Downsides Nobody Talks About

But it wasn't all positive. First, the social aspect was tough. I couldn't eat at restaurants with friends, because almost everything on the menu was off-limits. I attended a birthday party and spent the whole time sipping water. Second, the cost. The ProLon kit is expensive, and even the regular food — organic vegetables, quality fish, nuts — adds up. I spent about $200 more on groceries than usual. Third, I lost muscle mass. I do strength training three times a week, and my lifts went down. I lost about 2 pounds of muscle, according to my smart scale. Longo's diet is low in protein for longevity, but it's not ideal for athletes.

Would I Recommend It?

It depends. If you're overweight, have metabolic issues, or want to improve your biomarkers, the longevity diet is worth trying. The science is strong, and my results speak for themselves. But if you're already healthy and active, the trade-offs might not be worth it. I've decided to keep some elements — the 12-hour eating window, the plant-focused meals, the occasional fast — but I'm going back to a more flexible diet. I need my cheese and chocolate. Everything in moderation, right?

If you're curious, I'd recommend starting with the 12-hour eating window and see how you feel. You don't need to go all-in. Small changes matter more than perfect adherence. And talk to your doctor before trying the fasting-mimicking diet. It's not for everyone.