Keto: what’s the science behind the diet?
17:16 Share

This is The Guardian. If you're a parent or share a fridge with someone, Instacart is about to make grocery shopping so much easier. Because with family carts, you can share a cart with your partner and each add the items you want. Since between the two of you, odds are you'll both remember everything you need.

And this way, you'll never have to eat milkless cereal again. So, minimize the stress of the weekly shop with Family Carts. Download the Instacart app and get delivery in as fast as 30 minutes. Plus, enjoy $0 delivery fees on your first three orders. Service fees apply for three orders in 14 days. Excludes restaurants.

This podcast is brought to you by Aura. Imagine waking up to find your bank account drained, bills for loans you never took out, a warrant for your arrest, all because someone stole your identity. Hackers aren't waiting.

Why are you? That's why we're thrilled to partner with Aura. Your personal data is a goldmine for hackers, and Aura helps lock it down. Aura monitors the dark web, blocks data brokers from selling your information, includes a VPN for private browsing, and a password manager to secure your accounts before criminals break in. For a limited time, Aura is offering our listeners a 14-day free trial plus a dark web scan to check if your personal information has been leaked.

All for free at Aura.com slash safety. That's Aura.com slash safety to sign up and start protecting yourself and your loved ones. That's A-U-R-A dot com slash safety. Terms apply. Check the site for details. There's certainly no shortage of fad diets being espoused on social media. But there's a few that remain fashionable no matter what. One being the keto diet.

I swear by the ketogenic diet. What is that? It's a diet, simple, it's just no sugar and no carbs. And what you force your body to do is instead of burning sugar for fuel, you start burning healthy fats. This low-carb, high-fat diet actually first became popular in the 1920s as a treatment for epilepsy. And while it's still used today to help manage epilepsy and now type 2 diabetes,

it's also become prevalent as a way to lose weight. If you're thinking about doing the keto diet, you need to know this right now. I lost four pounds last week eating pretty much this exact breakfast. Every day it's packed with protein and healthy fats. Here are the five best tips I can give you if you're going to start the ketogenic diet. But as scientists begin to understand how the diet works, more evidence is emerging about some of the potential risks.

So today, what is the keto diet? How does it change our bodies? And why does such a restrictive way of eating appeal to so many of us? From The Guardian, I'm Madeleine Finlay, and this is Science Weekly.

I must say, I personally prefer a higher carbohydrate diet. That's Javier Gonzalez, a professor in the Department of Health at the University of Bath with a special interest in human nutrition. I do love pasta and tend to go for low energy density foods if I'm looking to control body weight. But I think that really comes down then to what works for individuals in terms of their preferences. Despite Javier's love of carbs, he's studied the benefits and risks of the ketogenic diet and

So I asked him, what exactly would a day's food look like on the diet? Yeah, the ketogenic diet is a version of a low-carbohydrate diet. So that might look something like an omelette with cheese for breakfast.

It could be perhaps salmon and vegetables for lunch, but specifically low carbohydrate vegetables, so non-starchy vegetables. And something similar for dinner. So some kind of typically fatty meat and then some low starch vegetables on the side. So things like the green leafy vegetables rather than, say, your carrots and potatoes.

I'm a vegetarian who doesn't much like eggs. Do you think I could do the keto diet? Are there enough foods? Because, you know, you want variation in your diet, but I wonder how much there actually is to eat.

Yeah, it's really tricky, actually. So it's possible to be vegetarian and eat a ketogenic diet, but it is very tricky. It ends up being a lot of things like avocado and nuts. And actually, whether you're vegetarian or not, the ketogenic diet does tend to be quite expensive with the types of foods that are consumed as well. So yeah, these are all really important considerations. And where does the ketogenic diet come from? Yeah, so it's been around for quite some time.

and goes back historically to treating people with epilepsy. So there's something about the ketogenic diet that seems to help people with epilepsy to prevent them from having seizures. And this might relate to one of the specific effects of the ketogenic diet. So when we restrict carbohydrate intake to very low levels, then our body starts burning fat as a fuel,

And when specifically the liver is exposed to high amounts of fatty acids, the liver will convert some of those fatty acids into these things called ketone bodies.

So when we see high levels of ketone bodies in the blood that the liver is producing, we're technically in ketosis, and that gives the name to the ketogenic diet. Now, these ketone bodies can be used as a fuel by the muscles, but also by the brain. And that might be one way in which they're affecting the risk of seizures during epilepsy.

