Episode 510: Layne Norton, PhD: The Best Diet to Follow + Is Diet Coke Actually Bad For You

Summary

Habits and Hustle Podcast Episode 510:

Layne Norton, PhD: The Best Diet to Follow + Is Diet Coke Actually Bad For You
Host: Jen Cohen
Guest: Dr. Layne Norton, PhD
Original Air Date: December 12, 2025

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Overview

In this episode of Habits and Hustle, host Jen Cohen sits down with acclaimed nutritionist and scientist Dr. Layne Norton to dissect two hot-button topics: What is truly the "best" diet for long-term health and weight loss, and whether diet sodas (like Diet Coke) are actually bad for you. Dr. Norton brings a practical, data-driven perspective, challenging diet dogma and media-fueled fears, and offers actionable, sustainable advice for listeners striving for healthier habits.

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Key Discussion Points & Insights

1. Is There a “Best” Diet for Everyone?

• Key Research Findings ([01:54]–[03:23])

  • Dr. Norton cites two major systematic reviews: one examining four diets, another looking at fourteen, both finding no significant difference in long-term weight loss between different diets.
  • Adherence is the Real Key: The most significant predictor of success was how well individuals stuck to whatever diet they were following, regardless of the specific macronutrient breakdown.
    • Quote:

      “Whatever you can stick to, whatever you can sustain is going to be the best diet for you.”
      —Dr. Layne Norton [02:23]

  • People differ widely in what feels “sustainable”. What feels restrictive to some may feel easy to others.

• Personal Story: Flexible Dieting ([03:24]–[04:02])

  • Layne shares his own early struggles with “eating clean” and bingeing, discovering that allowing himself flexibility (tracking calories and macros, but eating foods he wanted) ended cycles of overeating.
    • Quote:

      “For me, if I know I can have it, it actually makes me want it less.”
      —Dr. Layne Norton [03:39]

• Coaching Others & Selection Bias ([04:03]–[05:48])

  • As a coach, Layne noticed that people succeeded best with the method they chose and believed in, not necessarily what was “objectively best.”
    • Quote:

      “Flexible dieting has worked the most. But that’s a selection bias because people come to me because they know I’m a flexible dieting guy.”
      —Dr. Layne Norton [04:25]

  • Customization and autonomy in dietary preference matter most; there’s no universal best approach.

• Practical Tools ([05:04]–[05:48])

  • Dr. Norton developed the Carbon Diet Coach app, which gives users choices (plant-based, keto, balanced, etc.) and allows adjustment, reinforcing sustainability over dogma.

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2. Diet Wars, Belief, and Cognitive Dissonance

([05:48]–[07:31])

• Dr. Norton points out that people often cling to what has worked for them, becoming “tribal” about their diet and resistant to new evidence—a phenomenon known as cognitive dissonance.
  • Quote:

    “What they found is…both things were equally as effective as causing the person to become more entrenched in their beliefs. …It actually caused them to double down.”
    —Dr. Layne Norton [07:12]

• Changing beliefs is hard—even when faced with contradicting facts.

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3. Artificial Sweeteners & Diet Sodas: What Does the Science Say?

Addressing the Stigma Around Diet Coke ([09:55]–[10:00])

• Jen Cohen raises the social stigma and panic over diet soda, noting, “If you hold a Diet Coke around these days, it’s like, you might as well just hold a machete…”

The Data on Diet Sodas ([10:01]–[10:57])

• Correlation ≠ Causation:

  • People often cite studies showing links between diet soda and obesity, but Dr. Norton clarifies these are correlations, not proof of causation.
    • Quote:

      “That’s like saying basketball is causing people to be tall.”
      —Dr. Layne Norton [10:00]

• Randomized Controlled Trials:

  • When diet sodas replace regular sodas, studies show significant weight loss. In a recent meta-analysis, people who drank diet soda lost more weight than those substituting with water, likely because water drinkers often compensated with calories elsewhere.

• Metabolic & Gut Health: ([10:58]–[13:08])

  • The bulk of fear around artificial sweeteners and gut health comes from limited human studies—most evidence is from petri dish or high-dose rodent studies.
  • Some changes in gut microbiota have been observed, but it’s unclear whether these are harmful, beneficial, or neutral.
    • Quote:

      “When it comes to gut health, [Diet Coke] is one of the last things I’m worried about.”
      —Dr. Norton referencing Suzanne Devcona [11:56]

  • Real-world health tradeoffs matter: the benefit of someone dropping significant weight by switching to diet soda is very likely to outweigh any theoretical or unknown gut microbiome effects.

