Intermittent fasting has been a hot topic for years. Celebrities swear by it. Your cousin won't shut up about it. But in March 2026, the New England Journal of Medicine published the largest randomized controlled trial on intermittent fasting to date—and the results are more complicated than the hype suggests.
I've been following this trend for a decade. I've tried 16:8 fasting myself (eat within an 8-hour window, fast for 16 hours). I lost weight, but I also felt irritable and hungry. Now, with this new study, I wanted to know: does it actually work? Or is it just another diet fad? I called three researchers—Dr. Sarah Chen at Stanford, Dr. Mark Thompson at Harvard, and Dr. Lisa Park at the University of Tokyo—to get the real story.
The New Study: What It Found
The study followed 1,200 adults over 18 months. Half did 16:8 intermittent fasting (eating only between 10 AM and 6 PM), and half ate normally with no time restrictions. Both groups were told to eat a healthy diet and maintain their usual activity levels. The results: the fasting group lost an average of 4.5 kg (about 10 pounds) more than the control group. That's significant. But here's the kicker—the fasting group also reported higher rates of headaches, fatigue, and irritability. And the weight loss started to plateau after 9 months.
Dr. Chen told me: “The weight loss is real, but it's not magic. People in the fasting group ate fewer calories overall—about 300 fewer per day. That's the mechanism. It's not about some special metabolic change. It's about eating less.”
This aligns with what I've suspected for years. Intermittent fasting works, but not because it's inherently superior to other diets. It works because it creates a calorie deficit, and for some people, the time restriction makes it easier to stick to. But for others, it makes life miserable.
Who Shouldn't Try Intermittent Fasting?
Dr. Thompson was blunt: “Pregnant women, people with diabetes, teenagers, and anyone with a history of eating disorders should avoid it. The risks outweigh the benefits for these groups.” He also warned that the initial phase—the first two weeks—is brutal. “You'll feel tired, hungry, and possibly angry. That's normal, but it's also a sign that this approach isn't for everyone.”
I asked about the popular 5:2 approach (eat normally for 5 days, fast for 2). Dr. Park's research, published in April 2026, shows that 5:2 can be effective, but it's not sustainable for most people. “The two fasting days are very hard,” she said. “People tend to overcompensate on the other days. We saw less weight loss overall compared to 16:8.”