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Written by The Thriva Editorial Team
8th Apr 2026 • 19 minute read

Dr. Lucia Aronica, an epigenetics and nutrigenomics scientist at Stanford University School of Medicine, discusses why personalised nutrition matters, and what the evidence actually shows about whether one-size-fits-all healthy eating really works.

Show notes

We all know that eating well matters. But what does that actually mean for you, specifically? Low-fat, low-carb, Mediterranean, keto, intermittent fasting. What if the reason no single diet works for everyone is that no single diet should?

In this episode, Greg and Charlie sit down with Dr. Lucia Aronica, an epigenetics and nutrigenomics scientist at Stanford University School of Medicine, who contributed to the DIETFITS study, one of the best-known trials in personalised nutrition. Lucia breaks down what factors shape personalisation and what the research really shows.

The discussion covers the DIETFITS findings, how individual responses vary, and which variables genuinely matter for a healthy diet. The central question: is there compelling evidence that a personalised nutrition plan beats a well-designed, healthy generic one?

In the practice segment, Lucia covers:

  • The healthy eating principles that apply to all of us (19:02)
  • The do's and don'ts of insulin testing (25:15)
  • Why pleasure is the key to long-lasting healthy eating habits (28:52)

In the experience section, Lucia answers listener questions on DNA-based nutrition, keto and the microbiome, meal timing, insulin spikes, and whether that daily tablespoon of olive oil lives up to the hype.

Episode resources

Mentioned in today's episode

Transcript

Charlie: I eat an astronomical amount of food. I think for someone of my size, it's always quite interesting watching people's faces when they've never been out for a meal with me. They're always like, "She's not gonna eat all that." Strapped in, you are about to see something.

Greg: Hold my beers.

Charlie: Hold my beers. And you know, it's like, can I have whatever's left on your plate? There won't be anything left. Just for absolute clarity.

Greg: Do you lick the plate? Sometimes it feels like.

Charlie: No, I'm not an animal, Greg.

Greg: All right. That's just me.

Charlie: Bread and butter. Mop it up.

Charlie: This is the Method, a podcast from Thriva about what health looks like in the real world.

Greg: I'm Dr. Greg Potter. I'm a scientist and health and performance consultant.

Charlie: And I am Charlie Edmondson. Whilst I love sports, I'm definitely not a science expert. I've got a regular job and I'm here to remind Greg of what life's actually like when you're not a nerd.

Greg: How dare you call me a nerd. On this show, we'll work out some sustainable changes to your routine that will actually make a difference to your health. We've got a simple three-step method. First, we bring in an expert to unpack the science behind one key health question. Second, we provide some tips and habits you can try right now. And then finally, we put the practice to the test.

Charlie: Each week we're gonna hear from those who have tried and tested our recommendations to help turn a so-called ideal lifestyle into something that actually works for you.

Greg: Charlie, how are you?

Charlie: Thank you, Lucia, for joining us today. So I just wanted to start off with the basics. Can you explain to us what personalised nutrition actually is, why it matters, and what factors shape it?

Lucia: Personalised nutrition means personalising your nutrition recommendations based on individual physiology—things like genetics, vitamin levels, even microbiome. Of course, some of these tests we can only currently measure in research labs. The microbiome testing available today isn't yet capable of really providing personalised information in my opinion. But the concept overall is using molecular testing to personalise nutritional recommendations.

Charlie: When you talk about microbiome, could you just explain what that is before we get into the more science side of things?

Lucia: There are more bacteria in our body than human cells. We have bacteria everywhere, and the gut microbiome in particular is fundamental to our health. They contribute to our immune defences, the way we break down some nutrients from food, even some food allergies, and how we tolerate fibre. You may think fibre is good or bad. It depends. Based on your microbiome, when you increase fibre, you may increase inflammation. There are studies showing that people with low microbiome diversity—fewer bacterial species—respond to increased fibre intake with increased inflammatory markers, whereas people with more bacteria diversity, when they eat more fibre, experience low inflammation. I'm telling you this just to give you an example of personalised nutrition right here. The specific study I'm talking about was published a few years ago at Stanford by my colleague Justin Sun Sandberg and Christopher Gardner. They used sophisticated microbiome testing that isn't available to everyday people listening today. But one day we may be able to tell people, "Maybe increasing fibre may not be the best thing for you right now."