But they also have a wide variety of other effects in terms of acting as signaling molecules, not just as fuel. It's really fascinating to hear about that connection to epilepsy. And so the idea behind keto is that by significantly reducing the carbohydrates available to use as a fuel, the body is forced to burn fat and...

To fuel the cells that would otherwise use carbs, for example, in the brain, the liver uses fat to make molecules called ketones. And so these ketones, the ketone bodies, are something that we've probably evolved so that when we undergo periods of fasting, we can still produce energy.

That's right. If you are starved and are fasting, then one of the problems is that the brain is lacking fuel because the brain will mainly use glucose and lactate, which are very similar to carbohydrate molecules. The brain can't use fat as a fuel.

The good thing about ketone bodies is that they can provide an alternative fuel for the brain when we're in this carbohydrate-restricted state. And there are a lot of other low-carb diets out there. What is it about the keto diet that kickstarts this process of ketosis? Yeah, it's really specifically the ketones.

carbohydrate availability. So the other types of low carbohydrate diets, such as Atkins or Paleo, tend to restrict carbohydrate to some degree, but they may differ in other ways to the ketogenic diet. So if we take the Atkins diet as one example, it might be low in carbohydrate, but it's got relatively high protein. And the protein can prevent some of this ketosis happening because when we eat protein, we get an insulin response and

And that will decrease the amounts of fats that are circulating in the bloodstream, reducing the amount available for the liver to convert them into ketone bodies. And the aim usually for doing this diet is weight loss. So dieting

does the keto work for weight loss? And if so, what is it about the diet that does help people lose weight? Yes, there is quite a lot of evidence that on average, the ketogenic diet does seem to result in weight loss. On average, it doesn't seem to be necessarily more effective than other approaches, but some people certainly report that they seem to do well on the ketogenic diet.

And there may be a number of things happening here. Some of them might perceive a change in their energy expenditure, and they feel like they're eating a lot of food, but still losing weight. Now, there isn't very much good evidence for any changes in energy expenditure on the ketogenic diet. It seems to be more related to fewer calories being ingested. So the reason for that could be still multiple fold. It could include some of the

hormonal changes that we see with the ketogenic diet. It could also be a little bit more of a simpler explanation, which is simply restricting any major nutrient, at least to a restrictive choice. And that restrictive choice can help people adhere to a lower total calorie intake. I do also find it really interesting, this kind of like psychological side, the idea that because the foods that you're eating on a keto diet aren't your typical diets,

that you may feel like you're not dieting at all and you're actually eating lots of food when...

you're actually eating fewer calories. I think that's really interesting. Yeah. And there might even be a bit of a motivational factor here because one of the things that happens in the first few days of a ketogenic diet is you lose weight quite quickly. And that's actually not fat mass or adipose tissue that you're losing there. It's mainly actually glycogen, which is the stored form of carbohydrate. And you also lose quite a lot of water weight very quickly as well because glycogen is stored with water.

So whilst that might not be actual fat loss, the very fat that people are seeing on the scales that they're losing weight quickly might be a motivational factor, which then helps them stick to that in the longer term. And they do see actual fat loss. So

Okay, so we can see why keto might be popular as a diet. People may lose weight on it and they may see this quick initial change in their bodies to give them that positive motivation to keep going. But are there any side effects to doing this diet?

Yeah, there are some side effects or at least some risks or potential risks to be aware of. One of the clearest ones is that people tend to see quite a large increase in their LDL or low density lipoprotein cholesterol, sometimes called bad cholesterol. And it's the type of cholesterol that is strongly associated with and probably causes actually atherosclerosis. And that's the furring up of the arteries that leads to heart disease. And...

Javier, you recently did a piece of research about some of these impacts of the ketogenic diet on the body. Perhaps you can describe that study to me and what you found.

Yeah. So we ran this project where we asked people to consume either a very low carbohydrate, so the ketogenic diet, or to continue with a fairly normal diet. And we also had a third type of diet, which was keeping total carbohydrates high, but just restricting their sugar intake. And we asked people to follow these diets for 12 weeks.

And what we found was that the ketogenic diet resulted in weight loss, but some of the trade-offs with that were an increase in this LDL cholesterol, also some changes in their gut microbiome, and also changes in how people then handled carbohydrate. They weren't able to control their blood sugar levels as effectively after the ketogenic diet. Right. So people on the keto diet lost weight.

but saw an increase in their LDL cholesterol and had adapted to burning fat as a fuel so that they were less able to control their sugar levels. Yeah. Now, I just emphasised that that was probably a short-term effect. And if people reintroduce carbohydrates, that's likely to normalise again fairly quickly, although it would be good to have some evidence to support that. And tell me a bit more about what you found with the microbiome. What happened there?

