Summary
Dr. Stephen Cabral breaks down whether sardine fasting actually delivers on its longevity promises. He argues that while sardines are one of the best protein sources available, eating 2-4 cans per day is not a true fast because the high protein and fat content activates mTOR and prevents autophagy. He contrasts sardine fasting with Valter Longo's Fasting Mimicking Diet, which uses low-mTOR plant foods to actually keep the body in a catabolic state. Cabral explains that sardine fasting is better understood as a hypocaloric day (~1000 calories) with anti-inflammatory benefits from omega-3s, balanced blood sugar, and good protein quality. He cautions cancer patients specifically against using it as a substitute for true fasting protocols, since the leucine and branched-chain amino acids in sardines keep mTOR high and prevent the cellular cleanup that real fasting provides.
Key Points
- Sardine fasting is not true fasting because protein and fat activate mTOR and prevent autophagy
- Sardines are high in leucine and branched-chain amino acids, which increase mTOR — the exact opposite of fasting
- True fasting requires low mTOR and high AMPK to trigger autophagy and cellular cleanup
- Valter Longo's Fasting Mimicking Diet (plant-based, ~3 cups veggies + olive oil) actually mimics fasting because it keeps mTOR low
- Sardine fasting is really a hypocaloric day (~800-1000 calories) with anti-inflammatory benefits
- Sardines are high in histamines and purines, making them unsuitable for some individuals
- Cancer patients should not rely on sardine fasting for autophagy — they need true fasting protocols
- Sardines remain one of the best foods for omega-3s, recommending them as part of regular meals rather than exclusive fasting
Key Moments
Why sardine fasting is not true fasting — mTOR stays elevated
Dr. Cabral explains that sardine fasting is not a real fast because sardines are high in leucine and branched-chain amino acids, which activate mTOR — the exact opposite of what fasting is supposed to achieve. True fasting requires low mTOR and high AMPK for autophagy.
"All right, everybody, we're back with a brand new Cabral concept. Today, we're talking about sardine fasting, and is it actually the biggest breakthrough we've seen in years in nutrition for longevity? Let's break it down here today. Maybe you haven't heard about it, but it is catching on and it's essentially eating nothing but anywhere between two and four cans of sardines per day. That's it. The sardines could be packed in olive oil or maybe just packed in water. You can do the skinless with the bones. There's different interpretations of it. And before we get started, I just want to say is that I've been doing this podcast now for about 10 years, and I've talked about for years the many benefits of sardines. They're one of the absolute best forms of protein that you can get. And it enables you to boost your omega-3 levels, even without supplementation, if you're eating them four plus days per week. So I've seen that in my practice from the very beginning around 2010. I started testing people's omega-3 levels and it was only However, like anything, if something is good, we try to overdo it in our Western-based mindset. And now we're eating nothing but sardines. Here's the thing. Sardines are not a form of true fasting. So it does not go together whatsoever. It does not improve your fat."
Fasting Mimicking Diet vs sardine fasting — opposite approaches
Cabral contrasts sardine fasting with Valter Longo's Fasting Mimicking Diet. The FMD keeps mTOR low with plant foods (veggies + olive oil), while sardine fasting keeps mTOR high due to protein content. He explains that sardine fasting proponents are focused on body transformation, not true cellular cleanup.
"You want that if you want to put on muscle, right? You want to keep mTOR high. I totally get it. One of the people who's a proponent of start eating fasting, it's not like they're not super smart, not like they're not knowledgeable, but they're big on body transformation. They're big on keeping a lot of muscle in their body, which is why they do it, right? But again, it's to keep anabolism high. It's to keep your leucine and branch seed amino acids high. That's the exact opposite of what we want when we're looking for the body to clean house. There can't be fuel for the body to clean house, right? So when you're only consuming, That does keep your body in a catabolic state, a breakdown state where the body's looking for real fuel. Because although there's a lot of micronutrients in your green veggies and your olive oil, there's not a lot of anabolic-based nutrients, protein, right? And we need that to replenish and rebuild the body. Well, a true fast, you're not looking to rebuild the body during that time. And that's why it's a fast. That's why it's That's why it's truly considered a fast. So, there's just a few more things that I want to share with you. It's also not a fast because you are not slowing or shutting down digestion. It's actually very difficult to break down true sardines. So, true dar sardines are higher in purines. I don't want to go too deep down the rabbit hole, but if you're someone with histamine issues, like sardines with the skin on, they're just not going to be the best thing for you. They're a great food, but not every food is right for every individual."
Sardine fasting is really just a hypocaloric day at ~1000 calories
Cabral breaks down the math: 70g protein plus 70g fat from sardines equals roughly 1000 calories per day. He concludes sardine fasting is simply a hypocaloric day with anti-inflammatory benefits from omega-3s and stable blood sugar, but it won't lower mTOR, IGF-1, or increase autophagy.
"Yes, you are then balancing insulin to a greater degree. Sardines are an amazing anti-inflammatory. Again, it's one of our favorite foods to include in people's diets. So it's not like I'm not saying they're not great. I've talked about it for years. I think I've never talked about anything more than sardines and wild blueberries, right? So like an olive oil. Okay. So like those are my three foods that I tell everyone. If you can't eat them, you want to eat them. They're that great for you. But I actually want to keep the science, the science, and I want to keep the marketing out of it. Our sardine fast is not."