Greg: I know you weren't an author on the original article, Lucia, but you've helped with analysis of the DIETFITS study, which is among the best-known personalised nutrition studies. The study randomised people who were overweight or obese at baseline into two groups—a low-carb group or a low-fat group—and followed those people for 12 months. What were the main findings?

Lucia: I was leading the epigenetic analysis of the Stanford DIETFITS study. I was really looking at how the different diets modified gene expression, and I've led the analysis of women versus men differences. The study included 609 healthy but overweight men and women randomised to either a healthy low-carb or healthy low-fat diet. I'm emphasising healthy here because both diets were really based on whole foods. No refined carbohydrates and sugar. I'm talking no pasta, no bread, no pizza. So both diets were actually lower-carb compared to the standard American diet, because if you cut refined carbohydrates and sugar, you're reducing carbohydrates overall.

Greg: Lucia, I was gonna say, you are Italian. They couldn't have run this study in Italy cutting pasta and pizza.

Lucia: I almost don't tell people this. I think Italy is still thinking about it. They're being generous with me right now. I am representing Italy abroad and working on science for the benefit of all Italians. So yes, both diets were lower-carb. This is very important. The main outcome was weight loss, and overall both groups improved lipids across the board, blood sugar. There was no difference in weight loss predicted by genetics. Specifically, we looked at three genes that supposedly were predisposing people to weight gain—FTO, APOA2, and FADS2. At the end, we didn't find that these genes made any difference in predicting weight loss success on either diet.

There's a bit of a misconception that some people are genetically predisposed to gain weight or struggle to lose. But essentially, what the Stanford DIETFITS study showed is that genetics bear little weight on that, if you'll excuse the pun. When it comes to carbs and fat, our bodies aren't as hardwired as we think. But where genes do matter is at the micro level—remember our example about fibre causing or calming inflammation. Testing our micronutrients can show us how to better develop the bacteria in our gut, or which vitamins we need to supplement.

So now if you're wondering: why is there such a difference between the micro and the macro? Well, it's because micronutrients are more directly connected to our genes. With macronutrients like carbs or fat, there are several factors to consider. For example, your baseline weight, your insulin resistance, your lipids. Look, you have great genes for metabolising carbohydrates. Telling you now that you can indulge in carbohydrates will be a very big mistake. I don't care whether you were born with great genes. If you eat pizza, pasta, and bread your whole life—let's say you're in your fifties and you've abused refined carbs and sugar for all your life—well, you're likely type 2 diabetic now. This is just a point to tell you: the micronutrient component is really heavily affected by other markers and other genetic variants.

Greg: What are some important limitations of personalised nutrition studies that our listeners should be aware of?

Lucia: In general, the issue is study design. Sometimes primary outcomes are cherry-picked to demonstrate that a diet or intervention is superior. The point is, you need to look at the study design, the population, the primary outcome, why they chose that outcome. And of course, study length. How long was the study? Is this enough to tell you something long term? Is it a two-month study? There are so many variables. I always encourage people: never just look at the title, not even the abstract. Always ask yourself, who are the people involved? What is the outcome being investigated? What are the methods and the potential confounding factors?

Greg: If we look at the literature at large, would you say that overall it's been shown that personalised nutrition interventions are meaningfully better than relatively healthy generic diets? Or is the difference really quite small?

Lucia: When we talk about personalised nutrition, rather than thinking "is this good or bad," we need to think that personalised nutrition is absolutely important just because any food can be good or bad for you depending on your individual physiology. I talked about fibre before, but I could name any food. Spinach is great, but if you have kidney stones it's full of oxalates and you probably don't want to overindulge. Eggs are great for most people, but if you're one of those 25.5% of people who are cholesterol hyper-responders, with high cholesterol, then no more than two a day. So personalised nutrition is the way to go. But we don't have programmes or companies or products that can systematise this right now in a way that tests your genetics or your microbiome and gives you personalised recommendations. I think we're not there yet.

Charlie: Once someone's obviously got those broad healthy eating habits in place—so the 80% of whole foods—where does personalisation actually start to matter? For example, if someone wanted to lose body fat.

Lucia: Thank you for this question, because it's very important. While everyone is obsessed with personalisation, I think personalisation is the 20% of the equation. The 80% of the equation of a healthy diet are universal principles. A diet based on whole, unprocessed foods. Minimise refined carbohydrates and sugar. This is 80%. Honestly, if everyone did this, we would defeat chronic disease and we wouldn't even be talking so much about which diet, whether vegan, omnivore, keto, low-fat. This is universal. And then the 20%, the personalisation, can be more important for some individuals. If I tell you, you know, there is great, but you're lactose intolerant, well, maybe it's not great for you. Vegans or vegetarians might need to prioritise omega-3 fatty acid sources because they can't get enough from plants. Then we have personalisation.