With the microbiome, we found changes in a couple of species of bacteria in particular, and the main one was the bifidobacteria. That might actually explain some of the cholesterol responses.

High saturated fat intake is well known to increase LDL cholesterol. But independent from that, the bifidobacteria seems to also play a role in cholesterol metabolism. So we think that it's probably a lack of fiber on the ketogenic diet that caused this change in bifidobacteria. And that might also contribute to the LDL cholesterol we saw.

So you have this increase in what's commonly called the bad cholesterol. You have this loss in good gut bacteria and that could be from a lack of fibre. And on this podcast, we hear so much about how we should all be increasing our fibre intake and that most of us already don't get enough. So through this diet, you've also got a risk of becoming nutritionally deficient.

Yeah, as with any restrictive diet, there are risks of nutritional deficiencies. And so one way to potentially mitigate that is to only use these diets in short-term timeframes when deemed appropriate. Another way might be to supplement with certain

nutrients to support that. Or another way might be to think very carefully about the types of foods that are provided. So for example, if we're thinking about fiber, then making sure enough vegetables are provided alongside the rest of the foods on the ketogenic diet.

And so, Javier, given what you've said about the fact that people can lose weight and the fact that that seems to come down to consuming fewer calories, why do you think this diet has taken off over and above simply eating a balanced diet? You know, we always have that picture of the plate in our heads of this amount of vegetables, this amount of carbs, this amount of protein. Yeah, I think there's a few possible reasons.

One is the fact that we have a good biomarker of compliance. So people can measure with just a finger stick sample, the concentration of these ketone bodies circulating in their blood. And so when people can see those ketone bodies rising, it's another positive motivational factor that they can see

Another one which is independent from weight loss actually is that the ketogenic diet does lower blood glucose concentrations whilst you're on the diet. And that might seem obvious because people are eating less carbohydrate. But what's interesting is that even fasting blood sugar levels are lowered by the ketogenic diet. And we think that is a special effect of the ketone bodies because these ketone bodies directly act on the liver.

to reduce the amount of glucose that the liver is releasing. And of course, blood glucose has gotten a lot of attention recently. But I mean, we did an episode not so long ago looking at the scientific evidence behind it and questioning some of the claims of health benefits of trying to lower your blood glucose and the spikes.

But for people who do need to control their sugar levels for medical reasons, say they have type 2 diabetes, this could be quite a helpful tool.

Yeah, it does seem to be helpful. Any form of carbohydrate restriction seems to produce some benefit to blood sugar levels. If people can achieve weight loss as well, then that can have further benefit for their ability to control their blood sugar levels. So when it comes to keto as a medical diet, there's some really interesting science there. And obviously you're studying some of the benefits and risks of

But go on any social media platform and you're going to see plenty of unfounded claims about keto. So what would you like to learn next about it? Yeah, we're really keen to understand the long-term effects of these kinds of diets. So we've got a series of studies that we're starting, which include things like looking at colon cancer risk,

One thing I'm keen to understand is whether we can mimic some of the positive effects of a ketogenic diet without some of the downsides. And one way to achieve that might be through ketone supplements. So new ways to increase the levels of ketones in the blood without having to restrict our dietary carbohydrate intake. Finally, Javier, what should people consider before they try a keto diet? I think it's worth considering whether you have any

contraindications to such diets, what your goals are. So for example, if you have high blood sugar levels and your cholesterol is in good check, then maybe it's worth trying some kind of carbohydrate restriction, but also to be aware of the potential nutrient inadequacies. For any listeners considering taking up the keto diet, do chat to a GP or other healthcare professional about whether it's the right step for you.

Thanks to Professor Javier Gonzalez. And that's it for today. This episode was produced by Rachel Porter. It was sound designed by Joel Cox and the executive producer is Ellie Burey. We'll be back on Thursday. See you then.

Hello, I'm Jonathan Friedland from the Politics Weekly America podcast. Donald Trump has started his second term. It's going to be a turbulent period and The Guardian will be here covering it all. We have no billionaire owners or shareholders pulling at the purse strings. So if you can afford it, please do support us. Every contribution powers our independent journalism. Do click the link in the episode description.

This is The Guardian.