The One Diet That Triathletes Should Fear

Why the ketogenic diet is potentially so harmful

As a sports nutritionist I’m all about finding the best way to optimise performance and health. Low carb diets or ketogenic diets for endurance athletes have been touted as a way to improve performance… But does the evidence agree with this?

Is a ketogenic diet for triathletes beneficial, and can a ketogenic diet improve endurance performance?

In this video I’ll delve into the research surrounding low carb diets for athletes and whether it might benefit performance, and whether a ketogenic diet is healthy for athletes.

00:00 Introduction
01:56 What is a Ketogenic diet?
03:26 Potential health benefits of a ketogenic diet
03:46 What evidence is there for performance?
05:21 Potential health risks of a ketogenic diet
06:46 Unsupported benefits of a low carb diet
09:01 Periodised carbohydrates

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Hi! I’m James. I’m a Sport and Exercise Nutritionist and I make videos on nutrition to give people simple, clear and easy to use information on a range of subjects. I focus on triathlon and how triathletes can use nutrition to help properly fuel their training and racing.

In my day job I work as an Advanced Clinical Practitioner in General Practice, or Family Medicine for those of you not in the UK, and work in a busy NHS GP practice. I’m a Specialist Paramedic by background and have full independent medicine prescribing rights.

Advanced Clinical Practitioner in Family Medicine, BSc, PGCert
Registered Sport and Exercise Nutritionist (SENr)
MSc Sport and Exercise Nutrition
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Qualified L2 British Triathlon Coach

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These videos shouldn’t be taken as direct, personal advice on medicine or nutrition but more for information purposes based on the latest research and evidence. Unless otherwise clearly stated, this information is more suited to adults as under 18s have different requirements and considerations. I’m happy to answer any questions you might have as an individual though!

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What’s the link between triathletes Goldilocks and the ketogenic diet today we’re going through what is a very dividing Topic in the triathlon world it’s about a diet which some suggest is incredible for endurance performance whilst others have concerns about how healthy or sustainable it is and that it might actually worsen performance I’m

Going to run through some of the evidence on sporting performance in health and why this diet concerns me so much and if you’re new here then hey my name is James I’m a registered Sports nutritionist and I work with amateur and professional endurance athletes I help them to train and race better improve

Their recovery and do all of this in a healthy fashion this topic is particularly important for me because of my interest in health and performance if there’s a nutrition strategy that I can leverage to improve performance whilst keeping an athlete healthy then I’m going to use it now most of you will be

Familiar with the story of Goldilocks and the Three Bears goldilock stumbles upon a cottage in a forest and she finds three bowls of porridge she tries the first one and it’s too hot she tries the second and it’s too cold she tries the third and it’s just right the same could

Be said for triathletes and their diet they dabble in different ones to find what suits them and some triathletes get drawn to the ketogenic diet perhaps to improve performance maybe for weight management or because they think it’s a healthier diet but is the key enic diet

Too extreme and does it really come with some of the benefits that people suggest well there are many athletes and academics who Advocate it and there’s examples of incredible athletes who follow low carb approaches people like Chelsea sadaro Dan ples Zack bitter and prominent authority figures like

Professor Tim noes they all have links to low carb approaches so what is it and what makes it so special a ketogenic diet diet is a diet where someone follows a pattern where they consume high fat moderate protein and low carbohydrate Foods now to be clear this is not the same as periodized

Carbohydrates which we’re going to cover later on by consuming a low amount of carbohydrates the aim is to put your body into a state of ketosis in a nutshell this means your body starts producing ketones to make up for the lack of dietary carbohydrates normally your body uses a mix of carbohydrates

And fats for energy but during ketosis your body shifts its main fuel source to Fat this results in ketones being produced so essentially it’s your body becoming adapted to burning fat when carbohydrates are scarce from an Endurance Sports point of view the aim is that you unlock the potential to

Essentially unlimited energy where you upregulate or increase your ability to burn fat for energy and you decrease your Reliance on on carbohydrates so people who get positive benefits from following a ketogenic diet report being able to run or cycle for hours so that might mean you have more stable energy

Levels during training or during a race you reduce the need for more frequent fueling and can reduce the risk of gastrointestinal upset and you do better over longdistance events because you have such great access to your fat stores but there are also potentially health benefits to a ketogen diet you’re

Consuming less carbohydrates which means the glucose load or burden on your body is less you have to produce less insulin to deal with all of those carbohydrates so all of that really sounds pretty awesome but what does the evidence say now there are definitely some studies within a sporting context that report

Benefits of a ketogenic diet as you become more fat adapted you’re able to work at a higher percentage of your V2 Max one study in 2023 found that those who are fat adapted could exercise at 85% of their V2 Max which was the highest they’ve ever seen in research studies

Consistently show that fat adapted athletes can burn more fat compared to those on a carbohydrate Rich diet the problem is though that in race specific scenarios there isn’t really any evidence that shows that they are equal or better to carbohydrate Rich diets now there are are plenty of anecdotal

