nutrition

Pull-Push and why brain prefers ketones as energy

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Ketones are the natural fuel for the brain

You’ve probably heard that brain cells need glucose and that’s why you need to eat high carb foods. Well, it’s true, but not completely correct.

If you eat standard western diet high in carbohydrates, and eat on average 6 or more times a day, indeed your body will use glucose for energy most of the time, excluding periods of overnight fasting.
It means that your brain cells almost most of the time use glucose for energy.

But if you are on a low-carb, ketogenic diets and/or doing intermittent fasting, then there are periods in a day, and in case of keto it can be throughout the day, that you brain cells will switch to using ketones for energy plus using glucose too.

If your doing prolonged fasts longer than 24 hours, say 48 hours or more or strict ketogenic diet, then brain cells will switch to using ketones as the main energy source.

Push-Pull strategy1

In his lecture prof. Stephen Cunnane described an interesting finding that brain cells consumption of glucose is independent of the level of glucose in blood. He calls this glucose pull. It means that brain will use more glucose for energy only when brain cells are more active, say you are thinking hard on a particular task, like playing chess.

It means that even if you consume a lot of sugar, energy drinks, fruits etc., it won’t help your brain metabolism, unless your brain works harder.

On the other hand, if there are ketones in your blood, then brain will try to use them as a fuel preferentially as much as possible. It means that when the level of ketones increases in the blood, brain cells will use more of them. Prof. Stephen Cunnane call this push of ketones.

Takeaway

To summarize, brain cells do need glucose, but glucose neither most efficient nor preferred brain fuel.

Cunnane SC. 2018. Ketones, omega-3 fatty acids and the Yin-Yang balance in the brain: insights from infant development and Alzheimer’s disease, and implications for human brain evolution. OCL 25(4): D409.

The use of both glucose and ketones as the brain’s two main fuels is governed by five principles: First, two distinctly different strategies regulate the use of glucose and ketones by the brain, a concept we call ’Push-Pull’ (Cunnane et al., 2016a, b). Brain glucose uptake is controlled by brain cell activity. Glucose is transported into the brain via glucose transporters in response to brain cell activation (Pull), so it is largely independent of blood glucose concentration. In contrast, ketones are transported into the brain via monocarboxylic acid transporters directly in response to plasma ketone concentration (Push), not brain activity. Hence, when ketones rise in the blood, they are immediately transported into the brain, an effect not seen with glucose.

  1. Cunnane SC, Courchesne-Loyer A, Vandenberghe C, St-Pierre V, Fortier M, Hennebelle M, Croteau E, Bocti C, Fulop T and Castellano C-A (2016) Can Ketones Help Rescue Brain Fuel Supply in Later Life? Implications for Cognitive Health during Aging and the Treatment of Alzheimer’s Disease. Front. Mol. Neurosci. 9:53. doi: 10.3389/fnmol.2016.00053 ↩︎

To lose weight first understand how you gain it

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If you struggle to lose weight following various diets and training regimens then there could be a couple of issues with your approach. But the most import thing to understand about weight loss is that you need to really know the root cause behind weight gain and what to do about it.

Blindly trying diets, without understanding how they work if at all, and going to the gym may cause a slight weight loss. But, most probably, you’ll gain weight back as soon as you stop following a diet, which happens to most of the people.

So what is the root cause you may ask?

Well, if you don’t have a rare genetic condition, then, most probably you are overweight, obese, pre-diabetic or even having type 2 diabetes due to excessive consumption of carbohydrates that causes Insulin level in the blood to be high throughout the day. This causes Insulin resistance in the long run in two ways: glucose in food you eat causes high level of insulin in the blood and fructose in food you eat causes high level of uric acid that causes insulin resistance indirectly.

As soon as insulin hormone is high in the blood it causes excess glucose in the blood to be stored as fat, and also prevents utilization of the fat that you already have as energy for the body.

Also, when insulin level is low, when you don’t eat for a period of time, due to fasting or after overnight fast this allows the body to use fat deposits that you have as energy for the body, hence weight loss.

Now, that we know that weight gain in most cases is caused by frequent consumption of foods rich in glucose and fructose, the solution is quite straightforward – there is a need to lower carbohydrates intake in any possible way. It can be a low-carb diet, it can be a ketogenic diet, it can be intermittent fasting alone or in combination with low-carb or keto. That’s it.

There is no need to be on a regular caloric restriction diets which cause you to be always hungry and have lower metabolism. There is no need to buy an expensive gym membership or any other sport equipment.

What you may find useful when you start losing weight is that you become more energetic and may find walking, which is free and affordable, enjoyable.

Personally, having been overweight for more than 10 years since my 30’s until 40’s, I wasn’t able to lose weight doing sport exercises or following a diet.

What helped me, was starting Intermittent Fasting regimen almost 2 years ago. Since then, I was able to lose 22 pounds (10 kg) and maintain this weight.
Yep, you’ve heard it right. It has been almost two years of quite effortless weight maintenance.

Prolonged Fasting is a piece of cake! Or is it?

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What is prolonged fasting?

Well, extended or prolonged fasting which is fasting for more than 24 hours is not your lovely 16/8. It’s more challenging and I should say it’s another level of fasting altogether.

First, it requires more dedication since unlike short fasts you still need to live in an environment where people continue to eat and you have to deal with food preparation for them and feel all the smells and looks of the food.

So if you can, do extended fasting when there is no one around, so not to be distracted.

Second, prolonged fasts are less comfortable than 16/8. After about 24 hours into a fast you start feeling a feeling of emptiness in the stomach that is a little bit annoying, but bearable. And at 8:00 PM as it also happens during regular fast you’ll feel hungry due to high levels of ghrelin hormone.

The good news is that in the morning of the second day of fasting if you do 42 hours for example, you don’t want to eat at all. Which is the same thing I feel during short fasts too.

Third, when you do prolonged fast you may feel coldness and low energy even though after about 24-36 hours (depending on the amount of glycogen in the liver) body should switch to using fat as main source of energy. Also, you may feel like going to sleep very early. Which is the case for me today, as usual when doing 42 hours fast.

Benefits of extended fasting

But, don’t forget that this is not in vain:

  1. During prolonged fasts you lose fat really fast.
  2. You have more time since you do not need to buy, cook or prepare food, unless you have kids. Then it sucks.
  3. You have an opportunity to look at your usual life from outside and see how our life is food-centric most of the time.
  4. Autophagy is in full swing only during prolonged fasts starting after 24 hours into fasting. I am not sure that 16/8 turns on autophagy at all (I’ll check this point in scientific papers later).

So there you have it


Extended fasting is challenging, but it comes with some benefits. If you don’t do it too frequently it can be even fun, when you do it with a partner, and kids are sent to spend time with grandpas and grandmas. And you use free time for walking, reading and sleeping.