But if we just eat whole, unprocessed food, we'll do the 80% that really matters for our health.

So once someone's obviously got those broad health eating habits in place, where does personalisation actually start to matter?

Specifically for body weight, this is tricky. For example, low-carb from a biochemical point of view makes more sense for people who are insulin resistant, just because you're reducing carbohydrate and therefore glucose load. If you have a problem with metabolism, this is physiologically better. However, we need to take into account also your food preferences, because as we say, the best diet is the one that you can stick to. So we need to collect more data for personalisation—your baseline weight, your insulin resistance, your food preferences.

But overall, I would say try first to focus on whole foods and really eliminate refined carbs and sugar and see how it goes. Then you can tweak based on your dietary preferences and vitamin levels and insulin resistance levels. If you have high insulin resistance, I would focus on vegetables that tend to grow above ground—green leafy vegetables, courgette, squash, tomatoes, avocado.

Charlie: You've mentioned a couple of times there about being insulin resistant. Would anyone know that they are insulin resistant without testing? Is there a symptom or a sign?

Lucia: Oh my goodness. First of all, I want to encourage people to test their insulin level, because doctors don't test for that. They test your blood sugar and not your insulin, which is crazy because insulin is the hormone that keeps your blood sugar in check. When you eat a high-carb meal, you produce insulin, which lowers your blood sugar—until it doesn't anymore. If you abuse this beautiful control system and eat too much sugar and carbohydrate for your whole life, here's what happens: you might have normal glucose because your insulin is sky high. It's working hard to lower the glucose because you're eating a lot of carbs and sugar. So you go to the doctor and the doctor tells you, "No problems. Your blood sugar is in check." Until after 10 or 20 years the system is broken, and you check your insulin and see that it's high. But now also your blood sugar is high because your body became insulin resistant and isn't responding anymore to that high insulin. I told this to my friends in their forties with normal, perfect blood glucose, and I told them, "Look, you need to measure your insulin." I have 10 times less insulin than my friend and his blood sugar is normal. So please, always test your insulin, because your glucose is meaningless at the beginning. It's meaningful only when it's too late, when you're already prediabetic and diabetic. Sorry, I'm very passionate about this, but it's like insane.

Greg: I'm glad you mentioned insulin because I think nowadays a lot of people are using continuous glucose monitors. These devices that were primarily used by people with diabetes that you typically put on your shoulder and they measure glucose concentrations in the interstitial fluid, not the blood. The problem is we don't have information about insulin at the same time, or levels of fats in the blood, or levels of ketones in the blood, or amino acids or other things you might be interested in. So I think some people tend to over-interpret those data.

The other thing I wanted to pick up on that you mentioned is people's preferences. We were discussing this in the context of the DIETFITS study. Were there differences between men and women in how well they adhered to the diets?

Lucia: Yeah. I think there is also a behavioural component. The women didn't stick to the low-carb diet as well. Traditionally, women have been brainwashed that fat makes you fat. So they are reluctant to increase dietary fat. For men, it was easier to stick to a low-carb diet because they were just increasing the fat and finding it easier. Whereas for women, this might be more difficult. So again, this is another example of personalisation: even if you just look at a subgroup of people—in this case, men versus women—well, the results look different.

Charlie: So the next question is from Alex in London, who asks: is it advisable to have two or three meals a day to avoid insulin spikes, or does this block metabolism? Are small, frequent meals more advisable to boost metabolism?

Lucia: I love this question because the answer is: it depends. First of all, the premise, right? Having more meals spikes your insulin—not necessarily. A piece of butter doesn't spike your insulin at all. It depends on what you eat. Your insulin will be spiked primarily by carbohydrates, very little by protein, and not at all by fat. So the premise depends on what you eat and how much you eat. I would say: we know that traditionally, for example, bodybuilders who really want to get lean and preserve muscle mass tend to eat very small meals very frequently, and they have great results. Believe me, they're not going to spike their insulin at all for two reasons. First, they really pay attention to what they eat. Plus they have a lot of muscle, which works as a sugar sponge. So even if they eat more sugar, their muscles are so hungry for that sugar that their blood glucose doesn't raise and their insulin doesn't spike.