Reports or case studies of athletes who have done extremely well on low carb or ketogenic diets but when you stack that against the evidence for carbohydrate Rich diets it becomes really difficult to see it as a viable strategy some of the best research we have on low carb

Versus high carb diets in Elite athletes seems to suggest that low carb diets cause worsening performance we also know categorically that high intensity exercise suffers with low carb diets this is consistently shown in the research and the mechanism is undisputable fat needs oxygen in order to be metabolized whereas glucose or

Carbohydrates doesn’t this means that someone performing high-intensity exercise is always going to struggle if they’re following a low carbohydrate or ketogenic diet there are also some studies which worry me when it comes from a health point of view two studies investigating short-term low carbohydrate diets suggest that may be a

Risk to your bone health as well as your immune function and your ability to absorb iron it’s also clear from the research that ketogenic diets are hard to follow people struggle to maintain them for a long period of time and they also struggle to consume sufficient calories while they follow them this

Definitely matches what I found from working with amateur and professional athletes in that those who follow the ketogenic low carb diets really struggle to eat enough food especially if they have high training volumes this then increases the risk of things like red s or relative energy deficiency in sport

Which can lead to a whole Myriad of health problems and finally I worry about the long-term Health consequences of a ketogenic diet we don’t have loads of research on what’s going to happen over the long term when someone follows a high fat low carbohydrate diet typically we see that when someone

Follows these high fat diets which are often high in saturated fat there’s an increase in cholesterol which can increase your risk of cardiovascular disease so heart attacks and strokes but we do have research for things like the Mediterranean diet which offers a balanced approach to food which includes

Carbohydrates now at some point some of you might be thinking but James you’ve forgotten some other potential benefits of the ketogenic diet what about your increased ability to burn fat which should be better for your metabolic health this is something which I’ve seen quite a lot on Twitter and people really

Get into it now on the face of things this is awesome and I’m all for this but the problem is again we don’t have much research that supports it but we do have research that essentially supports a carbo hydrater diet there’s a fantastic study that looks at V2 Max and its

Relation to all cause mortality essentially the higher your V2 Max is the lower your risk of death now we know that people can achieve very very very high V2 Max numbers while following a carbohydrate Rich diet and they might be extremely good at processing and burning sugar during exercise but actually not

That good at being able to burn fat and we know that that high VO2 max relates to that low risk of death but conversely there’s not really any metric that we currently have that does the same for fat metabolism I would love this to be something which comes out in the

Research over the coming years and some way we can test this Theory more but at the moment this isn’t really a potential benefit of the ketogenic diet the other thing which people suggest as a benefit to the ketogenic diet is that it reduces your need to produce insulin because you

Don’t have all of these carbs coming in which raise your blood glucose and mean your body has to produce insulin to deal with them so you have a lower glucose load you’re not working your pancreases hard again the problem is that research doesn’t really demonstrate that this is

An issue isue it’s absolutely normal for your blood glucose to rise when you consume carbohydrates and for your body to release insulin to counter this that is a normal physiological mechanism and we want that so as a bit of a side tangent you might be seeing a lot of

Advertising at the moment for cgms and how people are trying to keep their glucose readings flat and optimize their food in order to do this unfortunately this just seems to be a bit of a trend and a fad and there’s just no real research to suggest that this is

Necessary or healthy now I mentioned earlier about periodized carbohydrates and it’s worth talking about this if you follow a periodized approach to your carbohydrates it means you’re tailoring how many carbohydrates you’re consuming in a meal based on what exercise you’re doing how long you’re exercising for and

The intensity now this probably is the best approach to follow with your carbohydrates if you know that you’re not going to be exercising quite as much or you’re doing low intensity exercise you can reduce the amount of carbohydrates that you consume realistically carbohydrates as a macronutrient simply provide energy yes

They might also contain micronutrients so vitamins and minerals but that’s not really its core function so if you look at it like that then it makes perfect sense to reduce the amount of carbohydrates you eat so for example this might mean having smaller portions of rice or pasta or eating less bread

And instead opting for more protein and healthy sources of fat so after all of this we’ve kind of got to bring it back and have a bit of a summary my take on this is that whil there might be some benefits to a ketogenic diet the risks far outweigh them there’s not enough

Evidence out there that suggests that it’s Superior for performance or for health compared to a carbohydrate Rich diet and a carbohydrate diet that supports your training conversely there is evidence that suggests that a ketogenic is harmful for performance and potentially for your health now to be clear I’m not including someone who has

Got a medical reason to follow a ketogenic diet I’m talking about the average person who wants to optimize their performance but also look after their health overall I wouldn’t suggest that you follow a ketogenic diet unless you’ve been directed specifically by a registered Sports nutritionist dietician or doctor or physician now I mentioned

That carbohydrates are linked to improved sporting performance and I’ve put a couple of videos up on the screen for you now to watch where I explore this in more detail