Short Wave – “The Truth About Intermittent Fasting”

Date: February 20, 2026
Hosts: Regina Barber & Rachel Carlson
Guest Host: Mary Louise Kelly
Main Theme:
A lively science roundup covering new research on intermittent fasting’s effectiveness for weight loss, potential pitfalls in chatbot interventions for mental health, and the impact of ultra-endurance running on red blood cells.

Key Topics & Discussion Points

1. Intermittent Fasting: Does It Really Work for Weight Loss?

• What is Intermittent Fasting?

  • Celeste Campos Castillo sums it up: “This is where you restrict the times you eat, right, rather than what you eat.” (02:31)
  • Rachel Carlson explains: “Some people might fast every other day. Others might eat between the hours of 10 to 6, but do a 16 hour fast outside of that.” (02:38)

• The Research:

  • Due to lack of robust long-term studies, an international research team conducted a meta-analysis of 22 smaller studies comparing intermittent fasting against other diets or no intervention.
  • Results: “Intermittent fasting did not work for weight loss in overweight or obese adults as compared to either traditional dietary advice or even doing nothing.” – Rachel Carlson (03:14)

• Expert Reaction:

  • Dr. Matthew Steinhauser (not involved with the review):
    • “It does suggest that there's not a huge effect on body weight and certainly nothing approaching what we see with the GLP-1 drugs, for example, where patients can lose 10 to 20% of their body weight over the course of a few months to a year.” (03:39)

• Nuance and Caution:

  • Regina Barber: “The small size of all the studies within this larger review makes it hard to know for certain.” (03:26)
  • Rachel Carlson: The review “really focused in on weight loss as the standard. But like you said, that's not the only reason people choose to try intermittent fasting. And no matter what, Matthew told us that in medicine, very few things are risk free. So definitely talk to your doctor before making any big changes to your diet.” (04:09)
  • Celeste Campos Castillo: “Good evergreen advice there. Always talk to your doctor.” (04:28)

2. Chatbots, Mental Health, and the Risk of Harmful Interventions

• Backdrop:

  • Recent incidents with AI chatbots allegedly contributing to or not preventing youth suicides; regulatory interventions underway.
  • “A couple of those families believe that AI chatbots pushed their teenage sons to kill themselves. Our colleague Ritu Chatterjee reported that one family testified that one of the chatbots, ChatGPT, even offered to help write their son's suicide note.” – Regina Barber (04:45)

• Policy Solution: Reminders That You’re Talking to AI

  • In states like California and New York, chatbots must ping users every three hours, reminding them they're interacting with AI, not humans. (05:07)

• Does It Work? Concerns from Experts:

  • Linnea Listadius (University of Wisconsin-Milwaukee) & Celeste Campos Castillo (co-author):
    • The idea that reminders could fix the issue “struck us as a bit naive in some ways and potentially dangerously unrealistic in others. And also not engaging with potential downsides of reminders.” – Rachel Carlson quoting Linnea Listadius (05:50)
  • Downsides:
    • “If someone already feels lonely or if they're struggling with their mental health, a reminder that they're not talking to a real person could destabilize them and make them feel more isolated.” – Rachel Carlson (06:02)
  • Way Forward:
    • “Celeste and Linnea are urging these companies to share their data more openly so they can study these interventions better and hopefully help shape more effective policy.” – Rachel Carlson (06:31)

3. Ultra-Endurance Running: What Happens to Your Blood?

• Study Focus:

  • How running extreme distances affects red blood cells and inflammation markers.

• What Did They Find?

  • “They found that running extreme distances can damage red blood cells. These cells are super important... So damage to those red blood cells can trigger inflammation or lead to anemia.” – Rachel Carlson (07:02)
  • The study compared trail runners completing 24-mile races (just under a marathon) and ultra-marathoners running 106 miles. Both had evidence of blood cell damage, but it was more pronounced in the ultramarathon group. (07:24–07:53)

• Why Does This Happen?

  • Expert Travis Nemkov explains:
    • “When you're doing something like running, your body needs more oxygen, and that means blood is circulating through your [body] quickly, which can lead to the breakdown of red blood cells... The damage that is obtained by these red blood cells causes some of those red blood cells to be removed from circulation more quickly than they would have otherwise been.” (08:03, 08:15)

• Can Runners Recover?

  • Regina Barber: “But that damage isn't the end of the story. The runner's body starts generating new blood cells.” (08:24)

• Big Picture:

  • The study was small and doesn’t answer long-term health questions.
  • “Travis and the researchers do not know whether this extreme amount of exercise is bad... And then more broadly, Travis says, definitely do not stop doing regular exercise. It's the best tool we have to keep our bodies healthy and age well.” – Rachel Carlson (08:45)

Notable Quotes & Memorable Moments

• On Intermittent Fasting:
  • “Case closed.” – Celeste Campos Castillo, cheerily summing up the negative result (03:24)
  • “Good evergreen advice there. Always talk to your doctor.” – Celeste Campos Castillo (04:28)
• On Chatbots:
  • “A bit naive in some ways and potentially dangerously unrealistic in others.” – Rachel Carlson, quoting Linnea Listadius (05:50)
  • "If someone already feels lonely... a reminder that they're not talking to a real person could destabilize them and make them feel more isolated." (06:02)
• On Running:
  • “My ultra endurance is about four miles these days.” – Celeste Campos Castillo, humorously putting “ultra” in perspective (06:42)
  • “Here's to keeping healthy and aging well.” – Celeste Campos Castillo (09:07)

Timestamps for Major Segments

• [02:23] Intermittent Fasting—What Is It? & New Study
• [03:14] Study Results: Intermittent Fasting Not Superior for Weight Loss
• [03:39] Expert View: Matthew Steinhauser on Study Shortcomings
• [04:28] Reminder: Always Consult Your Doctor
• [04:45] AI Chatbots & Mental Health Crisis Discussion
• [05:07] Regulation: AI Chatbot Reminders
• [05:50] Potential Downsides of Reminders (Expert Opinion)
• [06:42] Science of Ultra-Endurance Running
• [07:53] Finding: More Blood Cell Damage in Ultramarathoners
• [08:15] Travis Nemkov on Why Red Blood Cells Get Damaged
• [08:45] The Big Picture: Is Extreme Exercise Dangerous?

Tone & Style

The conversation is accessible and relatable, balancing light humor ("my ultra endurance is about four miles") with thoughtful caution and clear science communication. The hosts foreground nuance, share expert insight, and repeatedly emphasize the limits of available data.

Takeaways

• Intermittent fasting is no silver bullet for weight loss compared to traditional diets or even making no change at all, according to a meta-analysis of small studies.
• Chatbot reminders about their non-human status may not help—and could even harm—mental health, especially among vulnerable users, suggesting regulation alone isn’t enough without deeper research and policy work.
• Ultra-endurance exercise damages red blood cells more as distances increase, but the body can recover. The health impacts of such extreme exertion remain uncertain, and regular exercise is still highly recommended.

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