Running on fat

4th April

In just over two weeks a group of runners, who in striking numbers are set to inspire us with their pain-bearing ambition, will descend on the London Marathon. I admire their aggressive will to win but, as a nutritionist who likes eating more than running, my mind is mostly on the enormous amount of carbs they will consume to cope with the long miles – jelly beans, pasta and all the other good stuff about running.


Thoughts of any form of an Italian carb (or croissants) are pure pleasure but, as much as I don't want to spoil anyone's fun, I feel responsible to share some bad news on the subject.

Remember how the government-fostered Food Pyramid urged you, and Everyone else, to stop eating fat and instead fuel up on healthy carbohydrates? We're all so familiar with the butter-is-bad-and-rice-is-good advice. What they never told us is were they screwed up; so get this - within only 10 years of the release of the F... Pyramid in the US, the rates of diabetes went up three fold. That's three times more incurable disease to go round and, to top it off, similar statistics for obesity. I wonder if the fact that for 99.9 % of our time on this planet we didn't have access to carbohydrates may have something to do with this.

In any case, this little experiment shows that a high carbohydrate diet deficient in fat is a bad idea for most human beings. This includes elite long distance runners who may not be as healthy as you think – a sadly significant number develop a grievous lot of nasty diseases shortly after retiring. It's known in Olympic circles that this is partly related to excessive consumption of carbohydrates that supported their competitive years.


Thankfully – for the pro athletes but also for you and me - science bears some good news here. Newest research shows that we don't need carbs 'for energy' – it turns out that the longer the distance of the race, the more our performance can be improved by ditching carbohydrates in favor of fat. A lot of fat.

Enter nutritional ketosis.

As you get further and further into your run and experience more fatigue, you know a carbohydrate top up will speed things up again. Your body starts to struggle because your glucose stores are down and this is precisely what makes your life as a runner so painful at times - there's only up to about 1500 kcals (and often less) of glucose in your tissues and organs, which is not a lot energy to use for a long run. Especially if you compare it to amounts contained in your fat stores that hold as much as 100 000 kcals (and often more)!

Why is your body unable, then, to efficiently tap into this enormous fuel tank?

Well... you've trained it to rely on carbohydrates (i.e. glucose) by repeatedly choosing them to fuel your runs as well as your daily life. As much as your body can, and does, use fat when needed it's a rather slow and inefficient process. That's not to say you are stuck! You can re-train your metabolism to use fat as a default, relinquishing virtually all dependence on glucose.


If you lower your carb intake sufficiently and add more fat, you can induce a metabolic state called nutritional ketosis. This is when your body becomes, literally, a fat burning machine because you've forced it to rely on fatty acids as its main, preferred source of energy. It doesn't want or need the glucose any more - you are now running on fat.

It gets better still because, as you switch to fat, your liver starts producing ketone bodies which bio hack your system to recover faster, prevent injuries (by sparing connective tissue) and... wait for it... you lose subcutaneous body fat (the one that spoils your appearance).

It may seem that 'doing keto' is a no brainer then but, in fact, it's not as easy as choosing between Asiscs and Sketchers. Even if fat is a superior fuel a lot of the time (by the way, the US Government has recently changed the Food Pyramid to include more fat and less carbs), shifting your metabolism toward reliance on fatty acids requires a process called keto adaptation (adapting to fat and its metabolites called ketone bodies) which lasts no less than a month. It's a big decision to make as once you're on the other side, you will pretty much have to stay there, eating a ketogenic diet made up of a ton of fats and virtually no carbs. Keto is a lifestyle. Stuff for those with the most intense commitment to long distance running. And dedicated fat lovers.

As a final word I feel the need to confess that I have been seen eating butter with a spoon – I am keto as they say – but I don't think carbs are bad and neither should you. It's only the abuse of carbs that causes problems. The tricky part is that (thanks to the likes of the Food Pyramid) most people have no idea how much carbohydrates they actually need and tend to enjoy way, way more than their metabolisms can handle.

If you're interested in the science behind all this, get in touch with Sonia and I'll forward you all the research links. I'm happy to answer questions, too!

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