So again, it depends on your diet, what you want to achieve, your initial body weight and lifestyle. If you have a food addiction, it's a very bad idea to eat every two or three hours because you're probably going to make poor dietary choices multiple times a day. This is why fasting works so beautifully for people who are making bad decisions every time they eat. So why would you eat two or three times a day? It depends. There's no universal answer.

Charlie: Then we have a question from James in London: does keto actually destroy your microbiome? And are meal replacement drinks actually healthy?

Lucia: I love these questions. What is keto, right? It is a label. There is a good way and bad way to do any diet. You can be on keto and be vegan and eat all plants with a lot of fibre, or you can be carnivore. So if your question is whether the carnivore diet would destroy your microbiome, the reality is we don't know because we don't have long-term studies. I think honestly I would be concerned to completely eliminate vegetables and fibre long term based on the values and benefits we know come from veggies.

Greg: Yeah. And what about this daily tablespoon of olive oil that everyone seems to talk about?

Lucia: I would say more. I think the PREDIMED study supports about four tablespoons a day. Olive oil is the best fat you can have in your diet, especially if it's raw and cold-pressed. If you keep it in a dark bottle, because those polyphenols—the good molecules inside olive oil—are really fragile.

Greg: Yeah. And I completely agree about the form of olive oil mattering, because if you look at the research on olive oil in general and look at extra-virgin olive oil versus refined olive oil, the findings from different studies have shown that extra-virgin olive oil can reduce some markers of inflammation. So on that subject, apart from olive oil, which oils are good? There's a lot of discussion about seed oils in particular, and there are some influencers who have thrown them under the bus and said they're really bad news for everyone. But what does the science actually show about seed oils?

Lucia: Processed seed oils are so processed that they really lack the bioactive molecules that are good for us. So they're less wise, traditionally, compared to olive oil. Extra-virgin olive oil has some polyphenols, especially hydroxytyrosol, which is an epi-nutrient. I teach at Stanford a framework called Epi Nutrition, where I talk about how certain nutrients can really signal to our genes to improve our health. Because there are natural sources of omega-6 fatty acids—nuts and seeds, right? Those are great. But a processed seed oil, I think, is not a great source. I would much rather eat nuts and other sources of fatty acids from natural whole foods. That's my point.

Greg: Yeah. And I completely agree with that, because those foods are so much more than the fatty acids alone, which is what the oils are. Also, just to add one more thought for completeness, I would just add that I think some people are concerned about the effects of cooking with those types of omega-6 fatty acid rich oils, but actually if you look at the totality of the evidence, the omega-3 to omega-6 ratio is comparing good to good. You need enough of both. Higher levels of omega-6 fatty acids in the blood actually tend to relate to better health outcomes. Going back to the PREDIMED study, I vaguely recall speaking about cooking oils: the addition of tree nuts to the diet probably had a larger overall positive effect on health than the addition of extra-virgin olive oil. So don't worry about using seed oils now and then, and with that said, bear in mind the other caveats, like the fact that whole seeds are better, extra-virgin olive oil is definitely a good source, but you shouldn't be overly concerned about cooking with things like sunflower oil.

Lucia: Yeah. I think behavioural change is the million-pound question that nobody has solved right now, because how can we make people stick to the plan? I will give you my Italian perspective on this. My philosophy is the following: we tend to think that pleasure is the opposite of health, right? It's indulgence in bad food. But I think pleasure is the compass to find health. And let me explain: you can't be consistent with something you hate, but you can and will be consistent with something you truly enjoy. That's why, for example, in Italy we don't see eating at the table with family and cooking food as a prescription.

I think pleasure is really something that we need to rediscover. Now, there are two problems with this philosophy. On one hand, pleasure is a good thing. It's an evolutionary mechanism. However, the processed food industry has hijacked this natural system, creating food that stimulates our pleasure centre in ways that natural food can't. So the bad part is not the pleasure itself. It's that there are now authentic pleasures and what I call Trojan horse pleasures—artificial pleasures like processed food or social media. This is, I think, why it's so complex: we've lost that natural mechanism that makes us want to stick long-term to a habit that makes us healthy. But it's pleasure. First, if you have an addiction for processed food—which is the bad pleasure—you first cure that. But then you need to replace it with a good addiction, right? If we want to white-knuckle our way to health by embracing protocols we hate, we're not going anywhere.

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