The 'Naturalistic Fallacy' and Chemical Breakdown ([13:08]–[14:21])

• Many oppose artificial sweeteners due to the “naturalistic fallacy”—the idea that artificial automatically means dangerous. Dr. Norton breaks down what aspartame metabolizes into (amino acids and a tiny amount of methanol, less than found in tomato juice), and explains artificial sweeteners are used in minute quantities due to their intense sweetness.
  • Quote:

    “You get 20 times aspartic acid and phenylalanine in a steak than you do in a Diet Soda.”
    —Dr. Layne Norton [13:49]

  • Rodent studies cited are often at doses thousands of times greater than humans would ever consume.

Final Take on Diet Soda ([14:22]–End)

• Dr. Norton is clear:
  • He’s not suggesting people should drink diet sodas.
  • Quote:

    “If somebody wants me to say that it’s bad for you, I don’t think you can objectively say that.”
    —Dr. Layne Norton [14:22]

  • If swapping regular soda for diet soda helps with meaningful, sustained weight loss, it’s almost certainly a “net win” from a health perspective.

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Notable Quotes & Moments

• “You have to follow some form of restriction, but you should choose the form of restriction that feels the least restrictive to you.”
  —Dr. Layne Norton [02:23]
• “For me, if I know I can have it, it makes me want it less.”
  —Dr. Layne Norton [03:39]
• “We get into these diet wars. Everybody wants to be the winner and have their diet be best. And I’m like, shouldn’t the goal be to just figure out what works for people?”
  —Dr. Layne Norton [05:46]
• “If I can get somebody to stop drinking regular soda and drink diet soda, and they lose 50 pounds… you’re going to have a hard time convincing me that person is not healthier now for having lost 50 pounds.”
  —Dr. Layne Norton [12:44]

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Timestamps for Important Segments

• 01:54 — Dr. Norton introduces the adherence-over-diet debate and summarizes key studies.
• 03:24 — Personal story about the shift from “clean eating” to flexible dieting.
• 04:25 — Coaching discoveries and the importance of dietary self-selection.
• 05:48 — Discussion about diet wars, bias, and cognitive dissonance.
• 10:01 — Sweep away fear about diet sodas with the actual science.
• 11:56 — Diet Coke's low priority in gut health concerns, quoting a leading microbiome expert.
• 13:08 — Debunking aspartame fears via its chemical makeup.
• 14:22 — Summing up: Is Diet Coke bad for you?

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Conclusion

This episode offers empowering, evidence-based advice emphasizing practicality and personalization over fad, fear, or rigidity. Dr. Layne Norton urges listeners to gravitate towards consistency and adherence, not diet tribalism, and he systematically disarms common health scares around diet sodas with up-to-date research and relatable analogies. If you want sustainable, sane nutritional guidance, this conversation is a must-listen.

Transcript

[A]

Hi guys, it's Tony Robbins. You're listening to Habits and Hustle. Crush it.

[B]

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[A]

Now if we look at does one diet stand out as better than the others? So there's two studies I'm thinking of. There was one looking at four different diets and one looking at 14 different diets. Both were systematic reviews and they looked at long term weight loss and what they found was basically no diet performed better than another diet. But in one of them they stratified people, regardless of diet type, from least adherent to most adherent. And wouldn't you know it from least adherent to most adherent, there was a linear reduction in body weight. So again, I know this sounds very like much like a cop out, but whatever you can stick to, whatever you can sustain is going to be the best diet for you. Now that appears to be extremely individual. I've had people say to me I did intermittent fasting and I didn't even feel like I was dieting. I've had people say I tried everything and I did low carb and it felt easy. Had people say I did a plant based diet and it I was so full all the time it felt easy. If you're going to lose weight and Keep it off. You have to follow some form of restriction, but you should choose the form of restriction that feels the least restrictive to you. And also, don't assume that'll be the same for everybody. So for me, I tried the whole eat clean. 20 years ago when I was getting into bodybuilding, what I felt, what I found out was I was binging on the weekends. And I remember one day I just had, like, mowed down a whole pizza, and I was like, you know, I feel like it's not the pizza itself that's, you know, screwing me up, it's the fact I'm eating the whole thing.

[B]

Yeah.

[A]

So I'm going to try and hit these calories and protein and carbs and fats and let myself, if I feel like I want something, let myself have it. And wouldn't you know it, I had no problems after that.

[B]

You were able to stop at just a little amount.

[A]

Yep. Now, that's my personality, my psychology. Right. So I'm somebody, like, if I know I can have it, it makes me actually want it less.

[B]

Yeah.

[A]

Right. So I track my calories, I track my protein, I track my carbs, my fats. Now, for some people, that feels very overwhelming. It feels extremely restrictive. They just say, well, I'd rather just like, reduce my carbohydrate intake and not worry about it. Okay, you can do that.

[B]

Depends on who you are.

[A]

But again, but funny enough, when I got into coaching people, I thought, well, I've got the solution. I'll just have everybody do this flexible dieting thing and this will solve all the problems. And of course, you know, learned, hey, dumb, dumb. Not everyone's like, you know, what did.

[B]

You find for the people that you've trained? Of all the people you've trained, what has been, what has worked the most in terms of what you've seen?

[A]

Well, flexible dieting has worked the most. But that's a selection bias because people come to me because they know I'm a flexible dieting guy.

[B]

Right.

[A]

And so then they end up wanting to gravitate towards that. And I'll always tell people in low carb or fasting, like, they're like, look at all these people who have gotten all these results. I'm like, yeah, because they're coming to.

[B]

You because they're already.

[A]

They're already sold on that.

[B]

Exactly.

[A]

So what I would say is, like, listen, you know, I think that this is great news personally, because it means the world is your oyster. Whatever dietary strategy helps you, like, be able to be consistent. Just do that. I Mean, we have like a nutritional coaching app that we designed.

[B]

Right?

[A]

Algorithm based coaching app.

[B]

What's it called?

[A]

It's called Carbon Diet Coach. So it's like basically like one on one nutrition coaching, but for a fraction of the price. So $10 a month, that's great. And it's all algorithm based algorithm that I helped write. And. But we don't. When it comes to dietary preference, we give people options. Do you want to be plant based? Do you want to be low carb, ketogenic? Do you want to be balanced? Do you want to be low fat? And you can pick. And then even within those, we let you shimmy the numbers a little bit so you can really get to something. And we don't say, hey, you've got to eat five meals a day or three meals a day or eight meals a day. You get to pick based on what you feel is most sustainable for you in terms of dietary strategy.

[B]

Oh, that's great.

[A]

So, you know, I really think that reframing this stuff is like, we get into these diet wars. Everybody wants to be the winner and have their diet be best. And I'm like, shouldn't the goal be to like, just figure out what works for people? Like.

[B]

Right, Exactly.

[A]

And when people say, you can't lose fat eating carbohydrates, I'm like, how many millions of examples of people eating low fat, higher carb diets and losing fat and getting very lean do we need before we say, well, that's Obviously not true.

[B]

100% true.

[A]

And I think people get so. And I'm guilty of this. It's like they find whatever worked for them and then try to justify why it's the best thing to do. It's almost like we're just like. It's like teams, right?

[B]

Totally.

[A]

It's like it goes to politics, the whole thing.

[B]

It goes with everything. But it's also like, because we want to, we don't. To change our mind is very difficult.

[A]

Difficult.

[B]

Oh, yeah, right. And so if we have that in our brain, it takes a. Is it cognitive dissonance? Is that what it's called, cognitive dissonance? Yes.

[A]

Great example of that. And this is an example of politics. But I think there was a study done like 10 years ago, and they showed both Democrats and Republicans facts that would either support or refute, like directly refute a position they held. Right?

[B]

Yeah.

[A]

What they found is that whether it refuted or supported their position, both things were equally as effective as causing the person to become more. More entrenched in their beliefs. So when they presented facts.

[B]

Yeah.

[A]

To these people and it didn't matter if it was Democrats or Republicans. Both. This is a people problem. This is not a party problem. When they presented facts to Democrats and Republicans that were. That refuted a position they held, people did not take the other side. They did not admit they were wrong. It actually caused them to double down.

[B]

Yeah.

[A]

And that's what's called cognitive dissonance.

[B]

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[A]

I'll tell people, do you want to discuss feelings or do you want to discuss what the data actually says?

[B]

I want the data.

[A]

So if we look at the effects on like type 2 diabetes on weight loss, so if you look at correlation data, which is basically, what characteristics do people who drink more diet sodas have? Well, you can find a correlation between obesity and diet soda. And so they've gone, aha. See, it's causing people to be fat. Well, that's like saying basketball is causing people to be tall, right? Yeah, right, like, but if we actually look at the randomized control trials where they substitute diet sodas instead of regular soda, they see significant loss of body weight. And actually people say, well, it's not better than water. There was a recent network meta analysis done where they compared diet soda versus regular soda, water versus regular soda, and water versus diet soda. The people drinking diet soda lost a little bit more weight than the people drinking water.

[B]

Stop it now.

[A]

That's. Diet soda is not a fat burner. Okay? They're just eating less. So what that suggests is people are, if they're substituting with water, they're still seeking out that sweet taste somewhere else. So now people will say, well, that's just weight loss. Like, it can't be healthy for your gut microbiome and whatnot. So there's only a couple studies in humans on the gut microbiome. Most of it's been in petri dishes and high dose rodent studies. It does appear that some of these artificial sweeteners do change the gut microflora. However, what we don't know is is it a bad change, good change, or neutral?

[B]

We don't know those things.

[A]

We don't know those things. No. And I've talked to several. One of my colleagues who did her master's at Illinois when I was doing my PhD in my lab. Suzanne Devcona is one of the world's leading researchers on the gut microbiome. And I asked her about diet soda and she said, when it comes to gut health, it's one of the last things I'm worried about.

[B]

Really?

[A]

Yeah. So for example, so there was a study done where they showed that, you know, artificial sweeteners. I, I don't know if it was aspartame. I think it was sucralose, which is Splenda. Yeah, yeah, Splenda. They showed that. And, and it does appear to be artificial sweetener dependent. I, I don't know if aspartame changes the gut microbiome. There was a study looking at It. I can't remember exactly which one it was. I know sucralose did, but if you look at the microflora that it changed in terms of reducing and increasing, they did note an increase in the production of things like butyrate and propionate. So if you go and look at the literature on butyrate and propionate, guess what? They actually appear to have health benefits. So now, I'm not saying that artificial sweeteners are necessarily good for your gut. What I'm saying is we don't know. But what I'll tell you is this. If I can get somebody to stop drinking regular soda and drink diet soda, and they lose 50 pounds, and every time I post about this, there'll be multiple people say, all I did was cut out regular soda and drank diet soda, and I lost £50, £70, £100. You're gonna have a hard time convincing me, regardless of whatever is happening with the gut microbiome, which we don't know, that that person is not healthier now for having lost £50.

[B]

That is amazing. So where did this all come from?

[A]

It's the natur. It's the naturalistic fallacy, which is if something is artificial, it must be bad for us. But if you look at, like, what aspartame breaks down into, it's aspartic acid, phenylalanine, and then it breaks down into methanol. Oh. Oh, gosh. Methanol. Let me get to that. Aspartic acid and phenylalanine are amino acids. You get 20 times aspartic. The aspartic acid and phenylalanine in a steak that you do in a diet soda. All right, so let's just take those out of it. The methanol, it's such a small amount, your body can easily metabolize it. And I believe you get more methanol in, like, a glass of tomato juice than you do in diet soda.

[B]

Really?

[A]

So, because you have to understand, while a Coke is like 40 grams of sugar, artificial sweeteners are hundreds of times sweeter than regular sugar. So aspartame, I think, is 200 times sweeter than sugar, and sucralose is, like 600 times sweeter. So you're talking about milligrams of this stuff. It's a very, very small amount, which is why, again, when they cite these rodent studies, where they're giving a thousand times the dose of what they would normally give humans, I kind of go, who cares?

[B]

Doesn't matter.

[A]

I'm not saying people should drink diet soda. I'm not encouraging it as a weight loss tool. What I'm saying is, right now, if you. If somebody wants me to say that it's bad for you. I don't think you can objectively say that. Do I think it warrants further investigation? Of course. But again, if it's a tool that helps people lose significant body weight and keep it off, then I think it's a net win.